Astronomers identify AGC 322753 as dark galaxy candidate with 2 billion solar masses of gas
Data from Arecibo and FAST reveal a massive rotating hydrogen cloud that lacks detectable stars, challenging star formation models.
Astronomers from Swinburne University of Technology have identified a promising dark galaxy candidate, designated AGC 322753, containing roughly 2 billion solar masses of neutral hydrogen gas without visible stars, ithome.com reported. The research, published in the Monthly Notices of the Royal Astronomical Society, is based on an analysis of archival radio observations gathered by the Arecibo Observatory in Puerto Rico and the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China ithome.com
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Deep optical exposures from the DESI Legacy Imaging Surveys showed no detectable starlight at the coordinates of the gas cloud. According to the team's calculations, the mass of hydrogen in the object exceeds any potential stellar mass by at least a factor of 40. Given the large reservoir of gas, the standard Lambda-CDM cosmological model typically predicts that high-density regions should collapse under self-gravity to trigger star formation.
Kinematic signatures of rotation
The radio frequency profiles of AGC 322753 exhibit a distinct double-horned profile, where emission from one side is blueshifted and the other is redshifted. This wavelength shift indicates that the neutral hydrogen may form a coherent rotating disc, mirroring the kinematics of standard spiral galaxies despite the absence of a luminous stellar counterpart. Theoretical models and simulations generally suggest that dark galaxies should not exhibit stable rotational dynamics.
Verification and alternative scenarios
Researchers emphasize that further radio interferometry, such as observations with the Very Large Array in New Mexico, is necessary to rule out alternative explanations. One possibility is that the gas represents a tidal tail stripped from an unobserved neighboring galaxy, an effect previously documented in candidates like VIRGOHI21 ithome.com
ithome.comithome.comOpen source ↗. However, no obvious donor galaxy has been detected near the object.
Discrepancies in the sky coordinates reported by the Arecibo and FAST surveys also suggest the object could be an extended structure rather than an isolated compact disc. If confirmed as an isolated system, AGC 322753 will help constrain why star formation halts, pointing to mechanisms such as high rotational shear preventing gas collapse or early ultraviolet heating.
