Most elements lighter than iron are created in the cores of stars. The white-hot core of a star promotes the fusion of protons, pushing them together to form ever heavier atoms. Beyond iron, scientists have struggled about what may give rise to gold, platinum, and the remainder of the universe’s heavy metals, the production of which needs more energy than a star can manage.
According to a new study conducted by MIT and the University of New Hampshire, one of two long-suspected sources of heavy metals is more of a goldmine than the other. Binary neutron star mergers, or collisions between two neutron stars, created more heavy metals than mergers between a neutron star and a black hole in the previous 2.5 billion years.
The work is the first to compare the two merger types in terms of heavy metal output, and it shows that binary neutron stars are a plausible cosmic source of the gold, platinum, and other heavy metals we see today. The discoveries may also aid scientists in determining the pace at which heavy metals are created across the cosmos.
Energy is required to combine protons to generate heavier atoms as stars undergo nuclear fusion. Stars are extremely efficient in producing lighter elements such as hydrogen and iron. However, fusing more than 26 protons in iron becomes wasteful in terms of energy. To move beyond iron and create heavier metals such as gold and platinum, it needs to find another technique to combine protons.
Supernovae have long been suspected as a possible solution. When a large star explodes as a supernova, the iron at its core may interact with lighter atoms in the severe debris to form heavier metals.
However, in 2017, a good possibility was verified in the form of a binary neutron star merger, which was observed for the first time by LIGO and Virgo, the gravitational-wave observatories in the United States and Italy, respectively. The detectors detected gravitational waves, or ripples in space-time, that began 130 million light-years from Earth from a collision between two neutron stars collapsed cores of huge stars that are filled with neutrons and are among the densest objects in the cosmos. The cosmic merging produced a burst of light with heavy metal traces.
Based on data from observatories, they also determined how frequently one merger happens vs the other. Finally, the researchers utilized computer models devised by Foucart to calculate the average quantity of gold and other heavy metals produced by each merger.
The researchers set out to calculate how much gold and other heavy metals each sort of merger might generally generate. They centered their investigation on two binary neutron star mergers and two neutron star–black hole mergers discovered so far by LIGO and Virgo.
The researchers then calculated the masses of each item in each merger, as well as the rotational speed of each black hole, reasoning that if a black hole is too huge or too sluggish, it would devour a neutron star before it can create heavy elements. They also calculated the resistance of each neutron star to disruption. The less probable a star is to produce heavy elements, the more resistant it is.
If the black holes had high spins and low masses, the scales may shift in favor of neutron star-black hole mergers. However, scientists have yet to see this kind of black hole in the two mergers discovered thus far.