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Astronomers flag a massive hydrogen cloud that may lack stars
Wired reports researchers identified AGC 322753, a hydrogen cloud with about 2 billion solar masses that appears to have no visible stars, pending follow-up.
- New headline Was: “Scientists May Have Discovered a Massive Starless Galaxy”
- Our desk filed its story
Researchers have identified a hydrogen-rich object, AGC 322753, that appears to contain little or no starlight, according to Wired, which cites a paper in Monthly Notices of the Royal Astronomical Society1.
The team, based at Swinburne University of Technology, compared radio surveys from the Arecibo Observatory and China's Five-Hundred-Meter Aperture Spherical Radio Telescope, both of which recorded a large hydrogen cloud, Wired reported1. The object holds about 2 billion times the sun's mass in hydrogen1.
Wired said the candidate stands out because its radio signal shows two peaks, a pattern often read as one side of a gas disc approaching Earth and the other receding1. Study author Marco Monaci told Wired that models of dark galaxies generally do not predict rotation1.
Most galaxy-formation models expect a cloud of this mass to have formed at least some stars, Wired reported1. The paper's authors say it is unlikely the object is completely starless and instead describe an "almost dark" galaxy whose stars, if present, are too faint for deep optical images from the DESI Legacy Imaging Surveys1. From those limits they estimate at least 40 times more mass in hydrogen than in stars1.
Robert Minchin of the National Radio Astronomy Observatory told Wired that more data, including from the Very Large Array, are needed1. He noted that VIRGOHI21, a dark-galaxy candidate from the early 2000s, was later reinterpreted as a tidal stream of gas1. Wired said no obvious nearby galaxy could have supplied AGC 322753 that way1.
Rhys Taylor of the Astronomical Institute of the Czech Academy of Sciences told Wired that reproducing the double-peaked profile with tidal debris is possible but unlikely1. Both Taylor and Minchin noted that the two radio surveys placed the hydrogen at different sky positions, which could mean an extended cloud rather than a compact galaxy1.
Elisabeth Adams of the Planetary Science Institute told Wired that objects like this could help distinguish explanations for suppressed star formation, including fast rotation that keeps gas too spread out or heating by ultraviolet light from early stars1. Confirmation would still be required before treating AGC 322753 as one of the most massive starless galaxies identified, Wired reported1.
