2023-09-02 17:09:00
Certain models of dark matter postulate the existence of very heavy particles which would pass through matter and be indistinguishable from Big Bang neutrinos in detectors on Earth. But these particles could transform neutron stars into black holes of abnormally low masses, like those that are perhaps detected with gravitational waves.
In retrospect, we can say that the idea of dark matter – we then spoke of missing mass or hidden mass – appeared in the noosphere almost a century ago with the work of the Swiss astronomer Zwicky. By studying the movements of the galaxies located within the Coma galaxy cluster, in the constellation Berenice’s Hair, he realized that the cluster did not seem to show any trace of ongoing dissipation despite the very high speeds galaxies. And yet, the mass deduced from the luminosity of the stars of these galaxies indicated that there did not seem to be enough of them for gravitation to oppose the evaporation of the clusters conceived as a kind of hot gas of self-contained galaxies. gravitating.
It was necessary to postulate the existence of hidden masses not emitting light, a hypothesis that we will take up again following the work of Vera Rubin on the speed of stars and gases, this time at the level of galaxies, and which will be called dark matter.
The hunt for these hidden masses really took off about thirty years ago, when several theories proposed to go beyond the known physics of the standard model of high-energy physics naturally predicted the existence dark matter particles. The zoo of these particles (millicharged particles, “fuzzy” dark matter, etc.) has only expanded since then as attempts to detect them by producing them in an accelerator or by exploring anomalies in the radiation cosmics have drawn a blank.
Giant detectors buried under mountains to filter ordinary cosmic radiation have also been failures so far, for example with XENON1T. To top it off, an alternative to dark matter particles is on the contrary gaining more and more weight, the Mond theory which proposes to modify Newton’s laws of celestial dynamics and therefore in fine Einstein’s theory of gravity.
Dark matter particle hunters have not said their last word, as a team of theoretical physicists from the Tata Institute for Basic Research in Mumbai (India), the Indian Institute of Science in Bengaluru and the University of California at Berkeley which studied a new method for flushing out and identifying dark matter in an article published in Physical Review Letters and accessible on arXiv.
Particles a billion times more massive than a proton
The method, already partly exposed in a previous Futura article, only applies to certain models of dark matter, however, these must be very massive particles (from about 1 to 1000 PeV, i.e. up to a billion times the mass of a proton) and which cannot self-annihilate. The central idea assumes that these particles can accumulate over billions of years in the cores of neutron stars.
There would then come a time when the density reached causes the collapse of the accumulation of dark matter particles into a mini black hole, mini black hole which will then swallow the whole neutron star by transforming it into a black hole. But we know since the work of Oppenheimer (inspired by the ideas of the mythical Russian physicist Lev Landau) and his thesis student Georges Volkoff) that there must be a mass limit for the stability of a neutron star.
Modern calculations point to a so-called Tolman-Oppenheimer-Volkoff limit of about 2.5 times the mass of the Sun. In fact, we do not know of heavier neutron stars. It follows that the vast majority of stellar black holes formed by the collapse of a star exploding in a supernova must not have a mass lower than this limit.
However, the detection of two particular gravitational wave sources by Ligo and Virgo, GW190814 and GW190425, suggest that they are the product of collisions of black holes, at least one of which may have had a mass below the Tolman-Oppenheimer limit. Volkoff.
Primordial black holes or neutron stars transmuted into black holes?
These could be examples of the primordial black holes postulated more than 50 years ago by Hawking and Zeldovich, black holes formed during the Big Bang by density fluctuations in very early plasma. But it could also be precisely binary black holes that would have formed with at least one component resulting from the transformation of a neutron star proposed by astrophysicists.
More generally, the existence of a population of low-mass black holes, betrayed by gravitational waves accessible by existing detectors such as Kagra but also in the near future by Ligo India, Cosmic Explorer and the Einstein telescope, could be used to test the hypothesis of the catalysis of the transformation of neutron stars into black holes by dark matter. Specifically, it would set bounds on the masses of dark matter particles in some theories as well as their ability to interact, albeit very weakly, other than by gravity with ordinary matter.
In fact, some dark matter detectors couldn’t tell the difference between the measurement of the cosmic neutrino background and some of the theorized dark matter particles, but luckily, precisely those that could, turn neutron stars. Also, the researchers conclude that gravitational wave detectors, which have already proven useful for direct detection of black holes and the gravitational waves predicted by Einstein, could also become a powerful tool for testing dark matter theories ».
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