Scientists
already knew that big galaxies like to chow down on smaller ones --
which is just a cute way of saying that when they collide, the larger
galaxy gains the mass of the smaller one.
According to a new study published
in the Monthly Notices of the Royal Astronomical Society, galaxies turn
to cannibalism when they get too big to keep growing on their own.
"All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars," Aaron Robotham, a postdoctoral researcher at the International Centre for Radio Astronomy Research and head of the study, said in a statement. "Then every now and then they get completely cannibalized by some larger galaxy."
As
galaxies grow, they get worse at making new stars -- but they also have
stronger gravity, which helps them pull neighbors into the fold. The
Milky Way reached this tipping point "recently," in cosmic terms (read:
not at all recently) and will now grow mostly by snacking on the little
guys. It's been a while since our neighborhood ate another one, but
astronomers can still see the signs of former galaxies that we've
digested.
But The Milky Way isn't going to be able to outrun Andromeda. In about 5 billion years we'll collide
with the nearby galaxy, which contains at least twice as many stars as
our own. To Andromeda, we'll be nothing but a cosmic candy bar.
These
cannibalistic mergers will continue until the whole universe is made of
just a few gigantic galaxies, but that's a long way off -- a destiny we
won't reach until the Universe is many times older than it is today.
Rachel Feltman runs The Post's Speaking of Science blog.
