Astronomers have worked out the origin of giant galaxies that seemed to have fizzled early in the Universe's history, just three billion years after the Big Bang.

To find out how massive elliptical galaxies became so big and stopped forming stars so quickly, Sune Toft of the Niels Bohr Institute in Copenhagen and his colleagues compared samples of these dead galaxies and an earlier generation of star-forming ones observed with the Hubble, Herschel and Spitzer space telescopes. The authors conclude that earlier, gas-rich galaxies merged, kicking off intense star formation that rapidly used up all the gas, resulting in the large, burnt-out galaxies.

Astrophys. J. 782, 68 (2014)