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Primordial Black Holes Can Explain Merely a Fraction of Dark Matter

What is Dark Matter? That question is a regularfixture in discussions about the nature of the Cosmos. There are several proposed explanations for dark matter, both within the Standard Model and exterior to it.One proposed constituent of dark matter is primordial black holes, created in the early Cosmos without a progenitor collapsing star.The dark matter conundrum is a missing mass problem. Galaxies should be simply unable to hold themselves together according to their observable mass. Their observable mass is stars, dust, gas,and a sprinkling of planets.

Some other form of mass must be existing to prevent galaxies from essentially disintegrating and dark matter is a placeholder name for that. Astronomer Fritz Zwicky was the first to use the term when he observed the Coma Cluster and found signs of missing mass. This happened in 1933. Around 90% of the Coma Cluster is missing mass, which Zwicky termed “dunkle Materie.”

Primordial black holes (PBHs) are one principal candidate for dark matter. In the Cosmos’s earliest times, pockets of dense subatomic matter might have formed naturally. Once sufficiently dense, they could’ve collapsed directly into black holes. Contrasting their astrophysical counterparts, they lacked any stellar progenitors.

Recent LIGO/Virgo results and JWST observations support the idea that PBHs are dark matter. Some researchers go further and claim that this evidence supports the notion that dark matter is exclusively made of PBHs and lacks any other components.Some of the early PBHs would in fact merge and that LIGO/Virgo can detect the gravitational waves from mergers, suggests new research. The research is “Constraints on primordial black holes from LIGO-Virgo-KAGRA O3 events.” M. Andres-Carcasona (a PhD student at the Institute of High Energy Physics at the Barcelona Institute of Science and Technology) is the lead author.

In 2015, LIGO (Laser Interferometer Gravitational-Wave Observatory) detected its very first black hole merger. At the time, scientists heralded this new window into the Universe. Until then, astronomical observations relied on electromagnetic radiation, but LIGO/Virgo changed that forever. Even Japan has now joined the LIGO/Virgo collaboration with their Karga gravitational wave observatory, and the international effort is called LIGO/Virgo/Karga. The three observatories collectively gather data on gravitational waves.

“Previous works have explored the use of GW data to find direct or indirect evidence of PBHs,” write the authors. “Specifically targeted searches of subsolar mass compact objects, which would provide a smoking gun signal of the existence of PBHs have so far been unsuccessful.”The authors draw attention to the fact that within their growing body of GW data, there may be signs of PBHs that were missed by other researchers’ approaches. They state that some of the component masses, “… fall in regions where astrophysical models do not predict them, potentially suggesting for a PBH population”.

The two underlying formation scenarios of PBHs that researchers mention are astrophysical and primordial. Within the primordial category, there are diverse ways that PBHs can form, and they’re all intertwined with mass function. The authors explain that PBHs could in fact explain the totality of dark matter, but only if they’re within the range of 10-16 to 10-12 solar masses.“Lighter PBHs would be evaporating today and can constitute only a small portion of the DM,” they state.

Astrophysical BHs form binaries and can in fact merge, sending out gravitational waves. If PBHs merge, even they would send out gravitational waves. It’s quite possible that some of these mergers are behind some of the GW data detected by LIGO/Virgo/Karga collaboration in its third observational run. The scientists present their results in terms of an optimistic caseand a pessimistic case. The pessimistic case states that all GW observations are from Astrophysical Black Hole (ABH) mergers, while the optimistic case suggests that some are from PBH mergers.Research of the scientists and its results involve an appallingly large number of complicated physical terms and relationships. But the chief question is whether PBHs can comprise dark matter, either partly or entirely. In that context, what exactly do the results boil down to?The researchers state that in their analysis of a population of both astrophysical and primordial binaries, PBHs simply cannot entirely comprise dark matter. At the most, they can make up a small portion of it.

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