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Monster Galaxies Bulk Up by Eating Smaller Neighbors

merger montage

Image credit: Some of the many thousands of merging galaxies identified within the Galaxy and Mass Assembly (GAMA) survey / Simon Driver and Aaron Robotham, ICRAR

According to the latest survey targeting on 22,000 galaxies, massive galaxies have ended up in producing their own stars, but begin with gobbling small nearby galaxies instead. In our own galaxy: Milky Way, we still can observe the remains of engulfed galaxies, however, it would take its comeuppance finally, because, our own galaxy would be devoured by Andromeda in around 5 billion years like some chocolate nougat candy bar.

As we know smaller galaxies could behave efficiently in producing stars from gas, but it is quite hard for the most massive galaxies to create any new stars themselves. When galaxies grow, the more gravity they have would enable them to pull in their neighbors easily.

As Aaron Robotham from the International Centre for Radio Astronomy Research (ICRAR) of the University of Western Australia said, all galaxies began in a small size and then grew through collecting gas and turning it into stars in an efficient way. However, time and again they would be totally cannibalized by some much bigger galaxy.

Star formation could be slower in the massive galaxies owing to extreme feedback events in the active galactic nucleus, the bright area at the center of a galaxy. Although astronomers know little of the actual mechanism, they guess that it is the active galactic nucleus that typically cooks the gas, thus stopping it from cooling down to form stars. In the end, gravity will make all the galaxies form in bound groups and clusters so as to merge into the super-giant galaxies.

Based on all data collected from the Anglo-Australian Telescope in New South Wales, the survey was part of the 7-year-long project named as Galaxy And Mass Assembly (GAMA). The result of survey was published in Monthly Notices of the Royal Astronomical Society recently.

In addition, the Milky Way—our own galaxy is coming to the   tipping point and it would be predicted to grow mainly by eating smaller galaxies instead of collecting gas. As Robotham said, although it had been long time since the Milky Way merged with another large galaxy, some remnants of all the old galaxies it had cannibalized were obviously observed. It seemed that the Milky Way would eat the Large and Small Magellanic Clouds, two nearby dwarf galaxies, in nearly four billion years.

As predicted Robotham, technically, the nearby Andromeda galaxy would eat our own galaxy in 5 billion years eventually,   because it was much more massive than the Milky Way.

If you want to know more what would occur when the Milky Way and Andromeda get closer together, collide, and then eventually form an even massive bigger galaxy, you had better to watch the following simulation shows.

Image: Simon Driver and Aaron Robotham, ICRAR

Video: Chris Power (ICRAR-UWA), Alex Hobbs (ETH Zurich), Justin Reid (University of Surrey), Dave Cole (University of Central Lancashire) and the Theoretical Astrophysics Group at the University of Leicester with video production by Pete Wheeler, ICRAR

Source: ICRAR

Journal reference: Robotham, A. S. G., et al. “Galaxy And Mass Assembly (GAMA): galaxy close pairs, mergers and the future fate of stellar mass.” Monthly Notices of the Royal Astronomical Society 444.4 (2014): 3986-4008.