Astronomy Test 5

Star distance by parallax
-Greater the distance, smaller the angle
-Good out to 3000 LY
Apparent Magnitude
-mm (symbol)
– If mmA=6 and mmB=1 star B is 100x brighter because of difference of 5
Absolute Magnitude
White Dwarf
-Approximately the size of Earth/ Mass of sun
-Electrons prevent further collapse
-Stellar cycle end point
-Incapable of nuclear reactions
Chandraskhar Limit
-If mass is less than 1.4 Mo must become white dwarf
Sun as a giant
-Mercury and Venus swallowed
-Earth is vaporized
Low Mass
-Planetary Nebula
-White Dwarf
Medium Mass
-Neutron Star
High Mass
-Black Hole
-Place where elements heavier than iron are formed (Heaviest element by fusion is iron)
-Catastrophic explosion releasing entire galaxy’s energy
Planetary Nebula
-(He) is exhausted in core
-Mass is too low to attain temp high enough to burn carbon
-Star becomes unstable and puffs away (30km/s)
Neutron Stars
-Discovered by Jocelyn Bell but stolen by Martin Hewish
-Theory credited to Tommy Gold
-More dense than white dwarfs
-Ex: Crab pulsar spins 33x a second
-Typical diameter ~25 miles
-Help up by pressure of degenerate neutrons
Black Hole
– S=singularity= Point of infinite density (center)
-EH=Event horizon= Not even light escapes
-Ergosphere is outer level if spinning
-Best candidate is Cygnus x-1 in which x-ray source
Milky Way
– N= nucleus (center)
– D= Disk (young, on ring)
– H= Halo (old, globular clusters)
– 30,000 LY as determined by Shapley using 21cmm radiation from hydrogen when electron flips spin
-Use radio telescopes
Period-Lumosity Relationship
-Discovered by Henrietta Leavitt
– Allows use of variable stars as distance indicators
Variable Stars
– Apparent magnitude mm varies
– Tells us M (luminosity)
– Milky way and Andromeda
– Lots of gas and dust forms new stars
– 15%
-Little gas and dust to form new stars
– 70%
– Formed by colliding spiral galaxies (Jane Charlton PSU)
-Magnetic Clouds
– Neighboring satellite galaxies
– 15%
Hubble Law
-Greater a distance to a galaxy, greater the recessional velocity (greater redshift)
– Slipher finds recessional velocities
Cosmic 3k Background
– Remnant of Big Bang predicted by Gamow
– Discovered by Pensiaz and Wilson
-Could have predicted the constant expansion of the universe (not enough mass to bring it back)
-Purely Convection
– Radiation first important
– Nuclear reactions turn on, not stable
– Main sequence (H–He) stable, internal pressure out= gravity in
– Helium Flash
– Giant (He–>C)
– Variable Star
– Planetary Nebula (explosion)
– White Dwarf
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