The artist’s impression of a galaxy surrounded by gravitational distortions due to a dark object. Galaxies reside in large concentrations of invisible dark matter (colored purple in this image), although the effects of dark matter can be seen by observing background galaxy disorders. Credit: Swinburne Astronomy Productions – James Josephides
A small team of astronomers has come up with a new way to ‘see’ the elusive dark matter haloes around galaxies, which, with new technology, is 10 times more accurate than the previous best method. The work is published Monthly instructions of the Royal Astronomical Society.
Scientists currently estimate that about 85% of the mass in the universe is effectively invisible. This ‘dark matter’ cannot be observed directly, as it does not interact with light like the ordinary matter that makes up the stars, planets and life on Earth.
So how do we measure what we can’t see? The key is to measure the effect of gravity that a dark object produces.
The processed image of the spiral galaxy is seen after distorting the true shape of the galaxy after lensing effects. By measuring the orbital motion of a gas within distant galaxies (shown in pink here), gravitational distortions can be measured more accurately than previously possible. Credits: Original Image by ESA / Hubble and NASA / Flickr User Date 58, Image Editing by Paul Gurry
Paul Guri, a PhD student at Swinburne University who led the new research, explains: “It’s like looking at a flag trying to figure out how much wind there is. You can’t see the wind, but the speed of the flag tells you how much the wind is progressing. ”
New research has focused on the effect of a weak gravity called lensing, a feature of Einstein’s general theory of relativity. “The dark matter will slightly distort the image of anything behind it,” says Edward Taylor, an associate professor of research. “The effect is like reading a newspaper through the base of a wine glass.”
Weak gravity lensing is one of the most successful ways to map the dark matter content of the universe. Now, the Swinburne team has used the ANU 2.3M telescope in Australia to map how gravitationally orbiting galaxies rotate. “Because we know how stars and gases move around the galaxies, we know roughly what a galaxy should be,” says Jupiter. “By measuring how distorted real galaxy images are, then we can figure out how much dark matter it will take to explain what we want.”
Photograph of the Australian National University (ANU) 2.3M telescope at the Siding Spring Observatory. Credit: Australian Australian National University
New research shows how this velocity information enables a more accurate measure of the lensing effect than is possible with the help of shapes alone. “With our new way of looking at the dark matter, we hope to get a clearer picture of where the dark matter is, and what role it plays in how galaxies form,” says Gururi.
Such as future space missions NASAThe Nancy Grace Roman Space Telescope and the European Space Agency’s Euclid Space Telescope have made such measurements based on the shapes of millions of galaxies. Taylor adds, “We have shown that we can make a real contribution to these global efforts with relatively small telescopes built in the 1980s, just by thinking differently about the problem.”
References: Paul Gurie, Edward Ann Taylor and Christopher J. Fluck, September 21, 2020 by “The first shear measurement with precision weak lensing” Monthly instructions of the Royal Astronomical Society.
DOI: 10.1093 / MNRS / STA 2893
