Chuck Bednar for redOrbit.com – Your Universe Online
When galaxies grow too massive to continue making their own stars, they begin cannibalizing other nearby galaxies, experts from the University of Western Australia and an international team of colleagues reported this week in the journal Monthly Notices of the Royal Astronomical Society.
Dr. Aaron Robotham, a postdoctoral researcher at the University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), and his associates looked at over 22,000 galaxies and found that the most massive galaxies were far less efficient at forming stars than their smaller counterparts.
Instead of making their own new stars, these galaxies grew by consuming other galaxies. This occurs because as galaxies grow, they have more gravity, and can therefore have an easier time pulling in their neighbors. The reason that star formation slows down in these massive galaxies, Dr. Robotham noted, is believed to be due to extreme feedback events occurring in the active galactic nucleus, a bright region located at its center.
“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,” he explained in a statement from the Royal Astronomical Society, adding that gravity is ultimately expected to cause all galaxies to merge into a handful of super-giant galaxies.
However, that process will take several billion years to take place. “If you waited a really, really, really long time that would eventually happen,” Dr. Robotham continued, “but by really long I mean many times the age of the Universe so far.”
What’s more, Washington Post reporter Rachel Feltman explained that our own Milky Way has already consumed other galaxies, and will ultimately be on the other end of this phenomenon. In approximately five billion years, the nearby galaxy Andromeda is expected to become large enough to consume the Milky Way, according to the study authors.
[ Watch the Animation: Milky Way Collides With Andromeda Galaxy ]
“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,” Dr. Robotham said in an ICRAR statement. “We’re also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years,” before it winds up being consumed by Andromeda approximately one billion years later.
The overwhelming majority of the research data was collected using the Anglo-Australian Telescope in New South Wales as part of the Galaxy And Mass Assembly (GAMA) survey. The GAMA survey is led by Professor Simon Driver at ICRAR, involved more than 90 scientists and took roughly seven years to complete. This new paper is one of more than 60 publications to have resulted from the project, and another 180 are currently in progress.
In addition to Dr. Robotham, researchers from the University of St. Andrews, the Australian Astronomical Observatory, the University of Central Lancashire, the Sydney Institute for Astronomy at the University of Sydney, Monash University, the University of Cape Town, the University of Queensland, the European Southern Observatory, the University of Melbourne and elsewhere were involved in the study.
Image 2 (below): Some of the many thousands of merging galaxies identified within the GAMA survey. Credit: Professor Simon Driver and Dr. Aaron Robotham, ICRAR
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The Milky Way Will Eventually Be Consumed By Nearby Andromeda Galaxy
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