# Why do black holes depend on density?

Why do we have Earth weighting trillions of tons and not forming a black hole, but then it I compress earth to a sphere of 10mm I get a black hole?

If the amount of energy in this small sphere is the same as the earth in terms of mass (they have the same mass, just different sizes), how come one is a black hole and the other is not?

What defines a black hole? Huge mass, or small size high density? If I compress an ant enough can I make a black hole out of her?

• Short answer: pressure, being a part of the stress-energy tensor, is a source of spacetime curvature (gravity). Dec 9, 2016 at 0:45
• A black hole is any object whose escape velocity exceeds the speed of light. Dec 9, 2016 at 0:46

## 1 Answer

If you look at this Wikipedia page section, Minimum mass of a black hole, you can see what the conjectured, totally unproven, mass of a micro black hole is, about 22 micrograms. A large ant has a mass of 5 milligrams. So if a micro black hole is formed by pressure, as larger black holes are (and if they exist, I don't know enough to answer those two questions) then you could, given sufficient pressure, make a black hole out of one, but it might evaporate before you had a chance to study it.