🔭 Hubble discovers a galactic structure, but without any stars

Some cosmic objects surprise by their unusual nature. This is the case for a cloud devoid of any stars, observed by astronomers using the Hubble Space Telescope. Named Cloud 9, this astonishing object is located some 14 million light-years away from us, near the spiral galaxy Messier 94.

Primarily composed of dark matter, this invisible component that represents the largest part of mass in the Universe, Cloud 9 has a very particular composition. Researchers estimate that this cloud contains about five billion times the mass of the Sun in this form, compared to only one million solar masses for hydrogen gas. Such an imbalance prevents any star birth, making Cloud 9 a sort of aborted galaxy, as detailed by the scientists in their work published in The Astrophysical Journal Letters.


Dark matter plays a fundamental role in cosmic evolution, as it shapes the gravitational attraction around it. In Cloud 9, gas did accumulate, but not enough to trigger star formation. This phenomenon corresponds to models of hydrogen clouds limited by reionization, a type of theoretical object now confirmed by this direct observation. For astronomers, it is a privileged opportunity to examine dark matter in a nearly pure state.

The Hubble Space Telescope was crucial for this identification. Thanks to its Advanced Camera for Surveys instrument, the absence of stars could be established with great precision. Without this technology, Cloud 9 could have been mistaken for a dwarf galaxy too faint to be distinguished from Earth.

Unlike the hydrogen clouds surrounding the Milky Way, Cloud 9 is distinguished by its more compact and spherical shape, with a diameter of about 4,900 light-years. Its singular structure therefore sets it apart from other known gaseous formations. Scientists consider that to become a full-fledged galaxy, it would need to accumulate a much larger amount of gas; for now, it remains an isolated remnant.


This discovery indicates that other similar clouds could be hiding in the cosmos, waiting to be spotted. Future astronomical missions could reveal more, contributing to a better understanding of the earliest stages of galactic formation. Cloud 9 thus offers an observational window on the processes that shaped our Universe, free from the glare of stars.