| Some slides concerning black holes. |
| Nothing can stop collapse after neutron pressure fails | ||
| Escape velocity from a surface at radius R: | ||
| As R shrinks (but M is fixed), Vescape gets larger and larger | ||
| At some point VEscape= c (speed of light) | ||
| Happens at Schwarzschild radius: | ||
| Not even light can escape from within this radius | ||
| The Schwarzschild Radius: | |||
| Mass in solar masses Rs (km) | |||
| 10 30 | |||
| 3 9 | |||
| 2 6 | |||
| 1 3 | |||
| 0.000003 (Earth) 0.9 cm | |||
| 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 RS = 2GM/c2 | ||
| 1 MSun: 3.0 km 106 MSun 3´106 km 1 MEarth 8.9 mm | ||
| If you do make material fall into a black hole, material will be falling at close to the speed of light when it reaches RS | ||
| If that falling gas collides with and heats other gas before it reaches RS, then light from that hot material (outside RS) can escape (important in quasars!). | ||
| By definition – can’t see light from black hole itself | ||
| Can see large amounts of energy released by falling material just before it crosses RS | ||
| Can see motion of nearby objects caused by gravity of black hole | ||
| 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 RS | |||
| 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 | |||
| Likely Black hole | ||
| High velocities | ||
| Large energy generation | ||
| At a=275 AU P=2.8 yr Ţ 2.7 million solar masses | ||
| Radio image of Sgr A about 3 pc across, with model of surrounding disk |
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| 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.” |
More Cool Stuff About Black Holes
| Time Dilation – originally “Frozen Stars” | |
| Gravitational Redshift | |
| Wicked Tidal Forces | |
| Hawking Radiation | |
| Gravitational Lensing on small scales. |