When it comes to galaxies, it’s survival of the largest. Monster galaxies grow by cannibalizing their smaller neighbors, instead of birthing new stars on their own.
In a new study, led by Aaron Robotham of the University of Western Australia, that looked at 22,000 galaxies, astronomers found that the more massive the galaxy, the more it grows in size by gobbling up their smaller “dwarf” counterparts.
“All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars,” said Robotham in a press statement. “Then every now and then they get completely cannibalized by some much larger galaxy.”
This galactic cannibalism appears to be self-perpetuating, since as the galaxies grow they gain more gravitational strength and therefore more easily pull in their neighbors, according the study released this month in the journal Monthly Notices of the Royal Astronomical Society.
And it turns out our own home galaxy, the Milky Way, may now be tipping the scale on the obese side—growing only by snacking on wayward islands of stars.
“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 explained.
“We’re also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years.”
Andromeda Big Bully
What goes around comes around, however, and the Milky Way too may fall victim to galactic cannibalization. Our neighbor, the Andromeda galaxy, now some 2.6 million light-years away from Earth, will likely approach and devour the Milky Way in about five billion years.
“Technically, Andromeda will eat us because it’s the more massive one,” Robotham said.
Eventually, a similar fate may await most monster galaxies. At one point in the distant future, the cluster members will slowly merge together into only a few supercolossal galaxies that will end up dominating the cosmos.
“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,” which is about 13.8 billion years old, said Robotham.
See for Yourself
Even if you can’t wait for the Milky Way merger, other opportunities abound to see galactic smashups. One of the best examples of interacting galaxies is the famous Whirlpool galaxy in the northern constellation Canes Venatici. It is a small stellar pattern just beside the famous constellation Ursa Major, the Great Bear.
Visible with small telescopes throughout the Northern Hemisphere, the Whirlpool galaxy, also known as Messier 51, is a spiral galaxy that has a visible bridge of gas, dust, and stars that connect it to a smaller, irregular galaxy known as NGC 5195.
Under dark skies you may even be able to glimpse the magnitude 8.4 galaxy with binoculars.
You can find M51 by looking 3.5 degrees southeast of the star Alkaid. Alkaid marks the end of the handle of the Big Dipper.
The Whirlpool is estimated to contain over 150 billion stars, making it at least as massive as our own Milky Way.
While you watch, ponder the amazing fact that its ghostly pinwheel structure sits a whopping 27 million light-years away from Earth.