Another day, another potential sign of the elusive dark matter. Scientists have spotted a new dwarf galaxy orbiting the Milky Way. And, it comes with a surprise. It looks like it’s radiating gamma rays, according to research conducted by physicists at Carnegie Mellon, Brown and Cambridge universities.

Scientists found this galaxy, called Reticulum 2, by pouring over data of the Dark Energy Survey. This experiment maps the southern sky to gain insight on the accelerated expansion of the universe.

Reticulum 2 lies 98,000 light years away from Earth. It’s one of the closest dwarf galaxies ever discovered. Publicly available data from NASA’s Fermi Gamma-ray Space Telescope shows gamma rays coming from the direction of Reticulum 2 at levels above what is normally expected.

Scientists aren’t entirely sure what’s causing these gamma rays, but it could be a signal of dark matter at the galaxy’s center.

“Something in the direction of this dwarf galaxy is emitting gamma rays,” said Carnegie Mellon’s Alex Geringer-Sameth, the paper’s lead author. “There’s no conventional reason this galaxy should be giving off gamma rays, so it’s potentially a signal for dark matter.”

Here’s a video showing an artist impression of the expected dark matter distribution around the Milky Way.

Why do they think it could be dark matter?

Brown’s Savvas Koushiappas says, “in the search for dark matter, gamma rays from a dwarf galaxy have long been considered a very strong signature.”

Koushiappas adds, “it seems like we may now be detecting such a thing for the first time.”

Here’s why gamma rays from a dwarf galaxy are so important.

The leading theory on dark matter suggests they are WIMPs, or weakly interacting massive particles. When two of these collide, they produce high-energy gamma rays.

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So, anywhere you find gamma rays there would be dark matter, right? One problem. Gamma rays are produced from other sources as well including black holes and pulsars.

That makes differentiating background noise from a dark matter signal tricky. And, that’s where dwarf galaxies come in to play. Scientists believe dwarf galaxies lack these other gamma-ray sources.

“They’re basically very clean and quiet systems,” Koushiappas said.

That’s why scientists are excited about spotting these gamma rays from the dwarf galaxy.

“Given the way that we think we understand how gamma rays are generated in this region of the sky, it doesn’t seem that those processes can explain this signal,” Geringer-Sameth said.

Scientists will continue studying Reticulum 2 to see if there’s any hidden source that would explain the gamma rays. For now, they remain optimistic.

“The fact that there are gamma rays and also a clump of dark matter in the same direction makes it quite interesting,” said Carnegie Mellon’s Matthew Walker.

You can read the entire paper here.

Image: Bright areas indicate a strong gamma ray signal coming from Reticulum 2’s direction. Credit: NASA

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