What is black hole in-universe?

1 Answer
Phillip E.
Feb 14, 2018

A black hole is a region of space once something enters it can never leave, not even light.

Explanation:

Albert Einstein published his field equations of General Relativity in 1915. Soon after Karl Schwarzschild solved the field equations for the vacuum around a massive body.

The Schwarzschild solution has a singularity where time stops and nothing can escape. It is called the Schwarzschild radius #r_s#.

#r_s = (2GM)/c^2#

Where #g# is the gravitational constant, #M# is the mass of the body and #c# is the speed of light.

This means that any mass which gets compressed to a radius below #r_s# is effectively isolated from the rest of the universe. Nothing which enters this radius can escape, not even light. This is a black hole.

The Sun is too small to collapse into a black hole, but we can calculate #r_s#. The mass of the Sun #M=1.989*10^30Kg#, #GM=1.327*10^20#, #c=299,792,458 m \/ s#. So, #r_s=2,953m#. This is less than 3 kilometers!

So, Schwarzschild predicted black holes in 1915. More recently objects have been discovered which are so small and massive that they can only be black holes.

Related questions
Impact of this question
1196 views around the world
You can reuse this answer
Creative Commons License