1	Science and Science Fiction Some slides concerning black holes.
2	Black Holes -- basics Nothing can stop collapse after neutron pressure fails Escape velocity from a surface at radius R: As R shrinks (but M is fixed), V_escape gets larger and larger At some point V_Escape= c (speed of light) Happens at Schwarzschild radius: Not even light can escape from within this radius
3	Examples: The Schwarzschild Radius: Mass in solar masses R_s (km) 10 30 3 9 2 6 1 3 0.000003 (Earth) 0.9 cm
4	Black Holes -- details Remember – gravity is same as before, away from mass Black holes do NOT necessarily pull all nearby material in A planet orbiting a new black hole would just keep on orbiting as before (assuming the ejected material or radiated energy didn’t have an effect) Any mass can potentially be made into a black hole – if you can compress it to a size smaller than R_S = 2GM/c² 1 M_Sun: 3.0 km 10⁶ M_Sun 3´10⁶ km 1 M_Earth 8.9 mm
5	Black Holes -- details If you do make material fall into a black hole, material will be falling at close to the speed of light when it reaches R_S If that falling gas collides with and heats other gas before it reaches R_S, then light from that hot material (outside R_S) can escape (important in quasars!).
6	Black Holes – detection By definition – can’t see light from black hole itself Can see large amounts of energy released by falling material just before it crosses R_S Can see motion of nearby objects caused by gravity of black hole
7	Black Holes – detection Example: Like White Dwarf accretion disk but w/ black hole instead Gas from red giant companion spills over towards black hole Gas spirals in toward black hole, through accretion disk Gas will be much hotter because it falls further, to very small R_S Gas will be moving at very high velocity Much faster than with white dwarf since much closer (P² µ a³) Signature of black hole: Very high energy release, very high velocity We find MASSIVE black holes in centers of most galaxies
8	Cygnus X-1
9	The Nucleus of the Galaxy Likely Black hole High velocities Large energy generation At a=275 AU P=2.8 yr Þ 2.7 million solar masses Radio image of Sgr A about 3 pc across, with model of surrounding disk
10	A movie of stars at the core www.mpe.mpg.de/www_ir/GC Very cool, and worth a look! This is the best evidence to date for a massive black hole at the Galactic core. Now essentially “proven.”
11	More Cool Stuff About Black Holes Time Dilation – originally “Frozen Stars” Gravitational Redshift Wicked Tidal Forces Hawking Radiation Gravitational Lensing on small scales.