If a star has a mass greater than the Chandrasekhar limit, will it definitely become a black hole in the future or does it need to satisfy additional conditions? Let me explain. Suppose the collapse of a star happens via the formation of the intermediate neutron star stage. Is it possible that the neutron star remains stable forever and stops evolving into a black hole in the future?
[Physics] Will a neutron star always collapse into a black hole in the future
astrophysicsblack-holesgeneral-relativityneutron-starsstars
Best Answer
Terminology note: the Chandrasekhar limit $M_C \approx 1.4 M_\text{sun}$ is for electron-degenerate matter. The analogous limit for neutron-degenerate matter, $M_\text{TOV} \sim 2.5 M_\text{sun}$, is named for Tolman, Oppenheimer, and Volkoff. We have much less confidence in our estimate for the TOV limit than we do in the Chandrasekhar limit, because we know less about the equation of state for neutron-degenerate matter than we do for electron-degenerate matter.
We are aware of several stable neutron stars with masses $M_C < M_\text{object}$; there’s a partial list in Wikipedia article linked above. But I suspect you were asking about the stability of neutron stars with masses above $M_\text{TOV}$.
There is speculation in the literature about the possible existence of quark stars, in which the nucleon degrees of freedom dissolve and the star is supported by degeneracy pressure among the free quarks. It’s possible in principle that a neutron star which accumulated mass beyond $M_\text{TOV}$ could collapse to a quark star, analogous to the collapse of a white dwarf (or of an electron-degenerate stellar core) to a neutron star. But we know even less about the equation of state for quark matter than we know for neutron matter. I don’t think it’s known for certain that the mass limit for a quark star is any larger than the mass limit for a neutron star. It’s also unknown whether quark stars would consist of up and down quarks, like normal baryonic matter, or whether the phase transition would produce a substantial fraction of strange quarks.
The Wikipedia page lists a number of (unconfirmed) quark star candidates, and describes why confirmation is so difficult. It may well be the case that quark stars don’t exist, and that an overmassive neutron star is definitely doomed to become a black hole.
The neutron-star merger event GW170817 produced an object with final mass $2.74^{+0.04}_{-0.01}M_\text{sun}$. That gravitational-wave event suggested the new object collapsed to a black hole on a timescale of a few seconds (as opposed to milliseconds, or hours). If you’re interested in the nitty-gritty details of black hole formation from “supermassive neutron stars,” that would be a path into the literature.