The 19th Century Universe Olbers Paradox Standard Candles Galaxies and Quasars The Big Bang The Universe The Missing Ma

1. The 19th Century Universe Olbers� Paradox Standard Candles Galaxies and Quasars The Big Bang The Universe The Missing Mass The Cosmological Constant Inflation The Future

2. 19th Century Cosmology http://www.galaxyphoto.com/gal_hub.htmhttp://www.galaxyphoto.com/gal_hub.htm

3. The 19th Century Universe

4. The inverse square law for intensity http://www.splung.com/cosmology/images/magnitude/inversesquare.jpghttp://www.splung.com/cosmology/images/magnitude/inversesquare.jpg

5. Olbers� Paradox

6. The Milky Way

7. The big problem in cosmology is determining how far away objects are.

8. Parallax allowed the discovery of Pluto. cseligman.com/text/planets/pluto.htm http://images.google.com/imgres?imgurl=http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap10/FG1021-01u.jpg&imgrefurl=http://physics.uoregon.edu/~jimbrau/astr121/Notes/Chapter13-pluto.html&start=3&h=599&w=677&sz=87&tbnid=TfsJz90LjHIUTM:&tbnh=123&tbnw=139&hl=en&prev=/images%3Fq%3Ddiscovery%2Bof%2Bpluto%26um%3D1%26hl%3Den%26safe%3Doff%26rlz%3D1T4GFRC_enUS212US212%26sa%3DN&um=1 NASA Launches Spacecraft on the First Mission to Pluto By�WARREN E. LEARY Published: January 20, 2006 NASA launched the first space mission to Pluto yesterday as a powerful rocket hurled the New Horizons spacecraft on a nine-year, three-billion-mile journey to the edge of the solar system. Gary I. Rothstein/European Pressphoto Agency The launch of NASA's New Horizons spacecraft. Forum: Space and the Cosmos As it soared toward a 2007 rendezvous with Jupiter, whose powerful gravitational field will slingshot it on its way to Pluto, mission managers said radio communications confirmed that the 1,054-pound craft was in good health. The $700 million mission began when a Lockheed Martin Atlas 5 rocket rose from a launching pad at the Cape Canaveral Air Force Station in Florida at 2 p.m., almost an hour later than planned because of low clouds that obscured a clear view of the flight path by tracking cameras. "We have ignition and liftoff of NASA's New Horizons spacecraft on a decadelong voyage to visit the planet Pluto and then beyond," declared Bruce Buckingham, NASA's launching commentator. Less than an hour later, all three stages of the booster rocket worked as planned, and the spacecraft separated from them and sprinted away toward deep space. The robot ship sped away at about 36,000 miles per hour, the fastest flight of any spacecraft sent from Earth, allowing it to pass the Moon in about nine hours. "This is a historic day," said Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission's principal scientist and team leader. Speaking at a news conference at the Kennedy Space Center in Florida, Dr. Stern said the timing assured that the New Horizons would arrive for its closest approach to Pluto on July 14, 2015 - the 50th anniversary of the first flyby of Mars by the Mariner 4, the mission that began the exploration of the planets. Yesterday's liftoff also paid homage to Pluto's discoverer, the astronomer Clyde W. Tombaugh, who in 1930 became the only American to find a planet in the solar system. (He died at 90, in 1997.) His widow, Patricia Tombaugh, 93, and other family members were present at the cape, and some of his remains were among the commemorative items aboard the spacecraft. "Some of Clyde's ashes are on their way to Pluto today," Dr. Stern said. The New Horizons is to reach Jupiter's gravitational field in 13 months. The trip to Pluto will take eight more years, most of which the craft will spend in electronic "hibernation" to save power and wear on the equipment needed for its seven experiments. The New Horizons is powered by a small plutonium-fired electric generator. Its instruments include three cameras, for visible-light, infrared and ultraviolet images, and three spectrometers to study the composition and temperatures of Pluto's thin atmosphere and surface features. It also carries a University of Colorado dust counter, the first experiment to fly on a planetary mission that is entirely designed and operated by students. This is the only experiment that will not hibernate during the mission. In addition to the two-hour delay, the launching was postponed twice in two days - on Tuesday by strong winds at the cape and on Wednesday by a storm that caused a power failure at the spacecraft's control center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. Mission planners had until Feb. 14 to launch the mission this year, but only until the end of this month to use the gravity boost from Jupiter, which will shorten the trip to Pluto by five years. Once near its target, the New Horizons is to conduct about five months of studies, including a closest-approach dash that takes it within 6,200 miles of Pluto's surface and 16,800 miles from the planet's large moon, Charon. The craft will also study two smaller moons found late last year by the Hubble Space Telescope and any new features discovered while it is on its way, scientists said. The mission is to continue past Pluto, possibly visiting large objects in the Kuiper Belt, an outer zone of the solar system that includes Pluto. The belt is made up of thousands of icy, rocky objects that include comets and small planets. Scientists believe that this material is left over from the creation of the solar system 4.6 billion years ago and that studying it will provide clues to how the Sun and planets formed.cseligman.com/text/planets/pluto.htm http://images.google.com/imgres?imgurl=http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap10/FG1021-01u.jpg&imgrefurl=http://physics.uoregon.edu/~jimbrau/astr121/Notes/Chapter13-pluto.html&start=3&h=599&w=677&sz=87&tbnid=TfsJz90LjHIUTM:&tbnh=123&tbnw=139&hl=en&prev=/images%3Fq%3Ddiscovery%2Bof%2Bpluto%26um%3D1%26hl%3Den%26safe%3Doff%26rlz%3D1T4GFRC_enUS212US212%26sa%3DN&um=1 NASA Launches Spacecraft on the First Mission to Pluto By�WARREN E. LEARY Published: January 20, 2006 NASA launched the first space mission to Pluto yesterday as a powerful rocket hurled the New Horizons spacecraft on a nine-year, three-billion-mile journey to the edge of the solar system. Gary I. Rothstein/European Pressphoto Agency The launch of NASA's New Horizons spacecraft. Forum: Space and the Cosmos As it soared toward a 2007 rendezvous with Jupiter, whose powerful gravitational field will slingshot it on its way to Pluto, mission managers said radio communications confirmed that the 1,054-pound craft was in good health. The $700 million mission began when a Lockheed Martin Atlas 5 rocket rose from a launching pad at the Cape Canaveral Air Force Station in Florida at 2 p.m., almost an hour later than planned because of low clouds that obscured a clear view of the flight path by tracking cameras. "We have ignition and liftoff of NASA's New Horizons spacecraft on a decadelong voyage to visit the planet Pluto and then beyond," declared Bruce Buckingham, NASA's launching commentator. Less than an hour later, all three stages of the booster rocket worked as planned, and the spacecraft separated from them and sprinted away toward deep space. The robot ship sped away at about 36,000 miles per hour, the fastest flight of any spacecraft sent from Earth, allowing it to pass the Moon in about nine hours. "This is a historic day," said Alan Stern of the Southwest Research Institute in Boulder, Colo., the mission's principal scientist and team leader. Speaking at a news conference at the Kennedy Space Center in Florida, Dr. Stern said the timing assured that the New Horizons would arrive for its closest approach to Pluto on July 14, 2015 - the 50th anniversary of the first flyby of Mars by the Mariner 4, the mission that began the exploration of the planets. Yesterday's liftoff also paid homage to Pluto's discoverer, the astronomer Clyde W. Tombaugh, who in 1930 became the only American to find a planet in the solar system. (He died at 90, in 1997.) His widow, Patricia Tombaugh, 93, and other family members were present at the cape, and some of his remains were among the commemorative items aboard the spacecraft. "Some of Clyde's ashes are on their way to Pluto today," Dr. Stern said. The New Horizons is to reach Jupiter's gravitational field in 13 months. The trip to Pluto will take eight more years, most of which the craft will spend in electronic "hibernation" to save power and wear on the equipment needed for its seven experiments. The New Horizons is powered by a small plutonium-fired electric generator. Its instruments include three cameras, for visible-light, infrared and ultraviolet images, and three spectrometers to study the composition and temperatures of Pluto's thin atmosphere and surface features. It also carries a University of Colorado dust counter, the first experiment to fly on a planetary mission that is entirely designed and operated by students. This is the only experiment that will not hibernate during the mission. In addition to the two-hour delay, the launching was postponed twice in two days - on Tuesday by strong winds at the cape and on Wednesday by a storm that caused a power failure at the spacecraft's control center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. Mission planners had until Feb. 14 to launch the mission this year, but only until the end of this month to use the gravity boost from Jupiter, which will shorten the trip to Pluto by five years. Once near its target, the New Horizons is to conduct about five months of studies, including a closest-approach dash that takes it within 6,200 miles of Pluto's surface and 16,800 miles from the planet's large moon, Charon. The craft will also study two smaller moons found late last year by the Hubble Space Telescope and any new features discovered while it is on its way, scientists said. The mission is to continue past Pluto, possibly visiting large objects in the Kuiper Belt, an outer zone of the solar system that includes Pluto. The belt is made up of thousands of icy, rocky objects that include comets and small planets. Scientists believe that this material is left over from the creation of the solar system 4.6 billion years ago and that studying it will provide clues to how the Sun and planets formed.

9. The 20th Century Universe: Standard Candles

10. Standard Candle #1: Cepheid Variables http://ircamera.as.arizona.edu/NatSci102/lectures/milkyway.htm http://ircamera.as.arizona.edu/NatSci102/lectures/milkyway.htm

11. Standard Candle #1: Cepheid Variables http://ircamera.as.arizona.edu/NatSci102/lectures/milkyway.htm Certain stars that have used up their main supply of hydrogen fuel are unstable and pulsate. RR Lyrae variables have periods of about a day. Their brightness doubles from dimmest to brightest.http://ircamera.as.arizona.edu/NatSci102/lectures/milkyway.htm Certain stars that have used up their main supply of hydrogen fuel are unstable and pulsate. RR Lyrae variables have periods of about a day. Their brightness doubles from dimmest to brightest.

12. Galaxies http://astrohow.org/astroconcepts/M31_hallas.jpg http://astrohow.org/astroconcepts/M31_hallas.jpg

13. Okay, so what does our neighborhood of the universe look like?

14. Galaxies http://www.naturespeak.com.au/Milky%20Way%20Wide%20Field.htm http://chandra.harvard.edu/photo/2006/w3/milkyway_ill.jpghttp://www.naturespeak.com.au/Milky%20Way%20Wide%20Field.htm http://chandra.harvard.edu/photo/2006/w3/milkyway_ill.jpg

15. There�s a gigantic black hole at our galaxy�s center! http://www.mpe.mpg.de/ir/GC/index.phphttp://www.mpe.mpg.de/ir/GC/index.php

16. Orbits of stars near the galactic center

17. Nearby galaxies http://www.daviddarling.info/images/Sagittarius_Dwarf_Elliptical.jpg A satellite galaxy of the Milky Way and the second closest external galaxy after the Canis Major Dwarf. It is populated, as is usual for a dwarf elliptical galaxy, by old yellowish stars. Obscured by large amounts of dust in the galactic plane, SagDEG was discovered as recently as 1994. SagDEG orbits our galaxy in less than one billion years and must therefore have passed through the dense central region of the Milky Way at least 10 times during our galaxy�s lifetime. The fact that it has remained intact suggests that SagDEG may contain a significant amount of dark matter that helps to bind it together. It is, however, apparently now in the process of being disrupted by tidal forces of its massive neighbor. This may lead to its globular clusters and many of its other stars finding a new home in the Milky Way�s halo, while its remaining stars escape to become solitary intergalactic travelers.  http://www.rigel.org.uk/blog/CanMajDwarf.jpg One particular model of the universe suggests that large galaxies, like our own Milky Way, formed as an amalgamation of smaller galaxies, proto-galaxies if you like. One of the consequences of this theory is that these larger galaxies should be surrounded by a halo containing the dispersed debris left over from the mergers of these smaller dwarf galaxies. Evidence for this theory is seen within our own Galaxy. The first dwarf galaxy remnant discovered in the Milky Way is known as the Sagittarius dwarf because it is seen in the direction of the constellation of Sagittarius. In 1994, while investigating the motions of stars in the Galactic halo, researchers discovered a large group of comoving stars, stars moving with the same speed in the same direction. It seems that this poor little galaxy is slowly being ripped apart as it passes through our Galaxy again and again. Each pass through the plane of the Galaxy causes the dwarf to become more stretched out until, eventually, it becomes absorbed into the much larger Milky Way. Credit: Dr R. Ibata et al More recently, a group of researchers have found another dwarf galaxy being torn apart by a close encounter with the Milky Way. The Canis Major dwarf is the closest known dwarf galaxy to the centre of the Milky Way, there could be others there that we haven't seen yet, and is only about 2500 light years away from our solar system. If it is so close, why hasn't it been seen before? Well, the trouble with the centre of the Galaxy is that there is a lot of stuff in the way. The bulge is full of gas, dust and stars that block out any light coming from the far side. This new galaxy was discovered by looking at infra-red data from the 2-Micron All Sky Survey which is able to penetrate this junk and reach us. Stars which appear bright at infra-red wavelengths are cooler, older stars, implying that the Canis Minor dwarf is very old. As well as finding the core of the interloper, the astronomers also found streamers of associated stars that were pulled off by tidal interactions as the galaxies got close to each other. These contribute to the disk of the Milky Way, so it seems that smaller galaxies do indeed contribute to the formation of larger ones. Today, B. Conn and colleagues report observations of a stream of stars known as the Monoceros Ring which is tidal debris that is possibly associated with the Canis Major dwarf. This ring is behind the Canis Major dwarf and is thought to be a tidal stream from the Canis Major dwarf itself, a scenario which these new observations support. This all shows that, far from being evolved, our Galaxy is still forming as these interactions continue. An international team of astronomers from France, Italy, the UK and Australia has found a previously unknown galaxy colliding with our own Milky Way. This newly-discovered galaxy takes the record for the nearest galaxy to the centre of the Milky Way. Called the Canis Major dwarf galaxy after the constellation in which it lies, it is about 25000 light years away from the solar system and 42000 light years from the centre of the Milky Way. This is closer than the Sagittarius dwarf galaxy, discovered in 1994, which is also colliding with the Milky Way. The discovery shows that the Milky Way is building up its own disk by absorbing small satellite galaxies. The research is to be published in the Monthly Notices of the Royal Astronomical Society within the next few weeks. The discovery of the Canis Major dwarf was made possible by a recent survey of the sky in infrared light (the Two-Micron All Sky Survey or "2MASS"), which has allowed astronomers to look beyond the clouds of dust in the disk of the Milky Way. Until now, the dwarf galaxy lay undetected behind the dense disk. "It's like putting on infrared night vision goggles," says team-member Dr Rodrigo Ibata of Strasbourg Observatory. "We are now able to study a part of the Milky Way that has been previously out of sight".  The new dwarf galaxy was detected by its M-giant stars -- cool, red stars that shine especially brightly in infrared light. "We have used these rare M-giant stars as beacons to trace out the shape and location of the new galaxy because its numerous other stars are too faint for us to see," explains Nicolas Martin, also of Strasbourg Observatory. "They are particularly useful stars as we can measure their distances, and so map out the three-dimensional structure of distant regions of the Milky Way disk." In this way, the astronomers found the main dismembered corpse of the dwarf galaxy in Canis Major and long trails of stars leading back to it. It seems that streams of stars pulled out of the cannibalised Canis Major galaxy not only contribute to the outer reaches of the Milky Way's disk, but may also pass close to the Sun. Astronomers currently believe that large galaxies like the Milky Way grew to their present majestic proportions by consuming their smaller galactic neighbours. These cannibalised galaxies add stars to the vast haloes around large galaxies. However, until now, they did not appreciate that even the disks of galaxies can grow in this fashion. Computer simulations show that the Milky Way has been taking stars from the Canis Major dwarf and adding them to its own disk - and will continue to do so.  "On galactic scales, the Canis Major dwarf galaxy is a lightweight of about only one billion Suns," said Dr. Michele Bellazzini of Bologna Observatory. "This small galaxy is unlikely to hold together much longer. It is being pushed and pulled by the colossal gravity of our Milky Way, which has been progressively stealing its stars and pulling it apart." Some remnants of the Canis Major dwarf form a ring around the disk of the Milky Way. "The Canis Major dwarf galaxy may have added up to 1% more mass to our Galaxy," said Dr Geraint Lewis of the University of Sydney. "This is also an important discovery because it highlights that the Milky Way is not in its middle age - it is still forming." "Past interactions of the sort we are seeing here could be responsible for some of the exquisite detail we see today in the structure of the Galaxy," says Dr Michael Irwin of the University of Cambridge. http://www.daviddarling.info/images/Sagittarius_Dwarf_Elliptical.jpg A satellite galaxy of the Milky Way and the second closest external galaxy after the Canis Major Dwarf. It is populated, as is usual for a dwarf elliptical galaxy, by old yellowish stars. Obscured by large amounts of dust in the galactic plane, SagDEG was discovered as recently as 1994. SagDEG orbits our galaxy in less than one billion years and must therefore have passed through the dense central region of the Milky Way at least 10 times during our galaxy�s lifetime. The fact that it has remained intact suggests that SagDEG may contain a significant amount of dark matter that helps to bind it together. It is, however, apparently now in the process of being disrupted by tidal forces of its massive neighbor. This may lead to its globular clusters and many of its other stars finding a new home in the Milky Way�s halo, while its remaining stars escape to become solitary intergalactic travelers. http://www.rigel.org.uk/blog/CanMajDwarf.jpg One particular model of the universe suggests that large galaxies, like our own Milky Way, formed as an amalgamation of smaller galaxies, proto-galaxies if you like. One of the consequences of this theory is that these larger galaxies should be surrounded by a halo containing the dispersed debris left over from the mergers of these smaller dwarf galaxies. Evidence for this theory is seen within our own Galaxy. The first dwarf galaxy remnant discovered in the Milky Way is known as the Sagittarius dwarf because it is seen in the direction of the constellation of Sagittarius. In 1994, while investigating the motions of stars in the Galactic halo, researchers discovered a large group of comoving stars, stars moving with the same speed in the same direction. It seems that this poor little galaxy is slowly being ripped apart as it passes through our Galaxy again and again. Each pass through the plane of the Galaxy causes the dwarf to become more stretched out until, eventually, it becomes absorbed into the much larger Milky Way. Credit: Dr R. Ibata et al More recently, a group of researchers have found another dwarf galaxy being torn apart by a close encounter with the Milky Way. The Canis Major dwarf is the closest known dwarf galaxy to the centre of the Milky Way, there could be others there that we haven't seen yet, and is only about 2500 light years away from our solar system. If it is so close, why hasn't it been seen before? Well, the trouble with the centre of the Galaxy is that there is a lot of stuff in the way. The bulge is full of gas, dust and stars that block out any light coming from the far side. This new galaxy was discovered by looking at infra-red data from the 2-Micron All Sky Survey which is able to penetrate this junk and reach us. Stars which appear bright at infra-red wavelengths are cooler, older stars, implying that the Canis Minor dwarf is very old. As well as finding the core of the interloper, the astronomers also found streamers of associated stars that were pulled off by tidal interactions as the galaxies got close to each other. These contribute to the disk of the Milky Way, so it seems that smaller galaxies do indeed contribute to the formation of larger ones. Today, B. Conn and colleagues report observations of a stream of stars known as the Monoceros Ring which is tidal debris that is possibly associated with the Canis Major dwarf. This ring is behind the Canis Major dwarf and is thought to be a tidal stream from the Canis Major dwarf itself, a scenario which these new observations support. This all shows that, far from being evolved, our Galaxy is still forming as these interactions continue. An international team of astronomers from France, Italy, the UK and Australia has found a previously unknown galaxy colliding with our own Milky Way. This newly-discovered galaxy takes the record for the nearest galaxy to the centre of the Milky Way. Called the Canis Major dwarf galaxy after the constellation in which it lies, it is about 25000 light years away from the solar system and 42000 light years from the centre of the Milky Way. This is closer than the Sagittarius dwarf galaxy, discovered in 1994, which is also colliding with the Milky Way. The discovery shows that the Milky Way is building up its own disk by absorbing small satellite galaxies. The research is to be published in the Monthly Notices of the Royal Astronomical Society within the next few weeks. The discovery of the Canis Major dwarf was made possible by a recent survey of the sky in infrared light (the Two-Micron All Sky Survey or "2MASS"), which has allowed astronomers to look beyond the clouds of dust in the disk of the Milky Way. Until now, the dwarf galaxy lay undetected behind the dense disk. "It's like putting on infrared night vision goggles," says team-member Dr Rodrigo Ibata of Strasbourg Observatory. "We are now able to study a part of the Milky Way that has been previously out of sight". The new dwarf galaxy was detected by its M-giant stars -- cool, red stars that shine especially brightly in infrared light. "We have used these rare M-giant stars as beacons to trace out the shape and location of the new galaxy because its numerous other stars are too faint for us to see," explains Nicolas Martin, also of Strasbourg Observatory. "They are particularly useful stars as we can measure their distances, and so map out the three-dimensional structure of distant regions of the Milky Way disk." In this way, the astronomers found the main dismembered corpse of the dwarf galaxy in Canis Major and long trails of stars leading back to it. It seems that streams of stars pulled out of the cannibalised Canis Major galaxy not only contribute to the outer reaches of the Milky Way's disk, but may also pass close to the Sun. Astronomers currently believe that large galaxies like the Milky Way grew to their present majestic proportions by consuming their smaller galactic neighbours. These cannibalised galaxies add stars to the vast haloes around large galaxies. However, until now, they did not appreciate that even the disks of galaxies can grow in this fashion. Computer simulations show that the Milky Way has been taking stars from the Canis Major dwarf and adding them to its own disk - and will continue to do so. "On galactic scales, the Canis Major dwarf galaxy is a lightweight of about only one billion Suns," said Dr. Michele Bellazzini of Bologna Observatory. "This small galaxy is unlikely to hold together much longer. It is being pushed and pulled by the colossal gravity of our Milky Way, which has been progressively stealing its stars and pulling it apart." Some remnants of the Canis Major dwarf form a ring around the disk of the Milky Way. "The Canis Major dwarf galaxy may have added up to 1% more mass to our Galaxy," said Dr Geraint Lewis of the University of Sydney. "This is also an important discovery because it highlights that the Milky Way is not in its middle age - it is still forming." "Past interactions of the sort we are seeing here could be responsible for some of the exquisite detail we see today in the structure of the Galaxy," says Dr Michael Irwin of the University of Cambridge.

18. The Large and Small Magellanic Clouds These relatively small neighbors of ours are irregular dwarf galaxies visible to the naked eye in the Southern hemisphere. They are only about 180,000 and 200,000 light-years away, respectively, whereas the nearest major galaxy, Andromeda (M31), is over 2 million light-years away. They are named for the explorer Magellan who brought them to the attention of the European world in 1519. In the early 1980's still another was discovered, dubbed the Mini Magellanic Cloud (MMC), hiding behind the SMC, 20,000 light-years beyond, and appears to have been a part of the SMC until it was torn loose by a near collision with the LMC some 200 million years ago. http://www.cosmiclight.com/imagegalleries/beyond.htm There is active debate as to whether these galaxies are gravitationally bound to ours. They�re traveling too fast. But maybe we�re more massive than we thought. A closer dwarf galaxy is: The Sagittarius Dwarf Elliptical Galaxy (SagDEG) is an elliptically looped shaped satellite galaxy of the Milky Way Galaxy. The main cluster which, in 1994, was the first to be discovered, is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth and traveling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud). These relatively small neighbors of ours are irregular dwarf galaxies visible to the naked eye in the Southern hemisphere. They are only about 180,000 and 200,000 light-years away, respectively, whereas the nearest major galaxy, Andromeda (M31), is over 2 million light-years away. They are named for the explorer Magellan who brought them to the attention of the European world in 1519. In the early 1980's still another was discovered, dubbed the Mini Magellanic Cloud (MMC), hiding behind the SMC, 20,000 light-years beyond, and appears to have been a part of the SMC until it was torn loose by a near collision with the LMC some 200 million years ago. http://www.cosmiclight.com/imagegalleries/beyond.htm There is active debate as to whether these galaxies are gravitationally bound to ours. They�re traveling too fast. But maybe we�re more massive than we thought. A closer dwarf galaxy is: The Sagittarius Dwarf Elliptical Galaxy (SagDEG) is an elliptically looped shaped satellite galaxy of the Milky Way Galaxy. The main cluster which, in 1994, was the first to be discovered, is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth and traveling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud).

19. The Andromeda Galaxy http://www.coseti.org/milkyway.htm (But this really is Andromeda.)http://www.coseti.org/milkyway.htm (But this really is Andromeda.)

20. Galaxy shapes

21. Galaxies and their shapes

22. Galaxies and their shapes

23. What about the large-scale structure of the universe?

24. The cosmological constant

25. Standard Candle #2: Supernovae The Crab supernova occurred in 1054 and was recorded by the Chinese and Japanese. It was bright enough to see during the daytime. Other supernovae in our galaxy occurred in 1572, 1604 and 1987. Supernova 1604, also known as Kepler's Supernova or Kepler's Star, was a supernova which occurred in the Milky Way, in the constellation Ophiuchus. As of 2007, it is the last supernova to have been unquestionably observed in our own galaxy, occurring no farther than 6 kiloparsecs or about 20,000 light-years from Earth. Visible to the naked eye, it was brighter at its peak than any other star in the night sky, and all the planets (other than Venus), with apparent magnitude -2.5. The supernova was first observed on October 9, 1604.[2] The German astronomer Johannes Kepler first saw it on October 17, subsequently named after himself. His book on the subject was entitled De Stella nova in pede Serpentarii (On the new star in Ophiuchus's foot).Supernova 1604, also known as Kepler's Supernova or Kepler's Star, was a supernova which occurred in the Milky Way, in the constellation Ophiuchus. As of 2007, it is the last supernova to have been unquestionably observed in our own galaxy, occurring no farther than 6 kiloparsecs or about 20,000 light-years from Earth. Visible to the naked eye, it was brighter at its peak than any other star in the night sky, and all the planets (other than Venus), with apparent magnitude -2.5. The supernova was first observed on October 9, 1604.[2] The German astronomer Johannes Kepler first saw it on October 17, subsequently named after himself. His book on the subject was entitled De Stella nova in pede Serpentarii (On the new star in Ophiuchus's foot).

26. Standard Candle #2: Supernovae http://www-astronomy.mps.ohio-state.edu/~ryden/ast162_5/notes20.html Type Ia: no hydrogen lines, no helium lines, strong silicon lines Type Ib: no hydrogen lines, strong helium lines Type Ic: no hydrogen lines, no helium lines, no silicon lines Type Ib and type Ic supernovae are massive stars which lost their outer layers in a stellar wind before core collapse. Type Ib supernovae lost their hydrogen-rich outer layer, revealing the helium-rich layer immediately below. Type Ic supernovae suffered more mass loss as supergiants, losing both the hydrogen-rich layer and the helium-rich layer (revealing the carbon-rich layer below). Type Ib and type Ic supernovae are essentially the same as type II supernovae. In all these types, the iron core of a massive star collapses and rebounds; the differences in the spectra of type Ib, type Ic, and type II supernovae are due to superficial differences in the exploding stars. Type Ia supernovae, however, are a very different species of beast, arriving at their explosive end by a different life path. (2) Matter can be transferred between stars in a close binary system. Ordinarily, low mass stars (those with initial masses less than 4 Msun) don't explode. Instead, they lose enough mass when they are bloated giant stars to become stable white dwarfs with M < 1.4 Msun. However, the life of a star is not always ``ordinary''. Consider a white dwarf made of carbon and oxygen. (This is the end state for stars whose mass on the main sequence is between 0.4 Msun and 4 Msun.) When such a white dwarf is solitary, it leads a boringly stable existence. But now, let's ask a ``what if'' question. What if a white dwarf were to have matter poured onto it, bringing its mass up to the Chandrasekhar limit of 1.4 Msun? One way of pouring large quantities of matter onto a white dwarf is to place it in a close binary system. In most binary systems, the stars are well separated. (In the Sirius system, for instance, Sirius B and Sirius A are separated by 20 A.U., on average; that's about 4000 times the radius of the Sun.) However, in some systems, the stars are much closer together. (3) A Type Ia supernova is caused by the transfer of matter onto a white dwarf by a close companion star. If a white dwarf is in a close binary system with a main sequence star, the main sequence star, as it expands into a giant or supergiant, will start to dump gas onto the white dwarf. When the mass of the white dwarf is nudged up to the Chandrasekhar limit, it is no longer stable against collapse. Radius decreases. Density increases. Temperature increases. At the new higher density and temperature, the fusion of carbon and oxygen into iron occurs in a runaway fashion. The white dwarf is converted into a fusion bomb, and is blown completely apart by the explosion. (This represents a triumph of the outward force of pressure over the inward force of gravity.) The amount of energy released in the explosion is about 1044 joules, as much energy as the Sun has radiated away during its entire lifetime. The spectrum of a type Ia supernova contains no hydrogen or helium lines because the white dwarf that is blown apart consists of carbon and oxygen. (The gas dumped onto it by its stellar companion is likely to be hydrogen and helium, but the strong gravity at the white dwarf's surface compresses it to densities and temperatures high enough to fuse it into carbon and oxygen.)The spectrum of a type Ia supernova contains silicon lines because silicon is one of the products of fusing carbon and oxygen. However, the main product of the fusion is iron: a type Ia supernova ejects about 1 Msun of iron into the interstellar medium. The reason why iron is such a common metal (making up most of the Earth's core, for instance) is that type Ia supernovae keep dumping it into the interstellar gas. Okay, let's wind up by doing a ``compare and contrast'' exercise, comparing Type Ia supernovae to Type II supernovae. (Remember, type Ib and type Ic supernovae are very similar to type II supernovae.) Progenitor of the supernova: Type Ia: a white dwarf in a close binary system (the white dwarf might be very old -- up to 10 billion years) Type II: a massive supergiant star (the supergiant must be very young -- as young as 1 million years) Source of energy: Type Ia: nuclear fusion (carbon and oxygen to iron) Type II: gravity (collapse of the iron core) Type II supernovae are massive stars whose iron cores collapse and then rebound, shock heating the outer layers of the star, which then explode outward.http://www-astronomy.mps.ohio-state.edu/~ryden/ast162_5/notes20.html Type Ia: no hydrogen lines, no helium lines, strong silicon lines Type Ib: no hydrogen lines, strong helium lines Type Ic: no hydrogen lines, no helium lines, no silicon lines Type Ib and type Ic supernovae are massive stars which lost their outer layers in a stellar wind before core collapse. Type Ib supernovae lost their hydrogen-rich outer layer, revealing the helium-rich layer immediately below. Type Ic supernovae suffered more mass loss as supergiants, losing both the hydrogen-rich layer and the helium-rich layer (revealing the carbon-rich layer below). Type Ib and type Ic supernovae are essentially the same as type II supernovae. In all these types, the iron core of a massive star collapses and rebounds; the differences in the spectra of type Ib, type Ic, and type II supernovae are due to superficial differences in the exploding stars. Type Ia supernovae, however, are a very different species of beast, arriving at their explosive end by a different life path. (2) Matter can be transferred between stars in a close binary system. Ordinarily, low mass stars (those with initial masses less than 4 Msun) don't explode. Instead, they lose enough mass when they are bloated giant stars to become stable white dwarfs with M < 1.4 Msun. However, the life of a star is not always ``ordinary''. Consider a white dwarf made of carbon and oxygen. (This is the end state for stars whose mass on the main sequence is between 0.4 Msun and 4 Msun.) When such a white dwarf is solitary, it leads a boringly stable existence. But now, let's ask a ``what if'' question. What if a white dwarf were to have matter poured onto it, bringing its mass up to the Chandrasekhar limit of 1.4 Msun? One way of pouring large quantities of matter onto a white dwarf is to place it in a close binary system. In most binary systems, the stars are well separated. (In the Sirius system, for instance, Sirius B and Sirius A are separated by 20 A.U., on average; that's about 4000 times the radius of the Sun.) However, in some systems, the stars are much closer together. (3) A Type Ia supernova is caused by the transfer of matter onto a white dwarf by a close companion star. If a white dwarf is in a close binary system with a main sequence star, the main sequence star, as it expands into a giant or supergiant, will start to dump gas onto the white dwarf. When the mass of the white dwarf is nudged up to the Chandrasekhar limit, it is no longer stable against collapse. Radius decreases. Density increases. Temperature increases. At the new higher density and temperature, the fusion of carbon and oxygen into iron occurs in a runaway fashion. The white dwarf is converted into a fusion bomb, and is blown completely apart by the explosion. (This represents a triumph of the outward force of pressure over the inward force of gravity.) The amount of energy released in the explosion is about 1044 joules, as much energy as the Sun has radiated away during its entire lifetime. The spectrum of a type Ia supernova contains no hydrogen or helium lines because the white dwarf that is blown apart consists of carbon and oxygen. (The gas dumped onto it by its stellar companion is likely to be hydrogen and helium, but the strong gravity at the white dwarf's surface compresses it to densities and temperatures high enough to fuse it into carbon and oxygen.)The spectrum of a type Ia supernova contains silicon lines because silicon is one of the products of fusing carbon and oxygen. However, the main product of the fusion is iron: a type Ia supernova ejects about 1 Msun of iron into the interstellar medium. The reason why iron is such a common metal (making up most of the Earth's core, for instance) is that type Ia supernovae keep dumping it into the interstellar gas. Okay, let's wind up by doing a ``compare and contrast'' exercise, comparing Type Ia supernovae to Type II supernovae. (Remember, type Ib and type Ic supernovae are very similar to type II supernovae.) Progenitor of the supernova: Type Ia: a white dwarf in a close binary system (the white dwarf might be very old -- up to 10 billion years) Type II: a massive supergiant star (the supergiant must be very young -- as young as 1 million years) Source of energy: Type Ia: nuclear fusion (carbon and oxygen to iron) Type II: gravity (collapse of the iron core) Type II supernovae are massive stars whose iron cores collapse and then rebound, shock heating the outer layers of the star, which then explode outward.

27. Super-novae This is the mess that is left when a star explodes. The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The above image, taken by the Nordic Optical Telescope (NOT), is in three colors chosen for scientific interest. The Crab Nebula spans about 10 light-years. In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town. The Crab Pulsar rotates about 30 times each second. This is the mess that is left when a star explodes. The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The above image, taken by the Nordic Optical Telescope (NOT), is in three colors chosen for scientific interest. The Crab Nebula spans about 10 light-years. In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town. The Crab Pulsar rotates about 30 times each second.

28. Standard Candle #3: Galaxies MAGNIFICENT DETAILS IN A DUSTY SPIRAL GALAXY In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. An international team of astronomers, led by Dr. Wendy Freedman of the Observatories of the Carnegie Institution of Washington, observed this galaxy on 13 different occasions over the course of two months. Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters. Based on their discovery and careful brightness measurements of variable stars in NGC 4414, the Key Project astronomers were able to make an accurate determination of the distance to the galaxy. The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself. Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight. Image Credit: Hubble Heritage Team (AURA/STScI/NASA) http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-astro-galaxy.htmlMAGNIFICENT DETAILS IN A DUSTY SPIRAL GALAXY In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. An international team of astronomers, led by Dr. Wendy Freedman of the Observatories of the Carnegie Institution of Washington, observed this galaxy on 13 different occasions over the course of two months. Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters. Based on their discovery and careful brightness measurements of variable stars in NGC 4414, the Key Project astronomers were able to make an accurate determination of the distance to the galaxy. The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself. Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight. Image Credit: Hubble Heritage Team (AURA/STScI/NASA) http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-astro-galaxy.html

29. Hubble�s measure-ments

30. Hubble�s Law http://www.metaresearch.org/cosmology/QuasarsNearVersusFar.asphttp://www.metaresearch.org/cosmology/QuasarsNearVersusFar.asp

31. The Expansion of the Universe Distances between galaxies are increasing uniformly. There is no need for a center of the universe. http://shinymedia.blogs.com/photos/uncategorized/2007/05/29/einstein.jpghttp://shinymedia.blogs.com/photos/uncategorized/2007/05/29/einstein.jpg

32. How can the universe be expanding, yet continue to look the same? Proposed in 1948 by Hermann Bondi, Thomas Gold, and Sir Fred Hoyle, the Steady-State Theory held that the universe is infinite and expanding, and matter is continuously created with net constant density. Only a few atoms per cubic meter per century would be required, so no one would ever notice. Unfortunately, no mechanism has ever been found for matter creation, as required by the Steady-State theory. Also, in this view, the universe should look the same at all distances. But it doesn�t!

33. Quasi-stellar objects: Quasars A quasar (contraction of QUASi-stellAR radio source) is an extremely bright and distant active galactic nucleus. They were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light that were point-like, similar to stars, rather than extended sources similar to galaxies. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy. Quasars show a very high redshift which is an effect of the expansion of the universe between the quasar and the Earth. When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. To be observable at that distance, the energy output of quasars must dwarf that of almost every known astrophysical phenomenon in a galaxy, excepting comparatively short-lived events like supernovae and gamma-ray bursts. Quasars may readily release energy in levels equal to the output of hundreds of average galaxies combined. The output of light is equivalent to one trillion suns. In optical telescopes, quasars look like single points of light (i.e. point source) although many have had their "host galaxies" identified. The galaxies themselves are often too dim to be seen with all but the largest telescopes. Most quasars cannot be seen with small telescopes, but 3C 273, with an average apparent magnitude of 12.9, is an exception. At a distance of 2.44 billion light years, it is one of the most distant objects directly observable with amateur equipment. Some quasars display rapid changes in luminosity, which implies that they are small (an object cannot change faster than the time it takes light to travel from one end to the other; but see quasar J1819+3845 for another explanation). The highest redshift known for a quasar (as of January 2003) is 6.4.[1] Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. No other currently known mechanism appears able to explain the vast energy output and rapid variability. Knowledge of quasars is advancing rapidly. As recently as the 1980s, there was no clear consensus as to their origin. Properties of quasars More than 100,000 quasars are known. All observed spectra have shown considerable redshifts, ranging from 0.06 to the recent maximum of 6.4. Therefore, all known quasars lie at great distances from earth, the closest being 240 Mpc (780 million ly) away and the farthest being 4 Gpc (13 billion ly) away. Most quasars are known to lie above 1.0 Gpc in distance; since light takes such a long time to cover these great distances, the quasars are seen as they existed long ago. Although faint when seen optically, their high redshift implies that these objects lie at a great distance from earth, making quasars the most luminous objects in the known universe. The quasar which appears brightest in the sky is the ultraluminous 3C�273 in the constellation of Virgo. It has an average apparent magnitude of 12.8 (bright enough to be seen through a small telescope), but it has an absolute magnitude of -26.7. So from a distance of 10 parsecs (about 33 light-years), this object would shine in the sky about as brightly as our sun. This quasar's luminosity is, therefore, about 2 trillion (2 � 1012) times that of our sun, or about 100 times that of the total light of average giant galaxies like our Milky Way. The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of -32.2, although high resolution imaging with the Hubble Space Telescope and the 10�m Keck Telescope revealed that this system is gravitationally lensed. A study of the gravitational lensing in this system suggests that it has been magnified by a factor of ~10. It is still substantially more luminous than nearby quasars such as 3C�273. HS 1946+7658 was thought to have an absolute magnitude of -30.3, but this too was magnified by the gravitational lensing effect. Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours. This evidence has allowed scientists to theorize that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale to coordinate the luminosity variations. As such, a quasar varying on the time scale of a few weeks cannot be larger than a few light-weeks across. Quasars exhibit many of the same properties as active galaxies: Radiation is nonthermal and some are observed to have jets and lobes like those of radio galaxies. Quasars can be observed in many parts of the electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0.9 �m), in the near infrared. Iron Quasars show strong emission lines resulting from ionized iron, such as IRAS 18508-7815. Quasar emission generation This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. The quasar-starburst was found by a team of researchers from six institutions Since quasars exhibit properties common to all active galaxies, the emissions from quasars can be readily compared to those of small active galaxies powered by supermassive black holes. To create a luminosity of 1040 W (the typical brightness of a quasar), a super-massive black hole would have to consume the material equivalent of 10 stars per year. The brightest known quasars devour 1000 solar masses of material every year. Quasars 'turn on' and off depending on their surroundings, and since quasars cannot continue to feed at high rates for 10 billion years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy. Quasars also provide some clues as to the end of the Big Bang's reionization. The oldest quasars (redshift > 4) display a Gunn-Peterson trough and have absorption regions in front of them indicating that the intergalactic medium at that time was neutral gas. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest. This indicates that the intergalactic medium has undergone reionization into plasma, and that neutral gas exists only in small clouds. One other interesting characteristic of quasars is that they show evidence of elements heavier than helium indicating that galaxies underwent a massive phase of star formation creating population III stars between the time of the Big Bang and the first observed quasars. Light from these stars may have been observed in 2005 using NASA's Spitzer Space Telescope, although this observation remains to be confirmed. History of quasar observation The first quasars were discovered with radio telescopes in the late 1950s. Many were recorded as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size.[2] Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for the optical counterparts. In 1960, radio source 3C 48 was finally tied to an optical object. Astronomers detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum. Containing many unknown broad emission lines, the anomalous spectrum defied interpretation � a claim by John Bolton of a large redshift was not generally accepted. In 1962 a breakthrough was achieved. Another radio source, 3C 273, was predicted to undergo five occultations by the moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar. This spectrum revealed the same strange emission lines. Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15.8 percent. This discovery showed that 3C�273 was receding at a rate of 47,000�km/s.[3] This discovery revolutionized quasar observation and allowed other astronomers to find redshifts from the emission lines from other radio sources. As predicted earlier by Bolton, 3C�48 was found to have a redshift of 37% the speed of light. The term quasar was coined by Chinese-born U.S. astrophysicist Hong-Yee Chiu in 1964, in Physics Today, to describe these puzzling objects: So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper. � Hong-Yee Chiu in Physics Today, May, 1964 Later it was found that not all (actually only 10% or so) quasars have strong radio emission (are 'radio-loud'). Hence the name 'QSO' (quasi-stellar object) is used (in addition to 'quasar') to refer to these objects, including the 'radio-loud' and the 'radio-quiet' classes. One great topic of debate during the 1960s was whether quasars were nearby objects or distant objects as implied by their redshift. It was suggested, for example, that the redshift of quasars was not due to the expansion of space but rather to light escaping a deep gravitational well. However a star of sufficient mass to form such a well would be unstable and in excess of the Hayashi limit.[4] Quasars also show unusual spectral emission lines which were previously only seen in hot gaseous nebulae of low density, which would be too diffuse to both generate the observed power and fit within a deep gravitational well.[5] There were also serious concerns regarding the idea of cosmologically distant quasars. One strong argument against them was that they implied energies that were far in excess of known energy conversion processes, including nuclear fusion. At this time, there were some suggestions that quasars were made of some hitherto unknown form of stable antimatter and that this might account for their brightness. Others speculated that quasars were a white hole end of a wormhole. However, when accretion disc energy-production mechanisms were successfully modeled in the 1970s, the argument that quasars were too luminous became moot and today the cosmological distance of quasars is accepted by almost all researchers. In 1979 the gravitational lens effect predicted by Einstein's General Theory of Relativity was confirmed observationally for the first time with images of the double quasar 0957+561.[6] In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a general consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other classes, such as blazars and radio galaxies. The huge luminosity of quasars results from the accretion discs of central supermassive black holes, which can convert on the order of 10% of the mass of an object into energy as compared to 0.7% for the p-p chain nuclear fusion process that dominates the energy production in sun-like stars. This mechanism also explains why quasars were more common in the early universe, as this energy production ends when the supermassive black hole consumes all of the gas and dust near it. This means that it is possible that most galaxies, including our own Milky Way, have gone through an active stage (appearing as a quasar or some other class of active galaxy depending on black hole mass and accretion rate) and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation.A quasar (contraction of QUASi-stellAR radio source) is an extremely bright and distant active galactic nucleus. They were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light that were point-like, similar to stars, rather than extended sources similar to galaxies. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy. Quasars show a very high redshift which is an effect of the expansion of the universe between the quasar and the Earth. When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. To be observable at that distance, the energy output of quasars must dwarf that of almost every known astrophysical phenomenon in a galaxy, excepting comparatively short-lived events like supernovae and gamma-ray bursts. Quasars may readily release energy in levels equal to the output of hundreds of average galaxies combined. The output of light is equivalent to one trillion suns. In optical telescopes, quasars look like single points of light (i.e. point source) although many have had their "host galaxies" identified. The galaxies themselves are often too dim to be seen with all but the largest telescopes. Most quasars cannot be seen with small telescopes, but 3C 273, with an average apparent magnitude of 12.9, is an exception. At a distance of 2.44 billion light years, it is one of the most distant objects directly observable with amateur equipment. Some quasars display rapid changes in luminosity, which implies that they are small (an object cannot change faster than the time it takes light to travel from one end to the other; but see quasar J1819+3845 for another explanation). The highest redshift known for a quasar (as of January 2003) is 6.4.[1] Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. No other currently known mechanism appears able to explain the vast energy output and rapid variability. Knowledge of quasars is advancing rapidly. As recently as the 1980s, there was no clear consensus as to their origin. Properties of quasars More than 100,000 quasars are known. All observed spectra have shown considerable redshifts, ranging from 0.06 to the recent maximum of 6.4. Therefore, all known quasars lie at great distances from earth, the closest being 240 Mpc (780 million ly) away and the farthest being 4 Gpc (13 billion ly) away. Most quasars are known to lie above 1.0 Gpc in distance; since light takes such a long time to cover these great distances, the quasars are seen as they existed long ago. Although faint when seen optically, their high redshift implies that these objects lie at a great distance from earth, making quasars the most luminous objects in the known universe. The quasar which appears brightest in the sky is the ultraluminous 3C�273 in the constellation of Virgo. It has an average apparent magnitude of 12.8 (bright enough to be seen through a small telescope), but it has an absolute magnitude of -26.7. So from a distance of 10 parsecs (about 33 light-years), this object would shine in the sky about as brightly as our sun. This quasar's luminosity is, therefore, about 2 trillion (2 � 1012) times that of our sun, or about 100 times that of the total light of average giant galaxies like our Milky Way. The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of -32.2, although high resolution imaging with the Hubble Space Telescope and the 10�m Keck Telescope revealed that this system is gravitationally lensed. A study of the gravitational lensing in this system suggests that it has been magnified by a factor of ~10. It is still substantially more luminous than nearby quasars such as 3C�273. HS 1946+7658 was thought to have an absolute magnitude of -30.3, but this too was magnified by the gravitational lensing effect. Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours. This evidence has allowed scientists to theorize that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale to coordinate the luminosity variations. As such, a quasar varying on the time scale of a few weeks cannot be larger than a few light-weeks across. Quasars exhibit many of the same properties as active galaxies: Radiation is nonthermal and some are observed to have jets and lobes like those of radio galaxies. Quasars can be observed in many parts of the electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0.9 �m), in the near infrared. Iron Quasars show strong emission lines resulting from ionized iron, such as IRAS 18508-7815. Quasar emission generation This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. The quasar-starburst was found by a team of researchers from six institutions Since quasars exhibit properties common to all active galaxies, the emissions from quasars can be readily compared to those of small active galaxies powered by supermassive black holes. To create a luminosity of 1040 W (the typical brightness of a quasar), a super-massive black hole would have to consume the material equivalent of 10 stars per year. The brightest known quasars devour 1000 solar masses of material every year. Quasars 'turn on' and off depending on their surroundings, and since quasars cannot continue to feed at high rates for 10 billion years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy. Quasars also provide some clues as to the end of the Big Bang's reionization. The oldest quasars (redshift > 4) display a Gunn-Peterson trough and have absorption regions in front of them indicating that the intergalactic medium at that time was neutral gas. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest. This indicates that the intergalactic medium has undergone reionization into plasma, and that neutral gas exists only in small clouds. One other interesting characteristic of quasars is that they show evidence of elements heavier than helium indicating that galaxies underwent a massive phase of star formation creating population III stars between the time of the Big Bang and the first observed quasars. Light from these stars may have been observed in 2005 using NASA's Spitzer Space Telescope, although this observation remains to be confirmed. History of quasar observation The first quasars were discovered with radio telescopes in the late 1950s. Many were recorded as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size.[2] Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for the optical counterparts. In 1960, radio source 3C 48 was finally tied to an optical object. Astronomers detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum. Containing many unknown broad emission lines, the anomalous spectrum defied interpretation � a claim by John Bolton of a large redshift was not generally accepted. In 1962 a breakthrough was achieved. Another radio source, 3C 273, was predicted to undergo five occultations by the moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar. This spectrum revealed the same strange emission lines. Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15.8 percent. This discovery showed that 3C�273 was receding at a rate of 47,000�km/s.[3] This discovery revolutionized quasar observation and allowed other astronomers to find redshifts from the emission lines from other radio sources. As predicted earlier by Bolton, 3C�48 was found to have a redshift of 37% the speed of light. The term quasar was coined by Chinese-born U.S. astrophysicist Hong-Yee Chiu in 1964, in Physics Today, to describe these puzzling objects: So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper. � Hong-Yee Chiu in Physics Today, May, 1964 Later it was found that not all (actually only 10% or so) quasars have strong radio emission (are 'radio-loud'). Hence the name 'QSO' (quasi-stellar object) is used (in addition to 'quasar') to refer to these objects, including the 'radio-loud' and the 'radio-quiet' classes. One great topic of debate during the 1960s was whether quasars were nearby objects or distant objects as implied by their redshift. It was suggested, for example, that the redshift of quasars was not due to the expansion of space but rather to light escaping a deep gravitational well. However a star of sufficient mass to form such a well would be unstable and in excess of the Hayashi limit.[4] Quasars also show unusual spectral emission lines which were previously only seen in hot gaseous nebulae of low density, which would be too diffuse to both generate the observed power and fit within a deep gravitational well.[5] There were also serious concerns regarding the idea of cosmologically distant quasars. One strong argument against them was that they implied energies that were far in excess of known energy conversion processes, including nuclear fusion. At this time, there were some suggestions that quasars were made of some hitherto unknown form of stable antimatter and that this might account for their brightness. Others speculated that quasars were a white hole end of a wormhole. However, when accretion disc energy-production mechanisms were successfully modeled in the 1970s, the argument that quasars were too luminous became moot and today the cosmological distance of quasars is accepted by almost all researchers. In 1979 the gravitational lens effect predicted by Einstein's General Theory of Relativity was confirmed observationally for the first time with images of the double quasar 0957+561.[6] In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a general consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other classes, such as blazars and radio galaxies. The huge luminosity of quasars results from the accretion discs of central supermassive black holes, which can convert on the order of 10% of the mass of an object into energy as compared to 0.7% for the p-p chain nuclear fusion process that dominates the energy production in sun-like stars. This mechanism also explains why quasars were more common in the early universe, as this energy production ends when the supermassive black hole consumes all of the gas and dust near it. This means that it is possible that most galaxies, including our own Milky Way, have gone through an active stage (appearing as a quasar or some other class of active galaxy depending on black hole mass and accretion rate) and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation.

34. Quasars have huge red-shifts!

35. Quasars http://andyxl.wordpress.com/2007/06/08/quasars-donuts-and-the-unified-faith/ http://andyxl.wordpress.com/2007/06/08/quasars-donuts-and-the-unified-faith/

36. Event Horizon http://imagecache2.allposters.com/images/PF%5C142005/PF_1158151.jpghttp://imagecache2.allposters.com/images/PF%5C142005/PF_1158151.jpg

37. Abandoning the cosmological constant

38. Extrapolating backward in time, there had to be one hell of a Big Bang! http://www.meta-library.net/media/bigbang-lg.jpghttp://www.meta-library.net/media/bigbang-lg.jpg

39. Age of the Universe Radioactive dating of stars showed that no stars were formed earlier than 200,000 years after the Big Bang. Examining the relative intensities of elemental spectral lines of old stars yields ratios of thorium/europium and uranium/thorium isotopes, indicating an average age of 14 billion years.

40. Evidence for the Big Bang: Cosmic Microwave Background Radiation In 1964, Penzias and Wilson observed microwave blackbody background radiation that permeates the universe. The very hot blackbody radiation of several billion years ago has Doppler-shifted to 3�K today. Satellite measurements show a nearly isotropic 3�K radiation background. Penzias and Wilson pic from http://www.bell-labs.com/project/feature/archives/cosmology/Penzias and Wilson pic from http://www.bell-labs.com/project/feature/archives/cosmology/

41. Early Universe Nucleo-synthesis By considering current ratios of isotopes, we can learn more about the early universe. We find that it was hot and dense enough to create only the lightest few elements. So where did all the heavier elements come from?

42. Supernovae and nucleo-synthesis Supernovae provide the ultrahigh temperature and pressure to produce all the heavier elements. Supernova 1604, also known as Kepler's Supernova or Kepler's Star, was a supernova which occurred in the Milky Way, in the constellation Ophiuchus. As of 2007, it is the last supernova to have been unquestionably observed in our own galaxy, occurring no farther than 6 kiloparsecs or about 20,000 light-years from Earth. Visible to the naked eye, it was brighter at its peak than any other star in the night sky, and all the planets (other than Venus), with apparent magnitude -2.5. The supernova was first observed on October 9, 1604.[2] The German astronomer Johannes Kepler first saw it on October 17, subsequently named after himself. His book on the subject was entitled De Stella nova in pede Serpentarii (On the new star in Ophiuchus's foot).Supernova 1604, also known as Kepler's Supernova or Kepler's Star, was a supernova which occurred in the Milky Way, in the constellation Ophiuchus. As of 2007, it is the last supernova to have been unquestionably observed in our own galaxy, occurring no farther than 6 kiloparsecs or about 20,000 light-years from Earth. Visible to the naked eye, it was brighter at its peak than any other star in the night sky, and all the planets (other than Venus), with apparent magnitude -2.5. The supernova was first observed on October 9, 1604.[2] The German astronomer Johannes Kepler first saw it on October 17, subsequently named after himself. His book on the subject was entitled De Stella nova in pede Serpentarii (On the new star in Ophiuchus's foot).

43. The Cosmological Principle

44. Looking into the distance is looking back in time.

45. The Big Bang The Big Bang model rests on two theoretical foundations: The General Theory of Relativity The Cosmological Principle What does General Relativity have to say? The Robertson�Walker metric is the simplest space-time geometry consistent with an isotropic, homogeneous universe.

46. Possible geometries of the universe wikipediawikipedia

47. The Future of the Universe Looking into the past, there is little question that the age of the universe is about 13.7 billion years. What about the future? There are three possible futures�

48. The Missing Mass and Dark Matter Image from http://www.myastrologybook.com/Astrology-Book-Milky-Way-Galaxy-Sombrero.jpgImage from http://www.myastrologybook.com/Astrology-Book-Milky-Way-Galaxy-Sombrero.jpg

49. The Missing Mass http://news.bbc.co.uk/2/low/science/nature/318132.stmhttp://news.bbc.co.uk/2/low/science/nature/318132.stm

50. Microwave background fluctuations in the different universe shapes http://www.astronomynotes.com/cosmolgy/s10.htm Data: http://map.gsfc.nasa.gov/m_mm/sg_earlyuniv.htmlhttp://www.astronomynotes.com/cosmolgy/s10.htm Data: http://map.gsfc.nasa.gov/m_mm/sg_earlyuniv.html

51. The Missing Mass and Dark Matter Omage from http://coolcosmos.ipac.caltech.edu//cosmic_classroom/ir_tutorial/images/browndwarf.gif http://www.eclipse.net/~cmmiller/DM/ Dark Matter What do scientists look for when they search for dark matter? We cannot see or touch it: its existence is implied. Possibilities for dark matter range from tiny subatomic particles weighing 100,000 times less than an electron to black holes with masses millions of times that of the sun (9). The two main categories that scientists consider as possible candidates for dark matter have been dubbed MACHOs (Massive Astrophysical Compact Halo Objects), and WIMPs (Weakly Interacting Massive Particles). Although these acronyms are amusing, they can help you remember which is which. MACHOs are the big, strong dark matter objects ranging in size from small stars to super massive black holes (1). MACHOs are made of 'ordinary' matter, which is called baryonic matter. WIMPs, on the other hand, are the little weak subatomic dark matter candidates, which are thought to be made of stuff other than ordinary matter, called non-baryonic matter. Astronomers search for MACHOs and particle physicists look for WIMPs. Astronomers and particle physicists disagree about what they think dark matter is. Walter Stockwell, of the dark matter team at the Center for Particle Astrophysics at U.C. Berkeley, describes this difference. "The nature of what we find to be the dark matter will have a great effect on particle physics and astronomy. The controversy starts when people made theories of what this matter could be--and the first split is between ordinary baryonic matter and non-baryonic matter" (10). Since MACHOs are too far away and WIMPs are too small to be seen, astronomers and particle physicists have devised ways of trying to infer their existence. MACHOs Massive Compact Halo Objects are non-luminous objects that make up the halos around galaxies. Machos are thought to be primarily brown dwarf stars and black holes (2). Like many astronomical objects, their existence had been predicted by theory long before there was any proof. The existence of brown dwarfs was predicted by theories that describe star formation (7). Black holes were predicted by Albert Einstein's General Theory of Relativity (11).Brown Dwarfs. Brown dwarfs are made out of hydrogen--the same as our sun but they are typically much smaller. Stars like our sun form when a mass of hydrogen collapses under its own gravity and the intense pressure initiates a nuclear reaction, emitting light and energy. Brown dwarfs are different from normal stars. Because of their relatively low mass, brown dwarfs do not have enough gravity to ignite when they form (7). Thus, a brown dwarf is not a "real" star; it is an accumulation of hydrogen gas held together by gravity. Brown dwarfs give off some heat and a small amount of light (7).Black Holes. Black holes, unlike brown dwarfs, have an over-abundance of matter. All that matter "collapses" under its own enormous gravity into a relatively small area. The black hole is so dense that anything that comes too close to it, even light, cannot escape the pull of its gravitational field (11). Stars at safe distance will circle around the black hole, much like the motion of the planets around the sun (7). Black holes emit no light; they are truly black. Omage from http://coolcosmos.ipac.caltech.edu//cosmic_classroom/ir_tutorial/images/browndwarf.gif http://www.eclipse.net/~cmmiller/DM/ Dark Matter What do scientists look for when they search for dark matter? We cannot see or touch it: its existence is implied. Possibilities for dark matter range from tiny subatomic particles weighing 100,000 times less than an electron to black holes with masses millions of times that of the sun (9). The two main categories that scientists consider as possible candidates for dark matter have been dubbed MACHOs (Massive Astrophysical Compact Halo Objects), and WIMPs (Weakly Interacting Massive Particles). Although these acronyms are amusing, they can help you remember which is which. MACHOs are the big, strong dark matter objects ranging in size from small stars to super massive black holes (1). MACHOs are made of 'ordinary' matter, which is called baryonic matter. WIMPs, on the other hand, are the little weak subatomic dark matter candidates, which are thought to be made of stuff other than ordinary matter, called non-baryonic matter. Astronomers search for MACHOs and particle physicists look for WIMPs. Astronomers and particle physicists disagree about what they think dark matter is. Walter Stockwell, of the dark matter team at the Center for Particle Astrophysics at U.C. Berkeley, describes this difference. "The nature of what we find to be the dark matter will have a great effect on particle physics and astronomy. The controversy starts when people made theories of what this matter could be--and the first split is between ordinary baryonic matter and non-baryonic matter" (10). Since MACHOs are too far away and WIMPs are too small to be seen, astronomers and particle physicists have devised ways of trying to infer their existence.

52. The Missing Mass and Dark Matter Image and some text: http://zebu.uoregon.edu/~soper/Mass/WIMPS.html http://www.bookrags.com/sciences/physics/weakly-interacting-massive-particle-wop.html Weakly Interacting Massive Particles Weakly interacting massive particles, or WIMPs, are a theoretical construct which was proposed to account for apparently missing mass in the galaxy. These particles would have to have much more mass than traditional hard-to-detect particles like neutrinos, so that they could account for enough of the mass of the galaxy. However, they would have to interact exclusively with the weak force, making it difficult for them to be observed by other, more traditional means. They could not emit light or otherwise interact with the electromagnetic strong forces, making them almost impossible to detect directly. The rate of the universe's expansion can be measured, and by the current measurements, it is much slower than it ought to be for the amount of matter detected by current standards. Also, the observed movements of galaxies and galactic clusters is not consistent with the gravitational forces due to the visible matter. That is, there must be a great deal of unseen mass in the universe that is affecting the movements of the galaxies. The missing amount of gravitational matter is sometimes called "missing matter," or more commonly "dark matter." It is simply matter that does not emit electromagnetic radiation and thus is not visible to our astronomical instruments. The WIMPs would have to have a spherically symmetric distribution throughout the galaxy--that is, they would have to exist in about equal numbers in every direction--in order to explain the observed galactic dynamics. Some physicists think that neutrinos may account for the weakly interacting massive particle mass. However, there is a known upper bound on the neutrino mass. Even with the most massive possible neutrino, they could only account for about 10% of the dark matter. The missing matter would have to be composed of elementary particles similar to neutrinos, however. Usually WIMP candidates are considered to be nonbaryonic, that is, not composed of quarks like the proton and neutron. Baryonic candidates are separated into a different category of matter and are not properly WIMPs since they can undergo strong and electromagnetic interactions. Many different experimental searches for WIMPS have been carried out. Because WIMPs are massive, they can collect at the center of massive bodies such as the Earth or Sun. Some experimental searches have concentrated on looking for WIMP decay products which come from the Earth's core or the direction of the Sun. It is also possible for WIMPs to change the temperature profile of the Sun's interior by carrying energy out of the core. This, in turn, would affect the neutrino flux coming from the Sun. Other searches have looked for evidence of WIMPs moving through their experimental detectors. To date, no clear evidence of WIMPs has been uncovered. Given the continuing developments in astrophysics detector technology, the search for WIMPs shows promise. However, these particles are still only theoretical, their properties not completely agreed upon. There are even some physicists who think that a whole new view of gravity is more appropriate than new exotic particles to explain the behavior of our galaxy. The existence of WIMPs is one of the most interesting problems to combine astrophysical observations and particle physical theory at the beginning of the twenty-first century.Image and some text: http://zebu.uoregon.edu/~soper/Mass/WIMPS.html http://www.bookrags.com/sciences/physics/weakly-interacting-massive-particle-wop.html Weakly Interacting Massive Particles Weakly interacting massive particles, or WIMPs, are a theoretical construct which was proposed to account for apparently missing mass in the galaxy. These particles would have to have much more mass than traditional hard-to-detect particles like neutrinos, so that they could account for enough of the mass of the galaxy. However, they would have to interact exclusively with the weak force, making it difficult for them to be observed by other, more traditional means. They could not emit light or otherwise interact with the electromagnetic strong forces, making them almost impossible to detect directly. The rate of the universe's expansion can be measured, and by the current measurements, it is much slower than it ought to be for the amount of matter detected by current standards. Also, the observed movements of galaxies and galactic clusters is not consistent with the gravitational forces due to the visible matter. That is, there must be a great deal of unseen mass in the universe that is affecting the movements of the galaxies. The missing amount of gravitational matter is sometimes called "missing matter," or more commonly "dark matter." It is simply matter that does not emit electromagnetic radiation and thus is not visible to our astronomical instruments. The WIMPs would have to have a spherically symmetric distribution throughout the galaxy--that is, they would have to exist in about equal numbers in every direction--in order to explain the observed galactic dynamics. Some physicists think that neutrinos may account for the weakly interacting massive particle mass. However, there is a known upper bound on the neutrino mass. Even with the most massive possible neutrino, they could only account for about 10% of the dark matter. The missing matter would have to be composed of elementary particles similar to neutrinos, however. Usually WIMP candidates are considered to be nonbaryonic, that is, not composed of quarks like the proton and neutron. Baryonic candidates are separated into a different category of matter and are not properly WIMPs since they can undergo strong and electromagnetic interactions. Many different experimental searches for WIMPS have been carried out. Because WIMPs are massive, they can collect at the center of massive bodies such as the Earth or Sun. Some experimental searches have concentrated on looking for WIMP decay products which come from the Earth's core or the direction of the Sun. It is also possible for WIMPs to change the temperature profile of the Sun's interior by carrying energy out of the core. This, in turn, would affect the neutrino flux coming from the Sun. Other searches have looked for evidence of WIMPs moving through their experimental detectors. To date, no clear evidence of WIMPs has been uncovered. Given the continuing developments in astrophysics detector technology, the search for WIMPs shows promise. However, these particles are still only theoretical, their properties not completely agreed upon. There are even some physicists who think that a whole new view of gravity is more appropriate than new exotic particles to explain the behavior of our galaxy. The existence of WIMPs is one of the most interesting problems to combine astrophysical observations and particle physical theory at the beginning of the twenty-first century.

53. The universe expansion seems to be accelerating! The accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. In 1998 observations of Type Ia supernovae suggested that the expansion of the universe is speeding up.[1][2] In the past few years, these observations have been corroborated by several independent sources: the cosmic microwave background[citation needed], gravitational lensing[citation needed], age of the universe[citation needed] and large scale structure[citation needed], as well as improved measurements of the supernovae[3][4]. An expanding universe means that density drops. If acceleration continues eventually all galaxies beyond our own local supercluster will redshift so far that it will become hard to detect them, the distant universe will turn dark. Models attempting to explain accelerating expansion include the cosmological constant, quintessence, and phantom energy, with the latest WMAP data favoring the cosmological constant. The most important property of dark energy is that it has negative pressure which is distributed relatively homogeneously in space. Phantom energy in a scenario known as the Big Rip causes an exponentially increasing divergent expansion, which overcomes the gravitation of the local group and tears apart our Virgo supercluster, it then tears apart the milky way galaxy, our solar system, and finally even atoms. Measurements of acceleration are thought crucial to determining the ultimate fate of the universe, however we should expect the implications of such a major discovery to develop slowly over many years in the same way the big bang model has continued to develop. The density of dark matter in an expanding universe disappears more quickly than dark energy (see Equation of State (Cosmology)) and, eventually, the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant for a cosmological constant). The discovery by the Supernova Cosmology Project (SCP) and the High-Z Supernova team that the expansion of the universe is accelerating poses an exciting mystery � for if the universe were governed by gravitational attraction, its rate of expansion would be slowing. Acceleration requires a strange �dark energy� opposing this gravity. Is this Einstein�s cosmological constant, or more exotic new physics? Whatever the explanation, it will lead to new discoveries in astrophysics, particle physics, and gravitation. Observations of exploding stars called Type Ia supernovae use them as markers of the expansion, of the growth of the universe as a function of time. Variations in the growth of distances reveal a picture of the cosmic environment, and so the pull of dark energy, in the way that the width of tree ring growth indicates the Earth's climatic environment over time. Combined with other astrophysical measurements, supernovae imply that more than two-thirds of our universe must be this dark energy. To uncover its nature, we need to find many more supernovae over a much wider range of distances, from nearby supernovae all the way out to very distant supernovae that exploded when our universe was much younger and only a third of its present size. We will use as well gravitational lensing, the distortions of distant galaxies by foreground matter in other galaxies and clusters, as another measure of distances and growth of structure. Type Ia supernovae are so similar and so bright they can be calibrated to make excellent �standard candles� for measuring distance. Moreover, their energy spectra and changes in brightness over time are rich sources of information, allowing us to see small differences due to their local environments and to compare them, like to like, over the entire redshift range. Of course we also need tight control over uncertainties, like intervening dust or the properties of the stars that became supernovae. Gravitational lensing, and possibly other cosmological probes, will combine with the supernova data to determine the precise nature of the mysterious dark energy. The Supernova/Acceleration Probe (SNAP) satellite observatory is capable of measuring thousands of distant supernovae and mapping hundreds to thousands of square degrees of the sky for gravitational lensing each year. The results will include a detailed expansion history of the universe over the last 10 billion years, determination of its spatial curvature to provide a fundamental test of inflation - the theoretical mechanism that drove the initial formation of structure in the universe, precise measures of the amounts of the key constituents of the universe, OM and OL, and the behavior of the dark energy and its evolution over time.The accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. In 1998 observations of Type Ia supernovae suggested that the expansion of the universe is speeding up.[1][2] In the past few years, these observations have been corroborated by several independent sources: the cosmic microwave background[citation needed], gravitational lensing[citation needed], age of the universe[citation needed] and large scale structure[citation needed], as well as improved measurements of the supernovae[3][4].

54. The cosmological constant revisited

55. The Friedmann Equation The various key constants are related by the Friedmann Equation: Dividing both sides by H2 yields: Each of the terms in this equation has special significance:

56. The cosmological constant rules! Visible matter is only 4% of the total mass in the universe. Dark matter accounts for 23%, and 73% is mysterious dark energy. The star cluster and galaxy data are consistent with a low density universe. The cosmic microwave background is consistent with a flat universe. Distance determinations based on Type Ia supernovae data are consistent with an accelerating universe. These sets of data constrain the universe mass parameters to the values: Ok = 0, Om = 0.3, and OL = 0.7. The cosmological constant appears to be the dominant effect! But why? And what is it really? http://www.prime-spot.de/Bilder/BR/lambda_large.jpghttp://www.prime-spot.de/Bilder/BR/lambda_large.jpg

57. We don�t have a clue what it really is�

58. Issues for the Big Bang Why is the universe flat? Why does the universe appear to be homogeneous and isotropic? It is amazing that opposite sides of the universe that are 27 billion light-years apart have the same microwave background in every direction. Why have we never detected magnetic monopoles? Magnetic monopoles would bring symmetry to many theories in physics.

59. The Inflationary Universe A variation of the Big Bang model proposes that the universe suddenly expanded by a factor of 1050 during the time 10-35 to 10-31 seconds after the Big Bang. This is called the inflationary epoch. It is due to the separation of the nuclear and electroweak forces. After the inflationary period, it resumed its evolution from the Big Bang. The inflationary theory requires that the universe be flat and the mass density be near the critical density. The universe reached equilibrium before the inflationary period began. This explains the homogeneous universe. Magnetic monopoles would have to occur along the boundaries or walls of different domains. So this explains why we don�t see them.

60. The Inflationary Universe Image from http://en.wikipedia.org/wiki/Image:CMB_Timeline300.jpgImage from http://en.wikipedia.org/wiki/Image:CMB_Timeline300.jpg

61. Particle physics is the basis of cosmology, and even this breaks down for early enough times. Before 10-43 s after the Big Bang we have no theories because the known laws of physics don�t apply. In the beginning, the universe most likely had infinite mass density and zero spacetime curvature. The size of the universe at 10-43 s was < 10-52 m. The four fundamental forces of strong, electromagnetic, weak, and gravity were all unified into one force.

62. The Future of Earthlings The Demise of the Sun The sun is about halfway through its life as a star, which started 4.5 billion years ago. As its hydrogen fuel is exhausted, the sun will contract, but then heat up even more as it next burns helium. The heat will cause it to expand and even consume the Earth. The sun will become a red giant and the surface will cool from 5500 K to 4000 K. Eventually the light elements in the outer layers will boil off and the sun will contract to the size of the Earth with a final mass that will be half its current mass. The sun will cool down to become a white dwarf and then a cold black dwarf. Image: http://www.historyoftheuniverse.com/starold.htmlImage: http://www.historyoftheuniverse.com/starold.html

63. The Long-Term Future of the Universe The universe is flat, and it is expanding. And the expansion is accelerating. Eventually all the stars in our galaxy will die as well as those in all other galaxies. Black holes will consume them and eventually consume all available mass. It seems that the universe will evolve to a cold, dark place. And that�s even before protons begin to decay� But there�s so much we don�t know. We await the next revolution� Image from:http://images.google.com/imgres?imgurl=http://www.futurehi.net/images/deepfield.jpg&imgrefurl=http://www.futurehi.net/archives/000168.html&h=317&w=475&sz=20&hl=en&start=10&tbnid=30CfneoE9gFf2M:&tbnh=84&tbnw=126&prev=/images%3Fq%3Dfuture%2Bof%2Bthe%2Buniverse%26svnum%3D10%26hl%3Den%26lr%3D%26safe%3DoffImage from:http://images.google.com/imgres?imgurl=http://www.futurehi.net/images/deepfield.jpg&imgrefurl=http://www.futurehi.net/archives/000168.html&h=317&w=475&sz=20&hl=en&start=10&tbnid=30CfneoE9gFf2M:&tbnh=84&tbnw=126&prev=/images%3Fq%3Dfuture%2Bof%2Bthe%2Buniverse%26svnum%3D10%26hl%3Den%26lr%3D%26safe%3Doff