Astronomy Notes White Dwarfs A dead star No nuclear reaction in the star Core is helium or carbon or oxygen The star is not big enough to You need a balance of gravity and pressure in equilibrium The source of the pressure is the electron gas Fermi gas which is not an ideal In order for helium to go into carbon you need 100 million degrees gas this is a gas out of fermions electrons protons neutrons Any half integer spin particle is a fermion Any integer spin particle is a boson these are responsible for force interactions Fermions don t like to interact with each other Only one fermion can be in a single state Pauli exclusion principle they need to be in opposite spins to occupy the same state For every two electrons you have two protons Millions of bosons can be in the same state A neutron star is a Fermi gas Electrons in a metal is an example of a Fermi gas The more massive the white dwarf the smaller the radius The Sandrachekar limit is 1 4 solar masses When this limit is exceeded a supernova happens Radius cannot be negative The less massive the star is the more luminous for white dwarfs star The star sheds the mass and that mass becomes a planetary nebula The limit on the reduced white dwarf is 1 4 solar masses Stars greater than 8 solar masses can either become a black hole or a neutron star Let s say a star has 50 solar masses you can fuse heavier atoms Formation of iron and nickel is the death blow for a star At 3 billion degrees you can make nickel and iron A supernova occurs A neutron star and white dwarf are very similar Neutron star or a black hole can produce a supernova Crab nebula is the leftover from a supernova Atoms are made out of nucleus and electrons When you squeeze the atom electrons push each other Electrons repel one another You need a LOT of pressure to squeeze the atoms 10 15 density Beta decay a proton becomes a neutron or a neutron becomes a proton If a proton captures an electron it results in a neutron and a gamma ray this is B decay Charge is conserved If a neutron star doesn t collapse it is because of the Pauli exclusion principle Mass is also conserved You can t have a neutron star which is more massive than five suns If you pass the limit of too much mass the neutron star collapses into a black hole First observation of a neutron star is a pulsar Pulsar A neutron star is an ideal sphere Magnetar is a neutron star with an extraordinary magnetic field The magnetic axis and rotational axis do not match up The more they are squeezed by gravity the faster they spin So it s like a light house If your antenna happens to be in the way of the waves you hear ticks Black holes Light moves at 45 degrees on the space vs time graph Space and time are one thing Space and time do not exist independently Nothing can move faster than the speed of light How do you know if you live in flat space or curved space If you form a triangle If the internal angles are more than 180 degrees space is curved Stars are characterized by escape velocity The more massive and dense a star the higher the escape velocity If the escape velocity is the speed of light light cannot escape
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