Massive galaxies in the universe have stopped making their own stars and are instead cannibalizing their neighbors, say astronomers, who also created this computer simulation of our own Milky Way being devoured by the much larger Andromeda Galaxy in the distant future.
Scientists at the International Centre for Radio Astronomy Research in Australia looked at more than 22,000 galaxies and found that, while smaller galaxies were very efficient at creating stars from gas, the most massive galaxies were much less efficient, and instead grew by consuming other galaxies.
Astronomer Aaron Robotham, who led the study, says that the Milky Way is at such a tipping point and is now expected to grow mainly by eating smaller galaxies, rather than by collecting gas:
"The Milky Way hasn't merged with another large galaxy for a long time but you can still see remnants of all the old galaxies we've cannibalized. We're also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years."
But, Robotham added, the Milky Way will eventually get its comeuppance when it is consumed by the Andromeda Galaxy in about five billion years.
His team of astronomers theorizes that star formation slows down in really massive galaxies because of extreme feedback events in a very bright region at the center of a galaxy—known as an active galactic nucleus—which cooks the gas and prevents it from cooling down to form stars.