A vast molecular cloud, long invisible, is discovered near the solar system

An artistic representation of the Eos molecular cloud as it would appear in the sky to the naked eye. Credit: Composite image: Ilya Grigorik (London Skyline), YourCredit (Eos Cloud)

An international team of scientists, led by a Rutgers University-New Brunswick astrophysicist and including Dr Thomas Haworth of Queen Mary University of London, has discovered a potentially star-forming cloud that is one of the largest single structures in the sky and among the closest to the Sun and Earth ever detected. 

The vast ball of hydrogen, long invisible to scientists, was revealed by looking for its main constituent – molecular hydrogen. The finding marks the first time a molecular cloud has been detected using far-ultraviolet light and opens the way to further explorations with this approach. 

The scientists have named the molecular hydrogen cloud “Eos,” after the Greek goddess of dawn. Their discovery is outlined in a study published in Nature Astronomy. 

Professor Blakesley Burkhart, associate professor at Rutgers University and research scientist at the Flatiron Institute, led the study. She said: “This opens up new possibilities for studying the molecular universe. The data showed glowing hydrogen molecules detected via fluorescence in the far ultraviolet. This cloud is literally glowing in the dark.” 

Dr Thomas Haworth of Queen Mary University of London, a key contributor to the research, added:

“In astronomy, seeing the previously unseen usually means peering deeper with ever more sensitive telescopes – detecting those smaller planets... those more distant galaxies. Yet here we had completely missed a cloud right on our cosmic doorstep, one that would appear huge in the sky if visible to the naked eye. The key to this discovery was searching for UV light, and it makes me excited about the future of UV space telescopes. 

Following this discovery, Suryansh Saxena, one of our fantastic MSc Astrophysics students, is now working with me and the team to determine whether star formation has already taken place within the Eos cloud.” 

Dr Thavisha Dharmawardena, NASA Hubble Fellow at New York University and shared first author of the study, remarked: “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.” 

The crescent-shaped Eos cloud is located about 300 light-years from Earth, on the edge of the Local Bubble – a vast cavity of gas surrounding our solar system. Measuring roughly 40 moons in width across the sky and weighing about 3,400 times the mass of the Sun, Eos is expected to dissipate in six million years. 

The discovery was made using data from the far-ultraviolet spectrograph FIMS-SPEAR aboard the Korean satellite STSAT-1. Unlike traditional methods that rely on carbon monoxide signatures, this technique directly detected molecular hydrogen via far-ultraviolet fluorescence – a first in astronomical research. 

Eos provides a rare opportunity to study star formation up close. As Professor Burkhart explained: “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. 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 team is now searching for more molecular clouds using this technique, including potential discoveries with the James Webb Space Telescope (JWST). Burkhart noted: “Using JWST, we may have found the very furthest hydrogen molecules from the Sun. So, we have found both some of the closest and farthest using far-ultraviolet emission.” 

Other members of the scientific team included researchers from: Technion-Israel Institute of Technology, Haifa, Israel; Queen Mary University of London and University College London, both of London; University of Iowa, Iowa City, Iowa; Korea Astronomy and Space Science Institute, University of Science and Technology, and Korea Advanced Institute of Science and Technology, all of Daejeon, South Korea; Max Planck Institute for Astronomy, Heidelberg, Germany; University of Texas at Austin, Austin, Texas; University of Arizona, Tucson, Ariz.; University of California, Berkeley; Université Paris Cité, Gif-sur-Yvette, France; Space Telescope Science Institute and Johns Hopkins University, Baltimore; University of British Columbia, Vancouver, Canada; Columbia University, New York; and the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.