Nearly a century ago, scientists theorized that a mysterious, invisible substance they called dark matter accumulated around galaxies and formed a cosmic web that spanned the Universe.
What dark matter is made of and whether it exists at all is still an open question, but according to research, the first direct evidence of the substance's existence has finally been seen.
More work is needed to rule out less exotic explanations, but if true, the discovery would mark a turning point in the decades-long search for the elusive substance, which is said to make up 27% of the cosmos.
“This could be a decisive breakthrough in understanding the nature of dark matter,” said Professor Tomonori Totani, an astrophysicist at the University of Tokyo, who said gamma rays emanating from the center of the Milky Way appeared to carry traces of the substance.
Dark matter was first described in the 1930s, when Swiss astronomer Fritz Zwicky noticed that distant galaxies were spinning faster than their mass allowed. The observations led to the concept of dark matter—material that neither emits nor absorbs light but exerts an invisible gravitational pull on the galaxies it surrounds.
Since then, scientists have been searching for dark matter particles, but so far ground-based detectors, space telescopes and huge machines such as the Large Hadron Collider near Geneva have yielded nothing.
One of the many theories of dark matter postulates that it consists of so-called weakly interacting massive particles, or weaklings, which are heavier than the protons found inside atoms but hardly interact with ordinary matter. When two weaklings collide, they can destroy each other, releasing other particles and releasing gamma rays.
To find potential dark matter signals, Totani analyzed NASA's Fermi gamma-ray data. Space A telescope that detects the most energetic photons in the electromagnetic spectrum. He noticed a pattern of gamma rays that appeared to match the shape of a dark matter halo that spreads out into a sphere from the galactic heart.
The signal “matches very closely the properties of the gamma rays predicted to be emitted by dark matter,” Totani told the Guardian. Details published V Journal of Cosmology and Astroparticle Physics.
If Totani has seen dark matter at work, observations indicate that it is composed of elementary particles 500 times more massive than a proton. But much more work is needed to rule out other astrophysical processes and background emissions that could explain the signals.
Totani said the “decisive factor” will be the detection of gamma rays with the same spectrum from other regions of space, such as dwarf galaxies. According to Professor Justin Reed, an astrophysicist at the University of Surrey, the lack of significant signals from such galaxies strongly argues against Totani seeing gamma rays emitted by the annihilation of dark matter particles.
Professor Qinwa Wu, a theoretical astrophysicist at UCL, also urged caution. “I appreciate the author's hard work and dedication, but we need extraordinary evidence for an extraordinary claim,” he said. “This analysis has not yet reached that status. It is part of the work that serves as an incentive for workers in the field to continue working.”
