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Physicists are taking the temperature of darkish matter, the mysterious substance that makes up a few quarter of our universe.

We have now little or no concept of what darkish matter is, and physicists have but to detect a darkish matter particle. However we do know that the gravity of clumps of darkish matter can distort gentle from distant objects.


Chris Fassnacht, a physics professor on the College of California, Davis, and colleagues are utilizing this distortion, known as gravitational lensing, to study extra in regards to the properties of darkish matter.

The usual mannequin for darkish matter is that it’s “chilly,” that means that the particles transfer slowly in comparison with the velocity of sunshine, Fassnacht says. That is additionally tied to the mass of darkish matter particles. The decrease the mass of the particle, the “hotter” it’s and the quicker it’ll transfer.

148929main_image_feature_575_ys_full What’s the temperature of darkish matter?This picture from the Hubble Area Telescope reveals gravitational lensing of distant galaxies. Astronomers are utilizing this phenomenon to study extra in regards to the properties of darkish matter. (Credit score: NASA)

The mannequin of chilly (extra huge) darkish matter holds at very giant scales, Fassnacht says, however doesn’t work so nicely on the dimensions of particular person galaxies. That’s led to different fashions together with “heat” darkish matter with lighter, faster-moving particles. Observations have dominated out “sizzling” darkish matter with particles shifting near the velocity of sunshine.

The researchers used gravitational lensing to place a restrict on the heat and due to this fact the mass of darkish matter. They measured the brightness of seven distant gravitationally lensed quasars to search for modifications attributable to extra intervening blobs of darkish matter. Then the group used these outcomes to measure the scale of those darkish matter lenses.

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If darkish matter particles are lighter, hotter, and extra quickly shifting, then they won’t type constructions beneath a sure dimension, Fassnacht says.

“Beneath a sure dimension, they’d simply get smeared out,” he says.

The outcomes put a decrease restrict on the mass of a possible darkish matter particle whereas not ruling out chilly darkish matter, he says. The group’s outcomes characterize a significant enchancment over a earlier evaluation from 2002 and are similar to latest outcomes from a group at UCLA.

Fassnacht hopes to proceed including lensed objects to the survey to enhance the statistical accuracy.

“We have to take a look at about 50 objects to get a great constraint on how heat darkish matter will be,” he says.

A paper on the work seems within the Month-to-month Notices of the Royal Astronomical Society. Further coauthors are from UC Davis; the Max Planck Institute for Astrophysics, Garching, Germany; the Institute of Astronomy, College of Cambridge, UK; the Kapteyn Astronomical Institute, College of Groningen, The Netherlands; and the Netherlands Institute for Radio Astronomy.

The Nationwide Science Basis, the Netherlands Group for Scientific Analysis, and the Chinese language Academy of Sciences supported the work.

Supply: UC Davis