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22nd February 2022 (6 Topics)

Can dark matter be composed, even partly, of black holes?


A recent hypothesis says that dark matter comprises a large number of compact objects such as primordial black holes.


Dark Matter Vs Dark Energy:

  • Dark matter works like an attractive force, a kind of cosmic cement that holds our universe together.
    • This is because dark matter does interact with gravity, but it doesn’t reflect, absorb, or emit light.
    • Meanwhile, dark energy is a repulsive force, a sort of anti-gravity that drives the universe’s ever-accelerating expansion.
  • Dark energy is the far more dominant force of the two, accounting for roughly 68 percent of the universe’s total mass and energy.
    • Dark matter makes up 27 percent. And the rest, a measly 5 percent is all the regular matter we see and interact with every day.
  • In short, dark matter slows down the expansion of the universe, while dark energy speeds it up.

What is the recent proposition?

  • When the universe was very young, hot and dense – soon after the Big Bang, it must have had quantum fluctuations of its density.
  • This, in turn, would have caused some regions to become extremely dense, and therefore, to collapse under their own gravity to form the primordial black holes.
  • While we have no conclusive evidence of spotting these objects, some of the binary black hole mergers detected by the LIGO gravitational wave detectors might be primordial black holes.
  • The question is open there is good reason to believe that primordial black holes did form in the young universe.

Observing dark matter: Gravitational Lensing

  • The paper explores what happens when such objects get in the way of gravitational waves traveling towards the Earth from the distance.
  • It invokes a phenomenon called gravitational lensing that is used regularly in astronomy.

What Is Gravitational Lensing?

  • When taken to the extreme, gravity can create some intriguing visual effects that Hubble’s is well suited to observing.
  • Einstein’s general theory of relativity describes how mass concentrations distort the space around them.
  • A gravitational lens can occur when a huge amount of matter, like a cluster of galaxies, creates a gravitational field that distorts and magnifies the light from distant galaxies that are behind it but in the same line of sight.
  • The effect is like looking through a giant magnifying glass.
  • It allows researchers to study the details of early galaxies too far away to be seen with current technology and telescopes.

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