Studying how light bends in oddly distorted Einstein rings and other gravitationally lensed objects may help researchers identify dark matter.

Dark matter is estimated to comprise 85% of the cosmos. Dark matter’s gravitational effects and location have been observed, but scientists don’t know what it is. Dark matter does not generate electromagnetic radiation like baryonic matter, which causes confusion.

Scientists have proposed many dark matter theories since the late 19th century.

The scientific community currently suspects weakly interacting massive particles (WIMPs) and axions, tiny particles that may behave like waves due to quantum interference. Despite years of particle accelerator experiments, WIMPs and axions have not been found.

In a new study published April 20 in Nature Astronomy(opens in new tab), researchers examined several unusual gravitationally lensed objects—extremely far-away objects whose light is magnified when it travels through gravitationally warped space-time surrounding a closer object—to determine the most likely dark matter candidate.

Gravitational lensing bends light from a faraway galaxy or quasar around a closer, equally massive object between it and an observer. The massive foreground object, such as a galaxy, quasar, or black hole, bends space-time around it, thus light travels in a straight line through curved space-time. Scientists can analyze the faraway object in greater detail by observing a partial or complete ring of magnified light.

Unique gravitational lensing induced by “dark matter halos” around distant galaxies, researchers may have found dark matter.

In 1912, Albert Einstein predicted the Einstein ring, a flawless or almost perfect circle of light around the foreground object. The James Webb Space Telescope photographed one of the most perfect Einstein rings in August 2022.

Some Einstein rings and other lensed objects can look duplicated. Scientists believe “dark matter halos”—hypothetical bands of dark matter that surround some galaxies but have never been actually detected—bend space-time to create these oddballs.

“By studying how the rings or other lensed images are distorted, astronomers can learn about the properties of the dark matter halo surrounding the closer [foreground] galaxy,” University of Queensland cosmologist Rossana Ruggeri wrote in The Conversation (opens in new tab).

The researchers examined photos of many weirdly lensed objects, focusing on HS 0810+2554, a quadruply lensed quasar found in 2002(opens in new tab). They then contrasted these photos with two computer simulations: one where the halo was mostly particles, like WIMPs, and one where it was mostly waves, like axions. Images best fitted the axion model for every object, the scientists found.

“The result suggests axions are a more probable candidate for dark matter,” Ruggeri added, leaving some scientists “buzzing with excitement.” She stated that more research is needed to validate this notion.

Dark matter isn’t only axions and WIMPs. Past study claimed that invisible matter could be neutrinos, gravitons, or “Fermi balls”—tiny black holes. Dark matter may interact with itself in unknown dimensions, according to increasingly extreme studies.

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