Monster galaxies gain weight. But How?

 These are some of the many thousands of merging galaxies identified within the GAMA survey.  Credit: Professor Simon Driver and Dr Aaron...

 These are some of the many thousands of merging galaxies
identified within the GAMA survey.
 Credit: Professor Simon Driver and Dr Aaron Robotham, ICRAR

Massive galaxies in the Universe have stopped making their own stars and are instead snacking on nearby galaxies, according to research by Australian scientists.

Astronomers looked at more than 22,000 galaxies and found that while smaller galaxies are very efficient at creating stars from gas, the most massive galaxies are much less efficient at star formation, producing hardly any new stars themselves, and instead grow by eating other galaxies.
Dr Aaron Robotham, who is based at the University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), said smaller 'dwarf' galaxies were being eaten by their larger counterparts.
"All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars," he said.
"Then every now and then they get completely cannibalised by some much larger galaxy."
The study was released today in the journal Monthly Notices of the Royal Astronomical Society, which is published by Oxford University Press.
Dr Robotham, who led the research, said our own Milky Way is at a tipping point and is expected to now 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 cannibalised," he said.

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