Grav wave boffins are unsure if they just spotted the smallest black hole or the biggest neutron star seen yet Astronomers have detected what could be either the tiniest black hole or the largest neutron star found to date. Gravitational waves are emitted when two massive objects collide and merge with one another. The energy of the impact event ripples through spacetime, and these signals are detected by measuring the movement of …
I propose a new class of objects falling between 2 and 5 solar masses that shall be called Neutron Holes! Wait... No, lets name them Black Stars, much cooler sounding.
And look we just spotted one! My proposal is validated! Where do i collect my Nobel prize?
Hawking radiation is very feeble and has yet to be detected in practice. Most of the radiation from a black hole is from the extremely hot accelerated matter that is being pulled into it and swirled around it in ever decreasing circles - before disappearing over the event horizon. There are also the colossal magnetic poles around black holes that also cause matter to give off lots of light, x-rays etc as charged particles swirl through the field.
Also, for Hawkins radiation to even work, requires certain temperatures around the black hole, and most if not all SMBHs are already too large to start evaporating unless the background radiation gets cooler (or some other mechanism allows it to be cooler near them?).
For a black hole to emit more Hawking radiation than it absorbs from the CMB it would have to have a mass equal or less than the Moon (approximately). No stellar mass or higher black hole would be detectable by Hawking radiation, even in theory.
It could steal mass from a companion though that's probably not going to add enough material to matter much. They could merge with a white dwarf or another neutron star if a companion had a slowly decaying orbit. The fact neutron stars larger than 2 solar masses or so are hard to find is probably because this sort of thing is comparatively rare - and if they become too big as result of this they'll collapse into a black hole so like goldilocks it has to be "just right".
When neutron stars merge, as when anything merges, they tend to shed mass in spectacular fashion. (Astrophysics: the science for people who like big explosions seen from a safe distance.)
Accreting material gets burnt in a jet of X-rays. I'm not sure you could get enough mass from the ash to bulk up the star. But if it got too heavy, it would suffer explosive collapse which might produce a black hole or might produce another neutron star.
The real problem is we don't have a solid value for the upper limit for neutron stars. If Wikipedia is to be believed, this object is slightly lighter than the heaviest neutron star known (2.74M☉) And that's in pretty good agreement with the lightest stellar black hole (ibid - scroll down). But there's no theoretical minimum mass for a black hole and merging objects could, after shedding some mass, produce one that was, ahem. lighter than the upper limit for neutron stars. So it's probably a black hole
I think that the mass gap is an observational thing rather than a theoretical thing: people spend a lot of time looking at binaries for which one companion is a neutron star or a black hole, and inferring the mass of that object (I think you can infer the mass of neutron stars which are not in binaries as well, but that doesn't work very well for BHs). And what they saw is that there are neutron stars which are lighter than about 2 solar masses, and black holes which are heavier, but they don't see anything in between.
I think that the assumption is that the mass gap isn't real, and LIGO/VIRGO will fill it (and are starting to fill it with this observation).
No, not https://en.wikipedia.org/wiki/Quark_(Star_Trek), https://en.wikipedia.org/wiki/Quark_star
Of course, a black hole of any particular mass is possible, but if faces with a theoretically reasonable, but hard to observe phenomenon verses a really, really, really rare thing, it seems odd to exclude the theoretically reasonable hypothesis.
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