Half of the atoms making up everything around you are intergalactic interlopers. Large galaxies like our Milky Way amassed half their matter from neighbouring star clusters up to a million light years away, according to a new simulation.
“We did not realise how much of the mass in today’s Milky Way-like galaxies was actually ‘stolen’ from the winds of other galaxies,” says corresponding author Claude-André Faucher-Giguère at Northwestern University in Illinois
The theft occurs after a death. When some stars reach the end of their life cycle, they become massive supernovae, spewing high-speed gas out into the universe. The matter in these ejections is picked up by galactic winds, streams of charged particles powered by the exploding supernovae.
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