“This is the story of a failed galaxy” – and Hubble discovered it

Astronomers have identified a rare object in the nearby universe that could be a direct example of a “failed galaxy”.

An international consortium of astronomers identified, with the Space Telescope Hubble from NASA, a rare object in the nearby universe that could be a direct example of a “failed galaxy”: one compact cloud of gas without any visible stars and apparently dominated by dark matter.

The structure was named Cloud-9. The name Nube-9 reflects its position as the ninth gas concentration identified near the spiral galaxy Messier 94, with evidence of possible interactions between the two. For now, the cloud becomes a “natural laboratory” to investigate the limits of galaxy formation and the properties of dark matter.

According to the authors of , the discovery confirms long-term predictions of theoretical models about the existence of concentrations of dark matter capable of retaining gas, but unable to compress it enough to trigger star formation.

Alejandro Benitez-Llambayfrom the University of Milano-Bicocca and principal investigator of the study, emphasizes that the total absence of stars is not a void of information, but a key result: for scientists, the “failure” in forming stars is precisely the sign that they are facing a type of structure that was expected to be found, but that remained to be confirmed.

Nube-9 falls into the category of RELHICs (an acronym in English for “Limited Reionization HI Clouds”), objects composed of neutral hydrogen (HI) that appeared in the early stages of the Universe and that, despite containing gas, never started star formation.

To Andrew Fox, the cloud works as “a window to the dark universe”, for allowing the study of dark matter indirectly in a system where there is almost no light produced by stars, cites .

Confirmation required the sensitivity of Hubble: Gagandeep Anand, lead author, explains that previous observations did not exclude the hypothesis that it was an extremely faint dwarf galaxy, invisible to ground-based telescopes.

Using Hubble’s Advanced Camera for Research, the team concluded that there are no detectable stars associated with the object.

Unlike many hydrogen clouds near the Milky Way, which are generally extensive and irregular, Nube-9 is small, compact and almost spherical.

HI’s core will be about 4,900 light-years in diameter and will contain approximately one million solar masses of gas. From this value, the researchers estimate that, if the gas is in balance with the gravity of a dark matter halo, the total mass of the system could reach around five billion solar masses — enough to hold the gas together, but not enough to cause it to collapse and form stars.