The Milky Way is a dynamic system constantly moving through space, though it appears stable. The universe operates on principles of mutual gravitational attraction, meaning no object, from a planet to a galaxy, is truly stationary. This motion is hierarchical, with our galaxy participating in several gravitational dances at different scales. Understanding what the Milky Way “revolves around” requires looking outward to the surrounding cosmic structures that exert their powerful gravitational influence.
The Milky Way’s Local Neighborhood
The Milky Way is gravitationally bound to a small cluster of galaxies known as the Local Group. This group is a collection of over 100 galaxies, mostly dwarf galaxies, but dominated by two massive spiral galaxies: the Milky Way and the Andromeda Galaxy (M31). The gravitational interaction between these two giants dictates the overall motion of the Local Group. The system does not revolve around a central star or a single massive galaxy, but rather orbits an invisible point in space called the barycenter.
This barycenter represents the common center of mass for the entire Local Group, located approximately 1.5 million light-years from the Milky Way’s center. The third largest member, the Triangulum Galaxy (M33), also plays a role, orbiting either Andromeda or the shared barycenter. All members of the Local Group are gravitationally bound to one another, moving together through the larger universe.
Dynamic Motion Within the Local Group
The most dramatic motion within this galactic neighborhood is the inevitable trajectory between the Milky Way and Andromeda. The Andromeda Galaxy is currently rushing toward us at a velocity of approximately 110 kilometers per second. This approach is driven by the mutual gravitational pull of their immense masses.
Current measurements confirm that the two galaxies are on a collision course, a future event often nicknamed “Milkomeda.” The first contact is projected to begin in roughly 4 to 4.5 billion years. Despite the term “collision,” the vast distances between stars mean that individual stars are highly unlikely to physically strike one another. Instead, gravitational forces will distort the spiral shapes, causing a complex cosmic rearrangement that will eventually merge the two into a single, much larger elliptical galaxy.
The Pull of Larger Cosmic Structures
While the Milky Way is bound to the Local Group, the entire group is being pulled toward much larger concentrations of mass. The Local Group resides on the outskirts of the Laniakea Supercluster, Hawaiian for “immense heaven.” This supercluster is a massive network of galaxy groups and clusters, encompassing approximately 100,000 galaxies and spanning over 500 million light-years. Within Laniakea, the flow of galaxies is directed inward toward a gravitational low point.
The gravitational focal point driving the motion of all galaxies within Laniakea is a region called the Great Attractor. This immense, diffuse concentration of matter dominates the movement of our supercluster. The Local Group is moving toward the Great Attractor, located near the Norma and Centaurus galaxy clusters, at a speed of hundreds of kilometers per second. This phenomenon is a non-orbital flow, where the entire supercluster is streaming toward this one area of immense density.
Observing the Great Attractor directly in visible light is difficult because it lies behind the “Zone of Avoidance,” the plane of our own Milky Way, which obscures the view with gas and dust. However, its influence is clearly inferred from the peculiar velocities of thousands of galaxies. The Laniakea Supercluster, including the Great Attractor, appears to be moving toward an even larger concentration of mass. This larger structure is the Shapley Concentration, which is the most massive known supercluster in our cosmic vicinity.