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Dark matter, the invisible substance thought to make up around 85 percent of all mass in the universe, forms an essential part of the standard cosmological model, providing the gravitational glue that holds together entire galaxies. What it actually is, though — and even if it truly exists — remains one of the great mysteries of science.
Now, a bizarre event that occurred nearly a mile underground at the world’s largest dark matter detector in South Dakota, the LZ detector, could be the first direct evidence of the substance. Or it could be something else entirely. Either way, it has scientists mystified and excited.
In a new paper published Tuesday and has been submitted to the journal Physical Review Letters, physicists running the LZ Dark Matter Experiment say that their detector recorded a stunning subatomic interaction that doesn’t fit anything else ever documented in physics.
Again, it’s not necessarily a dark matter discovery — but it’s so unusual that it warranted sharing.
“How do you even make sense of one event?” Tom Shutt, a particle astrophysicist at SLAC National Accelerator Laboratory and cofounder of the LZ project, told Science magazine. “We just decided we should publish and think really, really, really hard about what that event could be.”
Dark matter is a sort of ghost haunting the cosmos. We can’t see it because it doesn’t emit, absorb, or reflect light, or otherwise interact with any ordinary matter — except through gravity.
We see the fingerprints of its gravitational pull all around the universe, in fact. Galaxies aren’t massive enough to hold themselves together with their own gravity, so without the invisible presence of something with incredible mass, the very realms that define the universe, and which we call home, would fly apart.
There are countless candidates for what dark matter is, but the prevailing theory is that it’s made up of weakly interacting massive particles, or WIMPs. As their feeble acronym suggests, WIMPs are thought to be a hundred times as massive as a proton, but have such a weak nuclear force that they don’t interact with ordinary particles.
Because of their mass, they move much slower than ordinary particles, too, allowing them to clump together and form giant “halos” that provide the gravitational pull for galaxies to form in. There is no single agreed-upon definition of a WIMP, though, and it’s possible that WIMPs could be a whole family of particles, rather than just one.
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