A vast and strange cloud of gas could be a galaxy that never managed to form a single star.
In the Universe, galaxies shine thanks to their stars. Yet astronomers believe that some could exist almost in darkness. They would contain gas and, above all, dark matter, but no stars bright enough to be detected. A recently discovered object could fit this description.
General view of the FAST radio telescope antenna in China's Guizhou province.
Image: Wikimedia Commons, credits on the file page.
It was detected with FAST, a giant radio telescope installed in China. This instrument notably captures waves emitted by hydrogen, the most abundant gas in the Universe. The researchers thus identified an isolated cloud, named J1351+0039, where no galaxy is visible.
They then searched it for stars. Nothing appeared. This does not mean there are absolutely none: a very small or widely dispersed population of stars could still escape observation. But the cloud is sufficiently vast and faint to intrigue scientists.
Measurements indicate that it contains hydrogen with a mass equivalent to about 480,000 Suns. Yet the movements of this gas suggest that the object's total mass reaches approximately 130 million Suns. It therefore appears to contain far more matter than can be seen.
Dark matter could explain this discrepancy. Invisible to telescopes, it nevertheless exerts a gravitational pull. Astronomers believe that it forms vast envelopes around galaxies that retain gas and stars. In this particular case, such an envelope could have held onto gas without ever producing stars.
Why? The object may be too small for its gas to cool and gather sufficiently. Ultraviolet light bathing the Universe since its earliest eras may have helped keep this gas warm. Without dense enough clouds, no star could be born.
Other clues point in the same direction: the gas rotates very slowly, and its disordered movements seem mainly to prevent it from collapsing in on itself. In addition, astronomers found no large nearby galaxy that could have stripped it of matter. J1351+0039 may therefore be an object that has remained isolated for a long time.
Even deeper observations with Hubble or James Webb will be needed to search for the faintest stars. The study was made public as a scientific preprint, before validation by a journal.