Andromeda is acting weird, and it could mean dark matter

Contributed by
Feb 28, 2017

Something strange is going on in the Andromeda galaxy, and it could mean something even stranger.

NASA’s Fermi Gamma Ray Space Telescope recently observed a super-powered gamma ray signal of indeterminate origin at the center of Andromeda (aka M31). While emissions of these penetrating high-energy beams often occur in galaxies and are typically scattered throughout, the gamma radiation issuing from Andromeda is unusually strong and concentrated at its core. Pulsars clustered in the middle of Andromeda could be one explanation for the mysterious surge of energy. So could dark matter.

Astrophysicist and research team lead Pierrick Martin of the National Center for Scientific Research and the Research Institute in Astrophysics and Planetology in Toulouse, France, is optimistic about what this find could reveal about the unknown.

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

Dark matter is a scientific conundrum. Invisible because it is non-luminous and does not interact with any form of light, it can still have its presence inferred from its gravitational influence on its surroundings. Hypothetical particles of dark matter otherwise known as WIMPs (Weakly-Interacting Massive Particles) supposedly go kamikaze and release bursts of gamma radiation when they crash into each other and self-annihilate. High concentrations of gamma rays therefore could indicate dense dark matter. Enter Fermi.

What Fermi, which can see photons with up to hundreds of billions of times more energy than anything visible to the naked human eye, captured in Andromeda reflects similar (though not as intense) emissions in the Milky Way. Mirrors between the two galaxies mean that what is already known about phenomena in the Milky Way — especially pulsars — can be applied to X-ray and radio observations of Andromeda when testing to determine where the gamma rays originate. Fermi is also able to observe Andromeda from a point of view impossible to attain within the Milky Way, and vice versa.

Illuminating an answer to the question of where exactly Andromeda's gamma rays emerge from is still problematic. Our neighboring galaxy is 2.5 million light years away, which will make it difficult to single out individual pulsars from its perceived cluster if that is confirmed to the source. Not to mention that for all the theorizing about its existence, anything definite about dark matter still eludes science. The mystery can only continue to unravel with more observations.

"We still have a lot to learn about the gamma-ray sky," said Regina Caputo, research scientist at the NASA Goddard Space Flight Center. "The more information we have, the more information we can put into models of our own galaxy."