1. How Does a Galaxy Collision Occur?
Galaxies are enormous systems composed of billions of stars, as well as gas, dust, and dark matter.
When two galaxies approach each other, the gravitational interaction between them becomes increasingly stronger. As galaxies begin to alter each other's structure, the motions of stars and gas clouds are also affected.
This process does not have to occur as a single collision. Galaxies can pass through each other, then move apart again, and approach each other once more due to their mutual gravity.
Eventually, the two galaxies may merge to form a larger galaxy.
2. Why Don’t Stars Collide With Each Other?
Although there are a huge number of stars within a galaxy, the distances between stars are also extremely large.
Therefore, as two galaxies pass through each other, the direct collision of stars is a very unlikely event.
The main factor in galaxy collisions is not the direct force exerted by stars on each other, but the alteration of the gravitational fields created by the galaxies as a whole.
For this reason, a star system can be significantly affected by a galaxy collision even without another star colliding with it.
3. How Does the Orbit of a Star System Change?
A star moves in a specific orbit around the center of its galaxy.
When another galaxy approaches, this regular motion can be disrupted.
The gravity of the approaching galaxy can change the star’s speed and direction of motion. As a result, the star may shift to a different path from its previous orbit.
Some stars may be drawn toward the center of the galaxy, while others may be swept into more outer regions.
In some cases, stars may be ejected from the galaxy’s gravitational field into intergalactic space.
4. Do Planetary Systems Themselves Break Apart?
The planets around a star are primarily bound by the gravity of their own star.
During a galaxy collision, it is generally not expected that the planets around a star will be directly pulled away by another star.
This is because the gravitational bond between a star and its planets is much stronger than the large-scale motions of the galaxy.
However, if a star passes very close to another star or if its galactic orbit changes significantly, the long-term dynamic structure of the planetary system may be affected.
Therefore, a galaxy collision is not an event that automatically destroys entire planetary systems.
5. The Role of Interstellar Distances
The large distances between stars within galaxies protect most star systems from direct physical collisions during galaxy mergers.
For example, as two large galaxies merge, the orbits of billions of stars may change, but most of these stars will transition to new galactic orbits without physically contacting another star.
This shows why galaxy collisions should be considered primarily as a gravitational restructuring process.
6. Compression of Gas and Dust Clouds
Unlike stars, gas and dust clouds can be much more strongly affected during galaxy collisions.
When gas-rich regions of two galaxies meet, gas clouds can interact and become compressed.
When the density of compressed gas increases, the formation of new stars can become easier.
Therefore, galaxy mergers can lead to much higher star formation rates than normal in some regions.
7. Formation of New Stars
The intense star-forming regions seen in colliding galaxies are closely related to the compressed gas clouds.
When gas becomes dense enough, it can begin to collapse under its own gravity.
This collapse can result in the formation of new star clusters.
These new stars are born in the dense gas environment created by the collision, unlike the stars that existed in the galaxies before the collision.
8. Changes in the Velocities of Stars
During the merging of galaxies, not only the positions but also the velocities of stars can change.
When the mass distribution of the galaxy a star is in changes, the gravitational field that determines the star’s motion also changes.
This can cause stars to move into more elliptical, wider, or differently oriented orbits.
Once the merger is complete, the motions of the stars may become quite different from the regular orbital structure in the previous galaxies.
9. Effects on Systems Like the Solar System
When evaluating the effect of a galaxy collision on a star system, the location of the star is important.
A star system located far from the center of the galaxy will not be affected by the same conditions as a system near dense star and gas regions.
For example, the galactic orbit of the star system may change, and the system may be moved to a region with a different stellar density.
This can alter the likelihood of close stellar encounters or environmental gravitational effects in the future.
However, a galaxy collision alone does not mean that planets will be stripped from their stars.
10. Changes in Galaxy Centers
Galaxy mergers can cause major changes, especially in the centers of galaxies.
The supermassive black holes at the centers of galaxies can also move toward each other.
During the merger, the compression of gas in the centers can increase the amount of matter around the black holes.
This can lead to the emergence of active galactic nuclei or an increase in existing activity in some galaxy mergers.
Star systems near the center of the galaxy may encounter different conditions compared to those in the outer regions due to the dense environment where these changes occur.
11. Ejection of Stars Outside the Galaxy
During a galaxy merger, some stars can reach very high speeds.
As a result of gravitational interactions, the energy gained by a star can reach a level sufficient for it to escape the galaxy’s gravitational field.
In this case, the star leaves the galaxy and begins to move through intergalactic space.
If such a star has planets orbiting it, the planetary system can also be carried outside the galaxy along with the star.
These kinds of systems show that galaxy mergers can change not only the orbits of star systems but also the galactic environment in which they reside.
12. The Milky Way and Andromeda Example
The Andromeda Galaxy (M31) and the Milky Way are moving toward each other.
In the future, these two galaxies are expected to interact and eventually merge.
When this process occurs, direct collisions between stars are not expected. Instead, the gravitational fields of both galaxies will alter the orbits of the stars.
The region of stars that includes the Solar System may be relocated to a different position in the newly formed galaxy.
Therefore, for the Solar System, a galaxy merger primarily means a change in galactic orbit; it does not mean that the Sun or the planets will directly collide with another star.
13. The Outcome of a Galaxy Merger
At the end of a galaxy collision, the structure of the two separate galaxies can be completely transformed.
The distinct disk structures of spiral galaxies may be disrupted, and after the merger, a larger galaxy with a different structure may form.
As stars are scattered into different orbits within the new galaxy, the regular structure of the previous galaxies may be lost.
This process can continue for millions or even billions of years.
14. Conclusion and Evaluation
The greatest physical changes in colliding galaxies arise not from direct collisions between stars, but from the alteration of the galaxies’ gravitational fields.
The galactic orbits of stars may change, some stars may be ejected from the galaxy, and the compression of gas clouds can accelerate the formation of new stars. Planetary systems, however, remain mostly intact because they are strongly bound to their stars.
A galaxy collision is not an event that directly destroys the planets of a star system, but rather a massive gravitational process that changes the galactic environment in which the star moves and its long-term orbit.