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Astronomy: Hypothetical black holes could be eating neutron stars

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Once inside, it spins fast enough for the star’s equator to reach escape velocity.

This is actually a pretty interesting idea. If true, it might explain creation of heavy elements that lately it no longer seems like supernovas can be creating, or creating enough of?

Ars Technica said:
Immediately after the Big Bang, the Universe's matter was incredibly dense and rippled with random fluctuations. Is it possible that some portions of it reached densities high enough to collapse into black holes?

The idea of primordial black holes has been kicking around in theoretical circles for a while, in part because they could provide much of the dark matter that seems to dominate the Universe's large-scale structures. But testing for their existence requires some sort of consequence that we could detect, and the theorists have largely come up short there. But now, a team of three physicists writing in Physical Review Letters has come up with a rather intriguing consequence: these black holes could swallow a neutron star that, under the right conditions, would spit out heavy elements.

Truth or consequences

Two things could distinguish primordial black holes from those formed in the collapse of a massive star. One is that they could be nearly any mass, from less than the mass of a star up to thousands of times heavier than anything formed during a supernova. The heavier end of the spectrum is appealing, since it could explain how supermassive black holes appeared so quickly (in astronomical terms) after the Universe's birth.

The second feature is that primordial black holes were present early in the Universe's history. The influence of dark matter is apparent long before the Universe formed any stars, which appear to be a necessary precursor for black holes that formed after the Universe started to spread out. Since they were present early, primordial black holes could account for a sizable percentage of the dark matter, though various studies have put some constraints on how much.

The problem is that we can't examine either of these issues in enough detail to know whether primordial black holes exist. So, while these objects remain physically plausible, there hasn't been any consequences to their existence that we can actually search for in the present-day Universe.

Unless, of course, the new paper has it right. In it, its authors describe the rather unusual consequences of a primordial black hole running into an equally exotic object: a rapidly spinning neutron star.

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dickson

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Clever paper! (Available for download as 2017arXiv170401129F.) Identifying the astrophysical site of r-process nucleosynthesis remains the most important open problem in nuclear astrophysics. This study sketches an exotic process that seems astrophysically plausible and does not violate any of the known upper limits on neutrino emission, gamma ray fluxes, and the like. It even supplies a candidate origin for the 511 keV electron-positron annihilation emission from the galactic center.

The scenario described, however, is an involved one (for the r-process, all the simple solutions are already pretty much ruled out...), which puts me in mind something Peebles wrote about helium synthesis, writing at a time when the Hot Big Bang model was not nearly so well established as it is today: "If {...the Big Bang explanation of the origin of helium turns out to be invalid..} we will have not learned much of theoretical interest...only that a very specific chain of events did not happen." (Peebles, P., Physical Cosmology, Princeton U. Press, 1971, p. 275)

The authors do suggest empirical observations that can rule out this mechanism. We shall see want aLIGO and radio searches for kilonovae have to say about it. Good fun.
 
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