|Posted: 2010-November-20 at 1:30pm | IP Logged
You've misinterpreted what they're saying - black holes don't have infinite mass. The mass is packed into an infinitely small (essentially zero) volume, and since density is mass over volume, that means it's the density
that is infinite and not the mass!
Black Hole masses are very finite though
- they can potentially be anywhere from barely above zero kilograms (in which case it's atomic scale and evaporates really quickly) to billions of suns (as in the supermassive black holes at the centres of galaxies).
To make a black hole, you need to collapse the object down to a size smaller its Schwarzschild radius
- once it gets to that point, light can't escape it, and gravity continues to collapse it from there into a black hole. For Earth, that radius is about 9 millimetres (say, the size of a pea) - if you do that, you end up with a black hole that has a mass of 1 earth mass.
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