A New Way To ‘See’ The Elusive Dark Matter

Astronomers have found a new way to see the mysterious dark matter haloes that surround galaxies. They report that this new method is 10 times more accurate and precise than the previous-best method.

A paper outlining the new technique appeared in the Monthly Notices of the Royal Astronomical Society.

We all know that current approximations suggest that around 85% of the mass in the universe is effectively invisible and it is called as ‘dark matter’. It is not visible because it does not interact with light in the same way as the ordinary matter that makes up stars, planets, and life on Earth.

So, the obvious question is how to measure it? One way is to measure the effect of gravity by dark matter.

Pol Gurri, the lead researcher and a PhD student at the Swinburne University of Technology, explains: “It’s like looking at a flag to try to know how much wind there is. You cannot see the wind, but the flag’s motion tells you how strongly the wind is blowing.”

The new research focuses on an effect called weak gravitational lensing, which comes straight from general theory of relativity. “The dark matter will very slightly distort the image of anything 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 base of a wine glass.”

In this research, the team has used the ANU 2.3m Telescope in Australia to map how gravitationally lensed galaxies are rotating. “Because we know how stars and gas are supposed to move inside galaxies, we know roughly what that galaxy should look like,” says Gurri. “By measuring how distorted the real galaxy images are, then we can figure out how much dark matter it would take to explain what we see.”

The new research shows how this velocity information enables much more precise measurement of the lensing effect than is possible using shape alone. “With our new way of seeing the dark matter,” Gurri says, “we hope to get a clearer picture of where the dark matter is, and what role it plays in how galaxies form.

Journal Reference:
Pol Gurri, Edward N Taylor, Christopher J Fluke. The first shear measurements from precision weak lensing. Monthly Notices of the Royal Astronomical Society, 2020; DOI: 10.1093/mnras/staa2893

Press Release: Royal Astronomical Society