In an incredibly rare find, astronomers have discovered a gargantuan galaxy cluster, 9.8 billion light years away, in which the brightest galaxy is rapidly creating about 800 stars every year.
The discovery, made with the help of the NASA/ESA Hubble Space Telescope, is the first to show that gigantic galaxies at the centres of massive clusters can grow significantly by feeding off gas stolen from other galaxies.
Our own galaxy, the Milky Way resides within a small galaxy group known as the Local Group, which itself is a member of the massive Laniakea supercluster.
Galaxies at the centres of clusters are usually made of stellar fossils – old, red or dead stars.
However, astronomers have now discovered a giant galaxy at the heart of a cluster named SpARCS1049+56 that seems to be bucking the trend, instead forming new stars at an incredible rate.
“We think the giant galaxy at the centre of this cluster is furiously making new stars after merging with a smaller galaxy,” said lead author Tracy Webb of McGill University in Canada.
The galaxy was initially discovered using NASA’s Spitzer Space Telescope and the Canada-France-Hawaii Telescope, located in Hawaii.
Follow-up observations using the Hubble Space Telescope allowed the astronomers to explore the galaxy’s activity.
The SpARCS1049+56 cluster is so far away that its light took 9.8 billion years to reach us. It houses at least 27 galaxies and has a combined mass equal to 400 trillion Suns.
The cluster’s brightest galaxy is rapidly spitting out 800 new stars per year. The Milky Way forms two stars per year at most.
“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 co-author Adam Muzzin of the University of Cambridge, UK.
Spitzer picks up infrared light, so it can detect the warm glow of hidden, dusty regions of starbirth. Follow-up studies with Hubble in visible light helped to pinpoint what was fuelling the new star formation.
It appears that a smaller galaxy has recently merged with the monster in the middle of the cluster, lending its gas to the larger galaxy and igniting a furious episode of new starbirth.
Beads on a string are telltale signs of something known as a wet merger. Wet mergers occur when gas-rich galaxies collide – this gas is converted quickly into new stars.
The new discovery is one of the first known cases of a wet merger at the core of a galaxy cluster.
Other galaxy clusters grow in mass through dry mergers, or by siphoning gas towards their centres.
The study will be published in The Astrophysical Journal.