Black Holes

Black holes may be one of the most strange features in the universe. These objects are so dense, light cannot even escape from them!





Amazingly enough, almost all black holes started out as a hot, bright, large star. These stars go through the same evolution that leads to a neutron star, but unlike a neutron star, these objects are so massive, even neutron degeneracy is not enough to overcome gravity. Gravity compresses the star so much that instead of having a small core remnant after the supernova explosion, all that's left is what is called a singularity. Singularities are thought to be an object so small but so massive that it has an infinite density. In reality, this isn't true, but a naked black hole has never been observed, so the assumption is accurate for now.





There are a couple of things that define a black hole. One is its Schwarschild (pronounced Schwartz-Shield), which is the theoretical distance from the center of the black hole where the escape velocity from the black hole equals the speed of light. The speed of light is approximately 300,000 kilometers per second, or fast enough that a beam of light can circle the Earth 12 times at the equator. The escape velocity is given by the square root of 2 times G (the gravitational constant ~ 6.67*10^-11 m³/kg*s²) times the mass of the star or planet divided by the radius of the planet squared.





Or in equation form:

If you change V_esc to the speed of light, c, you can solve for R, and solve for the Schwarschild radius, R_s.

where M_Star is the mass of the Star, or in this case a black hole.

Next time, we will learn more about black holes, like how they are observed and what else we know about them.