Astro Exam 2

• Describes fusion process in the sun
• -Two protons fuse to make deuterium nucleus (occurs twice)
• -Then a proton fuses with this to make hlium 3 (twice) 
• -Then the two helium 3's fuse to form helium 4 realeasing two protons
• - Result is gamma rays

• -made by hydrogen fusion in core
• -have very small masses
• -don't interact with anything

• -Pull of gravity = pull of pressure
• -Spherical nature of gravity makes it round
• -High pressure needed at the center

• -If suns temperature rose fusion rate would rise causing pressure to expand the core and cool it bringing it back to equilibrium
• -If suns temperature dropped fusion would slow and pressure would be low causing the core to contract and heat up bringing the sun back to equilibrium

• Neutrinos - they validate our hypothesis, direct product of fusion
• Mathematical models - know how how big it is, knowing the surface temp. knowing the mass
• Helioseismology - Sun earth quakes, the sun vibrates around, depending on how the sun is vibrating we can measure how certain parts of thesun are moving towards or away from us

• -prominences are gases released by two sunspots resulting in an arch trapped in these loops
• -When magnetic fields lines in a prominence snap energy and light is released in the form of flare
• -Charged particles are spewed out into space through coronal mass ejections

• Apparent brightness = luminosity / distance ^2
• -Apparent brightness - how bright it appears to us here on earth 
• -Luminosity - energy emitted (Joules/sec or watts

• Distance - parallax good to nearby stars but not beyond
• Luminosity - measure apparent brightness and distance, infer luminosity
• Temperature - spectral classification
• Mass - for binary orbits, get orbital parameters we can figure out mass

Depicts: temperature, color, spectral class, luminosity, radius and mass

• -burning hydrogen in their cores
• -Temps hotter for more massive stars
• -More luminous

• Protostar looks star like after surrounding gas is blown away, thermal energy comes from gravitational contraction not fusion
• Contraction continues until core is hot enough for nuclear fusion
• Contraction stops when internal energy equals surface energy

• Thermal: depends on heat content, main form of pressure in most stars, (think expanding balloon)
• Degeneracy pressure: particles can't be in the same state in the same place, not dependent on heat content

• -Protostar assembles from collapsing sloud
• -shrinks and heats as gravitational energy is converted into thermal energy
• -temperature rises as radiation becomes main form of energy flow
• -fusion rate increases until there is a balance of energy on the star

• -stars more massive than 100Msun would blow apart
• -stars less massive than 0.08Msun can't sustain fusion

• determines entire life story - determines core temp
• high mass - have shorter lives, make iron, end in supernovae explosions
• low mass - have long live, never fuse carbon and end as white dwarfs 
• intermediate mass - can make elements heavier than carbon but end as white dwarfs

• Energy released by collapse of core drives out outer layers into space
• produces most elements heavier than iron within a sec

• Low mass -> white dwarfs, gravity v. electron degeneracy
• High mass -> neutron stars, gravity v. neutron generacy
• Even more massive stars -> black holes, gravity wins

• If enough mass is accreted, electron degeneracy is overcome (limit is 1.4 solar masses (chandrasekhar limit))
• Star then collapses carbon fusion begins explosively dwarf is gone

• White dwarf SN - binary systems only, occurs in older star populations, nothing left inside
• Massive star SN - found in young star formation regions, make neutron stars or black holes

• Structure is determined by gravity vs. neutron degeneracy pressure
• About 10 km and 1 -3 M sun
• Made of degenerate neutrons
• Crushing gravity

• gravity imposes curature on space, light's path through space will be "bent by gravity, 
• As matter approaches event horizon, tidal forces are tremendous, object will be spaghettified

• -launched to a black hole time slows down as it approached event horizon
• from mothership the probe takes forever to reach event horizon
• light from probe is redshifted until you can't see it even in radio
• From probes view: it heads straight into blackhole, light from mother ship is blue shifted

• Harlow measured distances to globular clusters
• -appeared to be centered on a location tens of thousands of light-years from the sun
• conclusion: sun not in center, about 2/3 out

Atomic hydrogen clouds -> molecular clouds -> star formation -> stellar lives, neclear fusion, heavy element formation -> returning gas through supernovae and stellar winds ->hot bubbles