Stars which exceed the Tolman-Oppenheimer-Volkoff limit can become a black hole.
What happens to star after it becomes a black hole? Does it regain its status of star?
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$\begingroup$ Chandrasekhar limit is only std. max. mass of white dwarf... $\endgroup$– MithoronFeb 4, 2015 at 10:18
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2 Answers
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There's several ways this question could be answered, but they all come down to an emphatic "no" - a black hole will not return to being a main sequence star. The simplest way to see this is probably that a black hole has a much higher entropy than a star or even another type of stellar remnant of even vaguely similar mass and so there simply could not exist a spontaneous process by which a black hole develops back into a star.
A black hole once formed will stay a black hole, however it is believed that the Hawking process will lead to the black hole eventually evaporating. The time scale for evaporation though of a stellar remnant black hole is mindbogglingly long and they will not evaporate until long after stellar formation has ceased in the Universe.
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8$\begingroup$ A very long time indeed. Hawking radiation won't even be a consideration until the influx of mass/energy into the black hole drops below the rate at which Hawking radiation dissipated mass/energy. For a stellar black hole, even the incoming photons from the Microwave Background Radiation swamp Hawking radiation. The universe will have to get a lot older and a lot colder before black holes (except for tiny ones) stop gaining mass. $\endgroup$ Feb 4, 2015 at 6:43
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$\begingroup$ For anyone who doesn't want to do the math, he's a very convenient Hawking Radiation and Black Hole calculator: xaonon.dyndns.org/hawking - I can't swear to it's accuracy though. (and this doesn't take into account background radiation input, so, that changes the time a bit) $\endgroup$– userLTKAug 28, 2015 at 4:48
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Definitely not. When a star collapses, it may stop at the stage of a neutron star. This thing is still a physical "real" object, living within our space time. But when the mass of the original star is too big, the thing will go right through the neutron star stage and collaps further, because gravity is even stronger than the repulsive forces between the neutrons. In fact, no one knows where this thing goes. From a classical view, the collaps never ends, the thing vanishes out of the classical space time and cannot longer be reached. From a classical point of view there is no way back into space time. "Black hole" is a synonyme for a thing we do not understand.
