# Black holes

1. Dec 29, 2003

### Thallium

What is the mass of a black hole at the size of a tennisball? Can the mass of a black hole vary?

2. Dec 29, 2003

### Jimmy

The formula for finding the Schwarzchild Radius is:

$$r = \frac{2 M G}{c^2}$$

M is the mass in Kg
G is the gravitational constant. (6.6742*10^-11 m^3/Kg*s^2)
C is the speed of light in m/s
r is the radius in meters. This is the distance from the singularity at which the event horizon exists. If distance has any meaning in this case...

For a Schwarzchild black hole, we can find the mass with a given radius by simply arranging the above formula:

$$m = \frac{r c^2}{2 G}$$

The radius of a tennis ball is approximately 0.0328 meters (2.6 inches). Plugging that into the formula gives us 2.209 * 10^25 Kg.

This mass is too small to have formed a Schwarzchild black hole in the first place. The minimum mass this type of black hole can have is around 1.5 solar masses. I'm not sure how accurate that figure is. I've seen values that range from 1.4 to 3 solar masses.

It's been theorized that tiny black holes may exist that were created shortly after the big bang. However, there is no experimental evidence which supports this. Primordial Black Hole

A black hole can have any arbitrary mass above the minimum. A black hole's mass can increase as it pulls matter into itself. A black hole might lose mass through the quantum process of Hawking Radiation.

Last edited: Dec 29, 2003