Dark Matter

In News

• Recently, LUX-ZEPLIN (LZ) in South Dakota in the U.S. is being considered as the most sensitive dark matter detector in the world. 

Universe and Dark matter

• Many physicists strongly believe that the entire visible part of the universe forms only 5% of all matter in it. They believe the rest is made up of dark matter and dark energy. 
• Once this was convincingly demonstrated through various indirect observations and calculations, experiments started being set up to hunt for these elusive particles. 

About Dark Matter

• Dark matter is made up of particles that do not have a charge. They do not interact through electromagnetic interactions. 
• These are particles that are dark, namely because they do not emit light, which is an electromagnetic phenomenon, and matter because they possess mass like normal matter and hence interact through gravity.
• Detecting dark matter:
  • It is difficult to measure the evidence of dark matter.
  • Gravitational force is extremely weak. A particle that interacts so weakly becomes rather elusive to detect. 
  • This is because interactions from other known particles could drown out signals of dark matter particles.
  • The chamber of the LZ detector can contain only one gram of dust if it is to detect a dark matter particle. 
  • This is the extent to which researchers have to go to rule out unwanted signals coming from other entities.

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.

Image Courtesy: Next IAS 

• 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.

Dark Energy

• Dark Energy is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity. 
• It has been hypothesised to account for the observational properties of distant type Ia supernovae, which show the universe going through an accelerated period of expansion. 
• Like Dark Matter, Dark Energy is not directly observed, but rather inferred from observations of gravitational interactions between astronomical objects.
• Dark Energy makes up 72% of the total mass-energy density of the universe. The other dominant contributor is Dark Matter, and a small amount is due to atoms or baryonic matter.

Image Courtesy: NASA 

Source: TH