Dark Matter

In Context

• Astronomical observations suggest 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.

What is Dark Matter?

• Dark matter, though never detected, is believed to be present in the entire universe.
• Its existence is presumed because a number of observable celestial phenomena could not be possible if the universe did not have much more matter in it than is seen.
• It is believed to make up more than 95% of the universe.
• Its gravitational force prevents stars in our Milky Way from flying apart.
• Called dark matter: Unlike normal matter (i.e. stars and galaxies), dark matter does not interact with the electromagnetic force.

Recent Studies on Dark Matter

• Underground or accelerator experiments including the world’s largest accelerator, the Large Hadron Collider (LHC), have failed so far.
• Scientists considered Hawking’s 1974 Theory of the existence of primordial black holes, born shortly after the Big Bang, not completed.
• Gravitational lensing effect to look for primordial black holes between Earth and the Andromeda galaxy.
  • Gravitational lensing was first observed by Arthur Eddington in 1919. It is an effect of Einstein’s theory of general relativity.
  • Gravitational lensing is the phenomenon that occurs when a huge amount of matter, such as a massive galaxy or cluster of galaxies, creates a gravitational field that distorts and magnifies the light from objects behind it, but in the same line of sight.
  • Massive objects like galaxies can bend light significantly, producing multiple images, this is called strong lensing. Lighter objects like stars or black holes bend light less, and this is called microlensing. 

• XENON1T experiment: It uses the dual-phase (liquid/gas) xenon technique and is located underground at the Laboratory Nazionali del Gran Sasso of INFN, Italy.

New avenue on Dark Matter

• Black Holes can contribute only up to 50-80% of the dark matter in the universe.
• Place where gravity pulls so much that even light cannot get out. 

How is dark energy (Hypothetical) different from dark matter?

• Everything we see – the planets, moons, massive galaxies – makes up less than 5% of the universe. About 27% is dark matter and 68% is dark energy.
• While dark matter attracts and holds galaxies together, dark energy repels and causes the expansion of our universe.

Theory of General Relativity

• Invisible force that attracts objects to one another, gravity is a curving or warping of space.
•  Predicting that empty space can have its own energy.

Source: TH