Scientists have discovered the remnants of a galaxy hiding in plain sight.
The galaxy, named
M32p, was once the third largest in the group of galaxies nearest to our Milky
Way — known as the Local Group. The Andromeda galaxy and M32p existed in
harmony until around 2 billion years ago, but then something shifted.
According to
a new study published in the journal Nature
Astronomy today, Andromeda actually devoured the smaller galaxy, and its
remains can be see in the clouds, gas, and dust of the huge galaxy today.
Massive galaxies
like Andromeda automatically attract other galaxies to it when they're in close
enough range due to its size and its gravitational pull. Because of that, it’s
not unusual for a galaxy of that mass to effectively cannibalize other nearby
galaxies nearby.
“To give an analogy
from the business world, one can grow through mergers and acquisitions. One
could possibly grow by metering with other smaller businesses,” author of the
study Richard D’Souza said via email.
“But if one really
wants to grow in size to certain level, one needs to acquire and merger with
another large business.”
Previously,
scientists believed that the population of stars known as a stellar halo
surrounding Andromeda were all formerly parts of smaller galaxies Andromeda had
merged with.
But something in
the researchers clicked when they realized that there was no way a bunch of
individual merging events with smaller galaxies would leave a trail this big.
D’Souza called this
their “eureka” moment.
“We realized that
Andromeda's stellar halo could only be formed by the merger of a single large
galaxy," D'Souza said.
In fact, there
aren't enough small galaxies in the universe to merge and create Andromeda's
stellar halo, he added.
The stellar halo is
larger than Andromeda itself, which led scientists to believe that the size of
the intact galaxy is roughly 20 times larger than anything the Milky Way has merged
with.
The realization
also helped solve the mystery surrounding the formation of M32, an extremely
compact satellite galaxy, full of young and old stars, that hovers near the
center of Andromeda.
Previously not much
was known about M32, but now it seems clear that the smaller galaxy is the
surviving center of M32p.
The computational
method used in this study will help further investigations other large galaxies
as well as advancing the literature on how galaxies evolve in general.
And it's a good thing
too.
One day — about 4
billion years from now — Andromeda and the Milky Way will collide with one
another. And while Earth and the sun may not be effected by the cataclysmic
event, it'll put on quite the cosmic show.
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