ROYAL ASTRONOMIC SOCIETY
IMAGE: THE ARTIST'S IMPRESSION ON A GALAXY SURROUNDED BY DARK CENTER DISTORTIONS. GALAXIES LIVE IN LARGER CONCENTRATIONS OF INVISIBLE DARK QUESTIONS (COLORED PURPLE IN THIS PICTURE), BUT THE DARK … Show more
A small team of astronomers has found a new way to "see" the elusive dark matter halos that surround galaxies with a new technique that is ten times more precise than the best ever method. The work is published in Monthly Notices of the Royal Astronomical Society.
Scientists currently estimate that up to 85% of the mass in the universe is practically 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 stars, planets and life on earth.
So how do we measure what cannot be seen? The key is to measure the effect of gravity that creates dark matter.
Pol Gurri, the PhD student at Swinburne University of Technology 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 shows you how strong the wind is blowing. "
The new research focuses on an effect known as the weak gravitational lens, which is a feature of Einstein's general theory of relativity. "The 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 of mapping the dark matter content in the universe. Now the Swinburne team has used the 2.3 m ANU telescope in Australia to map the rotation of galaxies with gravitational lenses. "Since we know how stars and gas are supposed to move in galaxies, we roughly know what this galaxy should look like," says Gurri. "By measuring how distorted the real galaxy images are, we can find out how much dark matter it would take to explain what we are seeing."
The new research shows how this speed information allows for a much more accurate measurement of lens flare than can be done with shape alone. "With our new view of dark matter," says Gurri, "we hope to get a clearer picture of where dark matter is and what role it plays in the formation of galaxies."
Future space missions such as NASA's Nancy Grace Roman Space Telescope and the European Space Agency's Euclid Space Telescope are expected to make these types of measurements based in part 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,” Taylor adds.