Tuesday, September 27, 2022

Astrophysicists believe black holes can accidentally make gold

There may be more ways in the universe to forge heavy elements than we thought.

The creation of metals such as gold, silver, thorium and uranium requires energetic conditions such as a supernova explosion or neutron star collisions.

However, a new article shows that these elements can form in the swirling chaos that surrounds an active newborn black hole, absorbing dust and gas from the space around it.

Under these extreme conditions, the high rate of neutrino emission should facilitate the conversion of protons into neutrons, which leads to an excess of the latter required for the production of heavy elements.

“In our study, for the first time, we systematically investigated the conversion rates of neutrons and protons for a large number of disk configurations using sophisticated computer simulations, and we found that disks are very rich in neutrons when certain conditions are met. “said astrophysicist Oliver Just of the GSI Helmholtz Center for Heavy Ion Research in Germany.

In the beginning, after the Big Bang, there weren’t many elements around. Until stars were born and began to collide atomic nuclei in their cores, the universe was a soup made up mostly of hydrogen and helium.

Stellar nuclear fusion has filled space with heavier elements, from carbon to iron for the most massive stars sifted through space as a star dies.

But iron is where nuclear fusion meets challenges. The heat and energy required to make iron by fusion exceed the energy generated by the process, causing the core temperature to drop, which in turn causes the star to die in a spectacular kaboom – supernova.

This is that impressive kaboom (and kaboom of colliding neutron stars) in which heavier elements are fused. The explosions are so powerful that atoms, colliding with force, can capture neutrons from each other.

This is called the rapid neutron capture process or r-process; this must happen very quickly so that radioactive decay does not have time to occur before new neutrons are added to the nucleus.

It is unclear if there are other scenarios in which the r-process could take place, but newborn black holes are a promising candidate. Namely, when two neutron stars merge, and their combined mass is sufficient to tilt the newly formed object into the category of black holes.

Collapsars are another possibility: the gravitational collapse of the core of a massive star into a black hole of stellar mass.

In both cases, it is believed that the children’s black hole is surrounded by a dense, hot ring of material that swirls around the black hole and soaks into it like water into a sewer. In these environments, neutrinos are emitted in abundance, and astronomers have long hypothesized that r-capture nucleosynthesis could occur as a result.

Just and his colleagues have done extensive modeling to determine if this is actually the case. They varied the mass and spin of the black hole, the mass of the material around it, and the effect of various parameters on neutrinos. They found that under suitable conditions, nucleosynthesis of the r-process can occur in these environments.

“The deciding factor is the total mass of the disk,” Just said.

“The more massive the disk, the more often neutrons are formed from protons as a result of electron capture during the emission of neutrinos and are available for the synthesis of heavy elements using the r-process.

“However, if the mass of the disk is too high, the back reaction becomes more important so that more neutrinos are re-captured by neutrons before they leave the disk. These neutrons are then converted back to protons, which interferes with the r-process. “

This golden mean, in which heavy elements are most actively produced, is a disk with a mass of 1 to 10 percent of the mass of the Sun. This means that mergers of neutron stars with disk masses in this range can be factories for heavy elements. The researchers said that since it is not known how common collapsar discs are, a decision on collapsars has yet to be made.

The next step is to determine how the light emitted from a collision of a neutron star can be used to calculate the mass of its accretion disk.

“These data are currently insufficient. But with the next generation of accelerators, such as the Center for Antiproton and Ion Research (FAIR), it will be possible to measure them with unprecedented accuracy in the future, ”said astrophysicist Andreas Bauswein of GSI. Heavy Ion Research Center Helmholtz.

“The well-coordinated interaction of theoretical models, experiments and astronomical observations will allow us, researchers, in the coming years to verify the merging of neutron stars as a source of elements of the r-process.”

Research published in Royal Astronomical Society Monthly Notices

Nation World News Desk
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