Searching for dark matter: Stawell’s gift to the world

In the gold mine township of Stawell, about 200 kilometres north-west of Melbourne, researchers are having a crack at confirming the existence of dark matter.

One of the biggest yet most relevant challenges facing science today is to detect dark matter, which will both show how the universe was formed after the Big Bang and the gravitational pull that keeps our galaxy the Milky Way together.

In a laboratory one kilometre underground, the Stawell Underground Physics Laboratory (SUPL) is taking on that ‘proof of dark matter’s existence’ challenge. Funded with the help of $5 million from the Victorian Government, this 12-metre high, 30-metre long subterranean room is expected to deliver $18 million annually and support close to 80 local jobs.

A collaboration between domestic tertiary institutions (the universities of Melbourne, Swinburne, Adelaide, Western Australia and Australian National University); the Australian National Nuclear Research and Development Organisation; Princeton University and the Italian Institute for Nuclear Physics; SUPL – created within an active gold mine tunnel and now equipped with power, air filtration and Wi-Fi – joins a network of underground facilities in the US, Europe, UK, China and South Korea. Excavation was completed by owner/operator Stawell Gold Mines in 2019 and operations are expected to begin in 2021.

“People can feel pride in knowing Australia has created an underground lab that’s unique in the Southern Hemisphere,” says Alan DuffySwinburne University Professor Alan Duffy, an astrophysicist and member of the project. “The world’s attention is on what happens at the bottom of the Stawell gold mine.”

Better yet, notes Alan, lab teams from Europe and beyond might move their future experiments down under to confirm findings. “We can check on claims from experiments in the Northern Hemisphere, making us the only site in the world to be able to do that.”

The hope is that dark matter particles entering the SUPL will collide with a crystal target and make it briefly glow, proving that dark matter does exist. Such a test needs to be done deep underground as dark matter particles can’t be detected amid the constant cosmic rays from space pelting the Earth’s surface.

But let’s backtrack a tad: what is dark matter? How would Alan explain it?

“The galaxy we live in resides within an enormous invisible cloud of ‘stuff’ whose gravity holds our Milky Way together,” he says. “That stuff is most likely a new particle that’s able to pass through walls without impact, neither shining nor blocking light. Like a ghost. And yet, we owe our very existence and formation of the Milky Way galaxy to it.

“We hope that it’s not completely a ghost though and that eventually it’ll hit something.big And we hope a sensitive detector deployed in SUPL will allow us to see such a collision. We’ll have a chance of ‘catching it’ in the lab.”

To more fully grasp the concept, consider rain.

“When you drive through rain, even though it falls vertically, it appears at the last second to rush towards the car window screen at great speed because you’re moving through it,” Alan explains. “In the same way, as the Sun moves around the galaxy and hence through its cloud of dark matter, we experience that same headwind of dark matter rushing towards us.

“For half the year, the Earth goes in the similar direction to the Sun’s motion, meaning the headwind’s blowing faster, hitting our detector more. And for the next six months, we’re going against the Sun’s motion, so the headwind reduces and we should see fewer collisions.

“Such an experiment in Italy has claimed a change over the course of the year in their detector, but the seasons also change in the year, so how do we know their claim is not a mistake? Well, the dark matter headwind travels straight through the Earth so our Stawell detector should see the same increase/decrease at the same time. But if it’s something to do with the seasons, then we’ll see the opposite effect as we’re six months out of sync. It’s the most beautiful, simple way to test any claim of dark matter."

University of Melbourne physicist Professor Elisabetta BarberioLeader on the project is University of Melbourne physicist Professor Elisabetta Barberio. She believes the Stawell underground lab will champion innovation in Australian industry. “It’ll be the Southern Hemisphere's epicentre for dark matter research, and will enable Australia to lead the endeavour in understanding what the universe is made of, with potential for major discoveries. It brings a big opportunity for industry innovation in manufacturing and STEM education opportunities with a national lab that can host international world-class experiments.”

Future breakthroughs in our understanding of cancer may also be a benefit as the lab’s capabilities stretch beyond advanced physics and engineering to potentially hosting basic cancer research, such as looking at how cells respond to low radiation environments.

With all this in mind, it’s likely Stawell’s identity will change, being both a gold mining town as well as a dark matter town – both vital to all things local. Almost all of the SUPL’s construction and fit-out will be sourced from western Victoria, with 15 roles created during the first phase of work – for geotechnical engineers, earthmoving equipment operators, electrical tradespeople and transport operators. The project is also expected to deliver significant local education benefits, with an equivalent project in a Rome dark matter research laboratory attracting as many as 8000 school students each year.

As Alan sums up: “For Australian students, this lab will undoubtedly inspire them to study physics in school and university. And it also means that if they want to be part of a leading global scientific experiment, they can do that in Stawell.”