Astronomers detect unseen dark mass shaping distant galaxy light

Astronomers detect unseen dark mass shaping distant galaxy light
by Robert Schreiber
Berlin, Germany (SPX) Oct 10, 2025

Astronomers have identified a mysterious low-mass dark object nearly 10 billion light years away by tracing its faint gravitational distortion of light from a more distant galaxy. The object, weighing roughly one million solar masses, was detected through its subtle warping of a background galaxy's light rather than through any emitted radiation-a breakthrough that offers rare evidence supporting models of cold dark matter structure formation.

"Detecting dark objects that emit no light is a formidable challenge," explained Dr. Devon Powell of the Max Planck Institute for Astrophysics (MPA) and lead author of the study published in Nature Astronomy. "We use very distant galaxies as cosmic backlights, revealing the gravitational fingerprints of otherwise invisible matter."

The discovery relied on a global network of radio telescopes-including the Green Bank Telescope (GBT), the Very Long Baseline Array (VLBA), and the European Very Long Baseline Interferometric Network (EVN). Combined through the Joint Institute for VLBI ERIC (JIVE) in the Netherlands, the observatories formed an Earth-sized super-telescope capable of resolving the tiny lensing distortions caused by the unseen mass.

The dark object was found within a system known as B1938+666, where a luminous background galaxy appears as a ring of light, an effect known as an Einstein ring. "From the first high-resolution image, we immediately saw a pinch in the gravitational arc-a clear indication that something massive and unseen was intervening," said Professor John McKean of the University of Groningen, the University of Pretoria, and the South African Radio Astronomy Observatory (SARAO), who led the data acquisition.

To extract the faint signal, the researchers developed advanced computational models run on supercomputers. "We had to devise new numerical methods to analyze this enormous dataset-it had never been done at this level of precision," said Dr. Simona Vegetti of MPA. "Our findings support the prediction that galaxies like the Milky Way should contain numerous small clumps of dark matter."

The team applied a technique called gravitational imaging to map the distortions in the radio-bright arcs, revealing the influence of the otherwise invisible mass. "Given the sensitivity of our data, detecting at least one dark object matched expectations from the cold dark matter theory," Powell added. "Now the challenge is to find more and determine whether their abundance aligns with theoretical models."

Further surveys using the same radio interferometric method aim to identify additional low-mass dark objects, potentially reshaping theories about the structure and composition of dark matter in the cosmos.