Ancient galaxy is forming 1,000 times more stars than Milky Way

High levels of gas within the galaxy are triggering runaway star formation.
By Laurel Kornfeld | Dec 11, 2018
A 12.4-billion year old starburst galaxy is forming stars 1,000 times faster than the Milky Way, according to a team of scientists who studied it using the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in Chile.

The researchers found molecular clouds within the huge galaxy, designated COSMOS-AzTEC-1, to be very unstable, a condition that causes runaway star formation. Dense gas clumps within the galaxy are so concentrated that they are rapidly collapsing and forming stars. At this rate, the clouds may be completely gone within 100 million years.

Typically, molecular clouds in galaxies are kept stable by outward pressure from star formation and supernova explosions of dying massive stars. The clouds collapse and form stars when their gravity overcomes this pressure. New stars and supernova explosions then increase the pressure in what becomes a stable cycle, with moderate star-formation rates.

COSMOS-AzTEC-1's pressure is much weaker than its gravity, resulting in runaway star formation.

Scientists are also unclear as to how the galaxy gathered such a large amount of gas this early in its lifetime. One theory is that a merger or collision with another galaxy brought the gas into a small region, triggering star formation.

"At this moment, we have no evidence of merger in this galaxy. By observing other, similar galaxies with ALMA, we want to unveil the relation between galaxy mergers and monster galaxies," saidKen-ichi Tadaki of the Japan Society for the Promotion of Science (JSPS) and the National Astronomical Observatory of Japan (NAOJ).

Discovered just 20 years ago, huge star-forming galaxies like this one may be the precursors of today's elliptical galaxies.

In their ALMA observations, the scientists searched for the signature of carbon monoxide using the telescope's highest possible resolution, then created a detailed molecular map of the galaxy.

"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," Tadaki noted.

Before observing COSMOS-AzTEC-1 with ALMA, the international science team studied it using the James Clerk Maxwell Telescope (JCMT) in Hawaii and the Large Millimeter Telescope (LMT) in Mexico.

A paper on the findings has been published in the journal Nature.


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