University of California Los Angeles physicists have proposed a new theory of how the first black holes in the universe could form and what role they could play in the production of heavy elements such as gold, platinum and uranium.
The works were published in the journal Physical Review Letters.
Astrophysicists have long wondered when the very first black holes in the universe appeared – less than a second after the Big Bang, or many millions of years later, when the first stars died.
Alexander Kusenko, a professor of physics at the University of California, Los Angeles, and Eric Kotner, a graduate student at the university, developed a fairly simple new theory, which suggests that black holes could form soon after the Big Bang, long before the first stars began to shine . Astronomers have previously put forward assumptions that these so-called primary black holes can explain all or part of the mysterious dark matter and that they also could sow the formation of supermassive black holes that are in the centers of galaxies. The new theory suggests that primary black holes could help in creating a multitude of heavy elements that occur in nature.
The researchers began by examining a homogeneous field of energy pervading the universe right after the Big Bang. Scientists expect that such fields existed in the distant past. After the universe quickly expanded, this energy field crumpled. Gravity made these lumps meet and unite. Researchers from Los Angeles suggested that a small part of these growing lumps were dense enough to become black holes.
Their hypothesis is quite generalized, says Kusenko, and does not rely on, as he put it, "unlikely coincidences", which underlie other theories that explain primary black holes.
It follows from the work that these primary black holes can be found by means of astronomical observations. One of the methods involves measuring tiny changes in the brightness of a star, which are the consequence of the gravitational effects of the primary black hole passing between the Earth and this star. Earlier this year, American and Japanese astronomers published an article about the discovery of a star in a neighboring galaxy, which flickered brighter and dimmer as if it were a primary black hole.
In a separate study, Kusenko, Vladimir Takhistov and George Fuller suggested that primary black holes can play an important role in the formation of heavy elements such as gold, silver, platinum and uranium. The origin of these heavy elements has long been a mystery to researchers.
"Scientists know that these heavy elements exist, but are not sure where they will form," says Kusenko. "It's inconvenient."
Studies at the University of California show that the primary black hole periodically collides with a neutron star – a rapidly rotating remnant of a small-sized star after a supernova explosion – and sucks it into itself.
When this happens, says Kusenko, the primary black hole absorbs the neutron star from within within about 10,000 years. As the neutron star contracts, it begins to rotate faster, until at last small fragments from it separate and fly away. These fragments of a material rich in neutrons can be sources in which neutrons synthesize more and more heavy elements, Kusenko says.
However, the probability that a neutron star will capture a black hole is quite low, says Kusenko, which is consistent with the observations of some galaxies enriched with heavy elements. The theory that primary black holes collide with neutron stars, creating heavy elements, also explains the observed absence of neutron stars in the center of the Milky Way galaxy, a long-standing mystery of astrophysics.
This winter, Kusenko and his colleagues will work with scientists at Princeton University to simulate computer simulations of heavy elements that are generated in the interaction of black holes and neutron stars. Comparing the results of this simulation with the observations of heavy elements in neighboring galaxies, scientists hope to determine whether the primary black holes are responsible for the appearance of gold, platinum and uranium on Earth.