CMU Researchers Shed Some Light on Dark Matter

Mar 25, 2015

No one has ever seen dark matter, and its origin is unknown, but researchers at Carnegie Mellon, Brown and Cambridge universities believe they may have evidence of another characteristic of dark matter.

The researchers found that a newly discovered dwarf galaxy orbiting our galaxy, the Milky Way, shows evidence that it’s emitting gamma rays.

“We know that dark matter is there, and we want to know what it is, and we know something about what dark matter does, it has gravity and it moves in the same way that normal matter does by gravity,” said Alex Geringer-Sameth, a post-doctoral researcher in CMU’s Department of Physics. “But the real question is to learn something about the microscopic nature of dark matter, something about its particle physics nature.”

Gehringer-Sameth, the lead author of the paper submitted to the journal Physical Review Letters, said there’s no conventional reason why the dwarf galaxy should give off gamma rays. He said they look at dwarf galaxies because they tend to be “clean laboratories — old stars, dark matter and little else.”

“As far as we know they (dwarf galaxies) don’t emit gamma rays for any conventional reason; so if you do see gamma rays coming from the direction of a dwarf galaxy, it’s very interesting because those might be generated by some kind of dark matter effect.”

Dark matter, not to be confused with antimatter which has the same mass as ordinary matter but a different charge, was first postulated in the 1930s to explain the movements of galaxies  However, it wasn’t until the' 60s ,'70s and '80s that evidence mounted that its existence was proven to be a dominant component of the universe through its gravitational effects on visible matter, according to Geringer-Sameth.

He adds that the emission of gamma rays might be an indication of dark matter annihilation which could be the only way to learn about the microscopic nature of the dark matter as particles. 

“If they have any interactions with normal matter at all, that might take the form of  two dark matter particles finding each other and annihilate, and the mass is converted into normal particles that we can see” by looking for the release of energy, Geringer-Sameth said.

The paper’s co-author Matthew Walker, assistant professor of physics at CMU, said the non-gravitational detection showing dark matter behaving like a particle (giving off gamma rays), “is a holy grail of sorts.”

Geringer-Sameth agreed. 

“There’s a huge quest to figure out what is this stuff that we call dark matter," he said. "So any clues to its particle physics nature is potentially very important for extending our fundamental theories beyond the standard model that we have today.”

In other words, they are learning more about something that is believed to account for 80 percent of all matter in the universe.