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Black Holes

Black Holes. Introduction What are black holes Evidence of Black Holes Star like black holes Massive black holes Exotic properties of black holes. Escape velocity v = [2GM/R] ½ If v(escape) is more than c = 300,000 km/sec then light cannot escape and we have a black hole.

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Black Holes

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  1. Black Holes Introduction What are black holes Evidence of Black Holes Star like black holes Massive black holes Exotic properties of black holes

  2. Escape velocity v = [2GM/R]½ If v(escape) is more than c = 300,000 km/sec then light cannot escape and we have a black hole. Examples of escape velocities: Earth = 11 km/sec Sun = 610 km/sec. Introduction

  3. Event horizon [Schwarzschild radius] R The value of Rat v(escape) = c c = [2GM/R] ½ R = 2GM/c². Example: M=M (mass of Sun), R = 3 km. R(km) = 3 × (M / M) Density = M/V = M/[(4/3)πR³] α M/M³ =1/M² So density of black hole decreases as mass increases. Introduction

  4. Any object where the mass is inside the event horizon. Even though the mass can have any value, we only know the existence of black holes with masses greater than the mass of the Sun, all the way up to a several billion solar masses. Since we cannot “see” inside a black hole, we cannot find out the composition. In stellar size black holes the density exceeds that of neutron stars. Matter is squeezed beyond neutron star size. Black holes have mass (has gravitational force outside the event horizon), angular momentum and charge. What are Black Holes?

  5. Two sources Original. Formed at the beginning of time. Formed during supernova How Black Holes are formed

  6. NGC 6240-- Two Black Holes revolving around Each other, Observed by Chandra X-ray observatory p.280

  7. Bending of photons under gravity. Fig. 14-2, p.282

  8. Fig. 14-3, p.282

  9. Fig. 14-4, p.282

  10. The Cheshire cat From Alice in Wonderland Fig. 14-8, p.285

  11. Produced during supernova of massive stars. Look for double star system with only one visible star, but with a massive non visible star. Kepler’s Third Law (1618) M1 + M2 = a3/p2. where M is in units of M, a distance between stars in AU and p is the period of revolution in years. Cygnus X1 is the first detected black hole and has a mass of at least 6M. X-ray produced by in-falling matter from outside of event horizon. So far about 10 stellar size black holes been observed. Evidence of Stellar Size Black Holes

  12. Cygnus X-1 Fig. 14-10a, p.286

  13. Fig. 14-11, p.288

  14. Name Distance Period Mass Companion from us Cygnus X1 8K ly 5.6 d 10-15 Type O LMC X3 175K 1.7 4-11 B LMC X1 175K 4.2 4-10 O V616 3K 0.3 3-4 K V404 11K 6.5 8-15 K J0422+32 8K 0.2 4.5 M J1655-40 10K 2.6 4-5 F GS2000+25 8K 0.3 5-8 K Nova Ophiuchi 0.7 4-6 K A few black hole examples

  15. “Black Hole in Binary Stars

  16. Mass about that of mass of the Sun up to about 20 solar masses. Formed during supernovae. Evidence from binary (double) stars, where the mass of the unseen star can be computed. About ten such objects have been observed. Star Like Black Holes

  17. Center of each galaxy, except irregular galaxies. Center of globular clusters. Massive Black Holes M = 109M M = 3×109M

  18. Milky Way 2.6 Million Solar mass Andromeda 30 M32 3 NGC4261 400 M87 3,000 M104 1,000 NGC 3377 100 Massive Black Hole examples

  19. Black hole is a singularity. Black holes with spin collapse into a ring. If you can pass through the ring of a black hole, information on space and time is lost (discontinuous). I.e. you can end up at a different time and different space. Not too likely. Black holes that connect two different parts of the universe is called worm hole. Exotic Properties of Black Holes

  20. Hawkins has shown that black holes can radiate energy, called Hawkins radiation. The decay time of the black hole is related to the mass. The more massive , the longer the decay time. Very low mass black holes (micro black holes) decay almost instantly. Stellar or galactic black hole decay times are much longer than the age of the universe. Black Holes are not very BLACK

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