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Asked by laryssaa to Colm, Eoin, Joseph, Lauren, Stephen on 14 Nov 2013.
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Stephen Scully answered on 14 Nov 2013:
When a large star explodes, the outer layers blast off . If the centre of the star is massive enough and collapses small enough, it may be so dense as to form a black hole. It requires that the centre of the star collapses under gravity to a point where light travelling near the star is trapped causing it to appear black.
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Eoin O Colgain answered on 14 Nov 2013:
The eventual fate of a star depends on its mass, on the amount of matter in it.
Potential end states for stars include white dwarfs, neutron stars and black holes.
For white dwarfs, gravity is balanced by electrons meaning that the atoms should be more or less intact (recall most of the atom 99.999999% is empty space).
If the star is larger, gravity is larger and it can form a neutron star. In this case the repulsion between electrons is not enough to counteract gravity and the atoms also collapse. If one wants to escape from a neutron star one has to travel at 100,000 km/s, a third of the speed of light.
Finally, neutrons themselves are not fundamental. Inside neutrons one finds quarks. So it is conceivable that if gravity is strong enough, even neutrons can be compressed further. What happens next is not understood and one would need a quantum theory of gravity, however it is clear that at some point one would have to travel at the speed of light to escape….at this stage one has a black hole.
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colm bracken answered on 19 Nov 2013:
I cannot add much to the other guys answers. But I will try to give you some food for thought. A large amount of mass is not actually required to make a black hole. Strong gravity all comes down to density. For example it would be possible for a planet more massive than Earth to have weaker gravity on its surface. All that would be required would be that the planet has a larger radius.
So even if you had 1 kilogram of matter you could turn it into a blackhole. You would just have to squish it down into a tiny tiny space, so small that it would end up being smaller than an atom. If you were strong enough to do this then you would have a mini blackhole!
Comments
laryssaa commented on :
Thanks for answering my question!
But after the stars explode would the blackhole be bigger than the star itself?
Joseph commented on :
No it would not be bigger in terms of our idea of “size”. We usually talk about the size of a Black Hole in terms of its event horizon. The event horizon is refers to the location from the black hole where the escape velocity equals the speed of light. The event horizon is the point from the centre of the black hole at which no particle (or even light) can escape.