Eos, a newly discovered hydrogen cloud just 300 light-years from Earth, offers a rare look at hidden star-forming regions. Found via hydrogen fluorescence rather than carbon monoxide, Eos may reshape how astronomers detect and study molecular clouds in our galaxy.
Eos, a molecular cloud, ranks among the largest individual structures visible in Earth’s sky
Photo Credit: Thomas Müller (HdA/MPIA) and Thavisha Dharmawardena (NYU)
Astronomers found the nearest known molecular cloud to Earth, providing scientists with a unique up-close look at the cosmic recycling of matter that drives the formation of new planets and stars.
The newly discovered cloud, named "Eos" after the Greek goddess of dawn, is a massive, crescent-shaped mass of hydrogen gas that is only 300 light-years away from Earth. It is one of the biggest formations in the sky, spanning the equivalent of around 40 Earth moons arranged side by side at a width of nearly 100 light-years.
According to a paper published April 28 in the journal Nature Astronomy, Eos has so far escaped detection because of its low concentration of carbon monoxide (CO), a bright, easily detectable chemical signature that astronomers typically use to identify molecular clouds, despite its massive size and relative proximity to Earth. The researchers detected Eos through the fluorescent glow of hydrogen molecules within it — a novel approach that could reveal many similarly hidden clouds throughout the galaxy. Burkhart said to Live Sciences, "There definitely are more CO-dark clouds waiting to be discovered."
Eos has been shaped into its crescent shape through interactions with the North Polar Spur, a vast region of ionized gas. The shape aligns perfectly with the North Polar Spur at high latitudes, suggesting that energy and radiation from this massive structure have influenced the surrounding gas, including Eos. It will evaporate in about 6 million years due to its molecular hydrogen reservoir being torn apart by incoming photons and high-energy cosmic rays. A follow-up study found no significant bursts of star formation in the past, but it remains uncertain whether the cloud will begin to form stars before dissipating. A NASA spacecraft named after the newly discovered molecular cloud is being developed to observe in far-ultraviolet wavelengths to measure the molecular hydrogen content in clouds across the Milky Way.
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