STARS
I. Stellar Evolution
The Life Cycles of Stars Dr. Jim Lochner, NASA/GSFC
A. Nebula- cloud of gas and dust
B. Protostar- spinning disk
C. Main Sequence 1. When the protostar reaches 15 million C, nuclear fusion begins. (H He) and enormous amounts of E is released.
Main Sequence 1. When E begins to be released, a star is born
Main Sequence Stay a stable size because gravity counteracts H He fusion. H He http://physics.uwyo.edu/~stark/outreach/starlives/life +death/fusion.gif
A Balancing Act 2. Throughout its life, these two forces determine the stages of a star s life.
D. Red Giant/Supergiant 1. When H gets low, gravity causes the star to shrink & heat up. 2. Increased heat & pressure cause He to fuse to C. 3. The excess E released makes the star expand to a red giant or a supergiant. 10x bigger than the sun 100x bigger than the sun
He C H He http://physics.ship.edu/~mrc/pfs/108/node3.htm
http://www.physics.hku.hk/~nature/cd/regular_e/lectures/imag es/chap15/red_size.jpg
He supplies get low, and the red giant begins to shrink in a series of contractions, giving off a planetary nebula and leaving only a white, hot center. Planetary Nebulae
E. The Fate of a Red Giant 1. The white center is called a white dwarf. *It is the size of the Earth with the mass of the sun. * It weighs a ton per teaspoon. http://abyss.uoregon.edu
2. When the white dwarf burns out it becomes a black dwarf. http://library.thinkquest.org
http://www.physics.hku.hk/~nature/cd/regular_e/lectures/chap15.html
F. Nova 1. Sometimes a white dwarf has an explosion called a nova before becoming a black dwarf. ttp://www.astropix.com
G. The Fate of a Supergiant 1. After He gets low in a supergiant, the core collapses again until it becomes hot enough to fuse C into Mg or O 2. Through a combination of processes, successively heavier elements are formed and burned.
4. Fe is the most stable element and cannot be fused further. Instead of releasing E, it uses E
This is where the elements come from!
The massive E absorbed causes the Supergiant to explode in a Supernova! www.theage.com
Supernova
H. What s Left After the Supernova? 1. Neutron Star (If mass of core < 5 x Sun) OR Under collapse, protons and electrons combine to form neutrons. 10 Km across 2. Black Hole (If mass of core > 5 x Solar)
Neutron stars can have 2 beams of light coming off of them called pulsars.
www.sciencemus eum.org.uk
The Cycle Continues Supernovae compress gas and dust which lie between the stars. This compression starts the collapse of gas and dust to form new stars.
The Life Cycles of Stars Dr. Jim Lochner, NASA/GSFC
Twinkle, Twinkle, Little Star...
How I Wonder What You Are... Stars have Different colors Which indicate different temperatures The hotter a star is, the faster it burns its life away.
II. The H-R Diagram
A. Interpreting an H-R Diagram 1. An H-R diagram compares the surface temperature of stars with their absolute magnitude (how bright the stars actually are) RED ORANGE YELLOW WHITE BLUE COOLEST.HOTTEST +15 ----------------------------- -15 DIMMEST.BRIGHTEST
H-R Diagram 2. For most stars, as the surface temp increases, brightness increases 3. Main band of stars in the diagram are called main sequence stars 4. The cool bright stars in the upper right are red giants that appear bright because they are large 5. White dwarfs in the lower left are hot but appear dim since they are small
B. Analyzing Stars 1. Spectroscopedevice used to tell the composition of a star 2. Spectrum- The reading a spectroscope gives you. www.upscale.utoronto.ca/generalint erest/harrison/spectra/spectra.gif
3. You can tell how a star moves by observing its spectrum. 4. Red shift in a spectrum means a star is moving away. 5. Blue shift means a star is moving closer. www.upscale.utoronto.ca/generalint erest/harrison/spectra/spectra.gif
III. 3 Types of GALAXIES spiral elliptical irregular
A. Basic Galaxy Info 1. Avg 100,000 light-years in diameter 2. There are at least 1 billion galaxies 3. They are classified based on shape
B. Spiral 1. Has a bright nucleus of stars. 2. Flattened arms spiral around the nucleus. 3. The Milky Way is a spiral galaxy.
C. Elliptical 1. Shape ranges from nearly spherical to a flattened disk. 2. Very bright in center and has no spiral arms. 3. Usually older than other types & have little dust & gas.
D. Irregular 1. Have no particular shape. 2. Small and faint. 3. Stars are unevenly distributed
IV. Basic Star Info. A. Constellation- group of stars B. Big Dipper= Ursa major C. Little Dipper= Ursa minor D. The North Star= Polaris. We see it all year. E. Circumpolar stars- circle Polaris and can also be seen all year