Black holes as beacons on dark matter
Observations on the so-called dark matter present in our universe are more and more numerous and significant, but there are still several unanswered questions surrounding this fascinating field of modern physics.
Neutrino is the lightest elementary particle currently known; its mass is several million times lighter than the electron's. Some dark matter models have, however, suggested the existence of even lighter elementary particles, the masses of which may be billion times lighter than the neutrino's.
Due to their tiny mass and feeble interactions with "ordinary matter", detecting these elusive particles is almost impossible on Earth.
In a new paper, recently published on Physical Review Letters Journal, the team of researchers coordinated by Paolo Pani of the Department of Physics of Sapienza University, identified in the black holes an innovative method aimed at searching this ultralight dark matter.
Black holes can amplify radiations within a certain frequency range creating a surprising effect called "black hole superradiance".
To date, the superradiance and its signal, transmitted through gravitational-waves have been studied only for a specific group of particles, with similar properties as photons. Here, for the first time, they were applied to particles with similar features as gravitons, turning black holes into "gravitational-wave beacons".
According to the research, if such particles exist in nature and have a tiny mass, any black hole in the universe may be able to potentially emit recurring gravitational-waves at a given frequency (which is directly related to the dark matter's particles), similarly to a musical instrument which constantly repeats the same note with regular frequency.
"While searching for this signal – says Paolo Pani – gravitational-wave detectors such as LIGO and Virgo (and the future space mission LISA supported by ESA and NASA) will hunt for ultralight dark matter in a new, almost unexplored, regime."
This study is part of the Marie Skłodowska Curie project "FunGraW" (PI: Richard Brito), and of the ERC project, DarkGRA (PI: Paolo Pani) both hosted at the Departement of Physics of Sapienza University.
Black Hole Superradiant Instability from Ultralight Spin-2 Fields - Richard Brito, Sara Grillo, and Paolo Pani - Phys. Rev. Lett. 124, 211101 - Published 27 May 2020 DOI:https://doi.org/10.1103/PhysRevLett.124.211101
Department of Physics