A new study by scientists at the German Heavy Ion Research Center (GSI) and other academic institutions in Belgium and Japan has concluded that black holes surrounded by an accretion disk, composed of extremely dense material at high temperatures, could be the origin of much of the gold and other heavy elements that exist in the universe. Neutron star mergers would be the starting point for these enigmatic cosmic structures.
An accretion disk or accretion disk is a structure made up of gas and dust that revolves around a massive central object, in this case a black hole. The material of these discs, from the energy that is lost by the same rotational movement, falls towards the center of the system, adding its mass to that of the central object.
Synthesis of heavy elements
According to a press release, the synthesis of heavy elements such as gold is closely related to black holes and their accretion discs. In line with what is indicated in other recent studies, the new research also maintains that the formation of these colossal structures would take place after the merger of two massive neutron stars.
Another possible origin could be the so-called gravitational collapses: they originate after the death of a star, exactly when it runs out of fuel. At that moment, the stellar body collapses “inward” due to the effect of its own gravity. In this way, the star contracts until it finally forms a black hole.
Although it is known that heavy elements such as gold or uranium, which are present on Earth and in the rest of the universe, were created from huge explosions and stellar collisions, little is known or has been able to determine the exact conditions of their training. The big question that especially intrigues astrophysicists is which of all the cosmic phenomena of this type is the one that most energizes the production of heavy elements.
Neutron excess
When the first observation of gravitational waves took place in 2017, one of the discoveries derived from this key scientific fact was the possibility of studying in greater detail the events related to the generation and release of many heavy elements.
According to the new study, published in Monthly Notices of the Royal Astronomical Society, everything would indicate that the key would be hidden in black holes surrounded by accretion discs. The primary question is to determine the conditions in which an excess of neutrons is formed in these structures, the basic requirement for the synthesis of heavy elements.
In general, the researchers discovered that neutron star mergers that produce accretion discs with specific masses and in a certain range are capable of providing the exact conditions to generate a large fraction of the heavy elements. The characteristics of these structures would facilitate a rapid process of neutron capture and the conversion between protons and neutrons, resulting in the formation of gold and other heavy elements.
Reference
Neutrino absorption and other physics dependencies in neutrino-cooled black hole accretion discs. O Just, S Goriely, H-Th Janka, S Nagataki and A Bauswein. Monthly Notices of the Royal Astronomical Society (2021). DOI: https://doi.org/10.1093/mnras/stab2861