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2d ago

Hubble Confirms 'Cloud-9,' First Starless Dark-Matter Cloud Near M94

Deep Hubble imaging verified the starless nature of a radio-identified cloud, opening a new window on low-mass dark halos.

This image shows the location of Cloud-9, which is 14 million light-years from Earth. The diffuse magenta is radio data from the ground-based Very Large Array (VLA) showing the presence of the cloud. The dashed circle marks the peak of radio emission, which is where researchers focused their search for stars. Follow-up observations by the Hubble Space Telescope’s Advanced Camera for Surveys found no stars within the cloud. The few objects that appear within its boundaries are background galaxies. Before the Hubble observations, scientists could argue that Cloud-9 is a faint dwarf galaxy whose stars could not be seen with ground-based telescopes due to the lack of sensitivity. Hubble’s Advanced Camera for Surveys shows that, in reality, the failed galaxy contains no stars.
The Hubble Space Telescope, a partnership of NASA and the European Space Agency, has made a discovery — not by what it saw, but by what it didn't see.
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Overview

  • The object, interpreted as a Reionization‑Limited H I Cloud (RELHIC), is the first confirmed example of its kind and is reported in The Astrophysical Journal Letters with results presented at the AAS meeting.
  • Cloud‑9 lies roughly 14 million light‑years away on the outskirts of the spiral galaxy Messier 94 and appears physically associated with that system based on radio mapping.
  • Hubble’s Advanced Camera for Surveys found no stars within the VLA‑defined region, ruling out even an ultra‑faint dwarf and confirming the cloud is truly starless.
  • Radio measurements indicate a neutral hydrogen core about 4,900 light‑years across containing ~1 million solar masses of H I, implying an enclosing dark‑matter halo of ~5 billion solar masses.
  • First flagged by FAST and confirmed with the Green Bank Telescope and the VLA, Cloud‑9 provides a testbed for models of failed galaxy formation, and researchers say deeper surveys could uncover more such relics.