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6 Cards in this Set
- Front
- Back
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How is a black hole formed? |
If the mass of the collapsed core of a high mass star is more than 3 solar masses, the degeneracy pressure of neutrons cannot support it, and it collapses into a single point -- a singularity in spacetime. |
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Why are they called black holes? |
Recall the concept of escape velocity. For a given mass (M) as the radius (R) is reduced, Vesc increases, and could become greater than the speed of light C(=300,000km/s). Then nothing, including light, can escape the gravity of the body. |
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What is the Schwarzschild radius Rs? |
It is a distance from the body within which the escape velocity is greater than the speed of light. Rs (in km) = 3M (in solar masses) |
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What is the observational evidence for black holes? |
One looks for a binary system of a normal star and an invisible companion with a mass of at least 3 solar masses which is a strong source of X-rays (produced by acceleration of stellar wind particles as a result of a strong gravitational pull by the black hole). |
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Describe the first observation of a black hole. |
Tom Bolton observed one in 1071 using 1.9m reflector telescope at the David Dunlap Observatory in Richmond Hill. The normal star was Cygnus (27 solar masses) and the black hole was named Cygnus X1 (15 solar masses). |
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How do you describe the vicinity of black holes? |
Using Einstein's general theory of relativity: mass or energy bends space and other objects move in that bent space along the paths of shortest distance (geodesics). |
