• Recently, scientists investigating how the shape of dark matter affects the motion of stars in the centre of some galaxies (stellar bars) have found that out-of-plane bending can be explained through dark matter halos in barred galaxies.
  • Out of plane bending of the bar in barred galaxies is a rare violent bar thickening mechanism known as buckling.
  • A dark halo is the inferred halo of invisible material (dark matter) that permeates and surrounds individual galaxies, as well as groups and clusters of galaxies.
  • A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars.
  • For example, the Milky Way is a disk galaxy made up of stars moving in circular orbits around the center in a flattened disk, with a dense collection of the stars at the center called the bulge.
  • These bulges can have shapes ranging from nearly spherical to as flat as the galaxy disk. The Milky Way has a flat boxy or peanut-shaped bulge in its center.
  • Such bulges are formed due to thickening of the stellar bars in galaxies.
  • One of the violent thickening mechanisms is buckling, where the bar bends out of the plane of the galaxy disk.

Important points:

  • Dark matter, though never detected, is believed to be present in the entire universe.
  • It is presumed that primordial black holes, those that were formed in the early age of the universe, are a source of dark matter. It was proposed by Professor Stephen Hawking.
  • It is believed that combined with dark energy, it makes up more than 95% of the universe.
  • Its gravitational force prevents stars in our Milky Way from flying apart.
  • However, attempts to detect such dark matter particles using underground experiments, or accelerator experiments including the world’s largest accelerator, the Large Hadron Collider (LHC), have failed so far.

Dark Matter Presence :

  • Laws of gravity expect us to see stars closer to the center of galaxies rotating faster than the stars on the edge.
  • However, in most galaxies, the stars closer to the center and the stars at the edge of the galaxies take almost the same time to make one revolution.
  • This implied that something invisible and enveloping the galaxies was giving an extra push to the outer stars, speeding them up.
  • This entity has remained as one of the unresolved puzzles in cosmology since the 1930s. It was named `Dark Matter’.
  • The material is considered to be a ‘matter’ since it has gravitational attraction and it is ‘dark’ because it does not seem to interact with light (or any part of the electromagnetic spectrum).
  • Dark Matter and Dark Energy:
  • While dark matter attracts and holds galaxies together, dark energy repels and causes the expansion of our universe.
  • Despite both components being invisible, a lot more is known about dark matter, since its existence was suggested as early as the 1920s, while dark energy wasn’t discovered until 1998.


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