by 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: In order to reconcile our current understanding of physics with what we observe in the cosmos, there must be vast amounts of matter that we cannot see. Scientists are certain that this “missing matter” exists because of the gravitational effects it exerts, but discovering it firsthand has eluded scientists who had to indirectly deduce how dark matter occupies the universe.
Nearly a century after the first theory of dark matter, a Japanese astrophysicist says he may have found the first direct evidence of its existence – gamma rays propagating in a halo-like pattern – in a region near the center of our Milky Way.
“Of course I’m so excited!” Study author Tomonori Totani, a professor at the University of Tokyo’s astronomy department, told NBC News in an email. “Although the research began with the goal of detecting dark matter, I thought the chances of success were like winning the lottery.”
Totani’s claim to have discovered dark matter for the first time is extraordinary and not all experts are convinced. But the results, published Tuesday in the Journal of Cosmology and Astroparticle Physics, offer insight into the wild hunt for dark matter and the difficulties of searching the cosmos for what you can’t see.
According to NASA, dark matter makes up about 27% of the universe, while ordinary matter – people, everyday objects, stars and planets, for example – only makes up about 5%. (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, which was aimed near the heart of the Milky Way. The telescope is designed to capture a type of intense electromagnetic radiation known as gamma rays.
Dark matter was first proposed in the 1930s by Swiss astronomer Fritz Zwicky, who encountered an anomaly while measuring the mass and motion of galaxies in the large Coma galaxy cluster. The galaxies were moving too fast for his calculations, and instead of escaping the cluster, they were somehow held together.
The resulting theories suggested a truly strange form of matter. Dark matter cannot be seen because it does not emit, absorb, or reflect light. However, since it theoretically has mass and occupies physical space in the cosmos, its existence can be inferred based on its gravitational effect throughout the universe.
There are various 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 are 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. However, if two WIMPs collide, they could annihilate each other and release powerful gamma rays.
In his research, Totani, an astronomer and astrophysicist, discovered intense gamma-ray emissions that he said were about one-millionth the brightness of the entire Milky Way. The gamma rays also appeared to spread in a halo-like structure over a large area of the sky. If the emissions were instead concentrated from a single source, it could suggest that a black hole, star or other cosmic object is responsible for the gamma rays, rather than diffuse dark matter.
Map of gamma ray intensity extending about 100 degrees toward the galactic center. The horizontal gray bar in the central area corresponds to the area of the galactic plane that was excluded from the analysis to avoid strong astrophysical radiation. (Tomonori Totani / University of Tokyo)
“To my knowledge, no phenomenon emanating from cosmic rays or stars has a spherically symmetrical and unique energy spectrum like that observed in this case,” Totani said.
However, some scientists who were not involved in the study were skeptical of the results.
David Kaplan, a professor in the department of physics and astronomy at Johns Hopkins University, said it is difficult to attribute the emissions with certainty to dark matter particles because too much is still unknown about gamma rays.
“We don’t even know all the things in the universe that can produce gamma rays,” Kaplan said, adding that these high-energy emissions could also be produced by rapidly rotating neutron stars or black holes that devour normal matter and spew violent jets of material.
Even when unusual gamma-ray emissions are detected, it is often difficult to draw meaningful conclusions, according to Eric Charles, a research scientist at Stanford University’s SLAC National Accelerator Laboratory.
“There are a lot of details that we don’t understand,” he said, “and when we see a lot of gamma rays from a large part of the sky that are associated with the galaxy – it’s 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 structures described in the study lie in a region of the sky “that is really the most difficult to model.”
“Therefore, all claims must 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 pursuing,” but said he wasn’t entirely convinced that follow-up analyzes would confirm the results. However, he hopes that scientists will directly confirm the existence of dark matter in the future.
“It would be a total game changer because it really seems to be something that seems to dominate the universe,” he said. “It explains the formation of galaxies and therefore stars, planets and us and is an important part of our understanding of the formation of the universe.”
Totani himself said that additional studies are needed to prove or disprove his claim.
“If the results were correct, they would be too conclusive, so researchers in the community will carefully examine their validity,” he said. “I am confident in my results, but hope that other independent researchers will repeat these results.”
This article was originally published on NBCNews.com
