Astronomers may have found dark matter traces in Andromeda Galaxy

22 Feb 2017

The gamma-ray excess (shown in yellow-white) at the heart of Andromeda. Image: NASA/DOE/Fermi LAT Collaboration and Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF

A signal has been detected in the centre of our neighbouring Andromeda galaxy, and while it might not be extraterrestrial life, it could still be very important indeed.

Despite years of trying, there is yet to be a true confirmation of the existence of dark matter, with some claiming that it doesn’t exist at all.

Existing theories suggest it could make up the vast majority of the universe, a placeholder for a type of matter different from our own, completely unknown to modern science.

But from within the centre of our nearby Andromeda galaxy – also known as M31 – a gamma-ray signal has been emitted that might just offer the best clue yet.

Using NASA’s Fermi gamma-ray space telescope, a team of international astronomers has discovered that, unlike a typical galaxy, gamma rays in Andromeda are confined within its bright centre, rather than being spread throughout.

This, the astronomers suggest, could indicate that the gamma-ray emission comes from several undetermined sources, and one of them might be dark matter.

“We expect dark matter to accumulate in the innermost regions of the Milky Way and other galaxies, which is why finding such a compact signal is very exciting,” said lead scientist Pierrick Martin, an astrophysicist at the National Center for Scientific Research and the Research Institute in France.

“M31 will be a key to understanding what this means for both Andromeda and the Milky Way.”

Checking out our own twin

If it’s not dark matter, another possible source for this peculiar emission could be a rich concentration of pulsars in the centre of the galaxy.

With a mass twice the size of our own sun, these spinning neutron stars would be some of the densest objects in the known universe – a single teaspoon of matter from one of them would weigh 1bn tonnes.

“Our galaxy is so similar to Andromeda, it really helps us to be able to study it, because we can learn more about our galaxy and its formation,” said co-author Regina Caputo. “It’s like living in a world where there’s no mirrors but you have a twin, and you can see everything physical about the twin.”

A scientific paper on the latest findings will appear in an upcoming issue of The Astrophysical Journal.

Colm Gorey was a senior journalist with Silicon Republic