Two astronomers from Greece have managed to model the three-dimensional structure of an interstellar gas cloud, and found that it’s 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. “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 hairlike 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 said.
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 caused by magnetic waves leaving their imprint on the cloud’s gas.
From our vantage point, Musca looks like a needle. But the magnetosonic waves revealed that the gas cloud was shaped like a pancake. All in all, the cloud seems to measure roughly 24 light-years wide by 18 light-years across and one light-year thick. “Musca very clearly vibrates like a pancake, not a needle,” Tassis said. “It is not a subtle effect, it is eye-popping!”
This meant that the gas cloud was far more voluminous than previously thought and much less dense, Tassis said. “It was a huge surprise to us,” Tassis said.
The revelations change scientists’ understanding of the balance of forces that shaped this gas cloud and influenced its star-forming process, Tassis said.