Most Detailed Observation Of A Distant Monster Galaxy

Artist's impression of COSMOS-AzTEC-1. National Astronomical Observatory of Japan

Over 10 billion years ago, the universe experienced an intense phase of star formation, with galaxies producing new stars at a rhythm never seen before or after. The most prolific galaxies had a monstrous rate of star formation, a thousand times higher than what the Milky Way currently achieves. These are the starburst galaxies, and now researchers have seen a distant one in more detail than ever before.

The target object is called COSMOS-AzTEC-1, located 12.4 billion light-years from us. The galaxy has all the right components to make stars at a high rate and we now know how the gas in it moves. As reported in Nature, the gas didn’t just flow in the center but swirled in several clouds.

“We found that there are two distinct large clouds several thousand light-years away from the center,” lead author Ken-Ichi Tadaki, from the National Astronomical Observatory of Japan, said in a statement. “In most distant starburst galaxies, stars are actively formed in the center. So it is surprising to find off-center clouds.”

The observations were only possible thanks to the resolution power of the Atacama Large Millimeter/submillimeter Array (ALMA). Using ALMA, the international team was able to work out that the clouds are not stable. This instability is possibly the key to the galaxy's runway star formation.

The ALMA observations of the galaxy show the two unstable clouds. ALMA (ESO/NAOJ/NRAO), Tadaki et al.

In regular galaxies, the pressure created by the stars and gravity is balanced out so that the star formation moves at a moderate pace. In COSMOS-AzTEC-1, the pressure is far weaker than the gravity and thus churns out stars at an incredible rate. The gas in the galaxy will be all converted into stars in just 100 million years, 10 times faster than in other star-forming galaxies.

The reason for the instability is not clear. It could be an internal mechanism or it could be something external. Maybe COSMOS-AzTEC-1 interacted with another galaxy.

“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,” explains Tadaki.

More observations of similar starburst galaxies are clearly needed. Galaxy mergers are crucial in the evolution of massive galaxies after all, and they might be the way to explain just how these star-forming monsters occur.

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