An international consortium of astronomers has achieved a major scientific milestone, capturing the sharpest radio image ever recorded of a gravitational lens. This feat was accomplished using Very Long Baseline Interferometry (VLBI), an advanced technique that links radio telescopes across continental distances. By leveraging the distortion of light caused by gravitational lensing, this method not only provided exceptional detail but also enabled the identification of the smallest mass object yet found at cosmological distances. The groundbreaking findings from this research have been published in prestigious journals, including "Monthly Notices of the Royal Astronomical Society" and "Nature Astronomy."
The investigation centered on the JVAS B1938+666 system. In this arrangement, a massive elliptical galaxy, situated approximately 6.5 billion light-years away, acts as the lens, bending the radiation emanating from a more distant radio source located over 11 billion light-years from Earth. To achieve this unparalleled resolution, the VLBI technique was employed, virtually synchronizing 22 global radio telescopes, including the European VLBI Network and the VLBA array. A crucial component of this global network was the "Gavriil Gruff" 32-meter antenna located in Medicina, operated by the National Institute of Astrophysics (INAF). Data processing, coordinated at JIVE, effectively created a single virtual antenna whose size was determined by the maximum separation between the network's elements, yielding an angular resolution of one-thousandth of an arcsecond.
Fourteen hours of observation conducted at a frequency of 1.7 GHz unveiled an "extremely thin and nearly complete gravitational arc—the clearest ever observed using this methodology." Through meticulous modeling of the mass distribution within the lensing galaxy, the scientists were able to reconstruct the true morphology of the background radio source. The resulting data suggests that the distant object, 11 billion light-years away, possesses a compact and symmetrical structure, characteristic of an early phase of supermassive black hole activity. This structure spans roughly 2000 light-years and is notable for lacking a distinct central core, instead featuring two bright radio-emitting regions at its edges. Researchers, including Cristiana Spingola of INAF, noted that this publication initiates a series of papers dedicated to complex VLBI observations. John McKean of Groningen University, the observation coordinator, emphasized that the anomaly within the gravitational arc was immediately apparent, serving as a clear indicator that they were on the right track.
Building upon the same VLBI dataset, a second, complementary study successfully identified the smallest object ever detected in the distant universe purely through its gravitational influence. By applying new, sophisticated analysis algorithms, the team detected an additional concentration of mass, likely residing at the same distance as the lensing galaxy (6.5 billion light-years). This object possesses a mass of approximately one million solar masses, a figure significantly smaller than the typical trillions of solar masses associated with a galaxy. Spingola confirmed that this marks the first time an object of such minimal mass has been confirmed at a cosmological distance based solely on its gravitational effect. The object could potentially be a dark matter halo, a dense stellar cluster, or a small, defunct dwarf galaxy. Simona Vegetti of the Max Planck Institute for Astrophysics highlighted that confirming the existence of dark matter clumps requires immense computational power. If further analysis validates the presence of dark bodies of this magnitude, the discovery could provide a critical test for understanding the nature of dark matter and potentially reshape established cosmological theories.