There are few things in the universe that are as perplexing as dark matter is an invisible and exotic “stuff” that is believed 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 space, there must be vast amounts of matter that we cannot see. Scientists are confident that this “missing matter” exists because of the gravitational effect it exerts, but detecting it directly has eluded scientists, who have had to indirectly infer how dark matter occupies the Universe.
A Japanese astrophysicist says that nearly a century after the theory of dark matter was first proposed, he may have found the first direct evidence of its existence – gamma rays spreading out in a halo – in a region near the center of our Milky Way galaxy.
“Of course I'm so excited!” Study author Tomonori Totani, a professor in the Department of Astronomy at the University of Tokyo, told NBC News in an email. “Even though the research started with the goal of finding dark matter, I thought the odds of success were like winning the lottery.”
Totani's claim of the first detection of dark matter is an extraordinary one that not all experts are convinced of. But the findings, published Tuesday in the journal Journal of Cosmology and Astroparticle Physicsoffer a glimpse of wildlife hunt for dark matter and the difficulties of searching for something invisible in space.
Dark matter is thought to make up about 27% of the universe, while ordinary matter – such as people, everyday objects, stars and planets – makes up only about 5%. according to NASA. (The rest consists of an equally mysterious component known as dark energy.)
Totani's research used observations from NASA's Fermi Gamma-ray Space Telescope, aimed at the heart of the Milky Way. The telescope is designed to detect intense electromagnetic radiation known as gamma rays.
Dark matter was first proposed in the 1930s by Swiss astronomer Fritz Zwicky, who stumbled upon an anomaly while measuring the mass and motion of galaxies in the large Coma galaxy cluster. According to his calculations, the galaxies were moving too fast, and instead of leaving the cluster, they were somehow 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, since theoretically has mass and occupies physical space in space, its existence can be inferred based on its gravitational influence in the Universe.
There are different models to potentially explain dark matter, but scientists believe the mysterious material is made up of exotic particles that behave differently than the normal matter we're all familiar with.
One popular school of thought suggests that dark matter is composed of hypothetical particles known as WIMPs (short for “weakly interacting massive particles”), which interact very little with ordinary matter. However, when two WIMPs collide, they can destroy each other and release powerful gamma rays.
In his study, Totani, an astronomer and astrophysicist, discovered intense gamma rays that he said were roughly equivalent to one millionth the brightness of the entire Milky Way. Gamma rays also appeared to be distributed in a halo-like structure over a large area of the sky. If the emissions were instead concentrated from a single source, it could indicate that a black hole, star or some other cosmic object, rather than diffuse dark matter, is to blame for the gamma rays.
“To my knowledge, no phenomenon originating from cosmic rays or stars exhibits a spherically symmetric and unique energy spectrum like that observed in this case,” Totani said.
But some scientists not involved in the study were skeptical of the findings.
David Kaplan, a professor in the department of physics and astronomy at Johns Hopkins University, said it is difficult to trace the emissions to dark matter particles with any certainty because so 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 rapidly spinning neutron stars or black holes that gobble up normal matter and spit out strong streams of material.
So even when unusual gamma rays are detected, it is often difficult to draw meaningful conclusions, according to Eric Charles, a postdoctoral fellow at Stanford University's SLAC National Accelerator Laboratory.
“We don't understand a lot of the details,” he said, “and seeing a lot of gamma rays from a large part of the sky associated with the galaxy, it's just very difficult 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 the region of the sky “that is really the hardest to model.”
“Any claims should therefore be treated with great caution,” Brout told NBC News via email. “And, of course, extraordinary claims require extraordinary evidence.”
Kaplan called the study “interesting” and “noteworthy” but said he was not entirely convinced that subsequent analysis would confirm the findings. But he hopes that in the future, scientists will directly confirm the existence of dark matter.
“This is a total game changer because this is really what seems to be dominating the universe,” he said. “It explains the formation of galaxies and therefore stars, planets and us, and is a key part of our understanding of how the universe formed.”
Totani himself stated that more research is needed to prove or disprove his claim.
“If this is true, the results will be too impressive, so researchers in the community will carefully check their validity,” he said. “I am confident in my findings, but I hope that other independent researchers will replicate these results.”
