In the vast universe, there are clouds of matter that come in all shapes and sizes. While we often think of massive galaxies like our Milky Way, many smaller clouds are out there too. These smaller clouds can take a long time to collapse into stars. Interestingly, some might never collapse, especially if they receive energy from outside sources.
This brings us to a fascinating concept called a Reionization-Limited HI Cloud (RELHIC). It’s a type of neutral hydrogen cloud within a dark matter halo, maintaining a balance with the cosmic ultraviolet background. Most known hydrogen clouds are large and have stars, but now we’ve discovered a new one dubbed “Cloud 9.” This cloud might be the first of its kind.
Cloud 9 defies the usual characteristics of gas clouds. Instead of being massive, it spans over 4,000 light-years and contains only about one million solar masses of neutral hydrogen—far less than typical clouds. What’s more intriguing is that studies combining data from various telescopes, including the Hubble Space Telescope, show no stars within it.
Cloud 9 is located near the bright galaxy Messier 94, just 16 million light-years away. This galaxy has around 20 known satellite galaxies, which all host stars. Researchers initially used the Five-hundred-meter Aperture Spherical Telescope to look for more satellite candidates and discovered several gas clouds, including Cloud 9.
What makes Cloud 9 stand out? There are several key observations:
- It moves at a speed matching Messier 94’s recessional speed.
- It’s about 250,000 light-years away from Messier 94.
- It shows a strong signal of neutral hydrogen but no signs of stars.
- A massive dark matter halo, over a billion solar masses, likely surrounds it.
This gas cloud presents a unique opportunity to study an untouched piece of the universe, potentially tracing back to the very origins of matter post-Big Bang. If future observational technologies, like the James Webb Space Telescope, can confirm Cloud 9’s lack of stars, it could redefine our understanding of cosmic evolution.
Research indicates that dark matter halos usually pull in gas, leading to star formation. However, if the gas remains too warm or has been impacted by ultraviolet radiation from nearby stars, it might not collapse to form stars at all. This suggests that Cloud 9 could retain pristine hydrogen, untouched by stellar evolution.
Recent observations have started to shift our perspective on such clouds. For example, another discovery in 2021 identified a dark, primordial galaxy with a billion solar masses of hydrogen but no visible stars. Such findings echo the importance of exploring and questioning the conventional stories we tell about galaxy formation.
In the future, astronomers plan to use a variety of observational methods to learn more about Cloud 9, looking for elemental signatures that could reveal its structure and history. The potential to find a whole new type of cosmic object adds excitement to our ongoing exploration of the universe.
For further reading on this topic, check out recent publications in the Astrophysical Journal Letters, where details about Cloud 9 and its implications for galaxy evolution are thoroughly discussed.
