‘Waiting for a ghost’: the search for dark matter 1 km below an Australian city | Australia news

Dark matter is flowing through you, right now.

This mysterious, invisible thing makes up more than 80% of the universe, an elusive network of particles that pass freely through matter. To observe it, get rid of all interference.

To study the things of the universe, you must block the universe.

That’s what the Australian Research Council’s expertise center for particulate matter physics in dark matter is doing a mile underground in a disused gold mine under the town of Stawell in the Victoria region.

Workers inside the laboratory for dark matter
Stawell’s goldmine, where a team of Australian researchers are researching dark matter. Photo: ARC Center of Excellence for Dark Matter Particle Physics

A cave will be transformed into a dark matter hunters laboratory, and it is nearing completion by the end of the year.

Swinburne University astronomer Alan Duffy, director of space technology and industrial institute, describes dark matter as a “ghost”.

“Dark matter is a cloud that surrounds us … it flies through us, through solid walls, through the Earth,” he says, likening it to the wind seen only through its effects.

“It forms enormous universe-spanning structures, cosmic orbits and the galaxies we can see and live within lie along filaments of dark matter like morning dew on a spider web in the backyard.

“As you read this, you will experience a few hundred million particles per second, a few of which will actually collide with your atoms in the course of a day.”

The vast majority of particles pass through you, with just a few unlucky ones looking out of one of your atoms.

Therefore, you need radio silence to spot them.

The center’s chief scientist, Phillip Urquijo, says that while more than 80% of the universe’s mass is made up of dark matter, it is only visible through its interactions with other matter – its gravitational effect.

And to observe it means to block interference from other particles. Radiation from the sun and from the radioactive decay of ordinary matter and from radioactive particles that have infected metals since the first atomic bombs were launched (more on that later), all mess with the picture.

Inside the laboratory for hunters of dark matter
The laboratory for dark drug hunters must be completed in the new year. Photo: ARC Center of Excellence for Dark Matter Particle Physics

In the laboratory, there are 1,000 meters of stone between the scientists and the surface, stone slabs to block cosmic rays. But wait – there’s more.

“We put the experiment deep underground, as deep as we could in Australia, in one of the first operational gold mines,” says Urquijo. “We can block the cosmic rays of the sun, but the rock and all the material we use to construct the experiment may contain naturally occurring radioactivity.”

The cave is covered with a net and sprayed over with a concrete form. Then there is the search for pure metal.

The remnants sprinkled with radioactive dust from atomic bombs have infected metals since World War II, meaning that many people trying to detect dark matter will have to obtain metals from before the bombs were set off. For example, from old shipwrecks.

“When you produce steel, you have a combination of new steel from iron ore and recycled iron. Steel produced during and since World War II … a lot of steel ended up with a component of radioactivity that was remnants of weapons testing, ”says Urquijo. “One possibility is to rescue ships, ancient Roman ships and sunken submarines from a long time ago that have been sitting on the bottom of the ocean where cosmic rays have not penetrated.”

That’s what many dark matter hunters have had to do – but Urquijo says they have managed to get a cleaner version of steel, and Duffy says they have put in place some safety precautions.

Duffy, who is also the lead researcher for the project, says that unlike other projects that have saved lead from 2000-year-old sunken Roman galleys, they have set up a “veto system”.

The team created the purest possible crystals, sodium iodide crystals with lower levels of any kind of pollution than any produced before.

The pure crystals that glow when a particle hits them are stored in copper tubes inside a steel vessel, surrounded by a special liquid that also glows when struck by a particle (it is called a scintillator fluid).

“We are now looking in two places for this flash of light,” he says.

“If the crystal is lit, we look at the liquid around it, and if the liquid has also flashed, we know that it cannot be dark matter, for the chances of the dark matter hitting atoms twice are infinitely small.”

Inside the laboratory for hunters of dark matter
The Stawell project is part of the Sodium Iodide with Active Background Rejection Experiment. Photo: ARC Center of Excellence for Dark Matter Particle Physics

Think about the millions of particles that are flowing through you right now and how rarely you strike an atom. Another particle is likely to hit the water, then the pure, compact crystal. To blink. However, the ugly dark substance particle is so unlikely that it hits something that there will only be a flash.

Astronomers have long theorized about dark matter.

For decades, dark matter hunters looked outward at galaxies’ behavior as light bends and used space telescopes to track evidence of its existence. As the evidence grew, so did the realization that dark matter is around us so that it could be studied on Earth.

The Stawell project is part of the Sodium Iodide with Active Background Rejection Experiment (Saber), which attempts to detect dark matter particles directly, as opposed to observing it indirectly through its effects. It is the southern hemisphere partner of a similar company in Italy.

Duffy says that when we know more about dark matter, there will be technological spinoffs and spills – in the same way that learning to share the atom gave us nuclear medicine (and the unwanted weapons that have polluted everything on the planet).

There is also the not insignificant role of dark matter in ensuring that galaxies — and by extension us — exist at all. There must be something out there that provides the gravity that allowed galaxies to form and that still prevents them from flying apart.

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“You can create a universe in a supercomputer – that’s what I do,” he says. “If you do not put dark matter in there, there is not enough gravity for the galaxies to form. We owe our existence to the dark matter.

“It’s a big question about our universe that we want to answer, it was produced in the earliest moments of our universe, and it’s crucial to our understanding of basic physics.”

So the dark-dust hunters continue to hunt with the Hubble Space Telescope, the large hadron collider, and a lab one mile below the Victorian landscape in an ancient gold mine.

It is expected to be up and running in the new year. Then Duffy says, “we’re waiting for a ghost”.

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