June 16, 2024

Probing the Nature of Dark Matter Using Gravitational Waves

Microlensing of gravitational waves. Credit: Roshni Samuel/ Parameswaran Ajith/ ICTS
Among the greatest puzzles in contemporary cosmology is the presence of dark matter, which constitutes the majority of the matter in deep space. Recent research by a worldwide group of researchers has actually used gravitational waves to probe the nature of dark matter. This study was published just recently in the Astrophysical Journal Letters..
Dark matter.
A number of astronomical observations have developed the presence of dark matter, which interacts with conventional matter only through gravity. Dark matter does not emit any light and therefore averts a direct astronomical observation. Galaxies, including our own Milky Way, are surrounded by a halo of dark matter, whose size extends much further than the noticeable galaxy.
The Standard Model of Particle Physics explains all the primary particles that constitute all the normal matter. Particles that are not described by the Standard Model could exist in the universe and could make up dark matter. Several large experiments have been attempting to detect such elusive particles over the previous few decades, without success..

One of the greatest puzzles in contemporary cosmology is the existence of dark matter, which constitutes most of the matter in the universe. A number of astronomical observations have established the existence of dark matter, which interacts with traditional matter only through gravity. If a considerable fraction of dark matter is in the kind of black holes, they should trigger microlensing impacts in the observed signals. The present work utilizes the non-observation of such lensing impacts in the gravitational-wave signals to assess what fraction of the dark matter could be in the form of black holes. If scientists do not observe any signatures of microlensing in these gravitational wave signals, they will be able to conclude that just a really small fraction of the dark matter could be in the type of such heavy black holes.

Such black holes are different from the black holes that astronomers usually observe, which are produced by the death of huge stars. Prehistoric black holes are formed in the early universe and could exist in a range of masses.
Astronomers have not made a definitive detection of primitive black holes. Also, different huge observations have constrained the abundance of primordial black holes. Such black holes might flex light from far-off stars; a phenomenon called gravitational microlensing. Till now, researchers have actually been unsuccessful in observing microlensing produced by such great voids, in spite of searching thoroughly. This means that black holes that are much lighter than the Sun, which would have triggered microlensing of starlight, are uncommon. Even if they exist, they would make up only an extremely small portion of the dark matter. However, it is rather possible that black holes of some other masses could be adding to dark matter..
Microlensing of gravitational waves as a brand-new probe of dark matter.
Recent observations of gravitational waves have offered astronomers with a brand-new way of observing deep space. Gravitational waves are ripples in spacetime traveling with the speed of light. The observatories LIGO and Virgo, situated in USA and Italy, have actually observed around hundred gravitational-wave signals over the previous few years..
According to Einsteins theory, gravitational waves are also bent by huge items in between the source and observer. If a significant portion of dark matter remains in the kind of great voids, they ought to cause microlensing results in the observed signals. Microlensing will distort the gravitational waves in a manner scientists can determine precisely. However, the international team might not observe any such distortion in the signals observed by LIGO and Virgo..
The present work uses the non-observation of such lensing results in the gravitational-wave signals to examine what portion of the dark matter might be in the type of black holes. The researchers conclude that just less than half of the dark matter could be in the form of black holes within the mass variety of 100 to 100,000 solar masses.
Future observations.
The present restraints from gravitational-wave lensing observations are not as tight as compared to those obtained from other astronomical measurements. Other observations, such as the cosmic microwave background, tell us that such enormous primordial black holes might contribute only a much smaller sized portion of the dark matter. However, there are 2 reasons for researchers to get delighted about this approach. First, each observation includes its own mistakes; it is very important for researchers to get here at the same conclusions utilizing different observations and experiments. Second, gravitational-wave observations will be able to provide much better constraints in the future..
In the next couple of years, LIGO and Virgo, along with upcoming detectors such as KAGRA and LIGO-India, will observe thousands of gravitational-wave signals. If researchers do not observe any signatures of microlensing in these gravitational wave signals, they will have the ability to conclude that only a really little portion of the dark matter might be in the type of such heavy great voids. On the other hand, if a good portion of the gravitational-wave signals contains signatures of lensing, this would be a cigarette smoking gun evidence of the much desired prehistoric black holes. Either method, microlensing of gravitational waves uses a distinct method of probing the nature of dark matter.
Referral: “Constraints on Compact Dark Matter from Gravitational Wave Microlensing” by S. Basak, A. Ganguly, K. Haris, S. Kapadia, A. K. Mehta and P. Ajith, 21 February 2022, Astrophysical Journal Letters.DOI: 10.3847/ 2041-8213/ ac4dfa.