Astronomers have made a discovery that looks like something out of science fiction: a rare “Einstein Cross” with an extra image that shouldn’t exist.
This unusual cosmic pattern has given scientists a new window into the mysterious world of dark matter—the invisible substance that makes up most of the universe.
An Einstein Cross occurs when the light from a distant galaxy is bent by the gravity of galaxies in front of it, creating four distinct images of the same object.
But when researchers looked at a dusty galaxy called HerS-3, they saw something impossible: five images instead of four.
“I said, well, that’s not supposed to happen,” recalled Charles Keeton, a theoretical astrophysicist at Rutgers University.
Normally, the math behind gravitational lensing rules out such a fifth image. The only explanation, the team realized, was that something massive but unseen was bending the light even further: a halo of dark matter.
The anomaly was first spotted in France by astronomer Pierre Cox using data from the Northern Extended Millimeter Array (NOEMA), a powerful network of radio telescopes in the French Alps.
“It looked like a cross, and there was this image in the center,” Cox said. “I knew I had never seen that before.”
To be sure it wasn’t just a glitch, the team confirmed the strange pattern using another telescope array in Chile, ALMA (the Atacama Large Millimeter/submillimeter Array). The mysterious fifth image remained.
Computer modeling led by Keeton and graduate student Lana Eid showed that the four visible foreground galaxies alone could not account for the lensing pattern.
Only by adding a large, invisible halo of dark matter did the model finally match reality. “The only way to make the math and the physics line up was to add a dark matter halo,” Keeton explained.
This unexpected configuration isn’t just visually striking—it’s scientifically valuable. The gravitational lensing effect magnifies the background galaxy, allowing astronomers to study its structure in greater detail than usual.
At the same time, it provides a rare opportunity to learn more about the dark matter that surrounds galaxies but can’t be seen directly.
“This system is like a natural laboratory,” said Cox. “We can study both the distant galaxy and the invisible matter that’s bending its light.”
The team has even predicted that future observations might reveal outflowing gas from the galaxy. If those predictions are confirmed, it would strongly support their models. If not, the mystery deepens.
Either way, the finding is a reminder of how science moves forward: through surprises, challenges, and discoveries that reshape our view of the universe.
The Einstein Cross with a hidden fifth image may be rare, but it is already proving to be a powerful tool for understanding the invisible skeleton of the cosmos.
Source: Rutgers University.
