Using the Hubble Space Telescope, astronomers have identified Cloud-9, a gas-rich cloud dominated by dark matter with no stars, marking the first confirmed example of a failed galaxy. This relic from the early universe provides insights into cosmic evolution and dark matter structures. The discovery confirms predictions about starless hydrogen clouds known as RELHICs.
Astronomers have unveiled Cloud-9, a peculiar cosmic object observed through the Hubble Space Telescope. This cloud, rich in neutral hydrogen gas and dominated by dark matter, contains no stars whatsoever, making it a prime example of a "failed galaxy"—a primordial building block that never ignited star formation.
"This is a tale of a failed galaxy," explained Alejandro Benitez-Llambay, principal investigator from Milano-Bicocca University in Milan, Italy. "In science, we usually learn more from the failures than from the successes. In this case, seeing no stars is what proves the theory right."
Classified as a Reionization-Limited H I Cloud (RELHIC), Cloud-9 represents a long-predicted but elusive type of object from the universe's early stages. Team member Andrew Fox from AURA/STScI for the European Space Agency described it as "a window into the dark Universe," noting that dark matter constitutes most of the universe's mass yet is hard to detect due to its lack of light emission.
The cloud's discovery began three years ago with a radio survey using China's Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou. Confirmations followed from the Green Bank Telescope and the Very Large Array in the United States. Hubble's Advanced Camera for Surveys then ruled out any hidden stars, as lead author Gagandeep Anand from the Space Telescope Science Institute in Baltimore emphasized: "With Hubble... we're able to nail down that there's nothing there."
Located near the spiral galaxy Messier 94 (M94), Cloud-9 spans about 4,900 light-years in neutral hydrogen, with the gas mass equaling roughly 1 million solar masses. Balancing gas pressure against gravity suggests the total mass, mostly dark matter, reaches around 5 billion solar masses. Its compact, nearly spherical shape sets it apart from larger, irregular hydrogen clouds near the Milky Way.
RELHICs like Cloud-9 preserve early universe conditions, unaffected by star formation. They highlight how much of the cosmos lies beyond observable starlight. As Rachael Beaton from STScI noted, "Among our galactic neighbors, there might be a few abandoned houses out there."
This find, detailed in a 2025 Astrophysical Journal Letters paper, advances knowledge of galaxy formation and dark matter dynamics. Future surveys may reveal more such relics, deepening understanding of the universe's hidden architecture.