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The origins of the heavy elements of the solar system such as gold and platinum have aroused great interest for astronomers. One of the most popular theories is that they have been scattered in space by neutron star collisions.
New research, however, found another origin: a kind of star explosion, often neglected, or supernova. The researchers say that these could be responsible for at least 80% of the heavy elements of the universe.
The types in question are collapsed supernovae, produced by rapidly rotating stars representing more than 30 times the mass of the Sun; they explode dramatically before collapsing into black holes.
"Our research on neutron star mergers led us to think that the birth of black holes in a very different kind of stellar explosion could produce even more gold than mergers. Neutron stars, "said physicist Daniel Siegel of the University of Guelph.
The detection of neutron star collisions in 2017 provided the first solid evidence that such collisions produce heavy elements. In the electromagnetic data produced by GW 170817, scientists detected for the first time the production of heavy elements, including gold, platinum and uranium.
As we have already pointed out, this happens because a powerful explosion, such as a supernova or stellar fusion, can trigger the process of fast neutron capture, or process -r – a series of nuclear reactions in which atomic nuclei collide to neutralize elements that iron.
Reactions must occur fast enough that radioactive decay is unlikely to occur until more neutrons are added to the nucleus, which means that this must occur when many free neutrons float, such as star exploding.
In the case of GW 170817, these r-process elements were detected in the disk of material that has bloomed around the neutron stars after their melting. While working to understand the physics of this phenomenon, Siegel and his team realized that the same phenomenon could occur in association with other cosmic explosions.
Thus, with the help of supercomputers, they simulated the physics of supernovae in collapse. And, boy have they ever found gold?
"80% of these heavy elements that we see should come from collapsars," Siegel said.
"Collapsars are quite rare in supernova occurrences, even rarer than neutron star mergers – but the amount of materials they eject into space is far greater than that from mergers of neutron stars. "
In addition, the quantities and distribution of these elements produced in the simulation were "surprisingly similar" to what we have here on Earth, he noted.
Does this mean that 0.3% of the Earth's r-process elements do not arise from a collision between neutron stars 4.6 billion years ago, as 39, has already found another team of astronomers at the beginning of the year? Not necessarily. According to Siegel's simulation parameters, up to 20% of these elements could still come from neutron starburst and black hole bursts.
The team hopes that the James Webb Space Telescope, which is scheduled for launch in 2021, could provide further insight. Its sensitive instruments could detect the radiations pointing to a supernova collapsing in a distant galaxy, as well as the elementary abundances of the Milky Way.
"Trying to determine where the heavy elements come from can help us understand how the galaxy was chemically assembled and how it formed," Siegel said.
"It could actually help solve some of the big questions in cosmology because heavy elements are a good tracer."
The search was published in Nature.
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