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beecee

r-process nucleosynthesis

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https://phys.org/news/2017-08-primordial-black-holes-forge-heavy.html

Primordial black holes may have helped to forge heavy elements:
 

https://journals.aps.org/prl/accepted/55077Yb0Qcf1cb5c79b095a1a918b69bd6d2e6077

Primordial black holes and r-process nucleosynthesis

ABSTRACT

We show that some or all of the inventory of r-process nucleosynthesis can be produced in interactions of primordial black holes (PBHs) with neutron stars (NSs) if PBHs with masses {10}-14\,{\rm M}_\odot < {\rm M}\rm PBH < {10}-8\,{\rm M}_\odot make up a few percent or more of the dark matter. A PBH captured by a neutron star (NS) sinks to the center of the NS and consumes it from the inside. When this occurs in a rotating millisecond-period NS, the resulting spin-up ejects \sim 0.1-0.5\,{\rm M}\odot of relatively cold neutron-rich material. This ejection process and the accompanying decompression and decay of nuclear matter can produce electromagnetic transients, such as a kilonova-type afterglow and fast radio bursts. These transients are not accompanied by significant gravitational radiation or neutrinos, allowing such events to be differentiated from compact object mergers occurring within the distance sensitivity limits of gravitational wave observatories. The PBH-NS destruction scenario is consistent with pulsar and NS statistics, the dark matter content and spatial distributions in the Galaxy and Ultra Faint Dwarfs (UFD), as well as with the r-process content and evolution histories in these sites. Ejected matter is heated by beta decay, which leads to emission of positrons in an amount consistent with the observed 511-keV line from the Galactic Center.

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Interesting but looks highly theoretical. When has a black hole interacted with a neutron star? When has a black hole been characterised close up?

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On 8/24/2017 at 7:48 AM, jimmydasaint said:

Interesting but looks highly theoretical. When has a black hole interacted with a neutron star? When has a black hole been characterised close up?

Agreed it is as yet just a theoretical construct. But theoretical cosmologists are still looking for a complete scenario to explain some of the heavy elements that we do see. Also promordial BH's are themselves still theoretical, although many believe that they would have abounded at and just after the BB. And there still are other scenarios that are being investigated, such as hypernova ect. 

The point is of course we do have these heavy elements and we are still trying to find out the exact mechanism of how they were forged. We also have observed binary Neutron  star combinations, Neutron star/BH binary systems, or Neutron star/White Dwarf, and even binary BH's as detailed with recent discoveries of gravitational waves. So no, interactions with Neutron stars and BH's is not any fanciful situation.

With the new physics/cosmology of GW's, more hard evidence for explaining fully the heavy element observations, may be forthcoming in the course of time. 

  

Edited by beecee

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You are right, of course, we need a theoretical basis to explain the formation of heavy elements.  I like the theory of the triple alpha process - IIRC, it was proposed by Hoyle. who suggested that three alpha particles had the correct resonance (in the excited state) energy to form carbon. I take your point and agree with it.  I hope they are proved correct....  

https://www.faraday.st-edmunds.cam.ac.uk/CIS/polkinghorne/lecture4.html

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