• Despite the challenges in detecting dark matter, two Canadian researchers have found a way to map an image of the substance. (Image courtesy University of Waterloo)

In the time since dark matter was first hypothesized in 1922, it’s been a substance of mere theory; the matter doesn’t shine, reflect or absorb light, so astronomers could not see it. Until now.

Astronomers at the University of Waterloo have published the first image of dark matter. It confirms theories that there’s a web of dark matter between galaxies.

Despite the challenges in detecting dark matter, professor Mike Hudson and then-masters student Seth Epps found a way to map an image of the substance anyway. It relies on a process called gravitational lensing. When astronomers take photos of galaxies, different types of matter, like planets, stars or dark matter, can get between Earth and the galaxy. This matter causes distortion in the image.

“If you had a galaxy that would normally be perfectly round,” Hudson said, “the presence of the matter in front of it can stretch it and make it look sort of elliptical.”

The distortions tend to be predictable, so Hudson, Epps and a team of researchers working with the Canada-France-Hawaii Telescope measured the distortions between many pairs of galaxies to get an idea of what dark matter looks like. The final image is a composite of images taken from 12,000 pairs about 4.5-billion light-years away.

They learned that dark matter is sort of like a spider web, but instead of being flat Hudson said it’s “more like a sponge structure.”

Within that sponge, in the “knots in the web, where the galaxies are,” Hudson said there are even thinner filaments of dark matter. There may be even smaller galaxies within them.

From here, he and the other astronomers will be looking more deeply into the data to see if the theory holds up in the face of more quantitative analysis, with calculations and simulations.

They’ve also started to collect more, and hopefully better data, with the Canada-France Imaging Survey. This will look at a bigger part of the sky than the previous research.

Although the image hasn’t brought any new theories to light—yet—Hudson is still in awe of the work they’re doing.

“Occasionally I take a step back and I think, “You know, this is amazing: We’re making pictures of dark matter. Who would have thought that was possible?’”