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yesterday

Hubble Confirms First Starless Dark-Matter Cloud, ‘Cloud-9,’ Near Galaxy M94

Deep Hubble imaging of a FAST‑flagged target found no stars, confirming a reionization‑limited relic predicted by theory.

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

  • Cloud-9 lies about 14 million light-years away on the outskirts of Messier 94 and appears physically associated with the galaxy.
  • Hubble’s Advanced Camera for Surveys detected no stellar population at the radio peak, establishing Cloud-9 as a truly starless object.
  • Radio data from FAST, the Green Bank Telescope, and the Very Large Array map a neutral hydrogen core roughly 4,900 light-years across with about one million solar masses of gas.
  • Assuming gas pressure balances gravity, the team infers a surrounding dark-matter halo of approximately five billion solar masses.
  • The results, led by researchers at STScI, are published in The Astrophysical Journal Letters and were presented at the 247th American Astronomical Society meeting, with teams planning targeted searches for additional RELHICs.