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2w ago

Global VLBI Detects Lowest-Mass Dark Object at Cosmological Distance

Using gravitational imaging of a lensed radio arc, researchers measured a roughly one‑million‑solar‑mass perturber with no detected light.

Image
Ralf Kaehler/SLAC National Accelerator Laboratory, American Museum of Natural History
The Green Bank Telescope in West Virginia.
Image by Rudy and Peter Skitterians from Pixabay.

Overview

  • The object’s mass is tightly constrained to m80 = (1.13 ± 0.04) × 10^6 solar masses within 80 parsecs, with a 26σ detection significance.
  • An Earth-sized array combining the GBT, VLBA and EVN, correlated at JIVE, delivered the milli-arcsecond resolution needed to see the subtle lensing signature.
  • The signal appears as a localized pinch in the high-resolution radio arc of JVAS B1938+666, reaching two orders of magnitude lower in mass than previous cosmological lensing detections.
  • No optical, infrared or radio emission has been seen from the perturber, leaving its nature uncertain between a dark-matter clump and an extremely compact, inactive dwarf galaxy.
  • The peer-reviewed results (Nature Astronomy and MNRAS, with an arXiv preprint posted Oct 10) pave the way for expanded searches to test whether the abundance of such objects matches cold dark matter predictions.