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Up to 85% of the mass in the universe is effectively invisible. Unlike ordinary matter, this dark matter does not interact with light, so it cannot be observed directly.
So how do we measure what cannot be seen? The key is to measure the effect of gravity produced by dark matter.
A small team of astronomers has found a new way to “see” the elusive halos of dark matter. They come with a technique that is ten times more accurate than the previous best method.
Astronomers focused primarily on an effect called a weak gravitational lens. This effect is a feature of Einstein’s theory of general relativity.
Associate Professor Edward Taylor said, “Dark matter will slightly distort the image of anything behind it. The effect is a bit like reading a newspaper through the base of a wine glass. “
The team used the 2.3m ANU telescope in Australia to map the way galaxies rotate with gravitational lenses.
Pol Gurri, the Ph.D. student at Swinburne University of Technology who led the new research, explains, “Because we know how stars and gas should move inside galaxies, we know more or less what that galaxy should look like. By measuring how distorted the real images of the galaxy are, we can then understand how much dark matter it would take to explain what we see. “
The study showed that this speed information allows for a much more precise measurement of the lens effect than is possible using the shape alone. Through this new way of looking at dark matter, the team hopes to get a clearer view 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 make these kinds of measurements based on the shapes of hundreds of millions of galaxies.
Taylor said, “We have shown that we can make a real contribution to these global efforts with a relatively small telescope built in the 1980s, simply by thinking about the problem differently.”
Journal reference:
- Pol Gurri et al. The first shear measurements from weak precision lenses, monthly communications from the Royal Astronomical Society (2020). DOI: 10.1093 / mnras / staa2893
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