The Milky Way galaxy is in constant motion within the dynamic expanse of the universe. Our galactic home participates in multiple layers of movement, from its internal components to its grand journey across the cosmos. These motions provide insight into the universe’s dynamic nature, where gravitational forces sculpt celestial structures.
The Milky Way’s Internal Spin
Within the Milky Way, stars, gas, and dust rotate around a common center. This point is dominated by the supermassive black hole Sagittarius A (Sgr A). The collective gravitational pull of the galaxy’s total mass, including dark matter, dictates these orbits. The Sun, for instance, orbits the galactic center at about 220 kilometers per second, completing one rotation every 225 to 250 million years.
This rotation is not uniform; it exhibits differential rotation. Stars and gas closer to the galactic center orbit faster than those further out, similar to planets orbiting the Sun. This differential rotation provides evidence for dark matter. The observed speeds of stars at the galaxy’s outer edges are higher than what visible matter alone could explain, indicating a massive, unseen halo of dark matter influencing their motion.
Our Galaxy’s Journey Through the Local Group
Beyond its internal rotation, the Milky Way is also in motion as a whole, interacting gravitationally with its neighboring galaxies. Our galaxy is a member of a collection of over 80 galaxies known as the Local Group. This group spans about 10 million light-years across, with the Milky Way and the Andromeda Galaxy being its two most massive spiral members.
The Andromeda Galaxy (M31) is about 2.5 million light-years away and is the closest major galaxy to the Milky Way. These two galaxies are gravitationally bound and are approaching each other at speeds around 110 kilometers per second (about 250,000 miles per hour). This approach was once thought to inevitably lead to a head-on collision, potentially forming a new, larger elliptical galaxy dubbed “Milkomeda” in about 4.5 billion years. However, recent studies suggest there is about a 50% chance a direct collision will not occur within the next 10 billion years, with a glancing pass or delayed merger more likely. This gravitational interaction is stronger than the universe’s general expansion at this scale.
The Cosmic Dance of Superclusters
On an even larger scale, the Local Group is embedded within a vast cosmic structure called a supercluster. The Milky Way is part of the Laniakea Supercluster, a massive collection containing 100,000 to 150,000 galaxies. Discovered in 2014 by mapping galaxy motions, Laniakea means “immense heaven” in Hawaiian. This supercluster stretches over 520 million light-years and has a mass equivalent to 100 million billion Suns.
Within Laniakea, galaxies and galaxy clusters, including the Local Group, flow towards denser regions of matter. This phenomenon, known as cosmic flows, is driven by the gravitational pull of massive matter concentrations. A gravitational focal point within Laniakea is the “Great Attractor,” a region of immense gravitational influence near the Norma and Centaurus Clusters. The Great Attractor pulls vast regions of space, causing galaxies, including the Milky Way, to move towards it at speeds around 600 kilometers per second.
Despite these layers of motion and gravitational attractions, the universe does not revolve around a single, fixed center. The Big Bang was an expansion of space itself, not an explosion from a central point. On the largest observable scales, the universe appears homogeneous and isotropic, meaning it looks the same in every direction and from every point. While the Milky Way constantly moves under various gravitational forces, there is no ultimate central point around which the entire universe revolves.