What is the diameter or radius of a supermassive black hole?

1 Answer
Dec 15, 2016

A supermassive black hole has a similar radius to our solar system


The radius of a black hole is determined by its mass and is called the Schwarzschild radius #r_s#.

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

Where G is the gravitational constant, M is the mass of the black hole and c is the speed of light.

The Schwarzschild radius for our Sun is only about 3km.

Supermassive black holes have masses of over 100,000 solar masses and are often millions of solar masses. Supermassive black holes have been detected as massive as 20 billion solar masses.

The supermassive black hole at the centre of our galaxy, called Sagittarius A*, has a mass of about 4 million solar masses. That makes its Schwarzschild radius about 13 million kilometres. By comparison, the radius of the Earth's orbit is about 150 million kilometres.