Large galaxies will consume smaller ones, research says

Picture the Milky Way galaxy: our home, and the only galaxy that humanity has ever known. It is large and serene, a spiral of incredible beauty and unimaginable proportions. It is an inspiration to artists, philosophers and candy bar manufacturers alike. The earth resides peacefully in this galaxy, calm and seemingly endless — but the conditions of the Milky Way are far from static. In fact, our home galaxy will soon eat other galaxies and in turn be “eaten” — that is, merge with smaller dwarf galaxies. When this happens, life as we know it will cease to exist. This desolate finding was published recently in the prestigious journal, Monthly Notices of the Royal Astronomical Society, which is produced by the Oxford University Press.

Thankfully, none of these events will ever occur in any of our lifetimes. Our galaxy will “eat” the Large and Small Magellanic Clouds in four billion years, and the galactic merger of the Andromeda galaxy and the Milky Way is slated to occur in approximately five billion years. 

The discovery of this merging and consumption of smaller galaxies by larger ones was made by a team of scientists led by Aaron Robotham, a postdoctoral fellow at the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia. He discovered that much larger galaxies eat smaller dwarf galaxies because larger galaxies are less efficient at converting gases to stars. As they grow larger and less efficient, these galaxies consume other galaxies rather than make their own stars for themselves.

These groundbreaking findings were the product of a large study of data gathered by researchers throughout Australia. Robotham conducted a study of over 22,000 galaxies with data collected from the Anglo-Australian Telescope in New South Wales, which was in turn gathered in a seven-year study conducted by Simon Driver, also at ICRAR. 

According to Robotham’s paper, the process of galaxy material accumulation depends on the galaxy’s size. In younger, smaller galaxies, material is accumulated by gases cooling and building up directly onto the galactic disc.

In older, more massive galaxies, however, a different method of accumulating gas is seen: the eating of younger galaxies and their material by older ones. Robotham posits that a different method of gas collection is used in these older galaxies because of extreme feedback in the active galactic nucleus, or the center of the galaxy. This means that the active galactic nucleus is so hot and dense that it “cooks” the gas, preventing the cooling process so vital in star formation.

The eating of smaller galaxies by larger galaxies eventually means that there will only be several super-giant galaxies in the universe, rather than the millions upon millions of galaxies which currently exist. This merging of many into few, however, will take a very long time; Robotham estimates that it will occur in a period of time several times the age of the universe.

Robotham’s research in the evolution and interaction of galaxies has many far-ranging implications in our fundamental understanding of the universe and the interactions within it. The universe is far from still; it is incredibly dynamic, featuring temperatures at their highest and lowest, speed at its fastest, time at its slowest and gravity at its most extreme. Look up at the sky, and you’ll see the stars in their quiet dance across the universe — but look deeper, and you’ll see just how raucous, intense and fascinating their interactions truly are.