Somewhere in the sky, obscured from our view by the Milky Way, an unknown anomaly called the Great Attractor pulls a hundred thousand galaxies around.
Okay, so I find it really difficult to write about the large-scale structure of the universe. Not because the concepts are inherently difficult or confusing, but because it feels vertiginous to even consider objects at that scale. I think the term is “cosmic dread.”
(Side note: if you want to read more about the psychological effects of contemplating the vastness of the universe, check out the article “The Total Perspective Vortex and You” in the links below.)
Anyway, most people know that stars and solar systems accumulate in huge structures known as galaxies – the Milky Way, for example. But galaxies gather into groups and so form even larger structures: clusters, superclusters, and filaments. Some day I’ll write a blog post about these enormous entities, but for now I’m going to focus on just one: the Laniakea Supercluster.
Our galaxy, the Milky Way, is in a gathering of galaxies known as the Local Group, along with Andromeda, Triangulum, and a few others. But the Local Group is part of a supercluster known as the Virgo Supercluster, and the Virgo Supercluster is just one branch of an even bigger supercluster, only discovered / proposed in 2014 – the Laniakea Supercluster. It’s enormous, one of the biggest things we know, and it has a dark secret at its centre.
The galaxies in the Laniakea Supercluster are moving strangely. Their movement is bending in odd ways, as if they’re being dragged off-course by some huge mass in the middle of the supercluster. And by huge I mean a thousand times bigger than our galaxy. We’ve tried to spot it with telescopes. Unfortunately, the other stars in the Milky Way are directly between us and it, so we’re not entirely sure what it is. We’ve given it a name anyway: the Great Attractor.
The Great Attractor is very unlikely to be some new exotic entity in the universe. It’s probably another bunch of galaxies that we cannot see directly, and indeed some recent work suggests that it is just another supercluster itself. Obscured by our galaxy, though, and with such an alluring name, it continues to taunt and tantalise our imaginations.