(Image: NASA, ESA et al.)
It鈥檚 not something in your eye. It鈥檚 not smoke from a late-night barbecue. You鈥檙e looking at a map of the most massive ancient galaxy cluster ever seen.
Astronomers nicknamed the cluster El Gordo (鈥渢he fat one鈥� in Spanish) in 2012, when they estimated its mass. Now, after analysing images from the Hubble Space Telescope, they think it鈥檚 43 per cent fatter still, with a mass as much as 3000 times that of the Milky Way.
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Hubble鈥檚 images revealed the mass of the galaxy cluster, officially catalogued as ACT-CL J0102-4915, through the phenomenon of gravitational lensing. El Gordo鈥榮 immense gravity warps space 鈥� like a distorting mirror at a funfair 鈥� and thus also the appearance of background galaxies. The amount of warping tells us how much mass is locked up in the cluster.
Light from the hundreds of galaxies in the cluster began its journey to us 9.7 billion years ago. We know that clusters this big have existed more recently, but El Gordo is the first one seen from such an early time in the universe鈥檚 13.8-billion-year history.
The image above combines Hubble鈥檚 visual-light observations with X-ray emissions seen by the Chandra space telescope (in red) and a map of the cluster鈥檚 mass (the blue smoke).
