Researchers Explain Why Galaxies Look Different

Galaxies have different shapes, but nobody could explain why. A new study claims that the answer lies in their spin.

A team of Australian researchers claim that the speed with which galaxies rotate offers clues on why some spiral galaxies are fat and bulging and why a few galaxies are like flat discs.

This finding was led by the International Centre for Radio Astronomy Research (ICRAR) in Perth. The researchers discovered that spiral galaxies that rotate faster are flat and thin in shape while same size galaxies with slow spin rate look fatter. 

For this study, the researchers worked on the data accumulated at the Karl G. Jansky Very Large Array in the United States, well known radio telescopes in the world.

"Some galaxies are very flat discs of stars and others are more bulging or even spherical," ICRAR Research Associate Professor Danail Obreschkow, from The University of Western Australia, said. "Much of the last century of research has been dedicated to understanding this diversity of galaxies in the Universe and with this paper we've made a step towards understanding how this came about by showing that the rotation of spiral galaxies is a key driver for their shape."

Researchers focused on 16 galaxies using data from THINGS survey. These galaxies were located between 10 million - 50 million light years away from Earth. The THINGS survey reveals the presence of cold gas in the galaxies. Apart from the location of the cold gas it also shows the movement of the gas. This information is necessary in order to measure the spin rate of the galaxy.

The shape of the galaxies is determined using both the spin and mass that remain same for billions of years.

According to Obreschkow , the process of galaxy formation is slightly similar to carousel made of an elastic disc.

"If the carousel is at rest, the elastic disc is quite small," Dr Obreschkow said."But when the whole thing is spinning the elastic disc becomes larger because it's feeling the effects of centrifugal force."

The Milky Way galaxy is also a flat disc with a small portion protruding that is visible in the night sky.

"The white band of the Milky Way across the sky is a relatively thin band of constant thickness. However when you look right at the centre near the Sagittarius constellation you can actually see a thickening of the Milky Way, which is the bulge," Dr Obreschkow said.

The finding was published in Astrophysical Journal.