Primordial Black Holes Unlikely To Explain Existence Of Dark Matter
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redOrbit Staff & Wire Reports – Your Universe Online
Dark matter, the mysterious substance that comprises more than 85 percent of the universe, is unlikely to be made of primordial black holes due to the existence of neutron stars, astrophysicists from the University of Lisbon in Portugal and the Harvard-Smithsonian Center for Astrophysics (CfA) claim in a new study.
The theory, originally proposed by Stephen Hawking in 1971, suggested that the black holes were formed when dense regions of the early universe gravitationally collapsed. While the theory has never been widely accepted, it has persisted because it does not require changes to the standard model of particle physics, Nature’s Eugenie Samuel Reich explained on Friday.
“Even when a 2013 study ruled out the possibility that primordial black holes in a certain size range had passed in front of stars observed by NASA’s Kepler space telescope, Hawking’s hypothesis remained viable because the method used was not sensitive to holes with masses less than that of the Moon,” Reich said. “That motivated astronomers to continue to sleuth through astronomical data for evidence of smaller black holes – until now.”
Last week, the Lisbon and CfA researchers unveiled new research analyzing what would happen if one of these primordial black holes were to pass through neutron stars. They concluded that, despite the small mass of these black holes, they would destroy the neutron stars – meaning the continued existence of those very stars can be used to limit the prevalence of the black holes.
As CfA professor Avi Loeb explained, he and his colleagues are basically “using neutron stars as detectors for primordial black holes.” The study authors state that the prevalence of neutron stars in our galaxy almost entirely closes the mass range not previously eliminated by the 2013 research. In short, the two studies combine to prove that primordial black holes could not be the primary constituent of dark matter.
“Most researchers have assumed dark matter is unknown particles, but there has always been this nagging possibility that it could all be black holes,” Jonathan Feng, a dark matter researcher at the University of California, Irvine, told Nature. “This work appears to have removed this possibility.”
However, according to Brookhaven National Laboratory astrophysicist Agnieszka Cieplak – one of the authors of the 2013 study – the mass window is not yet entirely closed. She explains that there is one extremely small gap at just under the mass of the Moon, as the lower limit of her study does not quite overlap with the upper limit of the new paper.