Since high school, I've been told that the definition of mass is "quantity of matter" (which is absolutely wrong, I guess). If mass is actually a quantity of matter and it is a measure of inertia, when a giant-star dies, if it is massive enough to undergo a supernova, it could either transforms into a neutron star or a black hole. Now, in a supernova some amount of matter is lost, but how does the black hole manage to have such a greater mass than its parent star? Coming to the "definition", where has the excess matter come from? I know it hasn't, in practice it is not the case and it is not possible. So what is the actual definition of mass? What quantity does the mass define? And what are the factors creating/affecting inertia?
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1Black holes can merge together. So they combine and form a bigger black hole. Also, black holes made by stars are stellar mass black holes – Aug 12 '21 at 15:37
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Have you read the Wikipedia page? – franz_lyre Aug 12 '21 at 16:10
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@f_n_lyre Its too complicated to my standards. :( – Kavin Ishwaran Aug 12 '21 at 16:14
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1Hi! Are you asking, in principle, "what is mass?"... which is a more basic physics question. Or are you asking, what is the mass of neutron stars and of black holes, and how does supernova effect it? – Daddy Kropotkin Aug 12 '21 at 16:50
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3You may find my answer here helpful https://astronomy.stackexchange.com/a/43452/23762 – Daddy Kropotkin Aug 12 '21 at 16:51
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9"But How the Black hole manage to have such a huge mass than its Parent star?" A black hole has less mass than its parent star. – PM 2Ring Aug 12 '21 at 17:55
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1I’m voting to close this question because it probably belongs on Physics SE. – WarpPrime Aug 15 '21 at 23:06
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I’m voting to close this question because it's not about Astronomy – uhoh Aug 17 '21 at 06:46
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This answer addresses first the initial misconception that the mass of black hole is greater than the mass of its parent star. This is not true. The gravity may be more intense, but the mass is less.
The black hole or neutron star that forms after a supernova would have a lower mass than the star that it formed from, as some of the matter of the star is expelled in the explosion.
The black hole or neutron star would have more extreme gravity, because the mass that remains is concentrated in a much smaller volume of space (perhaps collapsed to a singularity).
The strength of gravity depends on both the mass (below you) and the distance you are from the centre. So a more massive star can have lower surface gravity than a small planet if that star is sufficiently large. Betelgeuse has a mass five million times that of the Earth, but its surface gravity is much less, because it is so puffed up.
So your definition of mass is fine. Mass is the factor that gives a body inertia. It is the ratio of momentum to velocity. If we give two bodies the same impulse then their mass is in inverse proportion to the resulting speed. Mass is also proportional to Energy, and through this to the curvature of spacetime and so gravitational effects.
James K
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