A Mysterious Signature

Recent decades have witnessed a number of astronomical firsts—improvements in telescopes and survey techniques have led to the discovery of many things that were, formerly, only hypothetical. Extrasolar planets, for instance, were finally detected in the ‘90s. And gravitational waves, one of the stranger implications of Einstein’s theories, were found just this year.

So there’s a great deal of optimism that the next, great mystery to be uncovered by modern astronomy will be elusive dark matter. Felt but not seen, we don't even know what dark matter really is—is it actually a form of matter, or is it the gravitational influence of unknown higher-dimensional objects?

Most astrophysicists incline to the former view, and they even suggest that it shares—along with gravity—the matter-antimatter duality of “normal” matter (that is, atoms and all the living things, planets, stars and galaxies they form). This theory posits the existence of “weakly interacting massive particles” (WIMPs), and if correct, the annihilation of matter-antimatter versions of these WIMPs should produce a predictable signature.

Which is precisely what a team of astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) claims to have found.

False-color image of suspected dark matter annihilation gamma rays from the galactic center.  Credit: Daylan et al./CfA
Strange Signals From the Galactic Center

The team studied the center of our galaxy, a notoriously energetic region—teeming with exotic astrophysics, such as a supermassive black hole, numerous pulsars, frequent supernovae, and furious star formation.

But the team focused on the signature of high energy gamma radiation emanating from the galactic core, and in particular, its distribution. Theoretical dark matter models involving WIMPs predict that, if the particles are indeed annihilating one another, the centers of galaxies would be a good place to look; the gravitational concentration causes dark matter, just like normal matter, to preferentially sink into these regions.

The CfA astronomers had to rule out the competing hypothesis—that the energetic photons are produced by fast-spinning pulsars. If the latter idea were true, the gamma rays would cluster in regions where stars form; but the actual signal is much more diffuse, which agrees well with the distribution predicted by dark matter models.

The discovery awaits confirmation, but if proven, it would be a huge step forward in our understanding of what our universe is actually made of.

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