“We were disappointed. This is not the result we were hoping for,” Safdi says. Their results don’t mean that sterile neutrinos aren’t the source of dark matter — just that they didn't find the X-ray signals that would suggest a connection. So now it’s back to the drawing board to see what else might link dark matter to the sterile neutrino.
Taking a closer look
Though other efforts to connect dark matter to those signals had peered into faraway galaxies, Safdi and his co-authors decided to look closer to home.
“The leap we made was that if [the X-ray signal is issuing] there, then it should also be [issuing] around our own galaxy.” The Milky Way, where our solar system resides, is surrounded by the mysterious substance, Safdi says. The team searched the absolute darkest, blankest portions of our galaxy — parts with presumably only dark matter — for the X-ray signal indicative of decaying sterile neutrinos. But they found no such signal.
It’s possible this X-ray signature appeared in other dark matter searches as a kind of contaminant, Safdi says. Looking at galaxies far away means interference from gases, stars, and other cosmic materials end up in the data. Dark matter information from our own galaxy is more pure. “We were looking for dark matter radiation on top of nothing,” Safdi says.
A new approach
Safdi and his team think that maybe other kinds of X-rays — ones with different wavelengths — might still prove that sterile neutrinos make up dark matter. They’re now applying their same research concept to these different X-rays to see if those might be radiating from the most desolate regions of the Milky Way.
“We now have this powerful method we can apply to this data,” Safdi says, “And, who knows? Maybe we’ll find evidence for dark matter.”