Laniakea: the supercluster we all float in

2014

In 2014, a team of astronomers led by R. Brent Tully at the University of Hawaii published a discovery that redefined our place in the universe. Using data about the velocities and directions of motion of galaxies, they mapped an immense cosmic structure they named Laniakea, from the Hawaiian "lani" (heaven) and "akea" (immeasurable, vast).

Laniakea is a supercluster: a massive collection of galaxy clusters, gravitationally bound, moving together through space. It contains approximately 100,000 galaxies, including the Milky Way, and spans roughly 500 million light-years.

For context: the Milky Way has a diameter of about 100,000 light-years. Laniakea is 5,000 times larger. Our galaxy is literally a tiny speck in a structure so large that light needs half a billion years to cross it.

At Laniakea's center lies something mysterious called the Great Attractor, a region of space with an enormous gravitational concentration toward which all galaxies in the supercluster are being pulled. The Great Attractor is roughly 250 million light-years from us, in the direction of the Centaurus constellation. We can't see it directly because the Milky Way's own disk blocks our view (the region is called the "Zone of Avoidance").

What's in the Great Attractor? We don't know exactly. It appears to be an enormous concentration of mass: thousands of galaxies packed together. But the gravity it exerts is greater than the visible mass would explain, suggesting enormous quantities of dark matter.

Laniakea isn't even close to the largest structure in the universe. Our supercluster neighbors the Perseus-Pisces supercluster and the Shapley supercluster. Together, these are part of even larger structures: cosmic filaments that form the "cosmic web," the largest structure in the universe.

The discovery changed how we think about our cosmic "address": Earth → Solar System → Milky Way → Local Group → Virgo Cluster → Laniakea Supercluster. We are a speck of dust on a speck of dust, in a structure so vast that the human mind cannot truly conceive of it.