# How can a Blackhole have mass?

It is said that in Blackhole 100% part of the mass is getting converted into energy. Then how come Blackhole is having mass ?

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They maybe doing so but if you know their mass is inversely proportional to the amount of radiation they emit. So, for a black hole to be of zero mass it will have to emit radiation for a fairly large amount of time. See Hawking Radiation – Yashbhatt Apr 30 '14 at 15:52
In gravitational terms mass and energy are similar - see special relativity for E=mc^2 etc. Perhaps you could reframe your question? – adrianmcmenamin Apr 30 '14 at 22:27
@AmitG Could you tell us your source? – HDE 226868 Sep 2 '14 at 15:11
@HDE226868 - I was watching Discovery channel and they were telling above thought in one of the episode. In yet another episode they were telling when star finishes it's fuel then it collapse into the center which creates hole in spacetime and star become Supernova. I still didn't understand, whether it is a hole in spacetime or big mass with little radius and having existance. – AmitG Sep 3 '14 at 16:35

I believe when most scientists refer to the mass of a blackhole - i.e. a blackhole having the mass of a billion Suns, what they really mean is that the calculated gravitational pull of the blackhole is equivalent to that of such a mass would it exists at the location of the blackhole.

PS: Perhaps you could also bring some reference with respect to where exactly have you heard that 'It is said that in Blackhole 100% part of the mass is getting converted into energy'

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The truth is no one truly knows if 100% of the mass is being converted into energy. So without this assumption many other things are possible. Some think that since there is a constant flow of mass into the black hole, the conversion into energy is not keeping up with the rate the matter is being consumed, therefore the mass would remain substantially large.

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I believe that in fact the conversion factor is at most ~ 42 % for a maximally spinning blackhole, and about 10 % for a non rotating one. Which is a lot more than nuclear energy ~ 0.05 %. cf www3.mpifr-bonn.mpg.de/staff/mmassi/lezione2WEdd.pdf – chris May 1 '14 at 10:16