Seeing dark matter in a new light

Scientists currently estimate that up to 85% of the mass in the universe is virtually invisible. This “dark matter” cannot be observed directly because it does not interact with light in the same way as ordinary matter that makes up the stars, planets and life on earth.

So how do we measure what cannot be seen? The key is to measure the effect of gravity creating dark matter.

Pol Gurri, Ph.D. The Swinburne University of Technology student who led the new research explains, “It’s like looking at a flag to see how much wind there is. You can’t see the wind, but the movement of the flag will tell you how strong the wind is. “”

The new research focuses on an effect known as a weak gravitational lens, which is a feature of Einstein’s theory of general relativity. “Dark matter will slightly distort the picture of everything behind it,” says associate professor Edward Taylor, who was also involved in the research. “The effect is a bit like reading a newspaper through the bottom of a wine glass.”

A weak gravitational lens is already one of the most successful methods for mapping dark matter content in the universe. Now Swinburne’s team has used the 2.3m ANU telescope in Australia to map the rotation of galaxies with gravitational lenses. “Because we know how stars and gas are supposed to move in galaxies, we know more or less what this galaxy should look like,” says Gurri. “By measuring how distorted the images of the real galaxy are, we can find out how much dark matter it would take to explain what we’re seeing.”

The new research shows how this speed information allows for a much more accurate measurement of lens flare than can be done with form alone. “With our new perspective on dark matter,” says Gurri, “we hope to have a clearer picture of where dark matter is and what role it plays in galaxy formation.”

Future space missions such as NASA’s Nancy Grace Roman Space Telescope and the European Space Agency’s Euclid Space Telescope are designed in part to perform these kinds of measurements based on the shapes of hundreds of millions of galaxies. “We have shown that with a relatively small telescope built in the 1980s, we can make a real contribution to this global effort by looking at the problem in a different way,” adds Taylor.

Dark matter and massive galaxies

More information:
Pol Gurri et al. The first precision weak lens cut measurements, Monthly Releases from the Royal Astronomical Society (2020). DOI: 10.1093 / mnras / staa2893

Provided by the Royal Astronomical Society