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Chapter 28 section 3 and 4. Stellar Parallax. The apparent shift in the position of an object when viewed from 2 locations. The closer an object is to an observer the greater its parallax.
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Stellar Parallax • The apparent shift in the position of an object when viewed from 2 locations. • The closer an object is to an observer the greater its parallax. • The measurement of parallax is used directly to find the distance of the body from the Earth and from the Sun. • The two positions of the observer and the position of the object form a triangle; if the base line between the two observing points is known and the direction of the object as seen from each has been measured, the apex angle (the parallax) and the distance of the object from the observer can be found simply.
http://video.google.com/videoplay?docid=-7444315722228433415#http://video.google.com/videoplay?docid=-7444315722228433415# • http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/007299181x/78778/Parallax_Nav.swf::Stellar Parallax Interactive
Life Cycle of Stars • Stars are born from great clouds of gas and dust. • They mature, grow old, and die. • When they die they can produce new clouds of dust and new stars can form here. • The more massive a star is the shorter its life will be.
The H-R diagram plots the luminosity of the stars against their temperatures. • There are several groups noted on the H-R diagram the groups represent the life cycles of stars. • The majority of the stars (90%) are in the band that crosses the entire diagram. This band is called the main sequence. • The stars in the main sequence are called main-sequence stars.
Main Sequence stars • Stars on the main sequence can also be known as happy, healthy stars. • They are all fusing hydrogen to helium. • They can differ in size, surface temperature, and absolute magnitude. • Some of them can burn for a million years, others can last billions of years.
Giant Stars • Larger, more luminous stars found above the main sequence stars on the H-R Diagrams. • They have diameters from 10 to 100 times greater than that of our sun.
Supergiant • Are more luminous than the giant stars • They are more than 100 times that of the sun • Even thought red super giants are cool, they are huge and therefore very luminous • Betelgeuse is an example of a red super giant
White Dwarfs • A white dwarf is a star that is near the end of its life. • These stars used to be red giants • As the star began to die it puffed off its outer layers to stabilize itself • What is now left is the inner core
Birth of a star • A nebula is a nursery for stars, it is where stars are born • A nebula contains gas and dust. 99% of the nebula is gas, mostly hydrogen. • A nebula may begin to condense in on itself when something like a shock wave from a super nova hits it.
The force compresses regions of the nebula where particles of gas and dust condense, and become denser, and hotter. • If it is a large nebula parts will begin to glow due to the increasing temperature. • These glowing nebula are called protostars • They are not stars yet because they are not producing H to He fusion. • Eventually as compression continues the center gets so hot that fusion begins in the center, and it is officially a star.
Death of a Star like the Sun • How do you think the sun will die? • Main sequence stars with a mass similar to the sun will remain the same size for billions of years. • Eventually they will begin to brighten • When all of the hydrogen is used the star begins to shrink. • The hydrogen core shrinks and contracts which causes the star to heat up. This triggers fusion outside the core.
The star begins to die when the temperature of the star is hot enough to fuse helium into heavier elements. • The heaviest elements that can form is Carbon and Oxygen due to the temperature and a Carbon, Oxygen core forms • The outer layers of the star are puffed off, until the only thing that is left is the carbon-oxygen core is left.
Planetary Nebula • The halo that surrounds a star that is dyeing. • Eventually the halo dissipates, and the white dwarf is all that is left.
Death of a massive star • Hydrogen is fused more quickly in larger stars, and fusion processes continue until iron is formed in the nucleus. • The lifespan is less than a billion years • When the star is no longer fusing H to He the star swells to become a super giant • When the core is Fe it no longer releases energy it absorbs it. • The Fe core quickly and suddenly collapses.
The collapse of the core produces a shock wave that blasts the star’s outer layers into space at thousands of km per seconds and produces a huge burst of light. • The explosion produces a supernova. • The supernova is millions of times brighter than the original star. • A single supernova can outshine all of the stars in its galaxy for a short period of time.
Supernova remnants • In 1987 there was a supernova in the Large Magellanic Cloud which is an irregular galaxy close to us. • When the star produces a supernova elements heavier than iron are produced. • We are star stuff: elements from earth came from stars that long ago exploded.
Populations of Stars • Population I: Sun like stars ( fairly young and recycled) High content of heavy elements. These are the most common. • Population II: Previous generations, less recycling, lower amount of heavy elements. Rare to find these. • Population III: Original generation of stars, no heavy elements in them. None of these have ever been seen. • Why?
Remnants of Massive Stars • Neutron star: The core of a supernova, which is trillion times more dense than our sun, and only 20 km in diameter! • Pulsar: when a neutron star is first born it gives off bursts of radio waves, and it spins rapidly. • Black hole: a remnant of a star that is 15 times more massive than the sun. The black hole the mass of 10 suns condensed in and area that is 30 km wide.
Black Holes • The gravitational force inside a black hole is so strong that even light can’t escape. • How can we find them? • They give off immense X-rays. • When atoms are pulled into the black hole they are ripped apart by the gravity of the back hole and give off x-rays. • Many scientists think that at the center of most galaxies is a super massive black hole.
Galaxies and the Universe • What is a galaxy? • A group of millions to billions of stars held together by gravity. • How many are there in our observable universe? • 50-100 billion
What is a universe? • The Universe comprises everything we perceive to physically exist, the entirety of space and time, all forms of matter and energy, and the physical laws that govern them.
The Milky Way Galaxy (our home) • Every star that you see in the sky is in the milky way galaxy • It is a spiral galaxy • It is shaped like a think disk with a central bulge • The diameter of the milky way is 100,000 light years. • Its greatest thickness is about 10,000 light years
The sun is about 26,000 light years from the center. • We see a hazy band of light we call the milky way, but the whole galaxy is the milky way. • Most spiral galaxies are larger than us. • The milky way belongs to a group of more than 30 galaxies known as the local group. • 2 Megallanic clouds, and Andromeda are the largest galaxies in the local group.
Center of our galaxy • Scientists know at the center of our galaxy must be: • An intense energy source • Motion of very heavy high mass stars • The center must be very small (smaller than our solar system: (9 billion km radius) Could be a super massive black hole.
Types of Galaxies • No two galaxies are the same, but they can be classified by shape. • Spiral • Elliptical • Irregular • lenticular
Spiral galaxies • Spiral galaxies come in a range of shapes • Some have large, bright nuclei of stars and tightly wound spiral arms. • Some have very small, dim nuclei, and open arms. • Two types: Spiral, barred spiral. • A: Large bulge, tightly wound • B: medium bulge, medium wound • C: small bulge, loose wound • Must look face on to see spirals!!!
Elliptical Galaxies • Range from nearly spherical to lens shaped. • Their stars are concentrated in their centers • They have no arms • They contain less gas and dust than spiral galaxies • They contain few, if any young stars. Why?
