Two astronomers from Greece have managed to model the three-dimensional structure of an interstellar gas cloud, and found that it’s on the order of 10 times more spacious than it originally appeared.
The shape and structure of Musca, described in the journal Science, could help scientists probe the mysterious origins and evolution of stars — and by extension, the planets that surround them.
Finding the 3-D structure of such clouds “has been a ‘holy grail’ in studies of the interstellar medium for many years now,” said senior author Konstantinos Tassis, an astrophysicist at the University of Crete.
Interstellar clouds serve as the celestial cradles for nascent stars, which condense out of these enormous conglomerations of gas and dust. These cold, dusty, magnetized clouds can reach a million times the mass of the sun. But because they’re filled with molecular hydrogen that blocks the light of background stars, they typically appear as holes in an otherwise bright night sky. They’re more easily studied using infrared light.
But even in infrared light, these clouds are difficult to study because we can see them only as flat structures, even though they’re actually three-dimensional. We know very little about how dense they are, what shape they are and how they’re organized inside.
“All sorts of different physical and chemical processes take place in their interior, and as a result, the process of star formation is poorly understood,” Tassis said in an email. “How does a giant cloud of a million solar masses break up into smaller pieces, and how do these fragments condense into stars similar to our sun? What makes a cloud form a lot of small stars or a few larger ones?”
“These problems, although they are directly related to the question of the origin of our sun, our planet, and, ultimately, ourselves, are still very much a mystery,” he added.
About a decade ago, astrophysicist Paul Goldsmith of the Jet Propulsion Laboratory in La Canada Flintridge and his colleagues discovered strange hair-like wisps surrounding such gas clouds, rather like the cilia of a bacterium. Amid the chaos of a gas cloud, these ordered structures drew astronomers’ attention. How did they form, and why?
“Understanding how you make new stars is really a critical challenge for modern astrophysics,” Goldsmith, who was not involved in the new paper, said in an interview. “These molecular clouds are where new stars are formed, and so understanding the structure of these clouds, and how deep they are, what their three-dimensional structure is, is obviously critical for understanding the whole picture.”
While completing his doctoral work at the University of Crete, lead author Aris Tritsis (now a postdoctoral fellow at Australian National University) concluded that these striations were actually caused by magnetic waves leaving their imprint on the cloud’s gas.
“It was then that we realized that these striations might encode a global vibration if the cloud is isolated, a ‘song,’ a pattern of frequencies that could reveal the true, 3-D shape of the cloud,” Tassis said.
To try and use those magnetosonic waves to understand the shape of an interstellar cloud, they pulled data from the European Space Agency’s infrared Herschel Space Observatory, which can see into the infrared. They focused on Musca, which lies in the Southern Hemisphere roughly 500 light-years from Earth.
