The birthplace of stars begins within large, cold clouds of gas and dust, which eventually collapse under the weight of gravity. Molecular clouds are vast cosmic entities that often stretch for hundreds of light-years, and scientists just discovered a massive one lurking in our celestial neighborhood.
The cloud, named Eos after the Greek goddess of dawn, was discovered around 300 light-years away from our solar system. It is one of the largest single structures in the sky, and may be the closest molecular cloud to Earth, according to a paper published this week in Nature Astronomy. Because it’s so close, it offers astronomers a unique front row seat to the star-forming process and to observe the molecular universe.
Stellar nurseries in our general galactic neighborhood lie along the surface of the Local Bubble, a large, hot cavity of plasma surrounded by a shell of gas and dust. In order to find the molecular clouds within that bubble, scientists have had to rely on observations of dust emissions. For the recent discovery, however, scientists found the nearby molecular cloud by detecting the fluorescent nature of hydrogen in the far-ultraviolet realm of the electromagnetic spectrum, according to the paper.
“This is the first-ever molecular cloud discovered by looking for far ultraviolet emission of molecular hydrogen directly,” Blakesley Burkhart, a physics and astronomy professor at the Rutgers School of Arts and Sciences and lead author of the study, said in a statement.
Molecular hydrogen, which is made up of two hydrogen atoms stitched together, is the most abundant molecule in the universe. It is also, however, difficult to detect as it glows in far ultraviolet wavelengths that get absorbed by Earth’s atmosphere. “The data showed glowing hydrogen molecules detected via fluorescence in the far ultraviolet,” Burkhart added. “This cloud is literally glowing in the dark.”
Aside from its glowing appearance, Eos is crescent-shaped and sits on the edge of the Local Bubble. It spans an apparent size of 40 full Moons in the sky, and with a mass that’s around 3,400 times that of the Sun. Using the same technique that revealed this previously invisible cloud, scientists could discover more hidden clouds across the Milky Way galaxy.
“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,” 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.”