Some monster galaxies have stopped making their own stars and are instead cannibalizing those unfortunate enough to exist nearby, and this may be bad news for our own Milky Way.
Researchers looked at more than 22,000 galaxies and noticed the most massive are not very good at generating new stars, and instead grew larger by feasting on smaller galaxies, the International Centre for Radio Astronomy Research reported.
"All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars," said Aaron Robotham based at The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR) "Then every now and then they get completely [cannibalized] by some much larger galaxy."
The researchers believe our own Milky Way is at a "tipping point," and now grows primarily through the practice of gobbling up smaller galaxies as a replacement for feeding on 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]," Robotham said.
The Milky Way is expected to eat the Large and Small Magellanic Clouds in about 4 billion years, but in about 5 billion years the Milky Way will most likelt get consumed by the monstrous Andromeda Galaxy.
The researchers believe the reason star formation slows in massive galaxies is because of "extreme feedback events" taking place in their active nuclei.
"The topic is much debated, but a popular mechanism is where the active galactic nucleus basically cooks the gas and prevents it from cooling down to form stars," Robotham said.
Gravity may also play a role; since massive galaxies have more gravity they can more easily pull in smaller ones. Gravity could one day cause all galaxies in bound groups and clusters to merge into larger entities.
"If you waited a really, really, really long time that would eventually happen but by really long I mean many times the age of the universe so far,"Robotham said.
The researchers made their findings through research collected by the Anglo-Australian Telescope in New South Wales as part of the Galaxy And Mass Assembly (GAMA) survey and was published in this month's edition of Monthly Notices of the Royal Astronomical Society.
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