The new work implies that the merger of galaxy clusters has a major impact on the formation of stars: the shocks lead to turbulence in the galactic gas which then triggers an avalanche-like collapse, leading to the formation of very dense, cold gas clouds, which are vital for the formation of new stars. Star formation at this rate leads to a lot of massive, short-lived stars coming into being, which explode as supernovae a few million years later. The explosions drive huge amounts of gas out of the galaxies and with most of the rest consumed in star formation, the galaxies soon run out of fuel. The cluster mergers make the galaxies even more red and dead.
Every cluster of galaxies in the nearby Universe has experienced a series of mergers during its lifetime, so they should all have passed through a period of extremely vigorous production of stars. Given that the shocks will only however lead to a brief (in astronomical terms) increase in star formation, astronomers have to be very lucky to catch the cluster at a time in its evolution when the galaxies are still being `lit up’ by the shock.
David Sobral, Andra Stroe, William A. Dawson, David Wittman, M. James Jee, Huub Röttgering, Reinout J. van Weeren and Marcus Brüggen, 2015, "MC2: boosted AGN and star formation activity in CIZA J2242.8+5301, a massive post-merger cluster at z = 0.19", MNRAS, 450, 630. Paper.
Andra Stroe, David Sobral, William Dawson, M. James Jee, Henk Hoekstra, David Wittman, Reinout J. van Weeren, Marcus Brüggen and Huub J. A. Röttgering, 2015, "The rise and fall of star formation in z~0.2 merging galaxy clusters", MNRAS, 450, 646. Paper.
"Giant cosmic tsunami wakes up comatose galaxies", RAS press release, 24 April 2015.