Monster galaxies are ancient and enormous relics of the universe’s early days. Believed to be ancestors of the massive galaxies we see today, including our own Milky Way, monster galaxies were formed when the universe was less than 2 billion years old and are known for being extreme starburst galaxies.
This means that they’re a lot more active than other galaxies, their molecular clouds churning out stars at much faster rates. For instance, the monster galaxy dubbed COSMOS-AzTEC-1 spews out stars 1,000 times faster than the Milky Way.
Discovered in 2007 with the help of the AzTEC instrument — built by the University of Massachusetts Amherst (UMass Amherst) and mounted on the James Clerk Maxwell Telescope in Hawaii at the time — this galaxy sits 12.4 billion light-years away and is somewhat of an oddball, notes Phys.org.
The staggering pace at which stars are born in COSMOS-AzTEC-1 have prompted astronomers to take a closer look at the monster galaxy’s internal structure in hopes of finding an explanation for its intense activity.
With the help of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, an international team of astronomers from Japan, Mexico, and UMass Amherst mapped out the galaxy’s molecular clouds and found something completely unexpected, according to the Alma Observatory.
Their observations have yielded “the most detailed anatomy chart of a monster galaxy,” achieving an angular resolution 10 times higher than ever before, ALMA officials announced earlier today.
#BreakingNews! ????ALMA observed an unstoppable monster in the early #Universe. Astronomers obtained the most detailed anatomy chart of a monster galaxy located 12.4 billion light-years away. ????https://t.co/q1vNR91Dw9 pic.twitter.com/x06DKux64f— ALMA Observatory (@almaobs) August 29, 2018
As it turns out, COSMOS-AzTEC-1 is unusual for a number of reasons. From the outside, it looks conspicuously more orderly than astronomers would gave expected from a young starburst galaxy formed just 1 billion years after the Big Bang. Instead of looking like “a disordered train wreck,” the galaxy is made up of an “ordered gas disk that is in regular rotation,” explains Min Yun, an astronomy professor at UMass Amherst and co-author of a new study on COSMOS-AzTEC-1 just published in the journal Nature.
Yun was part of the original team that first discovered this monster galaxy a decade ago. In his own words, finding out that its shape is so tame was “a real surprise.”
But a glimpse inside this gas disk uncovered that the galaxy is more turbulent than previously imagined. For one thing, aside from the dense molecular cloud that exists in the center of each galaxy, the astronomers found two more lurking on opposite sides of the central one.
“We found that there are two distinct large clouds several thousand light-years away from the center,” said study lead author Ken-ichi Tadaki, a researcher affiliated with the Japan Society for the Promotion of Science and the National Astronomical Observatory of Japan.
“In the most distant starburst galaxies, stars are actively formed in the center. So, it is surprising to find off-center clouds,” explained Tadaki.
In addition to discovering more star-forming clouds than anticipated, Tadaki’s team uncovered that these molecular clouds are “highly unstable,” fueling star formation at un uncontrolled pace.
“This galaxy shows runaway star formation and has morphed into an unstoppable monster galaxy,” ALMA officials said in a statement.
According to the research, the inward gravity of the galaxy is much stronger than the outward pressure exerted by its molecular clouds. Under normal circumstances, these two forces periodically balance each other out, allowing molecular clouds to create stars at a moderate pace. However, in the case of COSMOS-AzTEC-1, gravity constantly pulls the clouds inward, making them collapse into a star-forming frenzy.
Since these newly-formed stars don’t have enough time to go supernova and expel gas back into the galaxy, COSMOS-AzTEC-1 is churning out fresh stars on loop — working so fast that it will soon run out of fuel, reveals the new study.
This “unstoppable” monster galaxy is going through its gas reserves so fast that it will completely deplete them in about 100 million years, the astronomers found out. That’s 10 times faster than other star-birth galaxies.
These findings are particularly important, considering that the study of monster galaxies can offer us a glimpse into the Milky Way’s past, and help us learn more about how the huge galaxies in today’s universe were created, and how they evolved in time.
“How these galaxies have been able to amass such a large quantity of gas in the first place and then essentially turn the entire gas reserve into stars in the blink of an eye, cosmologically speaking, was a completely unknown question about which we could only speculate. We have the first answers now,” said Yun.