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Discovery of Eos: A Massive Molecular Cloud Near Earth
A collaborative effort among researchers from various institutions, spearheaded by an astrophysicist from Rutgers University–New Brunswick, has led to the discovery of a significant molecular cloud potentially involved in star formation. Dubbed “Eos,” this cloud represents one of the largest known structures in our vicinity, sitting among the closest to both the Sun and Earth that has ever been detected.
The molecular cloud, primarily composed of hydrogen, had previously gone unnoticed by scientists. The team successfully identified it by focusing on molecular hydrogen, its main component. This breakthrough marks the first instance of a molecular cloud being detected through light emitted in the far-ultraviolet spectrum, promising new avenues for future exploration using similar methodologies.
“This opens up new possibilities for studying the molecular universe,” stated Blakesley Burkhart, an associate professor in the Department of Physics and Astronomy at Rutgers and a co-author of the study, which is detailed in a research paper published in Nature Astronomy.
Molecular clouds serve as crucial environments for the formation of stars and planetary systems. Composed of gas and dust, they primarily contain hydrogen, the foundational element for creating stars and planets, along with other compounds like carbon monoxide. Traditionally, scientists have detected molecular clouds through radio and infrared observations that can easily identify the chemical signature of carbon monoxide.
In this groundbreaking work, the researchers employed an innovative method.
“This is the first-ever molecular cloud discovered by looking for far-ultraviolet emission of molecular hydrogen directly,” Burkhart explained. “Our data revealed glowing hydrogen molecules via fluorescence in the far-ultraviolet spectrum. This cloud is essentially glowing in the dark.”
Despite its proximity, Eos poses no threat to our planet or solar system. Instead, it provides an exceptional opportunity for scientists to investigate the features of an interstellar structure. The interstellar medium, which consists of gas and dust filling the space between stars, plays a vital role in star formation.
“When we observe through our telescopes, we see entire solar systems developing, yet the specific mechanics behind this process remain elusive,” Burkhart reported. “The discovery of Eos is thrilling because it allows us to directly measure how molecular clouds form and disintegrate, and how galaxies convert interstellar gas and dust into stars and planets.”
The crescent-shaped cloud is located approximately 300 light-years from Earth, sitting at the edge of the Local Bubble—a vast cavity filled with gas that encompasses our solar system. Eos is estimated to span about 40 times the diameter of the Moon and has a mass roughly 3,400 times greater than that of the Sun. Models suggest it might evaporate within the next 6 million years.
“The application of far-ultraviolet fluorescence emission techniques could revolutionize our understanding of the interstellar medium, potentially revealing hidden clouds scattered across the galaxy and beyond,” remarked Thavisha Dharmawardena, a NASA Hubble Fellow at New York University and a co-author of the study.
The team utilized data from a far-ultraviolet spectrograph known as FIMS-SPEAR (Fluorescent Imaging Spectrograph), which operated on the Korean satellite STSAT-1. This instrument analyzes far-ultraviolet light emitted from substances, much like a prism distinguishes wavelengths in visible light, thereby creating a measurable spectrum.
The data used for this discovery was only made publicly available in 2023 when Burkhart stumbled upon it.
“It felt like this data was waiting to be explored,” she said.
Burkhart emphasized the significance of innovative observational approaches in expanding our understanding of the universe. Although Eos is dominated by molecular hydrogen, it’s predominantly “CO-dark,” meaning it lacks significant amounts of carbon monoxide and therefore eluded previous identification. This characteristic explains why Eos went undetected for so long, according to researchers.
“The narrative of the cosmos is fundamentally about the transformation of atoms over billions of years,” Burkhart articulated. “The hydrogen currently within the Eos cloud can be traced back to the time of the Big Bang, eventually coalescing in our galaxy near the Sun—marking a journey of 13.6 billion years for these hydrogen atoms.”
The discovery was unexpected for the team.
“In graduate school, we were taught that observing molecular hydrogen directly was quite challenging,” said Dharmawardena. “It’s astonishing that we can now see this cloud in data we initially thought would not yield any results.”
Eos is also named after a proposed NASA space mission in which Burkhart and other team members are involved. This mission seeks to broaden the detection of molecular hydrogen, enabling further investigation of star formation by analyzing the evolution of molecular clouds.
Researchers are actively examining data for molecular hydrogen clouds near and far. A study by Burkhart and colleagues, available as a preprint on arXiv, tentatively reports the detection of the most distant molecular gas to date.
“With the James Webb Space Telescope, we may have identified the farthest hydrogen molecules from the Sun,” Burkhart noted. “In this project, we’ve discovered both some of the closest and furthest molecular clouds using far-ultraviolet emission.”
More information:
A nearby dark molecular cloud in the Local Bubble revealed via H2 fluorescence, Nature Astronomy (2025). DOI: 10.1038/s41550-025-02541-7
Source
phys.org