An enormous hydrogen-rich molecular cloud has been faintly glowing near our solar system – escaping detection until now.
This newly discovered cloud is one of the largest single structures in the sky and among the closest to Earth ever detected.
It’s called Eos, named after the Greek goddess of dawn. And it may even hold answers to some of the biggest questions in astronomy – like how stars are born.
Eos was discovered by scientists from Rutgers University–New Brunswick, and their research marks the first time a molecular cloud has been detected using far-ultraviolet light. This discovery could change how scientists search for star-forming regions in the universe.
“This opens up new possibilities for studying the molecular universe,” said Blakesley Burkhart, an associate professor in the Department of Physics and Astronomy at Rutgers University and a research scientist at the Center for Computational Astrophysics at the Flatiron Institute in New York.
Spotting hidden hydrogen clouds
Gas and dust form molecular clouds. They contain mostly hydrogen, along with other molecules like carbon monoxide. These clouds are where stars and planets begin to form.
Until now, astronomers mainly used radio and infrared signals to detect carbon monoxide in these clouds. That’s because molecular hydrogen – though more abundant – is hard to observe directly. This discovery changed that.
“This is the first-ever molecular cloud discovered by looking for far ultraviolet emission of molecular hydrogen directly,” Burkhart enthused.
“The data showed glowing hydrogen molecules detected via fluorescence in the far ultraviolet. This cloud is literally glowing in the dark.”
What makes Eos so special?
Eos is a crescent-shaped gas cloud about 300 light-years from Earth. It lies near the edge of a region of space called the Local Bubble – a cavity filled with gas that surrounds our solar system.
In size, Eos covers an area in the sky equivalent to 40 full moons. It has a mass around 3,400 times that of the sun. According to models, the cloud will evaporate in about 6 million years. Though it’s nearby, Eos poses no danger to Earth.
What it offers is a rare chance to study how molecular clouds behave in our part of the galaxy.
“When we look through our telescopes, we catch whole solar systems in the act of forming, but we don’t know in detail how that happens,” Burkhart noted.
“Our discovery of Eos is exciting because we can now directly measure how molecular clouds are forming and dissociating – and how a galaxy begins to transform interstellar gas and dust into stars and planets.”
Peering into the cosmic dawn
The team detected Eos using an instrument called FIMS-SPEAR – a far-ultraviolet spectrograph aboard the Korean satellite STSAT-1.
This device breaks ultraviolet light into its components, much like a prism splits visible light, letting scientists examine the details of the radiation.
When Burkhart found the data in 2023, it had just been released to the public. “It was kind of like just waiting to be explored,” she said.
The use of this technique could dramatically shift how scientists study the space between stars.
“The use of the far-ultraviolet fluorescence emission technique could rewrite our understanding of the interstellar medium, uncovering hidden clouds across the galaxy and even out to the furthest detectable limits of cosmic dawn,” said Thavisha Dharmawardena, a NASA Hubble Fellow at New York University and a co-first author of the study.
Why Eos was hidden
Hydrogen makes up almost all of Eos, but it contains little carbon monoxide. That makes it nearly invisible to conventional detection methods.
“The story of the cosmos is a story of the rearrangement of atoms over billions of years,” Burkhart explained.
Artist’s conception of what the Eos molecular cloud would look like in the sky if it were visible to the naked eye. Click image to enlarge. Credit: NatureLifePhoto/Flickr (New York City Skyline), Burkhart et al. 2025
“The hydrogen that is currently in the Eos cloud existed at the time of the Big Bang and eventually fell onto our galaxy and coalesced nearby the sun. So, it’s been a long journey of 13.6 billion years for these hydrogen atoms.”
For many scientists, the discovery came as a surprise. “When I was in graduate school, we were told that you can’t easily directly observe molecular hydrogen,” said Dharmawardena. “It’s kind of wild that we can see this cloud in data that we didn’t think we would see.”
Future of far-UV science
The discovery of Eos is not the end of the story – it’s just the beginning. Burkhart and her team are supporting a proposed NASA mission also named Eos. Its goal is to extend this detection method across wider regions of the galaxy.
The team is already using the James Webb Space Telescope (JWST) to look for more hydrogen clouds. Early results suggest they’ve identified the most distant molecular gas ever observed.
“Using JWST, we may have found the very furthest hydrogen molecules from the sun,” Burkhart said. “So, we have found both some of the closest and farthest using far-ultraviolet emission.”
Eos has revealed that some of the most important structures in the galaxy might still be hiding in plain sight – waiting for someone to look at them the right way.
