ASTR 1200 Announcements

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ASTR 1200Announcements
Problem sets 5 and 6 due this week. Third exam
November 20 (next week)
Website http//casa.colorado.edu/wcash/APS1200/AP
S1200.html
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A Newtonian Black Hole
Kinetic Energy
Energy Falling To Surface
OR
if vc
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Schwarzschild Radius
Two errors cancel.
This is the radius of the Event Horizon
The event horizon is a true singularity in
space-time. It is a place where time and space
cease to exist.
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Curved Space
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Rubber Sheet Analogy
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Properties - Basic

1. Mass (Schwarzschild Black Hole)
2. Electric Charge (doesnt happen)
3. Angular Momentum (Kerr Black Hole)

No Surface Features No Magnetic Fields No
Pulsing No Hair
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(No Transcript)
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Time Dilation
As r approaches Rs dt gets longer and
longer. When r reaches the event horizon, time
stops.
We know how to make a time machine with a forward
switch only! Just fly to a black hole and orbit
above the surface.
But you can fall in really fast as viewed from
outside.
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http//www.space.com/27701-interstellar-movie-scie
nce-black-holes.html
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Hawking Radiation
The vacuum makes pairs of electrons and positrons
that pop into existence and then
annihilate without any net effect. Above a black
hole, one can get sucked in. The other
annihilates above the surface to
cause radiation. Since its close to the surface,
the light gets redshifted escaping, but it
carries energy with it!
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Temperature
Hawking derived that the temperature of a black
hole is thermal.
Energy for the radiation comes from the mass of
the hole. The black hole shrinks with time.
Thats a really long time unless the black hole
is tiny.
A 1kg black hole would last only 10-16s.
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Artists impression of Cyg X-1 (NASA)
6M0 BH orbiting an O9 star. 2000pc away in Cygnus
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The Milky WayStars Beyond Counting
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100 Billion Stars
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Orbital Period
Takes the Sun 200million years to orbit Milky
Way. Sun is 4600 million years old. The Sun is
23 Galactic Years Old.
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A Spiral Galaxy Like Milky Way
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(No Transcript)
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Milky Way Edge-On
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The Milky Way
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Formation of Milky Way

• Analogous to formation of the Sun
• Start with big blob of gas
• Let it collapse

Disk Stability Again
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Globular Clusters
Gas has friction and collapses to disk. Stars
have huge momentum with small cross
section. When a star forms it remains frozen in
its initial orbit forever.
Little knots of high density are first to form
into stars. These are the globular
clusters. They each contain a million
stars. There are about 100 orbiting the Milky Way.
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The Globular Cluster M80