Gravitational wave detectors as probes of dark matter

Darkish matter is a keystone assumption within the present understanding of the universe. But, the fundamental id of dark matter shouldn’t be recognized, and its future discovery stays a main objective within the fields of cosmology and particle physics.

A group of theoretical physicists from the Tata Institute of Elementary Analysis in Mumbai, the Indian Institute for Science in Bengaluru, and the College of California at Berkeley, have proposed a brand new methodology to probe dark matter. The strategy leverages gravitational wave searches to search for dark matter via its predicted results on neutron stars.

Sulagna Bhattacharya, graduate pupil at TIFR and lead-author of the examine revealed in Bodily Assessment Letters, explains—dark matter particles within the galaxy can accumulate in neutron stars attributable to their non-gravitational interactions. The accrued particles kind a dense core, that collapses to a minuscule black hole within the situation that dark matter particle is heavy and has no antiparticle counterpart; a situation that has proved tough to check in any other case in laboratory experiments.

For a big allowed vary of dark matter particle mass, the preliminary seed black hole consumes its host neutron star and transmutes it to a neutron-star-mass black hole. Crucially, theories of stellar evolution predict that black holes kind when neutron stars exceed about 2.5 instances the mass of the sun, as encoded within the Tolman-Oppenheimer-Volkoff restrict, however right here dark matter results in low-mass black holes which can be sometimes smaller than the maximal neutron star.

Anupam Ray, who co-led the work, factors out that “for dark matter parameters that aren’t but dominated out by some other experiment, previous binary neutron star programs in dense areas of the galaxy must have developed into binary black hole programs. If we don’t see any anomalously low-mass mergers, it places new constraints on dark matter.”

Intriguingly, a number of the occasions detected by LIGO, e.g., GW190814 and GW190425, seem to contain at the very least one low-mass compact object. A tantalizing suggestion, based mostly on pioneering work by Hawking and Zeldovich from the Sixties, is that low-mass black holes may very well be of a primordial origin, i.e., created by exceedingly uncommon however massive density fluctuations in very early universe.

Motivated by these concerns, the LIGO collaboration has undertaken focused searches for low-mass black holes and set limits. The current examine by Bhattacharya and collaborators exhibits that very same non-detection of low-mass mergers by LIGO additionally places stringent constraints on particle dark matter.

The constraints introduced on this examine maintain important worth, as they discover parameter space that’s nicely past the attain of the present terrestrial dark matter detectors like XENON1T, PANDA, LUX-ZEPLIN, particularly for heavy dark matter particles.

Mergers of low-mass black holes are anticipated to be detectable not solely utilizing present gravitational wave detectors equivalent to LIGO, VIRGO, and KAGRA, but in addition by upcoming detectors like Superior LIGO, Cosmic Explorer, and the Einstein Telescope. By contemplating the deliberate upgrades of present gravitational wave experiments, and accounting for his or her elevated sensitivity and statement time, the examine forecasts the constraints that may very well be obtained inside the subsequent decade.

Specifically, the examine exhibits, gravitational wave observations can probe extraordinarily feeble interactions of heavy dark matter, nicely under the so-called “neutrino ground” the place typical dark matter detectors need to take care of the astrophysical neutrino backgrounds. As a substitute, if unique low-mass black holes are found sooner or later, it may very well be a worthwhile trace in regards to the nature of dark matter.

The authors sign-off optimistically noting, “gravitational wave detectors, which have already proved helpful for the direct detection of black holes and gravitational waves predicted by Einstein, might find yourself as a strong device to check theories of dark matter as nicely.”