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 most mysterious substance in the universe.
Dark matter was theorized in 1933 by the astronomer Fritz Zwicky, who discovered that visible galaxies Bunch of coma did not have the necessary gravitational influence to prevent this cluster from flying apart. Then, in the 1970s, an astronomer Vera Rubin and colleagues found that the outer edges of spiral galaxies rotate at the same rate as their centers, something that would only be possible if the bulk of the mass in these galaxies was not concentrated at their centers but rather more widely dispersed. These are not direct observations dark matter, of course, but conclusions made using the interactions of dark matter with gravity as well as the effect that gravity then has on ordinary matter and light. However, because of these discoveries, astronomers have since calculated that all large galaxies are embedded within vast haloes of dark matter that extend far beyond the limits of visible matter in galaxies (such as galactic star halos).
It is now estimated that the particles of this mysterious substance outnumber the particles that make up everyday matter by a ratio of five to one. This means that everything we see around us day to day – stars, planets, moons, our bodies, the neighbor’s cat and so on – makes up only 15% of the matter in the universe, and dark matter makes up the other 85%. Adding to the mystery of dark matter is the fact that because it interacts with electromagnetic radiation so weakly, if at all, it does not emit, absorb or reflect light. So it’s effectively invisible at all wavelengths of light – or so we thought it was.
There is one possibility that would result in dark matter producing light. If dark matter particles “destroy” when they meet and interact, much like matter and its counterpart antimatter do, then this should produce a shower of particles, including gamma-ray photons that, although invisible to our eyes, can be “seen” by sensitive space-based gamma-ray telescopes. One of the proposed “self-cancelling” particles theorized to contain dark matter are the so-called “weakly interacting massive particles” or “WIMPS.”
A team of researchers, led by Tomonori Totani of the University of Tokyo’s Department of Astronomy, trained the Fermi spacecraft on regions of the Milky Way where dark matter should be gathering, specifically at the center of our galaxy, and searched for this telltale gamma-ray signature.
Well, Totani thinks we’ve finally found that signature.
“We detected gamma rays with a photon energy of 20 gigaelectronvolts (or 20 billion electron volts, an extremely large amount of energy) propagating in a halo-like structure toward the center of the Milky Way galaxy,” Totani said. “The gamma-ray emission component closely matches the shape expected from a dark matter halo.”
And this is not the only close game. The energy signature of these gamma rays closely matches those predicted to be produced after the destruction of colliding WIMPs, which are predicted to have a mass about 500 times that of protons, ordinary particles of matter found at the heart of atoms. Totani suggests that there are no other astronomical phenomena that could easily explain the gamma rays observed by Fermi.
“If this is true, as far as I know, it would mark the first time that humanity has ‘seen’ dark matter. And it turns out that dark matter is a new particle that is not included in the current standard model of particle physics,” Totani said. “This marks a major development in astronomy and physics.”
Although Totani is confident that what he and his colleagues have discovered is the signature of dark matter WIMPs annihilating each other at the heart Milky Waythe scientific community in general will demand more hard evidence before closing the book on this nearly century-old mystery.
“This could be achieved when more data is collected, and if so, would provide even stronger evidence that gamma rays originate from dark matter,” Totani added.
The team’s research was published Tuesday (Nov. 25) in the Journal of Cosmology and Astroparticle Physics.
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