Stars and planets form in giant molecular clouds dotted around galaxies. Their locations are far from random, they are the crammed nodes of a complex network of filaments that transport gas around galaxies. A new study highlights how the motion of the gas from the smallest to the largest scale is interconnected.
As reported in Nature Astronomy, researchers have conducted detailed observations of the motion of gas in the Milky Way and in galaxy NGC 4321 from scales as small as one-third of a light-year to thousands of light-years. Their research shows that the evolution of the gas within a galaxy cannot be understood only on the smallest scales. Instead, the gas flowing through each scale is interconnected, and while star and planet forming occurs on the smallest scale, this is controlled by the hierarchal flow of matter that starts on galactic scales. The flows are interdependent and the bigger picture affects the local clouds and vice versa.
“Picture the giant molecular clouds as equally-spaced mega-cities connected by highways,” said lead author Dr Jonathan Henshaw, from the Max Planck Institute for Astronomy, in a statement. “From a birds-eye view, the structure of these cities, and the cars and people moving through them, appears chaotic and disordered. However, when we zoom in on individual roads, we see people who have traveled from far and wide entering their individual office buildings in an orderly fashion. The office buildings represent the dense and cold gas cores from which stars and planets are born.”
The vast majority of the gas is hydrogen, but the team tracked carbon monoxide as a proxy. This gas shines brightly in radio waves and many radio maps have been conducted of galaxies using radio observatories. The maps have millions of measurements that can be turned into velocity for a particular region of the gas flow, so the team had to come up with some clever software to analyze it all.
The research showed that the gas has crests and troughs, like waves on the surface of the sea. The motion was expected but the team did not expect to see the same pattern repeating at both the small and large scale.
“What surprised us was how similar the velocity structure of these different regions appeared. It didn’t matter if we were looking at an entire galaxy or an individual cloud within our own galaxy, the structure is more or less the same," said Steve Longmore, co-author of the paper, based at Liverpool John Moores University.
The team is already working on the next steps. They plan to study more regions to better understand this phenomenon and use galactic simulations to gain critical insight into how this gas flow is affected by the other properties of their host galaxy.
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