Primordial Black Holes Destroying Neutron Stars May Have Helped Make Heavy Elements

Artist impression of a neutron star. NASA's Goddard Space Flight Center

The 118 confirmed chemical elements in the universe have not all been there from the beginning. Some formed in the Big Bang, some are created in stars, and some we have only seen in the lab. Some elements require massive stellar explosions to form and now a group of researchers thinks that black holes could also help their creation.

According to a new study published in Physical Reviews Letters, heavy elements could form after a small primordial black hole enters a neutron star, the smallest and densest type of star. The black hole would begin to eat the dense stellar object in such a violent way that it would release enough energy to throw out some of the material, which would then turn into heavy elements.

"Small black holes produced in the Big Bang can invade a neutron star and eat it from the inside," lead author Professor George Fuller, from the University of California San Diego,  said in a statement. "In the last milliseconds of the neutron star's demise, the amount of ejected neutron-rich material is sufficient to explain the observed abundances of heavy elements."

"As the neutron stars are devoured, they spin up and eject cold neutron matter, which decompresses, heats up and make these elements."

It has long been theorized that small black holes might have formed during the Big Bang, although we have not found evidence for them yet. Fuller and his colleagues suggested the existence of black holes with a mass of between a small asteroid and a large dwarf planet (10-14 to 10-8 solar masses), and they would be one of the components of dark matter.

The black hole/dark matter connection (although excluded for bigger black holes) allowed the researchers to explain why bigger galaxies are more enriched with heavy elements, as they would have more dark matter and thus black holes, in their hypothesis. Also, it would explain why we see fewer neutron stars in the galactic center if they had been destroyed by black holes. 

They also suggest the ejection of matter from the tiny black holes devouring a neutron star could explain three more unexplained phenomena observed by astronomers.

"They are a distinctive display of infrared light (sometimes termed a "kilonova"), a radio emission that may explain the mysterious Fast Radio Bursts from unknown sources deep in the cosmos, and the positrons detected in the galactic center by X-ray observations," continued Fuller. "Each of these represents long-standing mysteries. It is indeed surprising that the solutions of these seemingly unrelated phenomena may be connected with the violent end of neutron stars at the hands of tiny black holes."

The hypothesis is interesting, we'll have to wait and see if it stands future observational tests.

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