‘Waiting for a ghost’: the search for dark matter 1km under an Australian town

Dark matter flows through you right now.
This mysterious, invisible stuff is more than 80% in the universe. It's a complex web of particles that move freely through matter. It is necessary to remove all interference in order to observe it.

You must block the universe from view in order to study the material of the universe.

This is what the Australian Research Councils centre for excellence in dark matter particle Physics is doing, a kilometre below the surface in a disused mine under Stawell in regional Victoria.

Stawells Goldmine is where an Australian team of scientists is researching dark matter. Photograph by ARC Centre of Excellence for Dark Matter Particle Physics

A cavern in the area is being converted into a laboratory for dark matter hunters. It is expected to be completed by the end the year.

Alan Duffy is the director of the space technology industry institute at Swinburne University. He describes dark matter like a ghost.

Dark matter is a cloud of dark matter that surrounds us. It flies through us through solid walls through the Earth, he said, likening it with wind that can only be seen through its effects.

It creates enormous, universe-spanning structures called cosmic webs. The galaxies that we can see and inhabit lie along dark matter filaments just like morning dew in a spidersweb in the backyard.

You will be reading this and experiencing hundreds of millions of particles per second. Possibly a few of these particles will collide with your atoms during the course of a single day.

Most particles pass through you. Only a few unlucky ones may glance off one of your Atoms.

Radio silence is necessary to detect them.

Phillip Urquijo is the centre's chief investigator. He says that while dark matter makes up more than 80%, it can only be seen through its interactions and its gravitational effects.

By doing so, you can block interference from other particles. The picture is distorted by radiation from the sun and radioactive decay of ordinary material, as well as radioactive particles that have infected metallics (more later).

In the New Year, the lab for dark matter hunters will be complete. Photograph by ARC Centre of Excellence for Dark Matter Particle Physics

The lab has 1,000m of rock between researchers and the surface. These slabs are made of rock to block cosmic radiations. There's more!

Urquijo says that the experiment was placed deep underground in one of Australia's first goldmines. Although we can block the sun's cosmic rays, the rock and other materials used in construction of the experiment may contain radioactivity.

The cavern is then covered with a net, and then sprayed with a concrete type. The next step is to search for pure metal.

Since the second world war, radioactive dust remnants from atomic bombs have infected metals. This means that many people who want to find dark matter must source metals before the bombs were detonated. For example, ancient shipwrecks.

Steel is made from a mixture of iron ore and recycled steel. Urquijo states that steel produced after the second world war had a large amount of radioactivity. This was due to remnants of weapons testing. There are several options. One is salvaging ships, sunken submarines, and ancient Roman ships that were left at the bottom, where cosmic radiations haven't penetrated.

This is what dark matter hunters have been forced to do, but Urquijo claims they've managed to source a purer form of steel and Duffy says they've taken precautions.

Duffy is also the chief investigator of the project. He says that unlike other lead ingot salvage projects from 2000-year old sunken Roman galleys they have set up a veto mechanism.

They created sodium iodide crystals that were purest possible. These crystals had lower levels of contamination than any previously produced.

Pure crystals that glow when a particle strikes them are kept in copper tubes inside a steel vessel. The liquid surrounding them is a scintillator fluid.

He says that we are now looking in two locations for the flash of light.

If the crystal glows we can see the liquid surrounding it. If it flashes again, it is likely to be dark matter. The chances of dark matter hitting atoms twice are infinitesimally low.

The Sodium Iodide with Active Background Rejection Experiment includes the Stawell Project. Photograph by ARC Centre of Excellence for Dark Matter Particle Physics

Consider all the millions of particles that are moving through your body right now. How rare is it for one to ping off an atom. One particle will likely hit water, and another one the pure, compact crystal. There will be two flashes. However, the wily dark matter particle is unlikely to hit anything so there will only be one flash.

Astronomers have been studying dark matter for a long time.

Dark matter researchers have been looking outwardly at galaxies and how light bends for decades. They then use space telescopes to find evidence of its existence. As the evidence grew, so did our understanding that dark matter was all around us and could be studied here on Earth.

The Stawell Project is part of the Sodium Iodide with Active Background Rejection Experiment. (Sabre) aims to directly detect dark matter particles, rather than indirectly by its effects. It is the southern hemisphere counterpart to an identical set-up in Italy.

Duffy claims that once we learn more about dark matter there will be technological spinoffs. This is similar to how learning how to split an atom gave rise to nuclear medicine and the unwelcome weapons that have contaminated the entire planet.

Dark matter plays an important role in galaxies, and therefore us, being alive. Something must exist that provides gravity to allow galaxies form and keeps them from falling apart.

He says that you can create a universe using a supercomputer. There is not enough gravity to allow the galaxies form if you don't put dark matter into it. The dark matter is responsible for our existence.

This is a huge question about the universe we are trying to answer. It was created in the earliest moments, which is crucial to our understanding fundamental physics.

The dark matter hunters continue to hunt, using the Hubble space telescope, large hadron colider and a laboratory located a kilometre below the Victorian countryside in an abandoned goldmine.

It will be operational in the new year. Duffy said that we then wait for a ghost.