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Neutron Star Collisions Are a “Goldmine” of Heavy Elements – Chief Cosmic Source for Gold, Platinum - SciTechDaily

Neutron Star Collisions Are a “Goldmine” of Heavy Elements – Chief Cosmic Source for Gold, Platinum - SciTechDaily

Neutron Star Collisions Are a “Goldmine” of Heavy Elements – Chief Cosmic Source for Gold, Platinum - SciTechDaily
Oct 25, 2021 3 mins, 19 secs

New research suggests binary neutron stars are a likely cosmic source for the gold, platinum, and other heavy metals we see today.

Mergers between two neutron stars have produced more heavy elements in the last 2.5 billion years than mergers between neutron stars and black holes.

But beyond iron, scientists have puzzled over what could give rise to gold, platinum, and the rest of the universe’s heavy elements, whose formation requires more energy than a star can muster.

A new study by researchers at MIT and the University of New Hampshire finds that of two long-suspected sources of heavy metals, one is more of a goldmine than the other.

The study, published today (October 25, 2021) in Astrophysical Journal Letters, reports that in the last 2.5 billion years, more heavy metals were produced in binary neutron star mergers, or collisions between two neutron stars, than in mergers between a neutron star and a black hole.

The study is the first to compare the two merger types in terms of their heavy metal output, and suggests that binary neutron stars are a likely cosmic source for the gold, platinum, and other heavy metals we see today.

The findings could also help scientists determine the rate at which heavy metals are produced across the universe.

“What we find exciting about our result is that to some level of confidence we can say binary neutron stars are probably more of a goldmine than neutron star-black hole mergers,” says lead author Hsin-Yu Chen, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research.

In 2017, however, a promising candidate was confirmed, in the form a binary neutron star merger, detected for the first time by LIGO and Virgo, the gravitational-wave observatories in the United States and in Italy, respectively.

The math showed that binary neutron stars were a more efficient way to create heavy elements, compared to supernovae.”.

Chen and her colleagues wondered: How might neutron star mergers compare to collisions between a neutron star and a black hole.

Under certain conditions, scientists suspect, a black hole could disrupt a neutron star such that it would spark and spew heavy metals before the black hole completely swallowed the star.

For their analysis, they focused on LIGO and Virgo’s detections to date of two binary neutron star mergers and two neutron star – black hole mergers.

The researchers first estimated the mass of each object in each merger, as well as the rotational speed of each black hole, reasoning that if a black hole is too massive or slow, it would swallow a neutron star before it had a chance to produce heavy elements.

The more resistant a star, the less likely it is to churn out heavy elements.

On average, the researchers found that binary neutron star mergers could generate two to 100 times more heavy metals than mergers between neutron stars and black holes.

They conclude then, that during this period, at least, more heavy elements were produced by binary neutron star mergers than by collisions between neutron stars and black holes.

The scales could tip in favor of neutron star-black hole mergers if the black holes had high spins, and low masses.

However, scientists have not yet observed these kinds of black holes in the two mergers detected to date.

Chen and her colleagues hope that, as LIGO and Virgo resume observations next year, more detections will improve the team’s estimates for the rate at which each merger produces heavy elements.

“You can use heavy metals the same way we use carbon to date dinosaur remains,” Vitale says.

“Because all these phenomena have different intrinsic rates and yields of heavy elements, that will affect how you attach a time stamp to a galaxy.

Reference: “The Relative Contribution to Heavy Metals Production from Binary Neutron Star Mergers and Neutron Star–Black Hole Mergers” by Hsin-Yu Chen, Salvatore Vitale and Francois Foucart, 25 October 2021, Astrophysical Journal Letters.

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