Short Wave – "A failed galaxy could solve the dark matter mystery"
Date: January 21, 2026
Hosts: Regina Barber (NPR)
Guests: Andrew Fox, Gagan Deep Anand (Space Telescope Science Institute)
Episode Overview
This episode explores a major discovery in astrophysics: an unusual “failed galaxy” called Cloud 9—a massive clump of dark matter and gas with no stars—recently observed by astronomers for the first time. The hosts and their guests explain how Cloud 9 helps confirm theoretical predictions about dark matter, addresses a big gap in cosmological theory, and could one day help reveal the very nature of dark matter itself.
Key Discussion Points & Insights
What is Dark Matter and Why Does it Matter?
- Only 15% of the universe’s mass is made of normal matter (galaxies, stars, planets, etc.); the rest is dark matter (00:15).
- Regina Barber: “Astronomers know that dark matter is there, but they don't know what it's made out of.”
The Discovery of Cloud 9: The First-Ever Observed 'Failed Galaxy'
- Cloud 9 is a “dark matter halo” containing gas but no stars (01:15).
- Previously, theory predicted that such objects should exist, but none had ever been directly observed this clearly.
- Regina Barber: “Cloud 9 is a failed galaxy. It's a dark matter halo with a cloud of gas devoid of stars.” (01:27)
- Cloud 9 is located on the outskirts of the spiral galaxy M94.
Theoretical Context: Lambda CDM Model
- The prevailing cosmological model, called Lambda CDM, predicts the existence of dark matter halos that aren’t massive enough to form stars—sometimes called 'relics' (05:01).
- Gagan Deep Anand: “With the discovery of this relic object, Cloud 9, it's a confirmation that you actually do indeed have Dark matter halos that are not massive enough to form stars, just like the simulations predict.” (05:39)
How Was Cloud 9 Found?
- Andrew Fox explains their team used the Hubble Space Telescope to look for stars in Cloud 9. They found a truly starless, gas-rich cloud:
- “We pointed the Hubble Space Telescope at this cloud expecting to find some stars…But what we found was that there are no stars, even though we pointed at this object for a very long time…We found just a blank piece of sky, a completely empty cloud.” (04:00)
- Previous searches found candidates but none as convincing; Cloud 9 is uniquely “empty” even with deep Hubble imaging (10:24).
What Are Dark Matter Halos? Why So Exciting?
- Dark matter halos are clumps or regions of dark matter—most galaxies form within them (05:01).
- Relics, like Cloud 9, are halos too small to form stars and are therefore invisible but are predicted by simulations (06:04; 08:45).
- Andrew Fox: “The cool thing about this model is that it predicts there are smaller halos, smaller halos that are beneath the scale that can form a galaxy, essentially failed galaxies...” (06:25)
- These relics are hard to observe because they’re dim and contain little/no stars.
Observational Techniques
- Cloud 9 was initially found via radio observations of its neutral hydrogen gas “glow”; Hubble was used to look for star signatures and found none (08:45; 09:45).
- This approach uniquely revealed a structure that was predicted by theory but not previously witnessed (10:24).
Implications for Cosmology and Dark Matter Research
- The discovery is a major win for the Lambda CDM model—it confirms a longstanding prediction (11:16).
- Gagan Deep Anand: “It's a big win for the theory. It's a big prediction of the model that these objects should exist. And just by finding one, you know you're on the right track.”
- Cloud 9 can be studied to better understand dark matter itself because there’s no messy “normal” matter (like stars) to complicate observations (12:05).
- Andrew Fox: “You can think of them as a window into a dark matter dominated cloud, a window into the dark universe.” (12:11)
Next Steps and Importance for the Future
- The hope is to find more such relics/clouds to strengthen models and constrain what dark matter is (13:00).
- The location of Cloud 9, far from the core of M94, makes it a pristine laboratory for study (12:11).
- The lack of stars makes Cloud 9 an “advantage”—enabling direct research into the properties and distribution of dark matter itself.
Notable Quotes & Memorable Moments
- Regina Barber (01:27): “Cloud 9 is a failed galaxy. It's a dark matter halo with a cloud of gas devoid of stars.”
- Andrew Fox (04:00): “If we'd seen stars, that would have confirmed that this cloud is really a small galaxy...but what we found was that there are no stars, even though we pointed at this object for a very long time…We found just a blank piece of sky, a completely empty cloud.”
- Gagan Deep Anand (11:16): “Just by finding one, you know you're on the right track.”
- Andrew Fox (12:11): “You can think of them as a window into a dark matter dominated cloud, a window into the dark universe.”
- Regina Barber (13:13): “We might be able to find what dark matter is.”
Timestamps for Key Segments
- 00:15 – What is dark matter? Setting the stage
- 01:15 – Introducing Cloud 9, the “failed galaxy”
- 04:00 – The discovery story: searching for stars, finding only gas
- 05:01 – What is a dark matter halo? The Lambda CDM model explained
- 07:34 – Relative size of Cloud 9 vs. the Milky Way
- 08:45 – How galaxies form within halos; what defines a “relic”
- 09:45 – How Cloud 9 was found: radio and Hubble observations
- 10:24 – Why Cloud 9 is a stronger candidate than ever before
- 11:16 – Theoretical and future implications
- 12:05–13:00 – Cloud 9’s potential as a window into dark matter; next steps
Conclusion
Cloud 9, a failed galaxy consisting of a dark matter halo and gas but no stars, has been observed for the first time, confirming a crucial prediction in contemporary astrophysics. This finding not only affirms current models but also opens up new, less cluttered avenues to study the elusive nature of dark matter, potentially revolutionizing our understanding of the universe’s hidden mass.