Astronomers say they've made a rare find — a galaxy at the center of a giant galactic cluster that's defying conventional thinking by spitting out new stars at an incredible rate.
Galactic clusters are vast groupings of individual galaxies all bound to each other by gravity, with the galaxies at their center almost always composed of older red stars, or even dead ones.
However, a giant galaxy within the core of a cluster known as SpARCS1049+56 is going against that trend by producing new stars at an incredible rate, more than 800 per year, researchers are reporting in a paper set to appear in The Astrophysical Journal.
For contrast, our own Milky Way galaxy manages to create just one or two a year.
NASA's Spitzer space telescope and ground-based telescopes in Hawaii have allowed astronomers to peek into the heart of the cluster 9.8 billion light years away that consists of at least 27 individual galaxies — where they suspect the galaxy at its core is powering its star-making with gas stolen from neighboring galaxies.
"We think the giant galaxy at the center of this cluster is furiously making new stars after merging with a smaller galaxy," explains lead study author Tracy Webb from McGill University in Montreal, Canada.
That merger of a smaller galaxy with the monster example at the cluster's center has given the larger galaxy the raw material for an explosion of star birth, the researchers explain.
After the initial discovery by Spitzer and the telescopes in Hawaii, astronomers turned to the Hubble Space Telescope to more closely probe the galactic cluster.
"Hubble found a train wreck of a merger at the center of this cluster," said researcher Adam Muzzin of the University of Cambridge in England.
Observations that pockets of gas are condensing where new stars are forming is evidence of what astronomers call a "wet merger," in which plentiful gas is available to create new stars. In a "dry merger," the merging galaxies contain little gas, with the result no new stars are formed.
Researchers say SpARCS1049+56 is one of the first known instances of a wet merger occurring at the very center of a distant galaxy cluster.
"The Spitzer data showed us a truly enormous amount of star formation in the heart of this cluster, something that has rarely been seen before, and certainly not in a cluster this distant," said Muzzin.
SpARCS1049+56 may be a rare type of cluster — or it may represent an early period in the universe when furious rates of star formation were normal, say the astronomers, adding that more exploration is needed to see if this type of mechanism is common in other galaxy clusters.
