Few things in the universe are as perplexing as dark matter — the invisible and exotic “stuff” that is thought to make up most of the matter in galaxies.
The theory goes like this: To reconcile our current understanding of physics with what we observe in the cosmos, there must be massive amounts of matter that we can’t see. Scientists are sure that this “missing matter” exists because of the gravitational effects it exerts, but detecting it firsthand has eluded scientists, who have had to indirectly infer how dark matter occupies the universe.
Nearly a century after dark matter was first theorized, a Japanese astrophysicist says he may have found the first direct evidence of its existence — gamma rays extending out in a halo-like pattern — in a region near the center of our Milky Way galaxy.
“I’m so excited, of course!” study author Tomonori Totani, a professor in the astronomy department at the University of Tokyo, told NBC News in an email. “Although the research began with the aim of detecting dark matter, I thought the chances of success were like winning the lottery.”
Totani’s claim of detecting dark matter for the first time is an extraordinary one that not all experts are convinced of. But the findings, published Tuesday in the Journal of Cosmology and Astroparticle Physics, offer insights into the wild hunt for dark matter and the difficulties of searching the cosmos for something that cannot be seen.
Dark matter is thought to make up about 27% of the universe, while ordinary matter — people, everyday objects, stars and planets, for instance — only makes up about 5%, according to NASA. (The rest is made up of an equally mysterious component known as dark energy.)
Totani’s study used observations from NASA’s Fermi Gamma-ray Space Telescope aimed near the heart of the Milky Way. The telescope is designed to pick up a type of intense electromagnetic radiation known as gamma rays.
Dark matter was first proposed in the 1930s by Swiss astronomer Fritz Zwicky, who stumbled on an anomaly while measuring the mass and movement of galaxies in the large Coma Cluster of galaxies. The galaxies moved too quickly for his calculations, and instead of escaping the cluster, they were somehow being held together.
The resulting theories proposed a truly strange form of matter. Dark matter cannot be seen because it does not emit, absorb or reflect light. However, because it theoretically has mass and occupies physical space in the cosmos, its existence can be inferred based on its gravitational effects throughout the universe.
Different models exist to potentially explain dark matter, but scientists think the mysterious material is made up of exotic particles that behave differently from regular matter that we’re all familiar with.
One popular school of thought suggests that dark matter is made up of hypothetical particles known as WIMPs (short for “weakly interacting massive particles”) that interact very little with ordinary matter. When two WIMPs collide, however, they could annihilate each other and unleash powerful gamma rays.
In his research, Totani, an astronomer and astrophysicist, discovered intense gamma-ray emissions that he said were roughly equivalent to one-millionth the brightness of the entire Milky Way. The gamma rays also appeared to be spread out in a halo-like structure across a large region of the sky. If instead the emissions were concentrated from a single source, it might suggest a black hole, star or some other cosmic object was to blame for the gamma rays, rather than diffuse dark matter.
“To my knowledge, no phenomenon originating from cosmic rays or stars exhibits a spherically symmetric and the unique energy spectrum like the one observed in this case,” Totani said.
But some scientists who were not involved with the study were skeptical of the findings.
David Kaplan, a professor in the department of physics and astronomy at Johns Hopkins University, said it’s difficult to trace emissions back to dark matter particles with any certainty because too much is still unknown about gamma rays.
“We don’t even know all the things that can produce gamma rays in the universe,” Kaplan said, adding that these high-energy emissions could also be produced by fast-spinning neutron stars or black holes that gobble up regular matter and spit out violent jets of material.
As such, even when unusual gamma-ray emissions are detected, it’s often hard to draw meaningful conclusions, according to Eric Charles, a staff scientist at Stanford University’s SLAC National Accelerator Laboratory.
“There’s a lot of details we don’t understand,” he said, “and seeing a lot of gamma rays from a large part of the sky associated with the galaxy — it’s just really hard to interpret what’s going on there.”
Dillon Brout, an assistant professor in the departments of astronomy and physics at Boston University, said the gamma-ray signals and halo-like structure described in the study are in a region of the sky “that is genuinely the hardest to model.”
“So, any claims have to be treated with great caution,” Brout told NBC News in an email. “And, of course, extraordinary claims require extraordinary evidence.”
Kaplan called the study “interesting” and “worth following,” but said he isn’t totally convinced that follow-up analyses will confirm the findings. But he is hopeful that scientists will directly confirm dark matter’s existence in the future.
“It would be a total game changer, because it really is something that seems to dominate the universe,” he said. “It explains the formation of galaxies and therefore of stars and planets and us, and it’s a key part of our understanding of how the universe formed.”
Totani himself said additional study is needed to prove or disprove his claim.
“If correct, the results would be too impactful, so researchers in the community will carefully examine its validity,” he said. “I am confident in my findings, but I hope that other independent researchers will replicate these results.”