Theories of beyond Standard Model physics allow for the production of ultralight bosons — hypothetical particles with masses less than a billionth the mass of an electron — that could constitute a portion or all of dark matter. If such subatomic particles exist, they could appear around spinning black holes due to quantum fluctuations. In a paper published this week on the arXiv.org preprint server, astrophysicists from the LIGO Scientic Collaboration, the Virgo Collaboration, and the KAGRA Collaboration described the first all-sky search for long-duration, quasi-monochromatic gravitational-wave signals emitted by ultralight scalar boson clouds around spinning black holes using data from the third observing run of the Advanced LIGO detectors.
“Our study is the first all-sky survey in the world tailored to look for predicted gravitational waves coming from possible boson clouds near rapidly spinning black holes,” said Dr. Lilli Sun, an astrophysicist in the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at Australian National University.
“It is almost impossible to detect these ultralight boson particles on Earth. These particles, if they exist, have extremely small mass and rarely interact with other matter — which is one of the key properties that dark matter seems to have.”
“By searching for gravitational waves emitted by these clouds we may be able to track down these elusive boson particles and possibly crack the code of dark matter.”
“Our searches could also allow to rule out certain ultralight boson particles that our theories say could exist but actually don’t.”
The LIGO gravitational wave detectors allowed the researchers to examine the energy of rapidly rotating black holes extracted by such clouds if they exist.
“We believe these black holes trap a huge number of boson particles in their powerful gravity field, creating a cloud corotating with them,” Dr. Sun said.
“This delicate dance continues for millions of years and keeps generating gravitational waves that hurtle through space.”
While the team hasn’t yet detected gravitational waves from boson clouds, gravitational wave science had ‘opened doors that were previously locked to scientists.’
“Gravitational-wave discoveries not only provide information about mysterious compact objects in the Universe, like black holes and neutron stars, they also allow us to look for new particles and dark matter,” Dr. Sun said.
“Future gravitational wave detectors will certainly open more possibilities. We will be able to reach deeper into the Universe and discover more insights about these particles.”
“For example, the discovery of boson clouds using gravitational wave detectors would bring important insights about dark matter and help advance other searches for dark matter. It would also advance our understanding of particle physics more broadly.”
In another significant breakthrough, the study also shed more light on the chance of boson clouds existing in our own Milky Way Galaxy by taking into consideration their ages.
“The strength of any gravitational wave depends on the age of the cloud, with older ones sending out weaker signals,” Dr. Sun said.
“The boson cloud shrinks as it loses energy by sending out gravitational waves.”
“We learnt that a particular type of boson cloud younger than 1,000 years is not likely to exist anywhere in our Galaxy, while clouds that are up to 10 million years old are not likely to exist within about 3,260 light-years from Earth.”