The two largest galaxies in our Local Group, the Milky Way and the Andromeda galaxy, are presently hurtling toward one another. This inevitable cosmic engagement is driven by the mutual gravitational pull between the two massive structures. The collision will not be a sudden catastrophic event but a slow-motion restructuring involving hundreds of billions of stars from the Milky Way and over a trillion stars from Andromeda. This event will reshape our local universe, creating a new stellar landscape over billions of years.
The Timeline of Approach and First Contact
The Andromeda galaxy is currently approaching the Milky Way at a speed of approximately 110 kilometers per second. This velocity is determined by measuring the blueshift in Andromeda’s light, which indicates motion directly toward us. For a long time, Andromeda’s tangential motion was unknown, leaving open the possibility that the two galaxies might simply graze past one another.
However, observations using the Hubble Space Telescope confirmed in 2012 that the tangential velocity is small enough to ensure a direct collision is certain. The initial gravitational interaction, where tidal forces begin to distort the shapes of both galaxies, is projected to begin in about 3.75 billion years. The first major close pass is predicted to occur around 4.5 billion years from now.
The collision is not a single impact but a long, drawn-out gravitational dance. After the initial pass, the two galaxies will separate and then be pulled back together by gravity for subsequent passes. The full merger will take several billion years to complete, with the final stable structure forming roughly 7 billion years from now.
Star Interaction During the Galactic Merger
Despite the sheer number of stars involved—over a trillion in the combined system—direct stellar collisions are incredibly improbable. The space between stars in a galaxy is vast. The galaxies will largely pass through one another, with individual stars remaining intact and simply being redistributed into new orbits by the powerful, changing gravitational field.
The most dramatic physical interaction will occur between the immense clouds of gas and dust that permeate both galaxies. When these diffuse clouds slam into each other at high speeds, they compress violently. This compression triggers intense, runaway star formation, leading to a “starburst” phase that will light up the merging system with countless new, hot, blue stars.
The primary effect of the merger is a large-scale gravitational restructuring of the stellar orbits. The orderly, rotating disks of both spiral galaxies will be torn apart and scrambled by the tidal forces of the encounter. This process, called “violent relaxation,” will transform the organized, flat structures of the Milky Way and Andromeda into a chaotic, three-dimensional arrangement of stellar paths.
The Birth of the New Galaxy
The ultimate outcome of this galactic merger will be the formation of a single, massive galaxy. The resulting structure is predicted to be a giant elliptical galaxy, characterized by a smooth, featureless appearance without the distinct spiral arms of its predecessors. This morphological transformation is a common result of major galaxy mergers, where the rotational motion of stars is converted into random orbits.
The new galaxy has already been given the informal names Milkomeda or Milkdromeda by astronomers. The merger will also bring the two central supermassive black holes into close proximity. The Milky Way’s Sagittarius A and Andromeda’s much more massive central black hole will spiral toward one another, forming a binary system.
This black hole pair will eventually coalesce, merging to create an even larger, more powerful supermassive black hole at the core of Milkdromeda. As they spiral inward, they will emit powerful gravitational waves, and the gas drawn into the combined black hole could briefly turn the nucleus into an extremely luminous, active galactic core. The settling into the new elliptical structure is expected to take over two billion years after the initial close pass.
The Fate of Our Solar System and Earth
The Earth and the rest of the Solar System will physically survive the galactic merger, as the probability of a direct stellar collision with the Sun or any planet is extremely low. However, the powerful, fluctuating gravitational forces of the colliding galaxies will certainly affect the Sun’s orbit. The Solar System is highly likely to be gravitationally ejected from its current position in the Milky Way’s disk.
Simulations suggest a high probability that the Solar System will be relocated much farther from the galactic center, potentially ending up in the extended halo of the new elliptical galaxy. There is even a small, approximately 12 percent chance, that the Solar System could be entirely ejected from Milkdromeda into intergalactic space. Such an ejection would not immediately harm the Sun or the planets.
Regardless of the galactic collision, Earth will already be uninhabitable by the time the merger begins. The Sun is naturally increasing in luminosity as it ages, and in about 1 to 1.5 billion years, its increasing heat will cause a runaway greenhouse effect, boiling away Earth’s oceans. By the time the first close pass occurs in 4.5 billion years, the Sun will be expanding into a red giant star, making Earth’s survival purely academic.