Dark matter breakthrough? Einstein Cross with five images stuns scientists. What is it?

A team of international scientists has discovered a rare cosmic formation which has never been seen before. Only about a dozen Einstein Crosses have been found in the universe to date. This makes them rare, yet the latest discovery makes them even more intriguing. An Einstein Cross only has four images. But this one has an extra image in the middle. Researchers at Rutgers University were shocked when a French astronomer sent them the photo. Pierre Cox, a French astronomer, Research Director at the French National Centre for Scientific Research and the study's lead author, first spotted the anomaly. He thought it was a glitch or that something was wrong with the instrument.

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What is an Einstein Cross?

Einstein Cross is a rare cosmic configuration. When the light from a distant galaxy is bent by the gravity of galaxies in front of it, four images are created that sit at about 90 degrees from each other. The gravity of the foreground body warps space-time, making it act like a lens.

Andrew Baker, a Professor in the Department of Physics and Astronomy in the School of Arts and Sciences at Rutgers, showed the photo of the Einstein Cross to his colleague, theoretical astrophysicist Charles Keeton, and asked, "Have you ever seen an Einstein Cross with an image in the middle?" Keeton was surprised. "You can't get a fifth image in the centre unless something unusual is going on with the mass that's bending the light," Keeton said. There had to be something at the centre that was making this fifth image.

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A regular Einstein Cross has four objects, while the fifth image is present too close to the central lensing object, which makes it invisible. However, this time it showed up. Pierre Cox, a French astronomer, Research Director at the French National Centre for Scientific Research and the study's lead author, first spotted the anomaly.

Cox saw the Einstein Cross while studying a distant, dusty galaxy called HerS-3. He was using the Northern Extended Millimeter Array (NOEMA) of radio telescopes in the French Alps and the Atacama Large Millimetre/submillimeter Array (ALMA) radio telescopes in Chile when he saw the light from HerS-3 split into five images. He tried to make the fifth image go away, but it wouldn't.

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No explanation for fifth image

The team at Rutgers carried out computer modelling of the gravitational lens to understand what was going on. The four visible foreground galaxies causing the gravitational bending failed to explain the details of the five-image pattern. "We tried every reasonable configuration using just the visible galaxies, and none of them worked," said Keeton.

Dark matter created fifth image in Einstein Cross?

However, it all came together when they added a dark matter halo. "That's the power of modelling. It helps reveal what you can't see," Keeton said. Dark matter is believed to make up most of the universe, but it has never been seen. "We only know it's there because of how it affects the things we can see, like the way it bends light from distant galaxies," said Baker, adding, "This discovery gives us a rare chance to study that invisible structure in detail."

The discovery made by Cox, Keeton, Baker and a Rutgers graduate student, Lana Eid, will soon be published in The Astrophysical Journal.