Most galaxies are notoriously slow at producing stars. The Milky Way makes only about one or two annually. So when astronomers discovered one that produces more than 800 per year, they were rightfully amazed.
The galaxy sits at the center of SpARCS1049+56, a cluster of 27 galaxies that’s located 9.8 billion light-years away. Scientists say a smaller galaxy seems to have merged with the galaxy in the middle of the cluster, lending its gas to the larger galaxy and fueling the mass production of new stars.
"Usually, the stars at the centers of galaxy clusters are old and dead, essentially fossils," said Tracy Webb, a physics professor at McGill University in Montreal and the lead author of a new paper on the findings, said in a NASA statement. "But we think the giant galaxy at the center of this cluster is furiously making new stars after merging with a smaller galaxy."
Professor Webb and her colleagues published their findings Thursday in The Astrophysical Journal.
The cluster was initially discovered by NASA’s Spitzer space telescope. Follow-up studies conducted with the Hubble space telescope “found a train wreck of a merger at the center of this cluster,” Adam Muzzin, an astronomy professor at the University of Cambridge in England, said in an ESA statement.
As NASA explains on its website:
Hubble specifically detected features in the smaller, merging galaxy called "beads on a string," which are pockets of gas that condense where new stars are forming. Beads on a string are telltale signs of collisions between gas-rich galaxies, a phenomenon known to astronomers as wet mergers, where "wet" refers to the presence of gas. In these smash-ups, the gas is quickly converted to new stars.
Dry mergers, in contrast, occur when galaxies with little gas collide and no new stars are formed.
The discovery is one of the first known cases of a wet merger at the core of a galaxy cluster. Galaxies at the centers of clusters are usually made of old, red, or dead stars, making them far less active.
So how rare are fast-producing galaxy clusters like SpARCS1049+56? Scientists aren’t sure. It could be an outlier or it could represent an early time in the universe when rapid star formation was the norm. That’s what they plan to research next.