Scientists may have finally ‘seen’ dark matter for the 1st time

Scientists may have “seen” dark matter for the first time, thanks to NASA’s Fermi gamma-ray space telescope. If so, this would mark the first direct detection of the universe’s most mysterious substance.

Dark matter was theorized in 1933 by astronomer Fritz Zwicky, who found that the visible galaxies of the Coma Cluster lacked the necessary gravitational influence to prevent this cluster from flying apart. Then, in the 1970s, astronomer Vera Rubin and colleagues found the outer edges of spiral galaxies were spinning at the same rate as their centers, something that would only be possible if the major amount of mass in these galaxies wasn’t concentrated at their centers, but rather more widely dispersed. These aren’t direct observations of dark matter, of course, but inferences made using dark matter’s interactions with gravity as well as the influence gravity then has on ordinary matter and light. Still, because of these findings, s astronomers have since calculated that all large galaxies are embedded within vast haloes of dark matter that expand way beyond the limits of visible matter in galaxies (such as galactic haloes of stars).

The particles of this mysterious substance are now estimated to outweigh the particles that make up everyday matter by a ratio of five to one. That means everything we see around us on a day-to-day basis — stars, planets, moons, our bodies, next door’s cat, and so on — all account for just 15% of the matter in the universe, with dark matter accounting for the other 85%. Adding to the mystery of dark matter is the fact that, because it interacts with electromagnetic radiation so weakly, or not at all, it doesn’t emit, absorb, or reflect light. Thus, it is effectively invisible in all wavelengths of light — or at least, we thought it was.

There is one possibility that would result in dark matter producing light. If dark matter particles “annihilate” when they meet each other and interact, much as matter and its counterpart antimatter do, then it should produce a shower of particles, including photons of gamma-rays that, while invisible to our eyes, could be “seen” by sensitive gamma-ray space telescopes. One of the suggested “self-annihilating” particles theorized to comprise dark matter are so-called “Weakly Interacting Massive Particles” or “WIMPS.”

A team of researchers, led by Tomonori Totani from the Department of Astronomy at the University of Tokyo, trained the Fermi spacecraft on the regions of the Milky Way where dark matter should congregate, namely at the center of our galaxy, and hunted for this telltale gamma-ray signature.

Well, Totani thinks we finally found that signature.

“We detected gamma rays with a photon energy of 20 gigaelectronvolts (or 20 billion electronvolts, an extremely large amount of energy) extending in a halolike structure toward the center of the Milky Way galaxy,” Totani said. “The gamma-ray emission component closely matches the shape expected from the dark matter halo.”

And this isn’t the only close match. The energy signature of these gamma-rays closely matches those predicted to emerge from the annihilation of colliding WIMPs, which are predicted to have a mass around 500 times that of a proton, the ordinary matter particles found at the heart of atoms. Totani suggests there aren’t any other astronomical phenomena that easily explain the gamma-rays observed by Fermi.

“If this is correct, to the extent of my knowledge, it would mark the first time humanity has ‘seen’ dark matter. And it turns out that dark matter is a new particle not included in the current standard model of particle physics,” Totani said. “This signifies a major development in astronomy and physics.”

While Totani is confident that what he and his colleagues have detected is the signature of dark matter WIMPs annihilating each other at the heart of the Milky Way, the scientific community in general will require more hard evidence before the book is closed on this nearly century-old mystery.

“This may be achieved once more data is accumulated, and if so, it would provide even stronger evidence that the gamma rays originate from dark matter,” Totani added.

The team’s research was published on Tuesday (Nov. 25) in the Journal of Cosmology and Astroparticle Physics.