Hypothesis of dark matter comprising a large number of compact objects such as primordial black hole
- Astronomical observations suggest that a significant part of the universe is made up of dark matter which interacts with the rest of the universe only through the gravitational pull.
- Many large lab experiments have tried to detect elementary particles that could be candidates for dark matter. However, such dark matter particles have not been detected until now.
- It's a region in space where stuff is so compacted that it creates a gravitational field that even light can't escape from.
- Albert Einstein proposed the concept in 1915, while John Archibald Wheeler coined the phrase ""black hole.""
- When a big star explodes in a supernova at the conclusion of its life, black holes develop.
- The leftovers of the explosion produce the black hole.
- The Event Horizon Telescope Project revealed the first-ever photograph of a Black Hole in April 2019 (more precisely, of its shadow).
Primordial Blach Holes (PBH)
- During the Hot Big Bang period, Primordial Black Holes (PBH) were produced.
- They are thought to develop as a result of collapsing radiations rather than enormous stars collapsing, as is the case with all other black holes.
- According to a recent research, this little increase in potential energy resulted in the formation of multiple PBHs as well as the emission of extremely intense gravitational waves.
- PBH can be as huge as 3000 kilometres or as small as the nucleus of an atom.
- In 1971, Stephen Hawking studied them. According to his calculations, the mass of primordial black holes might range from a tenth of a milligramme to more than the mass of Thousand Suns.
- Dark matter is thought to exist in the whole universe, despite the fact that it has never been detected.
- Its presence is assumed because a number of known astronomical events would be impossible if the cosmos did not contain far more matter than is visible.
- It is estimated that it makes up more than 95% of the whole universe.
- Stars in our Milky Way galaxy are held together by its gravitational attraction.
- Attempts to find dark matter particles via subsurface experiments or accelerator experiments, such as the world's biggest accelerator, the Large Hadron Collider (LHC), have so far failed.
Assessing dark matter
- Until now, individual black holes have not marked out these signatures on gravitational waves detected by the LIGO-VIRGO detectors.
- However, if all of the dark matter is made of primordial black holes, they should have produced detectable signatures on the gravitational wave signals.
- The researchers use the non-observation of the lensing signatures to assess what fraction of the dark matter could be made of black holes.
- Gravitational lensing is a phenomena that happens when a big quantity of matter, such as a giant galaxy, a cluster of galaxies, or a black hole, generates a gravitational field that distorts and amplifies light from objects behind it.
- Einstein's theory of general relativity is the foundation for gravitational lensing (Mass bend light).
- Normal lenses, such as those used in magnifying glasses, function by bending light rays passing through them in a process called as refraction to concentrate the light in a different location.
- Similarly, light beams travelling near to a huge object are bent and refocused somewhere else due to the gravitational field of that object.
- Gravitational lenses, in effect, operate as natural cosmic telescopes.
- Researchers may investigate the features of early galaxies that are too far away to be observed with even the most powerful space telescopes because of this phenomenon.
- Gravitational lensing, on the other hand, is extremely unusual since it necessitates a perfectly aligned distant star, black hole, and observer on Earth.
- It can also assist astronomers in learning about black holes, dark matter, and other topics.