The universe is filled with enormous galaxies moving under the influence of gravity. When these cosmic giants encounter one another, their interaction can reshape their structures, disturb clouds of gas and trigger new episodes of star formation. Despite the dramatic appearance of these encounters, direct collisions between individual stars are extremely rare.

A Cosmic Encounter That Changes Entire Galaxies

Galaxies contain vast collections of stars, planets, gas, dust and dark matter. Over millions or billions of years, their gravitational interactions can bring them into close contact, producing some of the most spectacular structures observed by astronomers.

As two galaxies approach, their gravitational fields begin to influence each other’s shapes. Spiral arms may stretch into long streams, clouds of gas can become compressed, and stars can be pulled into new orbits. Some encounters produce enormous tidal tails that extend far beyond the galaxies’ original boundaries.

These transformations can continue for hundreds of millions of years, making galaxy mergers among the most dramatic long-term processes in cosmic evolution.

Why Stars Usually Do Not Crash Into One Another

The term galaxy collision can create the impression that stars smash together throughout the encounter. In reality, the distances separating stars are enormous compared with their individual sizes.

Even when two galaxies pass through one another, most stars travel along altered trajectories without making direct physical contact. Gravity, rather than star-to-star impact, drives most of the transformation.

However, the gas and dust within galaxies can interact much more directly. Gas clouds may collide, compress and heat up, creating conditions that sometimes encourage the formation of new stars.

This difference explains why a galactic collision can dramatically change a galaxy without producing widespread stellar collisions.

Can Galactic Collisions Create New Stars?

Yes. Some galaxy encounters trigger periods of intense star formation, often called starbursts. Gravitational disturbances can push gas into denser regions, allowing parts of molecular clouds to collapse under their own gravity.

The resulting stars may form in clusters and illuminate previously quiet regions of a galaxy.

However, not every merger produces a powerful starburst. The outcome depends on factors such as the galaxies’ gas content, relative masses, encounter geometry and the efficiency of processes that heat or disperse gas.

Over time, some mergers can also exhaust or expel much of the gas needed for future star formation, leaving behind a galaxy with a different structure and a reduced rate of stellar birth.

The Milky Way and Andromeda: A Future Galactic Encounter

Our own Milky Way and the neighbouring Andromeda Galaxy are moving toward one another under their mutual gravitational attraction. For decades, astronomers have studied the possibility that they will eventually merge.

Newer simulations, however, show that the exact outcome is less certain than once assumed. Research published in 2025 indicated that a merger within the next five billion years is not inevitable, with the result depending on the gravitational influence of other nearby galaxies and uncertainties in their motions.

If a merger eventually occurs, the two galaxies’ spiral structures could be substantially altered. Their stars would mostly avoid direct collisions, although their orbits could change significantly.

The Solar System’s precise future location and surroundings would depend on the details of the encounter. There is no reason to assume that Earth itself would be struck by another star simply because the galaxies merge.

Why Galaxy Mergers Matter to Astronomy

Studying galactic encounters helps scientists understand how galaxies develop over cosmic time. Observations allow researchers to investigate how gravity redistributes matter, how stars form and how black holes and gas respond to changing galactic environments.

Astronomers use powerful telescopes to examine interacting galaxies at different distances, observing stages of the process that may take millions or billions of years to unfold. By comparing these observations with computer simulations, researchers can reconstruct possible histories and test theories of galaxy evolution.

Cosmic Destruction Can Lead to Transformation

Galaxy mergers demonstrate that the universe is constantly changing. Structures that appear stable over a human lifetime can undergo profound transformations across astronomical timescales.

A galactic encounter may stretch spiral arms, rearrange stellar populations and generate new generations of stars. In other cases, it may gradually turn two spiral galaxies into a single galaxy with a different shape.

What appears to be destruction on a cosmic scale can therefore become a process of transformation, offering scientists a deeper understanding of how the universe’s largest structures evolve.