Dark matter

Dark matter

Part of: Prelims and GS 3: Sci and Tech; Space

In News: Motion of some stars holds clue of dark matter shape in barred galaxies

• Scientists investigating how the shape of dark matter halo affects the motion of stars in stellar bars (found at the centre of some galaxies) have found that out-of-plane bending events of the bar explain the shape of dark matter halos in barred galaxies. 
• Out of plane bending of the bar in barred galaxies (central bar-shaped structure composed of stars) is a rare violent bar thickening mechanism known as buckling.
• The trillions of galaxies in our Universe have different shapes and sizes, which are determined by the motion of their stars. 
• Our own galaxy, 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.  
• 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 interesting and violent thickening mechanism is buckling, where bar bends out of the plane of the galaxy disk.  
• Many recent numerical and observational studies suggest that dark matter halos are spherical, prolate (a sphere squashed from the sides), or oblate (a sphere squashed from the top and bottom)   in shape. 

Importance: Shape of dark matter halos is important for understanding halo spin, which is an area of research being studied by many galaxy simulation groups over the world.

Dark Matter

• Dark matter forms the skeleton on which galaxies form, evolve, and merge.
• About 85% of the universe is dark matter
• Dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter.
• Dark matter attracts and holds galaxies together; dark matter exerts its influence on individual galaxies as well as the universe at large.
• Dark matter is called dark because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect or emit electromagnetic radiation, and is therefore difficult to detect.
• Primary evidence for dark matter comes from calculations showing that many galaxies would fly apart, or that they would not have formed or would not move as they do, if they did not contain a large amount of unseen matter.
• Professor Stephen Hawking: Proposed the theory that primordial black holes are a source of dark matter

News Source: PIB