Astronomers Witness Birth of Massive Galaxy Cluster

An illustration of the 14 galaxy clusters on a collision course to form what astronomers are calling 'one of the most massive structures in the modern universe.'. (Photo: ESO/M. Kornmesser)

Billions of years ago, well before our own solar system was born, 14 star-dense galaxies collided dramatically to form what astronomers now believe is likely "one of the most massive structures in the modern universe." Located some 12.4 billion light-years away, the so-called "birth of a protocluster core" appears today as it existed only 1.4 billion years after the Big Bang.

The astronomers made the remarkable discovery, detailed in the most recent issue of the journal Nature, after following up on the presence of a bright "fuzzy blob" in the night sky captured by South Pole Telescope in Antarctica. What they initially suspected was three galaxies turned out to be something much more dramatic when surveyed using the more sensitive Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

"It just hit you in the face because all of a sudden there are all these galaxies there," astrophysicist and study co-author Scott Chapman of Dalhousie University in Halifax, Canada, said in a statement. "We went from three to 14 in one fell swoop. It instantly became obvious this was a very interesting, massive structure forming and not just a flash in the pan."

The ALMA radio telescope captured these 14 galaxies, located some 12.8 billion light years away from Earth, on a dramatic collision course.
The ALMA radio telescope captured these 14 galaxies, located some 12.8 billion light-years away from Earth, on a dramatic collision course. (Photo: ALMA (ESO/NAOJ/NRAO)

While astronomers have observed massive clusters in the modern universe before, this is the first time they've captured one on the verge of forming. The statistics — as you might expect for 14 galaxies merging into one — are staggering. According to the researchers, the observed protocluster likely contained around 10 trillion suns’ worth of mass, growing to more than 1,000 trillion suns' worth of mass as it matured into one giant elliptical galaxy over billions of years.

In an interview with the BBC, co-author Dr. Axel Weiß of the Max Planck Institute for Radio Astronomy shared how all of this drama is unfolding in a region of space only four or five times the size of our own Milky Way galaxy.

"If you put all the planets into the orbit between the Earth and moon, it's the same sort of scale of mass concentration," he added.

Back to the future

Because light from the impending collision between these galaxies takes billions of years to reach Earth, researchers can only look to other clusters, such as the massive Coma Cluster, for what its form might look like today.

"The uniqueness of the Coma Cluster is it's one of the most massive structures we know about in the whole local Universe. [It has about] 10,000 billion solar masses. It's the most extreme structure that we know about," explained Weiß.

Leveraging the power of computer modeling also allows researchers to peer forward in time to see what this protocluster may have become. As shown below, the unfolding drama over "only" 1 billion years is as violently dramatic as anything you're likely to see in the universe.

Researchers say the discovery of the protocluster, designated SPT2349-56, is likely to rewrite current thinking of the origins and evolutions of galaxies so quickly after the Big Bang.

"How this assembly of galaxies got so big so fast is a bit of a mystery, it wasn’t built up gradually over billions of years, as astronomers might expect," Tim Miller, a doctoral candidate at Yale University and coauthor on the paper, said in National Radio Astronomy Observatory statement. "This discovery provides an incredible opportunity to study how galaxy clusters and their massive galaxies came together in these extreme environments."