Astrophysicists set constraints on compact dark matter from gravitational wave microlensing

Ingrid Fadelli is a writer for Phys.org.

One of the greatest mysteries of the universe is the existence of dark matter. The invisible nature of this substance makes it difficult to detect, thus it remains unknown.

Particles that are yet to be discovered could be made of dark matter. It could include primordial black holes, which were formed in the early universe.

Many teams of scientists worldwide have been searching for dark matter using a variety of techniques. Most of these searches were unsuccessful, but they helped to narrow down subsequent searches.

Researchers at the International Centre for Theoretical Studies in Bangalore, India, have recently set new constraints on the fraction of compact dark matter. Their paper was published in The Astrophysical Journal Letters and introduces a new way of probing the nature of dark matter.

According to Einstein's theory of general relativity, massive objects bend light as normal optical lenses do. This phenomenon has emerged to be a powerful tool for astronomy.

Astronomers have been unable to observe the microlensing effects of black holes despite their extensive research efforts. Black holes that are much lighter than the sun, which produce the microlensing of light, are rare.

Even if black holes exist, they are likely to be a small part of the dark matter. If primordial black holes that are more massive than the sun are abundant in the universe, they will distort the waves.

Physicists calculated the nature of wave distortions in 2003 The non-observation of these distortions by the LIGO and Virgo collaborations could help to constrain the abundance of black holes that are significantly.

The recent paper by Ajith and his colleagues draws inspiration from previous works. The team assumed that if a significant fraction of dark matter were comprised of compact objects, they would cause microlensing effects in the signals from the LIGO and Virgo detectors.

In collaboration with colleagues in the LIGO-Virgo Collaboration, we searched for signatures of distortions in the signals that were observed by LIGO.

The LIGO-Virgo Collaboration announced null results from its third observing run. They analyzed more than 50 events.

The researchers could not observe microlensing distortions in any of the signals they analyzed, but their analyses allowed them to set further constraints on compact dark matter. The dark matter consists of massive black holes.

The constraints that we have obtained so far are modest. In the next few years, LIGO and Virgo are expected to observe hundreds to thousands of signals. We will be able to improve these constraints significantly.

In the future, Ajith and his colleagues will analyze all the new events recorded by the LIGO-Virgo detectors. They hope that their recent work will encourage other teams to use the microlensing of gravitational waves to investigate the nature of dark matter.

As part of the LIGO-Virgo Collaboration, we are analyzing all the signals detected by LIGO and Virgo during their past three observing runs. We are looking forward to analyzing the data from the next observing run, where LIGO and Virgo are expected to observe hundreds of signals.

More information: S. Basak et al, Constraints on Compact Dark Matter from Gravitational Wave Microlensing, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac4dfa Journal information: Astrophysical Journal Letters

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