The study of a dwarf galaxy, stuffed with heavy elements, allowed scientists to find out that the main sources of gold may be dying neutron stars.
Initially, there were only the lightest atoms in the universe, hydrogen with small amounts of helium. The entire set of elements, up to iron, arose from them as a result of thermonuclear reactions that took place - and continue to take place - in the bowels of many generations of stars. However, the birth of heavier elements, including gold or uranium, requires even more severe conditions, reports Naked Science.
More than half a century ago, theorists described the possible mechanism of their formation. This is an r-process in which freely moving neutrons are captured by the nuclei of iron atoms, accumulating in it. Some of the neutrons can then lose an electron, turning into protons and forming increasingly heavier nuclei. Calculations show that such capture should occur quickly - faster than unstable iron isotopes with an increased number of neutrons decay. This requires special conditions for the r-process, and it is believed that in space it can be realized immediately before the explosion of a huge supernova or in the shock wave of this explosion when a pair of incredibly dense neutron stars merge and in other very extreme circumstances.
This picture is generally accepted in astrophysics, but in many respects remains theoretical. In particular, what kind of contribution to the filling of the Universe with these elements is made by supernovae, and what contribution is made by mergers of neutron stars, remains a subject of discussion. These disputes have developed as a result of new observations of the dwarf galaxy Grid II, discovered only about a year ago. Grid II is one of the many small satellites of the Milky Way and is only 98,000 light-years from Earth. And it's chock-full of elements heavier than iron.
Astronomers from the Kavli Institute were able to notice this, using the telescopes of the Las Campas observatory located in Chile. Observing seven of the nine largest and brightest stars in Grid II, they noted anomalously high abundance of elements heavier than iron. This is an extremely unusual feature that sharply distinguishes Grid II from the background of neighboring dwarf galaxies. In an article published in the journal Nature, the authors put forward the hypothesis of what kind of powerful event in the distant past of Grid II could saturate it with such elements.
The fact is that the number and relative composition of heavy elements produced by a supernova explosion or a merger of neutron stars may differ. “The explosion of a star eight times the mass of the sun will create gold about the size of the moon,” explains Enrico Ramirez-Ruz, professor at the University of California, Santa Cruz. "The merger of neutron stars will produce gold as much as the entire weight of Jupiter." The amount of heavy elements discovered by scientists in Grid II indicates precisely neutron stars as the main source of such nuclei. At least in dwarf galaxies.
