This image, using data from Spitzer and the Hubble Space Telescope, shows the galaxy cluster SpARCS1049. Credit: NASA/STScI/ESA/JPL-Caltech/McGill
A gargantuan galaxy cluster with a core bursting with new stars has been found: an incredibly rare find. The discovery is the first to show that gigantic galaxies at the centers of massive clusters can grow significantly by feeding off gas stolen from other galaxies.
Galaxy clusters are vast families of galaxies bound together by gravity. Our own galaxy, the Milky Way resides in the small galaxy group called 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 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,” explained Tracy Webb.
The galaxy was initially discovered using NASA’s Spitzer Space Telescope and Canada-France-Hawaii Telescope, Hawai’i and confirmed with W.M. Keck Observatory, also on Mauna Kea. Follow-up observations using Hubble 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 2 stars per year at most!
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. Hubble had previously discovered another closer galaxy cluster containing a wet merger, but it was not forming stars as vigorously. Other galaxy clusters grow in mass through dry mergers, or by siphoning gas towards their centres. eg the mega galaxy cluster Phoenix Cluster grows in size by sipping off gas that flows into its centre. The astronomers now aim to explore how common this type of growth mechanism is in galaxy clusters. Are there other “messy eaters” out there similar to SpARCS1049+56, which also munch on gas-rich galaxies? http://www.spacetelescope.org/news/heic1519/
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