The concept of our cosmic address involves understanding the nested layers of structure in the universe, which has evolved with advancements in astronomy. Historically, our galaxy was considered a member of the Virgo Supercluster. Modern scientific mapping reveals this structure is merely a small part of an even greater, dynamically defined system. Clarifying our true position requires considering the gravitational forces and flows that organize matter on the grandest scales.
Our Immediate Cosmic Neighborhood
Our home galaxy is the Milky Way, which is a barred spiral galaxy containing hundreds of billions of stars. The Milky Way is part of a small gravitationally bound collection of galaxies known as the Local Group. This group extends approximately 10 million light-years across and is dominated by the Milky Way and the Andromeda Galaxy, which are currently moving toward each other. The Local Group also includes the Triangulum Galaxy and dozens of smaller dwarf galaxies clustered around the two giants.
The Local Group is gravitationally drawn toward the Virgo Cluster, a massive collection of up to 2,000 galaxies centered about 54 million light-years away. The Virgo Cluster is the closest large galaxy cluster to us and is centered on the giant elliptical galaxy Messier 87. The cluster’s collective mass influences the motion of the entire Local Group, causing a bulk flow known as the Virgocentric flow.
This flow means that despite the overall expansion of the universe, our Local Group is falling toward the center of the Virgo Cluster. The cluster’s immense mass, estimated to be over a quadrillion times the mass of the Sun, dictates the movement of all surrounding groups and isolated galaxies. The Local Group and the Virgo Cluster represent the first two rungs of our immediate cosmic ladder.
Defining the Supercluster Scale
Scientists initially sought to map the universe by observing where galaxies and galaxy clusters appeared to concentrate. This effort led to the concept of a supercluster, which is a structure composed of multiple galaxy groups and clusters, spanning hundreds of millions of light-years. These structures are some of the largest concentrations of mass in the cosmos, though their low average density means they are not strongly bound by their own gravity.
The historical model for our galactic neighborhood was the Virgo Supercluster, also referred to as the Local Supercluster (VSC). This structure was initially mapped based on the observed distribution of galaxies, which appeared to form a flattened disk-like shape roughly 110 million light-years across. The VSC model placed the Virgo Cluster at its center, with the Local Group positioned near one of its outer edges.
The VSC was understood as the overarching framework containing the Local Group, the Virgo Cluster, and many other smaller groups and isolated galaxies. This model relied on positional data, treating the supercluster boundary as the region where galaxy density dropped off significantly. Before more detailed dynamic mapping was possible, the Virgo Supercluster served as the definitive label for our large-scale environment.
The Modern Cosmic Address
The definitive answer to our location shifted significantly in 2014 when astronomers published a new map of the local universe based on the motions of galaxies, not just their positions. This new approach analyzed the peculiar velocities of galaxies—the component of their movement that deviates from the smooth expansion of the universe. By mapping these velocity flows, scientists could identify “basins of attraction,” where all internal galaxy motions converge toward a common gravitational center.
This dynamic mapping led to the discovery and definition of the Laniakea Supercluster, a name meaning “immense heaven” in Hawaiian. Laniakea is a far larger and more comprehensive structure, spanning approximately 520 million light-years in diameter and containing the mass of one hundred million billion Suns. It encompasses the previously defined Virgo Supercluster, along with three other major components: the Hydra-Centaurus, Pavo-Indus, and Southern Superclusters.
The Laniakea Supercluster is defined by its central gravitational focal point, a region known as the Great Attractor. This immense concentration of mass is located about 250 million light-years away in the direction of the Norma constellation. The Great Attractor acts like the bottom of a gravitational well, drawing all the galaxies within Laniakea, including the Milky Way and the entire Virgo Supercluster, toward it at high speeds.
The former Virgo Supercluster is now understood to be merely a lobe or filament within the much grander Laniakea structure. While astronomers may still use the term Virgo Supercluster when discussing our immediate local region, our true, dynamically defined cosmic address is the Laniakea Supercluster. This vast structure represents the current boundary of the gravitationally connected volume of space that is home to our galaxy.