Where Are You?

Welcome to Laniakea, a place to call home in your own corner of the cosmos.

 

Have you ever seen a road sign that says, “If you lived here, you’d be home by now”? If you’re caught in the traffic of a long commute, that phrase may cause you some frustration or longing. But here in the cosmic superstructure Laniakea, there’s no need ever to feel anxious – because wherever you are, you’re always home in Laniakea.

What Is Laniakea?

We all know that we live on Earth, and that Earth is a planet in the Solar System, and that the Solar System is one of many star systems in our home galaxy, the Milky Way.   But is there another line in our cosmic address?

Several years ago, an international group of astronomers from the U.S., France, and Israel decided to find out. These intrepid scientists, led by Brent Tully, a researcher from the University of Hawaii, began by consulting an existing database called “Cosmicflows-2,” a catalog of the motions of known galaxies.

They then followed the movements of these galaxies, mapping them and analyzing how cosmic forces affected their movements and those of so-called galaxy clusters.

Our own cluster is called the Local Group, which in addition to the Milky Way includes Andromeda and other galaxies.

The team studied approximately 8,000 galaxies and measured for each what they call their “peculiar motion,” which they define as the resultant direction and speed of a galaxy when the motion contributed by the ongoing expansion of the Universe is subtracted from its total movement.

Laniakea, a supercluster of about 100,000 large galaxies, includes our own Milky Way and spans a half-billion light-years. Image credit: Nature Video

Using this measure, the team discovered that galaxies all move toward galactic centers, called “attractors.” The movements map out into strings, or “filaments,” of galaxies converging toward one general location.

“We have a new way of defining large-scale structures from the velocities of galaxies, rather than just looking at their distribution in the sky.”—Brent Tully, lead study author, astronomer, University of Hawaii, Honolulu

The galaxy filament we’re a part of is headed in the direction of a central point called the Great Attractor. And all the filaments approaching the Great Attractor together comprise the cosmic supercluster that the research team calls Laniakea, which in the Hawaiian language translates as “immeasurable heaven.”

Galactic Vectors and the Local Void

One unusual finding of this study is that galaxies that are relatively close to one another may in fact be moving toward separate attractors – and are therefore members of separate superclusters. Because we are located toward the far end of a filament, many galaxies that appear to be relatively nearby are actually members of a separate supercluster. Our closest supercluster neighbor is called Perseus-Pisces.

This illustration reveals the limits of the Laniakea supercluster. Image credit: R. Brent Tully (U. Hawaii) et al., SDvision, DP, CEA/Saclay

Interestingly, since we reside on the outskirts of the great cosmic real estate of Laniakea, we are closer to nothing than to either the Great Attractor or Perseus-Pisces. In fact, you could say we’re almost in the middle of nowhere.

That’s because we are closer to an area of sky that is called the Local Void, an area where not much is going on in terms of stars, galaxies, or clusters. But this is not uncommon in the Universe: All regions include voids as well as areas where objects are more concentrated. We just happen to be closer to a void than most, sort of like that last home on a road that ends at the ocean.

Laniakea is 520 million light-years wide.

And the Next Horizon?

By studying the structure of Laniakea, researchers hope to learn more about the properties of dark matter and dark energy, which seem to affect the movement of galaxies toward attractors.

 

Another avenue for further study is whether there are even more immense superstructures that might dwarf Laniakea. Brent Tully thinks so. He and his fellow researchers have pointed toward what appears to be an even larger assemblage of galaxies of which Laniakea is apparently a part. They call it the Shapley Concentration.

You Are Here

So, for now, our cosmic address may be complete. For your reference, here’s where you live: Earth, Solar System, Milky Way, Local Group, Virgo Supercluster, Laniakea, Shapley Concentration (?), Universe. Be sure to use it on your next piece of mail. You never know where a reply might originate.