Long invisible to astronomers, the newly-discovered molecular cloud is one of the largest single structures in the sky and among the closest to the Sun and Earth ever to be detected.
The Eos cloud sits on the edge of the Local Bubble, a large gas-filled cavity in space that encompasses the Solar System. Image credit: Thomas Müller, HdA & MPIA / Thavisha Dharmawardena, NYU.
Molecular clouds are composed of gas and dust — with the most common molecule being hydrogen, the most abundant molecule in the Universe and a key ingredient in all known star and planet formation.
These structures also contain other molecules such as carbon monoxide.
Molecular clouds are often detected using conventional methods such as radio and infrared observations that easily pick up the chemical signature for carbon monoxide.
Rutgers University-New Brunswick astrophysicist Blakesley Burkhart and colleagues employed a different approach.
“This is the first-ever molecular cloud discovered by looking for far ultraviolet emission of molecular hydrogen directly,” Dr. Burkhart said.
“The data showed glowing hydrogen molecules detected via fluorescence in the far ultraviolet. This cloud is literally glowing in the dark.”
Dubbed Eos, the newfound molecular cloud is located about 300 light-years away from Earth.
It sits on the edge of the Local Bubble, a large gas-filled cavity in space that encompasses the Solar System.
The astronomers estimate that the crescent-shaped cloud is vast in projection on the sky, measuring about 40 moons across the sky, with a mass about 3,400 times that of the Sun.
They used models to show it is expected to evaporate in 6 million years.
According to the team, the Eos cloud poses no danger to Earth and the Solar System.
Because of its proximity, the cloud presents a unique opportunity to study the properties of a structure within the interstellar medium.
The interstellar medium, made of gas and dust that fills the space between stars within a galaxy, serves as raw material for new star formation.
“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,” Dr. Burkhart said.
“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.”
The Eos cloud was detected in data from the FIMS-SPEAR far-ultraviolet spectrograph onboard the Korean satellite STSAT-1.
“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 Dr. Thavisha Dharmawardena, an astronomer at New York University.
The discovery is reported in a paper published today in the journal Nature Astronomy.
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B. Burkhart et al. A nearby dark molecular cloud in the Local Bubble revealed via H2 fluorescence. Nat Astron, published online April 28, 2025; doi: 10.1038/s41550-025-02541-7
