Black Holes Flashcards
What is a black hole?
A black hole is a region of space-time in which gravity is so strong that nothing - not even light - can escape it.
What is escape velocity?
The speed necessary for an object to completely escape the gravity of a large body.
V esc = the square root of 2GM/R
What happens to the escape velocity from an object if your shrink it?
TBA
Would light be able to escape Earth’s surface if you could shrink it to less than 1 cm?
No
What is the event horizon?
The “surface” of a black hole that is given by the radius at which the escape velocity is equal to the speed of light.
V esc = c
Nothing can escape from within the event horizon because nothing can go faster than light.
What is the Schwarzschild radius?
Radius of the event horizon:
Rs = 2GM/c(squared)
or in kilometers:
Rs = 3 times M (solar masses)
What is the radius of the event horizon of a 3 Msun black hole?
Rs = 3 x M
3 x 3 = 9
Answer: 9 kim
Out galaxy has a supermassive black hole in its center with a mass of about 4 million Msun. How big is the radius of the event horizon?
Rs = 3 x M
(Radius of the event horizon equation)
3 x 14 million = 12 million
Answer: 12 million
Singularity
The place at the center of a black hole where, in principle, gravity crushes all matter into an indefinitely tiny and dense point.
How can we detect black holes?
Black holes’ gravitational effects can be detected. They are easiest to find if they are in close binaries (stellar-mass black holes) or if they are in the center of a galaxy (supermassive black holes)..
What are stellar-mass black holes?
Small black holes approximately 3 to 10+ solar masses. They can form through supernovae, neutron stars or white dwarfs that accrete mass beyond 3 solar masses, and neutron stars that merge.
