if a black hole has a mass of 10^9 kg, & Sun mass is 10^30 kg, why does light escape from the Sun?

Answer 1

In a word, density.

It is not mass that makes a black hole, it is density. A small amount of mass crammed into a small enough space will be a black hole. This is because the force of gravity is inversely proportional to the square of the distance from the CENTER of the mass. If the mass is not very dense, then you can't get close enough to the center to feel the extremely strong gravity needed to make a black hole. Planets and stars are not nearly dense enough.

Answer 2

It has to do with density. If we collapse the sun into a small enough volume, it too will become a black hole.

Incidentally, I've never heard of a black hole that has a mass of 10^9 kg.

Answer 3

As long as the escape velocity of an object does not exceed the speed of light then light (..or anything else..) can escape from that object. The sun's escape velocity is 1.4-million meters/second which is well below the speed of light, 300-million meters/sec.

I can't compute the escape velocity of your 10^9 kg black hole without knowing its radius, but it seems obvious that it would also be well below the speed of light.

The equation for finding escape velocity ---

v = sqrt(2 * G * M / r)
'v' is escape velocity
'G' is gravitational constant
'M' is mass of object
'r' is radius of object

Answer 4

The key is the size. A black hole is tiny, in stellar terms, a few kilometres across. The gravity at the surface is determined by mass and radius. Since the black hole is so much smaller its surface gravity is much higher than the sun's, even if its mass is lower.

Answer 5

A black hole cannot have that low a mass and be the size of the sun. If there is a black hole that tiny, it has to have a radius of just a few meters. I think I heard that if our sun was a black hole, it would only be a few km acros

Answer 6

perhaps because the SUN is burning Hydrogen to make the light ?

A black hole's surface gravity is stronger than that of a normal star because all of its mass has been squeezed into an almost infinitely small point.


basically you are comparing apples and oranges.


a good analogie would be like trying to build a car out of a liquid.

Answer 7

The sun continues to radiate since it's surface escape velocity is less than the speed of light.

Answer 8

hey the sun has very less density than a black hole.a black hole has a very high such that light itself cannot escape its gravity,the escape velocity is very high.

Answer 9

My guess is because the sun is an energy SOURCE whereas a black hole is an energy SINK. (Similiar to a heat source versus a heat sink). Emits energy as heat and light into space as it seeks to achieve equilibrium. Just a guess though, as I'm not an astrophysicist! :)