Science

Scientists Are Hunting For Dark Matter With Huge Vats Of Liquid Xenon

Here's a conundrum: scientists can only identify 5 percent of the matter in the universe. The rest is what they call "dark"—unobservable stuff that we know is there, but we don't know the nature of. 68 percent of the universe is made up of so-called dark energy, which we think is driving its expansion. The other 27 percent is what's known as dark matter, which exerts an invisible but impressive gravitational pull. Scientists have a hunch about what dark matter actually is, and they think they've figured out a way to detect it. How? Really huge vats of an element called xenon.

Scientists assembling the XENON1T.

We All Need Somebody To Xenon

Scientists' big hunch is that dark matter is some sort of elementary particle. Whatever particle it is (the axion is one candidate, as is the neutralino), they think it must interact with regular matter, albeit very weakly. That's where the vats of xenon comes in. Usually a gas at room temperature, the element turns into a dense liquid when it's cooled down to -95 degrees Celsius. Xenon's superpower lies in its tendency to emit flashes of light and lose electrons when one of its atoms is struck by another particle. The hope is that if a dark matter particle strikes the nucleus of a xenon atom in one of these vats (or extremely sensitive scientific instruments, if you want to be technical about it), a series of photomultipliers and sensors will help pick up the signal and transmit it as a blip on a graph.

The XENON1T after assembly.
The cryostat, which hangs from the support structure within the water tank.
The entire XENON1T installation in the underground hall of Laboratori Nazionali del Gran Sasso.

No News Is Good News

There have been many such instruments over the years, but our most powerful dark matter detector yet is the XENON1T (The 1T stands for "1 ton," although it inexplicably contains three tons of xenon). This giant vat of liquid noble gas is buried beneath a mountain in Italy, since the further underground it is, the fewer stray particles there are to create false positives.

In May 2017, it got its first results: zilch. It didn't detect any dark matter—not yet anyway. Those results were made up of only 34 days of data, and as Gizmodo's Ryan F. Mandelbaum quips, "If you put a big bowl in your backyard and waited for a meteor to hit it, you wouldn't say 'meteors don't exist' just because you hadn't caught one in a month."

In fact, researchers were pretty happy with the results. They confirmed that XENON1T "hit the lowest low-energy background level ever achieved by a dark matter experiment," according to ScienceAlert. "In other words, if anything can spot the faint ripples of dark matter against the background noise of the Universe, XENON1T can." It's just a matter of waiting, watching, and hoping we can catch some dark-matter particles in our own backyard.

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Key Facts In This Video

  1. The known universe consists of about 70% dark energy, 25% dark matter, and 5% visible matter. 00:08

  2. Dark energy seems to be intrinsic to empty space, which has more energy than everything else in the universe combined. 03:45

  3. One theory of dark energy postulates that it comes from virtual particles in empty space that form and disappear constantly. 04:47

Written by Ashley Hamer June 13, 2017