Black holes “gold factories” – accumulation disks around black holes can form heavier elements

Cosmic element forges: Star black holes can be long-term formation sites for gold and other heavy elements. This is because the accumulation disks around these holes contain neutrons that are not high enough to generate these elements by rapid neutron capture, which model simulation now suggests. Candidates for such cosmic gold mines are black holes from neutron star collisions, but also from hypernova.

After the Big Bang – all elements of the timetable did not appear until the first stars formed in the universe. Hydrogen and helium did not melt into large atoms, including iron, until atomic fusion. For heavier elements, on the other hand, a neutron capture process is necessary. Free neutrons must collide with the atom, sometimes turning into protons to form a new element.

Where are the remaining member factories?

For gold, platinum, uranium and other particularly heavy elements, ordinary, Slow neutron capture But did not turn off. Free neutrons only arise if they have a certain minimum energy – among other things, they are released during the collision of neutron stars. In 2017, astronomers won the first such collision The first tracks Gold and co to prove 2019 This was confirmed With more detailed analysis.

However, neutron star collisions in the universe are too small to explain the full magnitude of the heaviest elements in the universe. For example gold, f comesFive times more According to researchers in 2020, this formation should be the only one in our galaxy. So they suspected it was too powerful Hypernova A collapsing neutron star and the resulting black holes allow rapid neutron capture.

Black holes in view

Oliver Just and his colleagues from the GSI Helmholtz Center for Heavy Ion Research in Darmstadt have now determined which black holes can be considered as factories and how their accumulation disks should be designed. “In our study, we systematically studied the conversion rates of neutrons and protons for a large number of disk configurations using complex computer simulations,” Just explains.

Effect: In fact, the accumulation disks of some black holes have good conditions for the formation of heavier elements by rapid neutron capture. Because they have neutrons fast enough, they collide with atoms to form new elements, the researchers said.

Disk mass is important

However, there are restrictions: “Resolution is the total mass of the panel. The larger the disk, the more often neutrons are formed from protons by capturing electrons and emitting neutrinos, which are available for assembly of heavier elements using the R-process. ” But if the disk is too heavy, it is reversed and more neutrons are converted into protons. Then there will not be enough materials for neutron capture. The team found that the optimal disk mass for element factories is 0.01 to 0.1 solar masses.

This confirms that the black holes that arise after collisions with neutron stars are actually good “factories” for gold, platinum and more. Because, according to Just and his colleagues, many of them have accumulation disks in this mass range. But black holes from hypernovae are theoretically possible – stellar explosions in which a star first turns into a neutron star and then collapses as it is further injected into the black hole. However, the researchers report that the arrival of the substance should be relatively high.

Many more questions remain unanswered

Black holes and their accumulating disks may be the places where heavier elements appear and continue to rise in space. The modeling of Just and his team has now helped to shed light on at least some aspects and requirements of such element factories. However, as researchers insist, the search for sites for rapid neutron capture is only just beginning and many more questions remain unanswered. (Monthly Announcements of the Royal Astronomical Society, 2021; doi: 10.1093 / mnras / stab2861)

Source: GSI Helmholtz Center for Heavy Ion Research

17. November 2021

– Nadja Podbregar