An invisible molecular cloud that could shed light on how stars and planets form has been detected surprisingly close to Earth.
Named Eos after the Greek goddess of the dawn, the cloud of gas would appear huge in the night sky if visible to the naked eye. It measures roughly 40 moons in width and has a weight about 3,400 times the mass of the sun, researchers reported in a study published Monday in the journal Nature Astronomy.
“In astronomy, seeing the previously unseen usually means peering deeper with ever more sensitive telescopes — detecting those smaller planets … those more distant galaxies,” said study coauthor Thomas Haworth, an astrophysicist at Queen Mary University of London.
“This thing was pretty much in our cosmic backyard, and we’ve just missed it,” he added.
Molecular clouds are composed of gas and dust from which hydrogen and carbon monoxide molecules can form. Dense clumps within these clouds can collapse to form young stars.
Scientists usually spot a molecular cloud using radio and infrared observations that can pick up the chemical signature for carbon monoxide, Haworth explained.
“We normally look for carbon monoxide, just one carbon atom and one oxygen atom, and that emits light pretty easily at wavelengths that we can detect,” he said. “(Carbon monoxide is) bright, and we have lots of facilities that can spot that.”
However, Eos eluded discovery despite being the closest molecular cloud to Earth because it does not contain much carbon monoxide, and therefore doesn’t emit the characteristic signature detected by conventional approaches, the researchers said. The key to unlocking this stunning find was searching for ultraviolet light emitted by hydrogen in the cloud.
“The only reason we managed to catch it in this instance is because we’ve been able to look with a different color of light,” Haworth added.
A window into solar system formation
Haworth and his colleagues detected Eos in data collected by a far-ultraviolet spectrograph called FIMS-SPEAR that operated as an instrument on a Korean satellite called STSAT-1.
The data had just been released publicly in 2023 when lead study author Blakesley Burkhart, an associate professor in the department of physics and astronomy in the Rutgers School of Arts and Sciences, came across it.
The spectrograph breaks down far-ultraviolet light emitted by a material into its component wavelengths, similar to what a prism does with visible light, creating a spectrum that scientists can analyze.
“This is the first-ever molecular cloud discovered by looking for far ultraviolet emission of molecular hydrogen directly,” Burkhart said in a news release. “The data showed glowing hydrogen molecules detected via fluorescence in the far ultraviolet. This cloud is literally glowing in the dark.”
The molecular cloud’s proximity to Earth provides a unique opportunity to study how solar systems form, 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,” Burkhart said.
Astronomers thought they had a good handle on the locations and properties of the molecular clouds within about 1,600 light-years of the sun, making this “pretty cool discovery” quite a surprise, said Melissa McClure, an assistant professor at the University of Leiden in the Netherlands.
“This new molecular cloud, Eos, is only 300 light-years away, which is closer than any of the molecular clouds that we’ve known about previously,” McClure, who wasn’t involved in the research, said.
“It’s puzzling why there’s something this big right in our solar neighborhood that we didn’t see before,” McClure added. “It would be a bit like living in a suburb with above-ground houses and open lots in it, and suddenly realizing that one of the open lots actually hosts a hidden underground bunker in it.”
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