Weird dark matter waves seem to warp the light from distant galaxies

Evidence is rising for an ultralight darkish matter particle known as the axion. A research of sunshine warped by galaxies has proven that it’s higher defined by axion darkish matter than weakly interacting huge particles (WIMPs), which have lengthy been the main candidate for darkish matter.

Researchers are pretty positive that darkish matter exists due to its gravitational results, however up to now all efforts to detect any darkish matter particle straight have failed. Amruth Alfred on the University of Hong Kong and his colleagues took one other oblique have a look at darkish matter by inspecting an impact known as gravitational lensing. This is the place mild from a distant object is warped and magnified by the gravitational area of a comparatively close by galaxy, creating a number of photos of the background object across the close by galaxy in what is named an Einstein ring.

Galaxies are anticipated to be surrounded by haloes of darkish matter, so the properties of that darkish matter ought to have an effect on how the sunshine is stretched. Axions are many orders of magnitude much less huge than WIMPs, so they’re anticipated to behave otherwise – whereas WIMPs behave like normal particles, axions are so mild that quantum results ought to make them behave extra like waves.

So if the foreground galaxy in gravitational lensing is surrounded by axions, we might anticipate that to have an effect on how the photographs of the background galaxies seem as soon as they’ve been lensed. “If you have a pool with waves in it, and you put a stone in it, you are able to see the oscillations in the wave when you look at the stone,” says Razieh Emami on the Harvard-Smithsonian Center for Astrophysics in Massachusetts, who was a part of the analysis crew. “In these observations, those wave structures would be directly translated to the position of the lensed images and their brightness.”

We know that there are anomalies between the patterns we now have seen in gravitational lensing and WIMP fashions, however the researchers discovered that when the WIMP fashions had been switched out for axion ones, these anomalies went away. They additionally examined the fashions on an actual lensing system and located that the axion mannequin match a lot better.

“Since dark matter only interacts via gravity (and maybe the weak force in some models), this is one of the purer tests that can be done to investigate the nature of dark matter,” says Alfred. “Wave-like dark matter… holds up to the scrutiny that we put it under.”

This is nice news for axions, which have been overshadowed by WIMPs as darkish matter candidates for many years. “The observations from gravitational lensing do tilt the scale from heavier particles towards lighter ones,” says Emami. “So far, there are no other explanations for this phenomenon.”

“I don’t think this counts as proof that ultralight axions exist, but it’s a compelling result,” says Chanda Prescod-Weinstein on the University of New Hampshire, who wasn’t concerned within the work. “It provides further evidence that axions as a class of dark matter candidates are compelling.”

Immense effort has gone into detecting WIMPs with no luck, so this work is a part of a renaissance for axions and different darkish matter candidates that haven’t been as totally explored. “Axions represent one of the simplest extensions to the standard model of particle physics, and a large portion of their plausible search space has not been explored yet,” says Jae Sub Hong, additionally on the Harvard-Smithsonian Center for Astrophysics and never concerned within the work. “In other words, there are low-hanging fruits waiting to be picked, relative to what’s been done for other candidates like WIMPs.”