Astronomers peering into the heart of a starburst galaxy 12.4 billion light years away have confirmed the presence of highly unstable molecular clouds believed to be fuelling runaway star formation. Because starburst galaxies are thought to be predecessors of the huge elliptical galaxies seen in the modern universe, the new observations may help fill in some of the blanks about how such galaxies form and evolve.
Using the Atacama Large Millimetre/submillimetre Array, or ALMA, a team led by Ken-ichi Tadaki, a postdoctoral researcher at the Japan Society for the Promotion of Science and the National Astronomical Observatory of Japan, studied a galaxy known as COSMOS-AzTEC-1, discovered with the James Clerk Maxwell Telescope in Hawaii.
“One of the best parts of ALMA observations is to see the far-away galaxies with unprecedented resolution,” said Tadaki, lead author of the research paper published in the journal Nature. “We found that there are two distinct large clouds several thousand light-years away from the center. In most distant starburst galaxies, stars are actively formed in the center. So it is surprising to find off-center clouds.”
Starburst galaxies form new suns 1,000 times faster than the rates observed in mature galaxies like the Milky Way. To understand how such monster galaxies can be so active, researchers must understand the environments in regions where such rapid star formation is taking place.
In “normal” galaxies, star formation is self regulating, in a sense, balancing the inward pull of gravity in dense molecular clouds with the outward pressure generated by stellar ignition, supernova blasts and related phenomena. But in a starburst galaxy, the clouds are unstable, gravity dominates and runway star formation results.
Tadaki’s team estimates COSMOS-AzTEC-1 will completely consume its supply of star-forming gas in just 100 million years or so, 10 times faster than the rate observed in other star-forming galaxies. The researchers do not yet know why the gas is so unstable. It could be due to an earlier merger with another galaxy, but no such evidence has been found.
“At this moment, we have no evidence of merger in this galaxy,” Tadaki said. “By observing other similar galaxies with ALMA, we want to unveil the relation between galaxy mergers and monster galaxies.”