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25 Cards in this Set
- Front
- Back
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three factors of white dwarfs? |
remaining cores of dead stars electron degeneracy pressur supports them against hte crush of gravity cool off and grow dimmer with time white dwarfs with the same mass of the sun are about the same size as earth higher mass white dwarfs are smaller |
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What is the white dwarf limit? |
quantum mechanics says that electrons must move faster as they are squeezed into a very small space as a white dwarf mass approaches 1.4msun its electrons must move at nearly the speed of light because nothign can move faster than light, a white dwarf cannot be more massive then 1.4msun, the white dwarf limit or chandrasekhar limit. |
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What can happen to a white dwarf in a close bianary limit? |
a star that started with less mass gains mass from its companion. eventually teh mass losing star will become a white dwarf the temperature of accreted matter eventually becomes hot enough for hydrogen fusion. fusion begins suddenly and explosively, causing a nova. |
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Nova |
caused by the fusion of the matter transfered from a white dwarf with a bionary main sequence star. happens suddenly and explosively.
temporairily the star system appears much brighter drives accreted matter out into space. |
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What ate the two types of super novae? |
massive star (core collapse super nova: iron core of a massive star reaches white dwarf limit and collapses into a neutron star, causing total explosion leaves behind nebula and neutron star.
white dwarf supernova: carbon fusion suddenly begins as a white dwarf in close binary system reaches white dwarf limit, causing total explosion. leaves behind nebula |
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How can you supernova types apart? |
light curves show how luminosity changes with time. supernovae are much more luminous, about 100000 times in a nova the h to he fusion of a layer of accreted matter, white dwarf is left in tact white dwarf supernova coplete explosion of a white dwarf where nothing is left behind, except nebula from debris of the explosion light curves differ spectra differ exploding white dwarfs dont have hydrogen absorption lines many more neutrinos from a massive star supernovae |
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Neutron star |
ball of neutrons left behind by a massive star supernova degeneracy pressure of neutrons supports a neutron star against gravity typically has a radius about 10km typically has the density of 3.7x10 ttp 17 kg/mttp3 |
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Baade and Zwicky 1934 |
heorized neutrons tars used a radio telescope of 1967, jocelyn bell noticed very regualr pulses of radio emission coming from a single par tof the sky the pulses were coming from a spinning neutron star-- a pulsar |
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Supernova Remnant |
Energy released by the collapse of the iron core of a dying massive star drives the stars outer layers into space the crab nebula is the remnant of the supernova seen in 1054 it is about 6500 light years away size is about 10 light years. |
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Pulsars |
a neutron star that beams radiation along a magnetic axis that is not aligned with the rotation axis
beams sweep through space like lighthouse beams as the neutron star rotates. |
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How do you determine the circumfrence of a neutron star? |
2pi times the radious usually equals approximately 60km |
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what is the spin rate of pulsars? |
1000 cycles per second |
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surface rotation velocity |
60000kms a second spins at 20% the speed of light escpae velosity from the neutron star anything other than a neutron star would be torn to pieces |
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Why do pulsars spin fst? |
a stellar core's spin speeds up as it collapses into neutron star. conversation of angular momentum |
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what happens to a neutron star in a close bianary system? |
Matter falling toward a neutron star forms an accretion disk, just as in a white dwarf binary |
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Is helium fusion possible in a neutrons tar? |
yes because matter acreting can eventually become hot eough the sudden onset of fusuin produces a burst of xrays |
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What is a neutron star? |
it is a ball of neutrons left over from a massive star supernova and supported by neutron degeneracy pressure |
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how were neutron stars discovered? |
beams of radiation from a rotating neutron star sweep through space like lighhouse beams makign them appear to pulse observations of these pulses were the first evidence of neutron stars. |
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What can happen to a neutron star in a close inary system? |
accretion disk around a neutron star can become hot enough to produce xrays and make he system an xray binary sudden fusion events periodically occur on a surface of an accreting neutron star, producing xray bursts |
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What is a black hole? |
an object whos gravity is so powerful that not even light can escape it. |
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What is the surface of a black hole |
the radius at which teh escape velocity equals the speed of light known as the event horizon also known as the schwarzschild radius |
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How big is an event horizon? |
one that is 3msun is about as big as a city. Therefore they are massively compressed. |
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What is a neutron star limit? |
neutrons in the same place cannot be in the same state. this generates neutron degenerasy pressure. this star cannot support a neutron star gagainst gravity if its mass exceeds about 3msun.
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how ca a supernovae make a black hole? |
some massive star supernovae can make a black hole if enough mass falls onto its core. stars with a main sequence mass of less than 20msun may end up as neutron stars after core collapse after shedding outer layers while heavier stars may end up as black holes. |
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Singularity |
beyond the neutron star limit no known force can resist the crush of gravity a singularity is where gravity crushes all the matter into a single point. |
