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Dark matter, the mysterious substance that exerts gravitational pull but emits no light, could actually consist of vast concentrations of ancient black holes created at the very beginning of the universe, according to a new study.
This conclusion comes from an analysis of gravitational waves, or ripples in space-time, produced by two distant collisions between black holes and neutron stars.
Ripples – labeled GW190425 and GW190814 – were detected in 2019 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Washington and Louisiana, and the Virgo interferometer near Pisa, Italy. Previous analysis suggested that the ripples were produced by collisions between black holes between 1.7 and 2.6 times the mass of our sun and either a smaller neutron star or a much larger black hole.
But that would make one of the objects in each collision what astrophysicists call a solar-mass black hole, with roughly the mass of the sun.
Related: 10 huge black hole finds
“Solar mass black holes are quite mysterious, because they are not expected from conventional astrophysics”, like star explosions, or supernovas, which smash larger stars into black holes, says lead author of the study, Volodymyr Takhistov of the University of California, Los Angeles, told Live Science in an email.
Instead, the authors propose in the study, published on February 16 in the journal Physical examination letters, these solar mass black holes can be “primordial” black holes created during the Big Bang. Or they may have formed later when neutron stars were transmuted into black holes – either after engulfing primordial black holes, or after absorbing some proposed types of dark matter, the mysterious matter that exerts gravitational pull. does not interact with light, Takhistov said.
Primordial black holes
The primordial black holes, if they exist, were probably created in large numbers in the first second of the Big Bang about 13.77 billion years ago. They would have come in all sizes – the the smallest would have been microscopic and the biggest tens of thousands of times the mass of our sun..
Calculations show that the smaller one would have “evaporated” by now, emitting quantum particles through a process known as Hawking radiation, so that only primordial black holes with masses greater than 10 ^ 11 kilograms – approximately the mass of a small asteroid – would still exist today.
If they existed, these ancient black holes could constitute the immense halos of “dark matter” that border galaxies, some astrophysicists believe.
The researchers wanted to know if they could distinguish primordial black holes from black holes formed from neutron stars, the glittering remnants of supernovas left behind when their mother stars exploded after depleting all of their nuclear hydrogen fusion reactions.
Astrophysicists have calculated that stars smaller than about five times the mass of the sun collapse to leave behind a neutron star of ultra-dense matter, with roughly the mass of our sun encased in a ball of the size of a city, Live Science reported.
In this theory, the intense gravity of certain neutron stars would have continuously attracted particles of dark matter; eventually, their gravity would have grown so great that the neutron star and dark matter collapsed together into a black hole, the new study suggests.
An alternative proposed by the study is that a neutron star could have attracted and merged with a small primordial black hole, which then settled in the center of gravity of the neutron star and fed on the matter. surrounding until all that remains is the black hole.
Gravitational waves
Takhistov and his colleagues believed that black holes transmuted from neutron stars should follow the same mass distribution of the neutron stars they came from, which depends on the size of their mother stars.
With this in mind, they looked at data from the fifty or so gravitational wave detections made to date and found that only two – GW190425 and GW190814 – involved objects with the right masses to be primordial black holes, found. wrote the study authors.
The research is inconclusive: It is still possible that these two collisions involve neutron stars of the masses detected, or black holes transmuted from neutron stars of these sizes. But the mass distribution of neutron stars thought to exist in the universe makes this unlikely, the authors wrote.
“Our work offers a powerful test to understand their origin and relationship to dark matter,” Takhistov said. “In particular, this test demonstrates that black holes significantly heavier than about 1.5 solar masses are very unlikely to be” transmuted “black holes as a result of neutron star disturbances.
And if so, it suggests that primordial black holes may really exist and that they could be a component of dark matter, according to the study.
The method will become more precise as gravitational wave detections are made, Takhistov said: “The test is statistical in nature, so collecting more data will allow better understanding.”
Originally posted on Live Science.
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