For all the discoveries we’re making of faraway galaxies, we’re still struggling to fully understand our own galaxy, the Milky Way. For example, researchers have known for decades of an odd concentration of gamma rays near the center of the Milky Way, although they weren’t sure where the high-energy light was coming from.
A new study proposes an entirely new perspective—that the light may actually be coming from neutron stars, as astronomers have suspected. If not, however, this could be the “first proof” of dark matter, according to the paper, published recently in Physical Review Letters. Given the evolution of the Milky Way, the researchers argue that the gamma ray excess most likely emerged from the collision of dark matter particles, the researchers claim.
The matter in question
The Fermi Gamma-ray Space Telescope first observed signs of these excess gamma rays in 2009. Since then, researchers have come up with various explanations for how the Milky Way ended up with this phenomenon, from energetic stars to simple instrumental errors.
Dark matter, on the other hand, refers to the “missing” mass constituting around 85% of our universe. Numerous investigations, both theoretical and experimental, have given ample evidence that it exists.
But the elusive stuff—for which scientists have proposed a range of candidate particles—rarely interacts with anything we can see. Scientists have devised numerous ways to indirectly search for dark matter, but no one has quite arrived at a definitive answer yet.
“Dark matter dominates the universe and holds galaxies together,” Joseph Silk, study co-author and an astrophysicist at Johns Hopkins University, said in a release. “It’s extremely consequential and we’re desperately thinking all the time of ideas as to how we could detect it.”
Maybe, maybe not
This isn’t the first time that researchers have suggested the Milky Way’s excess gamma rays have something to do with dark matter. But the new findings offer some promising theoretical support for this idea, which the paper notes could be vital in the search for dark matter lying “at a crossroads in the absence of any direct detection results from a number of deep underground experiments.”
The team’s simulations trace the Milky Way from its beginnings, testing different ideas about how the mysterious gamma-ray glow could have formed. And the numbers add up rather nicely if we assume that the gamma rays come from dark matter particle collisions—”though it’s not definitive proof,” the researchers said.
Then again, the model also worked decently for fast-spinning, older neutron stars emitting light. However, there was a small margin of error, as the team had to assume that the number of such light sources—millisecond pulsars—was higher than what was actually confirmed by observations.
Still, given how little we know about dark matter, the new findings aren’t conclusive, and the researchers acknowledge as much. The team does plan on continuing its investigations, however, in time for the activation of the Cherenkov Telescope Array—the next-generation telescope for gamma ray observations.
“It’s possible we will see the new data and confirm one theory over the other,” Silk said. “Or maybe we’ll find nothing, in which case it’ll be an even greater mystery to resolve.”