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This bright image shows the Andromeda Galaxy, also known as M-31, as seen on the evening of Nov. 10, 2013.NASA/MSFC/Meteoroid Environment Office/Bill Cooke

A spiral galaxy, Messier 31, M31, or NGC 224, might hint towards the presence of dark matter, currently defined as as an unidentified form of matter.

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Around 85% of the mass in the universe comprises dark matter, according to scientists.

In 2014, NASA's Fermi Gamma Ray Observatory detected a gamma signal in the Milky Way galaxy. Gamma rays are the most energetic form of rays produced in the universe, NASA stated.

These rays are produced by particles moving at almost the speed of light interacting with starlight and interstellar gas clouds.

"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 Pierrick Martin, an astrophysicist at the National Centre for Scientific Research and the Research Institute in Astrophysics and Planetology in France, according to Seeker.

"M31 will be a key to understanding what this means for both Andromeda and the Milky Way galaxies," Martin added.

A concentration of pulsars (neutron stars) present in the centre of M31 is also assumed to be the reason behind the strong gamma ray emissions. The pulsars weigh almost twice as much as the Sun and are said to be among the densest celestial bodies in the universe.

A teaspoon of pulsars matter is likely to weigh around a billion tons on Earth. It's also found that some of these neutron stars emit most of their energy via gamma rays. Detecting pulsars in M31, however, is a tough task as it's situated 2.5 million years away.

To detect the exact source of the gamma rays, researchers will use previously accumulated data about pulsars in the Milky Way, and compare that with Andromeda's new X-ray and radio observations.

The gamma rays in both the Milky Way and Andromeda galaxies were discovered by Fermi. This can help researchers solve the mystery behind their origins.

"We don't fully understand the roles cosmic rays play in galaxies, or how they travel through them," said Xian Hou, an astrophysicist at Chinese Academy of Sciences, as reported by Seeker.

"M31 lets us see how cosmic rays behave under conditions different from those in our own galaxy," Hou said further.

Both galaxies — Milky Way and M31 — can be used as models by space scientists to investigate them further and analyse them.

This observation is crucial in order to explore both galaxies, as well as dark matter.