For over a decade, astronomers have been staring into the center of the Milky Way and seeing something weird: a ghostly gamma-ray glow that shouldn’t be there.
The signal has been dubbed the Galactic Center GeV Excess, or GCE. It was first spotted in 2009 by NASA’s Fermi Gamma-ray Space Telescope. Since then, researchers have been trying to figure out what’s emitting that glow.
A new study in Physical Review Letters argues that we might be seeing dark matter annihilating itself—possibly the first direct sign of its existence.
Dark matter is the invisible stuff that makes up most of the universe’s mass. It doesn’t emit light or interact with ordinary matter in any way that’s immediately obvious to us here on Earth.
But suppose it’s made of hypothetical particles known as WIMPs, which also hilariously stand for weakly interacting massive particles. When those particles collide, they should destroy each other, resulting in a bunch of small high-energy explosions.
Those explosions would then release gamma rays, the same kind of radiation emitted by the core of the Milky Way galaxy.
The Light At The Center Of Our Galaxy Could Be Dark Matter Eating Itself
That’s one suspect. There’s another, more boring one: millisecond pulsars, which are the burned-out corpses of massive stars that spin hundreds of times per second while beaming out bursts of energy.
Imagine a cosmic lighthouse beacon spinning wildly, and the keeper can’t slow it down, no matter which levers and pulleys he yanks.
Led by cosmologist Moorits Mihkel Muru of the Leibniz Institute for Astrophysics Potsdam, researchers ran supercomputer simulations of Milky Way–like galaxies to see what kind of glow dark matter would create. They found that our galaxy’s dark matter halo probably isn’t perfectly round, but slightly squashed from ancient galactic collisions.
When viewed from our vantage point, that distortion makes the gamma-ray glow appear “boxy,” whereas everyone had theorized it would be more spherical.
This would mean that the shape doesn’t matter. Dark matter might still be involved, and the pulsar and dark matter annihilation explanations are still on the table. Their neck and neck, as far as plausibility goes.
Observatories like the Cherenkov Telescope Array may finally break the tie. Until then, you will continue to see a weird light flickering at the heart of our galaxy, representing one of the great mysteries of our celestial home.
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