Improved model shows gamma rays and gold at merging neutron stars

[notFritzArgelander]

Nice short clip of the simulation.

https://phys.org/news/2020-10-gamma-ray ... utron.html

[helicon]

Excellent vid. Thanks for the article notFritz.

[Michael131313]

Thanks nFA. Is there any way to estimate how much gold is produced?

[notFritzArgelander]

Thanks nFA. Is there any way to estimate how much gold is produced?

Thanks for asking this question! This is a point of current study and some controversy: 'How much of the gold (and similar elements) is produced in supernovae versus neutron star mergers?' With that as background I passed over the article's (misleading!) reference to the study having something to do with gold production. Neither the ApJ abstract nor the arXiv preprint of the full article make any reference to the results of this study having anything to do with gold production! What the paper DOES have is a discussion of how r-process elements (like gold) might be formed in the ejecta.

https://iopscience.iop.org/article/10.3 ... 213/abb6ef

We investigate the influence of magnetic fields on the evolution of binary neutron star (BNS) merger remnants via three-dimensional (3D) dynamical-spacetime general-relativistic magnetohydrodynamic (MHD) simulations. We evolve a post-merger remnant with an initial poloidal magnetic field, resolve the magnetoturbulence driven by shear flows, and include a microphysical finite-temperature equation of state. A neutrino leakage scheme that captures the overall energetics and lepton number exchange is also included. We find that turbulence induced by the magnetorotational instability in the hypermassive neutron star (HMNS) amplifies magnetic field to beyond magnetar strength (1015 G). The ultra-strong toroidal field is able to launch a relativistic jet from the HMNS. We also find a magnetized wind that ejects neutron-rich material with a rate of ${\dot{M}}_{\mathrm{ej}}\simeq 1\times {10}^{-1}\,{M}_{\odot }\,{{\rm{s}}}^{-1}$. The total ejecta mass in our simulation is 5 × 10−3 M ⊙. This makes the ejecta from the HMNS an important component in BNS mergers and a promising source of r-process elements that can power a kilonova. The jet from the HMNS reaches a terminal Lorentz factor of ~5 in our highest-resolution simulation. The formation of this jet is aided by neutrino cooling preventing the accretion disk from protruding into the polar region. As neutrino pair-annihilation and radiative processes in the jet (which were not included in the simulations) will boost the Lorentz factor in the jet further, our simulations demonstrate that magnetars formed in BNS mergers are a viable engine for short gamma-ray bursts.

So the short answer to your question is "Yes!" A slightly longer answer is "Yes, but these researchers only computed the environment in which r-process elements (like gold) can be made and folks with nucleosynthesis codes can settle that."

From https://en.wikipedia.org/wiki/R-process ... ical_sites

Current astrophysical models suggest that a single neutron star merger event may have generated between 3 and 13 Earth masses of gold.[29]

[Michael131313]

Thanks so much nFA. That is an amazing amount of gold. I assume that it is flung out into space, but do you think that it is coalesced and arrives at a place like Earth as a bunch, (of course if all of it came to Earth we would not be here and gold wouldn't be so precious ) or just spread out and is randomly distributed?

[notFritzArgelander]

Thanks so much nFA. That is an amazing amount of gold. I assume that it is flung out into space, but do you think that it is coalesced and arrives at a place like Earth as a bunch, (of course if all of it came to Earth we would not be here and gold wouldn't be so precious ) or just spread out and is randomly distributed?

It's spread out into the interstellar medium where it gets recycled into stars and planets or ...?

[Michael131313]

Thanks once again nFA. That's what I thought but had to ask anyway.