Welcome To Our New Galactic Supercluster Home: Laniakea
Your ultimate address just changed. Astronomers have discovered that the supercluster we’ve long-believed our Milky Galaxy resides in is actually just an appendage on the outskirts of an even more giant new supercluster called Laniakea.
Every now and then we receive an email from someone who lists their address in a much more complete way than most everyone else does. Instead of listing something like a town/state/country, they take a humorous much broader perspective that would seemingly be of interest only to an alien from the other side of the visible universe. They usually take the form of:
Earth/Milky Way/Local Group/Virgo-Cluster/Virgo-SuperCluster/Visible Universe.
We now know that this is wrong (and perhaps why inter-galactic email is so slow)
The organization of matter in the visible universe can be thought of as a hierarchy of groupings of stars. The fundamental unit, or atom, of the universe then is a star. From here all the way up the hierarchy is just names for how stars bunch together:
Galaxies: These are the tightest gravitationally bound groups of stars forming various shapes such as ellipticals, spirals, irregulars etc.
Galaxy Groups: Small collections (less than 50) of gravitationally bound galaxies. Our group is called the Local Group but there are at least 5 other similar groups nearby (astronomically speaking of course)
Clusters: These are structures consisting of galaxy groups and can consist of hundreds or thousands of galaxies. Our cluster is called the Virgo Cluster which spans 10 million light years and contains more than 1,300 galaxies
SuperClusters: These mega-structures contain bound groups and clusters of galaxies. They are essentially clusters of clusters containing as much as a quadrillion solar masses and can extend for a billion light years.
Even Bigger?: Aggregations larger than this have been variously called filaments, supercluster complexes, or walls and may span 10 billion light years.
Go ask google right now which supercluster we are in before most of the websites are updated. You will likely find many that still say we are in the Virgo Supercluster. We’ve been wrong about this for 50 years. My first thought upon reading this was that how could we miss something so big like that. This is because the boundaries of superclusters are hard to pin down. Many are near enough to each other that it’s hard to say where one ends and another begins.
To resolve this problem, Astronomers using the National Science Foundation’s Green Bank Telescope (among others) studied 8,000 galaxies in unprecedented detail. They were able to focus on how and where each one was moving by subtracting out their movement due to the universe’s expansion (which can be as much as 10,000 km/sec). What’s left is what’s called Peculiar Motion (roughly a few hundred km/sec) which allows us to see precisely how a superlcuster effects the motion of the galaxies. This subtraction method produces flow lines which are essentially arrows pointing directly to the gravitational center of the supercluster that that galaxy is converging towards and therefore belongs to.
This new approach has finally created the first crystal clear definition of what a supercluster is and using this new definition they realized that the Virgo Supercluster is actually on the outskirts of and part of a much larger, newly identified structure called the Laniakea Supercluster. The name Laniakea is especially apt meaning “immense heaven” in Hawaiian. This behemoth has a diameter of 500 million light-years and consists of 100,000 galaxies with the mass of a hundred quadrillion suns.
Welcome to your new home.
My Couch/Earth/Milky Way/Local Group/Virgo-Cluster/Laniakea-SuperCluster/Local Filament?/Visible Universe/Universe/Metaverse/?