Why 'starbursts' take place when galaxies collide

Researchers have for the first time explained a long standing mystery

The new simulations were made using two of the most powerful supercomputers in Europe.

The scientists, led by Florent Renaud of the AIM institute near Paris in France modeled a galaxy like our own Milky Way and the two colliding Antennae galaxies.

For the Milky Way type galaxy, the astrophysicists used 12 million hours of time on the supercomputer Curie, running over a period of 12 months to simulate conditions across 300,000 light-years.

For the Antennae type system, the scientists used the supercomputer SuperMUC to cover 600,000 light-years.

With these enormous computing resources the team were able to model the systems in great detail, investigating details that were only a fraction of a light-year across.

By simulating the impact of the Antennae collision and merger on material 1,000 times less massive than anything attempted before and comparing this with the Milky Way model, Florent and his team were able to demonstrate that the collision changes the nature of the turbulence in the galactic gas.

Instead of whirling around, the gas enters a state where compression is more likely. So when two galaxies collide, this generates an excess of dense gas that collapses into stars-and both galaxies experience a starburst.

The study has been published in the journal Monthly Notices of the Royal Astronomical Society.