Shining light on dark matter

New Queen’s professor Gilles Gerbier receives $10 million to study dark matter at Sudbury SNOLAB

Gilles Gerbier has studied dark matter for 25 years.
Gilles Gerbier has studied dark matter for 25 years.
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The University has received its first Canada Excellence Research Chair (CERC) holder, with Dr. Gilles Gerbier becoming the CERC in Particle Astrophysics.

The University will receive up to $10 million over seven years to support Gerbier’s research on dark matter, as well as $800,000 from the Canada Foundation for Innovation.

Gerbier’s research is on the detection of dark matter, and while here he has two primary goals: working on an international experiment that will link European and North American labs, and developing a new spherical gas detector that can be used for work other than detecting dark matter.

He came to Queen’s from the French Atomic Energy Commission in France, and said there were several reasons for his decision to come to Canada and work at Queen’s and at SNOLAB in Sudbury.

“There was an underground lab [in France] to look for dark matter and there is another one here which is actually deeper, so it’s a better site,” he said.

“The team who is working here in Queen’s at SNOLAB is composed of members I knew for years that I appreciated. And that’s also the main reason, is that the funding which was linked to this CERC grant, it’s very good to do experiments I wanted to do.”

Dark matter was first hypothesized in the 1930s as a way of explaining missing mass.

“Stars turn around the centre of galaxy … and the speed at which they turn around the centre is fixed by distribution of mass inside the galaxy and gravitational constant G. I mean, this is very simple, you know, the Earth turns around the sun at the speed which is fixed by the mass of the sun and the distance to the sun,” he said.

But when this law is applied to galaxies, it doesn’t add up if only the mass of the stars that can be seen is taken into account. The stars move faster than they should — which means there’s unseen, missing mass that accounts for the higher speed.

“We need some more mass and we do not see it by eye, it doesn’t radiate light. This is a reason why we say it is dark,” he said.

Researchers have some ideas about how dark matter, which they believe is composed of a type of subatomic particle, behaves. Gerbier said dark matter should move like a gas, adding while it doesn’t typically interact with matter, it does sometimes interact and leave tracks in detectors.

“Sensitive detectors can detect this expected hint of presence of these particles. So to do that, we cannot do that at the surface, because at the surface we are swamped by what we call cosmic rays — cosmic rays is known particles, like protons, electrons, neutrons which come in from the sky … produced in galaxies and active galactic nuclei, in supernovae,” he said.

“If we picked a very sensitive detector to detect dark matter, it will be swamped by this background. So we go underground because the earth acts as a filter and eliminate all this background from known cosmic rays. And then we can be in an environment quiet enough to be sensitive to these particles.”

Gerbier has been researching dark matter since about 1990.

“Of course you could say, well, you are not discouraged to do that? No. I think, well, you know, you always learn by doing new detectors, by tuning them, by having ideas to have better instruments to look for what you think you should find,” he said.

Gerbier said he’s looking forward to researching in a university environment and working with young people. He will start teaching next year.

“I am convinced also that doing physics is not only me — I need a team, I need people to work with. So this is very important, that there is good human relationship, good understanding between people.”

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