The Sky is Our Laboratory

1. The Sky is Our Laboratory

2. Your Questions first How far away can we get out out in space today? Do you believe we have been to the moon? How big is the Universe? What percent of the total known Universe is our star (Sun)? Could there be anything faster than the speed of light? Are the laws of physics universal? Is it dark in space? Would a spaceship need headlights? What are the exact definitions of galaxy and cosmos? How are stars formed? Why do hottest stars die young? What is the Orion Nebula? Is a white dwarf just a giant diamond? When were pulsars discovered? Do pulsars ever stop beaconing? What are the theories about black holes? Where do quasars come into the picture? What is a quasar? What is the big, main bright core in the middle of galaxies? How many different types of galaxies are there? What is the Local Group? What is a satellite galaxy? What will eventually happen to the Universe? What is the dark energy/matter?

3. 1. How far away have we gone into space?2. Do you believe we have gone to the moon?3. How big is the Universe? • As far as we know, humans have not gone any further than the Moon; about 384,000 km (~243,000 miles) or 1.28 light minutes . • Automatic spacecrafts (robots) have been and are exploring the planets; about 5,900,000,000 km or ~ 5.5 light hours. • Telescopes (which we will discuss today) have reached roughly back to when the Universe was `only’ 1-2 Gyr (1,000,000,000 - 2,000,000,000 yrs) old. Today the Universe is about 13.5 Gyr old. Its size, calculated as the `event horizon’ is 13.5 billions of light years (~225,000 Galaxy’s radii) • 1 light year (ly) = 9470 billions km = 5900 billions miles • distance Sun-Earth = 8.3 light minutes • size of the Solar System ~ 5.5 light hours • size of our Galaxy ~ 60,000 ly ~ 100 millions solar system radii

4. 4. What percent of the total known Universe is our star (Sun)? 5. Could there be anything faster than the speed of light?6. Are the laws of physics universal? • M(Sun) = 7.5 x 10-22 M(Universe) • We don’t know of anything faster than the speed of light in vacuum (about 300,000 km/s or 186,000 miles per second) • the speed of light through transparent or translucent media is slower; e.g., it is about 124,000 km/s in diamond • Scientists work with the assumption that the laws of physics are universal. This has worked well so far, but challenges can always raise.

5. 7. Is it dark in space? Would a spaceship need headlights?8. What are the exact definitions of galaxy and cosmos? • Yes, it is very dark in space. Outside the solar system, the next closest star, Proxima Centauri, is about 4.3 ly away. On average in our own Galaxy each star is about 10 ly away from every other star in every direction. • more than headlights, I would advice installing a radar in the spaceship (especially within and around solar systems) to avoid collision with dark bodies. • A galaxy is a body of stars, gas, and dark matter kept together by gravity; • The `cosmos’ is a loose definition to indicate the Universe, or components of it. It comes from Greek, to indicate an harmonious whole, opposed to chaos.

6. 9. How are stars formed? Why do hottest stars die young?10. What is the Orion Nebula? • Hottest (more massive) stars die young because they use up their nuclear fuel more quickly than less massive stars: • L ~ M3.5 ~ R2 T4 • A star 10 times our Sun is about 3,000 times more luminous and about 3 times hotter (not 7 times, as also the radius grows)

7. 11. Is a white dwarf just a giant diamond?12. When were pulsars discovered? Do pulsars ever stop beaconing? • A white dwarf is a dying star, which has terminated its nuclear fuel, and has contracted to roughly the size of the Earth. • This fate is shared by all stars with masses below 8 M(Sun), and they end up with masses below 1.4 M(Sun) [the Chandrasekar limit]. Most WDs have masses around 0.6 M(Sun) • The core of a WD is commonly a mixture of Carbon and Oxygen, and is releasing as light the contraction heat. • When cold (~6,000-8,000 K) they may crystallize into `giant diamonds’ (first confirmed observationally from WD oscillations in 2004). • Pulsars are fast rotating neutron stars, first discovered in 1967. The spinning magnetic field of the star is producing the pulses. Neutron stars form from collapsing stars with masses below 3.2 M(Sun).

8. 13. What are the theories about black holes?14. Where do quasars come into the picture? What is a quasar? • Black holes are collapsed stars with M>= 3.2 M(Sun). Their gravitational pull is so large that not even the light can escape! We can only see them when surrounding matter spirals into the hole. • A quasar is a very (super-)massive black hole in the center of a young galaxy, which is accreting large amounts of mass, and emitting large amounts of energy. Quasars are a very active phase of the life of galaxies, found at high redshifts.

9. 15. What is the big, main bright core in the middle of galaxies?16. How many different types of galaxies are there? • It is called the `bulge’ and it consists of stars, generally fairly old. Most galaxies have bulges.. For instance, elliptical galaxies could be considered to consist entirely of a `bulge’. Most spiral galaxies have bulges. There is a (now) well-known relation between the size of a bulge and the mass of the supermassive black hole in the center of a galaxy (the Magorrian Relation) • Many….

10. 17. What is the Local Group?18. What is a satellite galaxy? • It is a group of galaxies bound together by gravity. The Milky Way and the Andromeda Galaxy are the two largest and most massive galaxies in the Local Group. • The existence of galaxy groups is predicted by current theories of galaxy formation • Another strong prediction is the presence of `satellite galaxies’, small galaxies that orbit large galaxies like the Milky Way. • The Milky Way has about 15 satellites within ~450,000 light years

11. 19. What will eventually happen to the Universe?20. What is the dark energy/matter? • Excellent question! It is currently accelerating, but its actual destiny depends on the density of matter and energy, and their nature. • The Universe has been accelerating for the past 3/4 of its life, and this acceleration has been attributed to Dark Energy (nobody really knows what this is). • Dark Matter is also unknown, but we have evidence for its existence because of its gravitational pull (e.g., in groups of galaxies, and in the external regions of galaxies). • Most of the energy content of the Universe is currently attributed to Dark Energy (70%), with only or less than 30% for Dark Matter (and about 4.5% for ordinary matter or baryons).

12. Telescopes: Our Eyes in the Sky The twin 10-m Keck telescopes (Hawaii) are currently the largest telescopes in existence. Plans for larger telescopes (up to 42-m) are currently being considered (ESO, USA)

13. Why do you need large telescopes? Telescopes are `light buckets’. The bigger, the more light they collect, and the more distant the objects they can observe.

14. Telescopes for probing the Universe The Universe is expanding (Ho=71 +/- 5 km/s/Mpc), and is ~13.5 billions years old.

15. Different telescopes for different types of light Spitzer Hubble Herschel LMT

16. Electromagnetic spectrum

18. The Multiwavelength Sun Infrared Radio Optical X-ray

19. A Multiwavelength Universe • Different wavelengths carry different information: • Shorter wavelengths carry information on very energetic phenomena (e.g. black holes, star formation) • Optical wavelengths carry information on the structures of galaxies and their motions (the assembly of the bodies of galaxies, their size) • Longer wavelengths carry information on the chemical composition, physical state (gas and dust, presence, chemical elements; temperature)

20. Angular Resolution • The bigger the telescope, the smaller the detail it can discriminate •  = 0.02(nm) / D(cm) • This also depends on the type of light the telescope detects (the wavelength ) • On the ground, the limitation is due to the `blurring’ of our own atmosphere (called `seeing’). Typical values are around 0.5-1 arcseconds, but it really depends on the atmopheric conditions.

21. We can go to space Space Ground No atmosphere in space

22. For some types of light, space is the only solution, as the atmosphere is opaque

23. What is up there now… • HUBBLE: • Launched early 1990 • Serviced 4 times • 2.4-m mirror • 4(5) UV/Optical/IR instruments Instruments: ACS and WFPC2: UV/Optical imagers STIS: UV spectrograph/imager NICMOS: Near-IR imager/spectrometer

24. CHANDRA: • Launched mid-1999 • Non-serviceable • 4 nested mirrors • 2 instruments for low/high energy X-ray photons PKS 0637 Instruments: ACIS: CCD imager/spectrometer (+ HETG) HRC: High resolution camera (+ LETG) 3C273

25. SPITZER: • Launched mid-2003 • Non-serviceable • 0.85-m mirror • 3 mid/far-infrared instruments Instruments: IRAC: Mid-infrared imager MIPS: Far-infrared imager/spectrometer IRS: Mid-infrared spectrometer

26. Are there radio telescopes in space?

27. Astronomy Picture of the Day Sept 21st, 2007: An X-ray (Chandra) and infrared (Spitzer) light composition of a young stellar cluster, located only 420 ly away in the Corona Australis. The X-ray emission comes from the hot coronae of the young, massive stars; the infrared light is a combination of dust and protostars emission.