Huge Invisible Molecular Cloud Discovered Near Earth

In a discovery that challenges conventional astronomical observation techniques, a team of researchers led by Rutgers University–New Brunswick has identified a colossal molecular hydrogen cloud, one of the largest structures in the sky and one of the closest to Earth. The cloud, named Eos after the Greek goddess of the dawn, was detected using an innovative technique that employs far-ultraviolet light, marking a milestone in the exploration of the interstellar medium.

The study, published in Nature Astronomy, reveals that Eos is located about 300 light-years from our planet, on the edge of the Local Bubble, a vast cavity of gas that surrounds the Solar System. With a mass equivalent to 3,400 times that of the Sun and an apparent size in the sky of about 40 full moons, this crescent-shaped structure could be key to understanding how interstellar gas condenses to form stars and planets.

Until now, molecular clouds have typically been detected through radio or infrared observations, which capture the chemical signature of carbon monoxide (CO), a common component in these regions. However, Eos is what scientists call “CO-dark”—that is, it contains very little of this compound, which explains why it had remained invisible for decades.

invisible molecular cloud near earth — Location of the Eos molecular cloud in relation to the Sun and the Solar System. Credit: Burkhart et al. 2025

This is the first time a molecular cloud has been discovered by directly searching for the far-ultraviolet emission of molecular hydrogen, explained Blakesley Burkhart, associate professor in the Department of Physics and Astronomy at Rutgers and lead author of the study. The data showed hydrogen molecules glowing by fluorescence in the far ultraviolet. This cloud literally glows in the dark.

The discovery was made possible by data from the FIMS-SPEAR spectrograph, an instrument aboard the South Korean satellite STSAT-1, which analyzes far-ultraviolet light. Burkhart and her team stumbled upon the cloud while reviewing newly released information in 2023. It was as if it were waiting to be explored, the researcher commented.

A Window into the Origin of Stars

Eos poses no danger to Earth, but its proximity offers a unique opportunity to study how the interstellar medium—the gas and dust that fills the space between stars—gives rise to new solar systems.

When we look through our telescopes, we see solar systems forming, but we don’t understand in detail how it happens, Burkhart noted. The discovery of Eos is exciting because we can now directly measure how molecular clouds form and break apart, and how a galaxy begins to transform gas and dust into stars and planets.

According to models, Eos will evaporate in about six million years, but in the meantime, its study could reveal secrets about the chemical evolution of the universe. The story of the cosmos is a story of atoms being rearranged over billions of years, Burkhart reflected. The hydrogen in this cloud has existed since the Big Bang and eventually fell into our galaxy, near the Sun. These atoms have traveled a journey of 13.6 billion years.

The success of this technique opens the door to discovering other hidden clouds in the Milky Way and even in distant galaxies. Thavisha Dharmawardena, a researcher at New York University and co-author of the study, emphasized that the use of ultraviolet fluorescence could rewrite our understanding of the interstellar medium, revealing hidden clouds to the farthest edges of the cosmic dawn.

The team is already applying this method to other data sets. A preliminary study, available on arXiv, suggests that the James Webb Space Telescope (JWST) may have detected the most distant hydrogen molecules ever observed. With JWST, we may have found the most distant ones, while with Eos, we have the closest, Burkhart stated.

SOURCES

Rutgers, the State University of New Jersey

Burkhart, B., Dharmawardena, T.E., Bialy, S. et al. A nearby dark molecular cloud in the Local Bubble revealed via H2 fluorescence. Nat Astron (2025). doi.org/10.1038/s41550-025-02541-7