a “galaxy” that never lit up
If a galaxy is, above all, a collection of stars, what do we do when we find something that looks like a galaxy, but doesn’t have one? That’s the question it poses. Cloud-9an object detected in the nearby cosmic environment that defies common definitions. There are no explosions or flashes, just a silent cloud whose existence invites us to look at the first steps of galactic formation in a different way. What the researchers have identified is a type of object that had been in the realm of theory for years. Cloud-9 fits into the category of so-called RELHICa primitive cloud of neutral hydrogen associated with a halo of dark matter that never became a galaxy. According to NASAit would be a vestige of the first stages of galactic formation, preserved to this day in the local universe. Hubble as definitive proof. The key to the discovery was not to find something new, but to confirm an absence with an unprecedented level of precision. Where radio telescopes had detected hydrogen, Hubble found no trace of stars, not even the faintest ones. That combination of data ruled out the hypothesis of a dim dwarf galaxy and placed Cloud-9 in a different category. “Seeing that there are no stars is what shows that the theory is correct,” said Alejandro Benitez-Llambay, principal investigator of the program. “It tells us that we have found in the local universe a primordial block that never formed.” Cloud-9 is located about 14 million light years from Earth, in the vicinity of the spiral galaxy Messier 94, with which it appears to maintain a physical relationship. Its structure is compact and almost spherical, a rare feature among known hydrogen clouds in the nearby environment. The core is made up of neutral hydrogen and has a diameter of approximately 4,900 light years. Radio measurements indicate a mass of gas equivalent to around a million suns and, from that gas and assuming that the pressure of the material itself compensates for the gravity of the halo, the team estimates that the associated dark matter would be around 5 billion solar masses. When dark matter is not enough. Cloud-9 fits into a scenario long anticipated by theory, but difficult to verify: structures dominated by dark matter that manage to retain gas without transforming it into stars. For researchers, this type of object acts as a missing link between cosmological simulations and the observable universe. The cloud illustrates that not all dark matter halos evolve into luminous galaxies. Some are trapped in an intermediate state, offering a direct window into the processes that regulate when and how star formation is triggered. The object first appeared three years ago in a hydrogen gas survey by the Chinese FAST radio telescope, as a discrete signal on the fringes of Messier 94. Subsequent observations with the Green Bank Telescope and the Very Large Array reinforced the detection, but did not resolve its nature. Detecting these types of systems is especially complex because nearby, luminous objects tend to eclipse them, and because clouds can lose gas as they move through intergalactic space, further reducing their visibility. In addition, high-resolution radio data show slight distortions in the gas, compatible with some type of interaction with the nearby galaxy. Between being born or disappearing. The authors of the study suggest that the fate of Cloud-9 is not closed. A sufficient increase in mass would upset the current balance and push the gas toward star formation, something that has not happened so far. But there is also the possibility that the environment works against you. The proximity to Messier 94 could favor processes that remove part of the gas, further reducing its ability to evolve. In that case, Cloud-9 would end up dissipating without ever becoming a proper galaxy. The finding has also raised caution among researchers outside the study. Jacco van Loon, an astrophysicist at Keele University, has pointed out that other hydrogen clouds initially considered dark ended up showing unexpected stellar populations. In his opinion, proving that an object is really a relic of dark matter requires evidence that is difficult to obtain even with Hubble. This caution marks the next step of the work: expanding the search and using higher resolution observations to confirm whether Cloud-9 is an isolated case or part of a broader population. Images | POT | THAT In Xataka | If we want to colonize the Moon, we will most likely have to live in caves. And South Korea is already planning it
