Chapter 13
White dwarfs cool off and grow dimmer with time.
Size if a dwarf: what dwarfs with the same mass as the sun
are about the same size as the earth. Higher mass white dwarf are smaller
Quantum mechanics says that elections must move faster as
they are squeezed into a very small place.
A star that started with less mass gains mass from its
companion.
Mass falling towards a white dwarf from its close binary
companion has some angular momentum.
The temperature of accreted matter eventually becomes hot
enough for hydrogen fusion
Fusion begins suddenly and explosively causing a nova the
ova star system temporarily appears much brighter
The explosion drives accreted matter out into space
Tyler of supernova
Massive star supernova iron core of massive sat reaches
white dwarf limit and collapses into a neutron star causing an explosion
White dwarf supernova carbon fusion suddenly begins as white
dwarf in close binary system reaches white dwarf limits causing a total
explosion.
On way to tell supernova types apart is with a light curve
showing how luminosity changes with time.
Supernova are much more luminous than novae
Nova H to He fusion of a layer of accreted matter white
dwarf left intact
Light curves differ
Spectra differ exploding white dwarfs don't have hydrogen
absorption lines.
****13.2 neutron stars****
A neutron star is the ball of neutrons left behind by a
massive star supernova.
The degeneracy pressure of neutrons supports a neuron star
against gravity
Electrons degeneracy pressure goes away because electrons
combine with protons making neutrons and neutrinos
Neutrons collapse to the center forming a neutron star
Pulsar at center of Crab Nebula pulses 30 times per second.
A pulsar is a neutron star that beams radiation along a
magnetic axis that is not aligned with the rotation axis.
The radiation beams sweep through space like lighthouse
beams as the neutron star rotates.
Quantum mechanics says that neutrons in the same place
cannot be in the same state.
****13.3 black holes gravity's ultimate victory****
A black hole is an object whose gravity is so powerful that
not even light can escape it.
Light would not be able to escape earths surface if you
could shrink it to 1 cm.
The surface of a black hole is the radius at which the
escape velocity equals the speed of light.
This spherical surface is known as the event horizon
The radius of the event horizon is known as the
schwarzschild radius.
The even horizon of a black hole is also about as big
as a small city
A black holes mass strongly wraps space and time in the
vicinity of the even horizon.
Nothing can escape from within the event horizon because
nothing can go faster than light.
No escape means there is no more contract with something
that falls in. It increases the holes mass changes its spin or charge, but
otherwise loses its identity.
Beyond the neutron star limit no known force can resist the
crush of gravity
As far as we know, gravity crushes all the. After into a
single point known as a singularity.
If the sun shrink into a black hole, its gravity would be
different only new the event horizon.
Light waves take extra time to climb out of a deep hole in
space time, leading to a gravitational redshift.
Time passes more slowly near the event of horizon
Tidal forces would be gentler near a super massive black
hole because it radius is much bigger.
Need to measure mass, use orbital properties of companion
measure velocity and distance of orbiting gas
It's a black hole if it is not a star and its mass exceeds
the neutron star limit
****13.4 the mystery of gamma ray bursts****
Brief bursts of gamma rays coming from space were first
detected in the 1960.
Observations in the 1990 showed that many gamma rays bursts
were coming from very distant galaxies.
Observation show that at least some gamma ray bursts are
produced by supernova explosions.
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