Physicists have developed a new way to study dark matter using gravitational wave detectors, potentially revealing the impact of dark matter particles on neutron stars. This approach provides new insights into dark matter beyond the detection range of current detectors, paving the way for future dark matter discoveries using advanced gravitational wave observatories.
Dark matter is fundamental to our understanding of the universe, but its exact nature remains a mystery. Uncovering the properties of dark matter is an important goal in cosmology and particle physics.
Physicists from the Tata Institute of Fundamental Research, the Indian Institute of Science and the University of California, Berkeley, have collaborated to launch a new way to study dark matter. This method uses gravitational wave searches to detect the potential impact of dark matter on neutron stars.
Suragana Bhattacharya, a graduate student at TIFR and first author of the study published in Physical Review Letters, explained that dark matter particles in the Milky Way accumulate in neutron stars due to their non-gravitational interactions. The accumulated particles form a dense core, which collapses into a tiny black hole if the dark matter particles are heavy and have no antiparticle counterpart.
Within the larger allowed range of dark matter particle masses, the initial seed black hole will engulf its host neutron star and transform it into a neutron star-mass black hole. Crucially, stellar evolution theory predicts that black holes form when neutron stars exceed about 2.5 times the mass of the Sun, as encoded by the Tolman-Oppenheimer-Volkofflimit, but here, low-mass black holes resulting from dark matter are typically smaller than the largest neutron stars.
Anupam Ray, co-leader of this work, pointed out: "For dark matter parameters that have not been ruled out by other experiments, old binary neutron star systems in dense regions of the Milky Way should have evolved into binary black hole systems. If we do not see any unusual low-mass mergers, this puts new constraints on dark matter."
Linking dark matter to black holes
Intriguingly, some of the events detected by LIGO, such as GW190814 and GW190425, appear to involve at least one low-mass compact object. One tantalizing suggestion, based on pioneering work by Hawking and Zeldovich in the 1960s, is that low-mass black holes may have a primordial origin, created by extremely rare but massive density fluctuations in the early universe.
Because of these considerations, the LIGO collaboration conducted targeted searches for low-mass black holes and set limits. The study by Bhattacharya and collaborators shows that the phenomenon of low-mass mergers not detected by LIGO also imposes tight constraints on particle dark matter.
The constraints proposed in this study are of great value because the parameter space they explore is far beyond the detection range of current ground-based dark matter detectors (such as XENON1T, PANDA, LUX-ZEPLIN), especially for heavy dark matter particles.
The future of gravitational wave observations
Mergers of low-mass black holes are expected to be detected not only by existing gravitational wave detectors such as LIGO, VIRGO, and KAGRA, but also by upcoming detectors such as AdvancedLIGO, Cosmic Explorer, and the Einstein Telescope. By taking into account plans for upgrading current gravitational wave experiments, and taking into account increases in their sensitivity and observation time, the study predicts what constraints may be obtained over the next decade.
In particular, the research shows that gravitational wave observations can detect extremely weak interactions of heavy dark matter, well below the so-called "neutrino floor" at which conventional dark matter detectors must contend with the astrophysical neutrino background.
Conversely, if exotic low-mass black holes are discovered in the future, this could provide valuable clues about the nature of dark matter. The author optimistically points out: "Gravitational wave detectors have proven helpful in directly detecting black holes and the gravitational waves predicted by Einstein, and may eventually become a powerful tool for testing dark matter theories."
Reference: "Article published by Sulagna Bhattacharya, Basudeb Dasgupta, Ranjan Laha and Anupam Ray in "Physical Review Letters" on August 29, 2023: "Can LIGO detect non-destructive dark matter"
DOI:10.1103/PhysRevLett.131.091401
Compiled source: ScitechDaily