A distant galaxy that outshines our own by a thousand times set a new record when it was spotted in 2015 by NASA’s Wide-field Infrared Survey Explorer (WISE) satellite. The galaxy is the most luminous ever discovered, but if it is so intrinsically bright, why did it take until 2015 to detect it? One reason is its sheer distance – WISE is detecting light that has travelled for 12.5 billion years to reach us – but it is also buried beneath an immense cloud of dust produced by the rapid cycle of star birth and death. WISE could only see this galaxy because its extreme luminosity heats up the dust, causing it to glow brightly in the infrared.
There’s only one possible way that a galaxy could grow so bright: the radiation is pouring out from frenetic activity around a black hole thousands of times more massive than the black hole at the centre of our Galaxy.
Inside the magazine
Our top ten greatest stories of 2015 first appeared in the December edition of Astronomy Now.
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