Free Astronomy Magazine November-December 2015

SPACE CHRONICLES truly enormous amount of star for- mation in the heart of this cluster, something that has rarely been seen before, and certainly not in a cluster this distant,” commented co-author Adam Muzzin of the University of Cambridge, UK. Spitzer picks up infrared light, so it can detect the warm glow of hid- den, dusty regions of starbirth. Follow-up studies with Hubble in vis- ible light helped to pinpoint what was fuelling the new star forma- tion. It appears that a smaller galaxy has recently merged with the mon- ster in the middle of the cluster, lend- ing its gas to the larger galaxy and igniting a furious episode of new starbirth. “Building on our other observa- tions, we used Hubble to explore the galaxy in depth — and we were not disappointed,” added Muzzin. “Hubble found a trainwreck of a merger at the centre of this cluster. We detected features that looked like beads on a string.” Beads on a string are telltale signs of something known as a wet merg- er. Wet mergers occur when gas-rich galaxies collide — this gas is con- verted 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 (which involve the coming together of two galaxies lacking in gas), or by siphoning gas towards their centres. For example, the mega galaxy cluster known as the 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 gal- axies? SpARCS1049+56 may be an outlier — or it may represent an ear- ly time in our Universe when messy eating was the norm. T his image, made with data obtain- ed through Spitzer and the Hubble Space Telescope, shows the central region of the galaxy cluster SpARCS1049 +56. The brightest cluster gal- axy in the center of the cluster is current- ly undergoing a wet merger which pro- duces enormous amounts of new stars. The tidal tail — an in- dicator of the merger — as well as the brightest cluster gal- axy itself are shown. [NASA/STScI/ESA/JPLC altech/McGill] T his image shows the region of sky around the the distant galaxy cluster SpARCS1049+56. It took the light of the cluster 9.8 billion light-years to reach us. The cluster houses at least 27 galaxies, probably more, and has a combined mass equal to 400 trillion Suns. [NASA, ESA, Digitized Sky Survey 2] n