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2d ago

Hubble Confirms First RELHIC, a Starless Dark-Matter Cloud Near M94

Deep imaging paired with radio mapping shows a compact gas cloud held by a low-mass halo at the brink of galaxy formation.

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, nicknamed Cloud-9, lies about 14 million light-years away on the outskirts of the spiral galaxy Messier 94.
  • First identified by FAST and confirmed by the Green Bank Telescope and the Very Large Array, it was shown by Hubble’s ACS to contain no stars, with injection simulations indicating any faint population would have been seen.
  • Observations find a neutral-hydrogen core roughly 4,900 light-years across with about one million solar masses of gas inside a dark-matter halo estimated at around five billion solar masses.
  • Cloud-9’s compact, nearly spherical morphology and slight gas distortions in high-resolution radio maps suggest a physical association or interaction with M94.
  • The study, led by STScI researchers, is published in The Astrophysical Journal Letters and presented at the AAS meeting, and the team expects deeper surveys to uncover more such failed galaxies.