Dark matter clouds around black holes revealed by gravitational waves?

All the matter we see and interact with every day, from people to planets, represents only about 15% of the matter in the universe. The vast majority of it is related to dark matter, the enigmatic substance that appears to interact with normal matter only through its gravitational influence. What exactly dark matter is, what properties can it have, where it might be found and how we might detect it, are all the subject of ongoing speculation and investigation.

Ultralight bosons are one such candidate. Bosons are a class of particles that includes photons and the legendary Higgs boson, but some models suggest that unknown versions with extremely small masses may exist. If true, they could help plug one of the biggest holes in our understanding of the cosmos.

"It is nearly impossible to detect these ultralight boson particles on Earth," says Dr Lilli Sun, co-lead author of the study. “Particles, if they exist, have extremely small mass and rarely interact with other matter, which is one of the key properties dark matter appears to have.”

So, for the new study, the team looked for in the skies the kind of signal that ultralight boson clouds could produce. As dark matter interacts primarily through gravity, astronomers have turned to gravitational waves, ripples in the very fabric of spacetime.

Photo: depositphotos

Dozens of gravitational wave signals are been detected since 2015, usually produced during collisions between compact objects such as black holes and neutron stars. But they could also come from minor phenomena, generating a much longer and more delicate wave at particular frequencies.

The team says ultralight bosons could congregate in clouds around rapidly rotating black holes, where they "drag" the object and slow its rotation. Eventually, the cloud itself begins to shrink as the bosons annihilate into other particles, which generate gravitational waves that could be detected with a particular fingerprint detector.

To test this theory, the researchers examined the data collected during the third observation of the Advanced LIGO detector. Unfortunately, no such signal was detected, but this does not completely rule out the hypothesis. Instead, it places constraints on the type of bosons that could be involved and the age and distance of the clouds. As the cloud shrinks with age, gravitational wave signals would be much weaker for old clouds than for young clouds.

More sensitive detectors in the future may find weaker signals from older or other clouds. younger who are however more distant. Or, of course, we may find that we are all wrong and dark matter turn out to be something entirely different.