Record-breaking 'dark object' found hiding within a warped 'Einstein ring' 10 billion light-years away

Astronomers have discovered a surprisingly small "dark object" lurking within a distant ring of warped light. The record-breaking find could help shed light on the mysterious identity of dark matter, which would have major implications for the field of cosmology.

The hidden object, likely a clump of invisible dark matter, was spotted within B1938+666 — an "Einstein ring" located around 10 billion light-years from Earth. This luminous halo (which appears dark in the black-and-white images) is made up of light from a distant galaxy that has been bent around a closer foreground galaxy (the dark dot at the center of the ring). This is an effect of gravitational lensing, a phenomenon that was first proposed by Albert Einstein's theory of general relativity in 1915.

Gravitational lensing not only warps light but also significantly magnifies it. When the lensing object is perfectly aligned between the distant object and the observer, the light bends into a circle around the foreground object, known as an Einstein ring. However, an imperfect alignment can also create other strange shapes, such as crosses, zig-zags and question marks, and duplicate individual points of light within the same image.

B1938+666 was discovered in the 1990s. But in a pair of new studies, published Oct. 9 in the journals Nature Astronomy and Monthly Notices of the Royal Astronomical Society, researchers took a closer look at the gravitationally lensed object and found a subtle wobble within a prominent arc of radio waves in the outer ring (colored red and yellow in the image). They quickly realized this was a gravitational disturbance caused by a hidden object.

"From the first high-resolution image, we immediately observed a narrowing in the gravitational arc, which is the tell-tale sign that we were onto something," John McKean, an astronomer at the University of Groningen in the Netherlands and the University of Pretoria in South Africa, and co-author on both new studies, said in a statement. "Only another small clump of mass between us and the distant radio galaxy could cause this."

The object is around 1 million times more massive than the sun, which sounds like a lot. However, this actually makes it around 100 times smaller than the previous record-holder for the least-massive object ever detected via gravitational lensing.

The study teams uncovered this object by combining data from radio observatories located across the globe, including the Green Bank Telescope in West Virginia, the Very Long Baseline Array in New Mexico and the European Very Long Baseline Interferometry Network. This enabled the researchers to achieve the equivalent observing power of an Earth-size telescope, which helped them to detect such a subtle fluctuation in the data. But there was so much information that the researchers had to come up with a new way of sorting it.

"The data are so large and complex that we had to develop new numerical approaches to model them," Simona Vegetti, an astronomer at the Max Planck Institute for Astrophysics in Germany and co-author on both new studies, said in the statement. "This was not straightforward as it had never been done before."

While they cannot be certain, the researchers are confident that the new object is a small clump of dark matter — the invisible matter that makes up 27% of the known universe and does not interact with light. This is unsurprising, given that gravitational lensing is one of the only ways we can detect and measure dark matter, making Einstein rings and other warped objects one of our greatest weapons in unmasking its true identity.

Finding isolated dark matter clumps like this is especially useful for testing the "cold dark matter theory," which posits that dark matter can only clump together if it moves at relatively slow speeds, meaning it would give off relatively low amounts of energy, Live Science's sister site Space.com reported.

And the researchers predict that these clumps are far more common than we currently realize. "We expect every galaxy, including our own Milky Way, to be filled with dark matter clumps, but finding them and convincing the community that they exist requires a great deal of number-crunching," Vegetti said.

To date, only three other similarly small, potential dark matter clumps have been identified, the researchers wrote. However, the new methodology will make it easier to spot more clumps around existing Einstein rings, and the number of known rings is also climbing fast, thanks to the James Webb Space Telescope, which has proved to be exceptionally good at finding them.

"Having found one, the question now is whether we can find more," Devon Powell, an astronomer at the Max Planck Institute for Astrophysics and co-author on both new studies, said in the statement.