Unlike galaxies, stars rarely collide with each other. The reason for this problem depends on the two measurement scales that we mention.
How likely are space objects to collide? Everything depends on two numbers: size and distance. Using these two simple numbers, we can show why stars, unlike galaxies, never collide with each other.
Why don’t stars collide
Space collisions are one of the popular subjects of the science fiction genre. Over the past few decades, we’ve seen and heard about these encounters in books, movies, TV shows, and video games. For example, the chase of spaceships in the space filled with asteroids in the movie “Empire Strikes” is one such example. The heroes of the film must find their way through the huge space rocks that collide with each other while escaping from the enemy fighters.
However, in reality, how likely are objects to collide in the darkness of deep space? To answer this question, we need to focus on two familiar types of celestial: stars and galaxies.
Rewriting the stars

Advanced Camera for Surveys (ACS), the newest camera on NASA/ESA Hubble Space Telescope, has captured a spectacular pair of galaxies engaged in a celestial dance of cat and mouse or, in this case, mouse and mouse. Located 300 million light-years away in the constellation Coma Berenices, the colliding galaxies have been nicknamed “The Mice” because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy
First, we must acknowledge an astronomical truth: stars rarely collide, But galaxies often collide so this collision is the key to their evolution; But what is the difference between the fate of stars and galaxies? There is an interesting astronomical answer, But first, let’s focus on a powerful type of simple physical reasoning.
One of the first points in this review is to provide an approximate solution to the problem before performing complex calculations. In this way, you should think about some fundamental characteristics of the review subjects and their characteristics. Regarding the question of the collision of objects in space, two important features should be considered:
- 1. How big are the objects?
- 2. How much space is there between them?
We do not need to consider factors such as temperature, density, magnetic fields or even the wavelength of the emitted light. None of these matters at first glance. All we need is size and distance.
Stars size and distance from each other
Let’s start with the stars. The diameter of the Sun is approximately one billion meters. Now that we know how big the stars are, what would be the average distance between them? Proxima Centauri is the closest star to the Sun, which is four light years away. This distance means more than ten million billion meters or 10 to the power of 16 meters.
If you divide the radius of the sun by the distance between it and Proxima Centauri, you get the number 0.0000001, so why stars do not collide with each other? The stars are much smaller than the distance between them. They don’t find each other wanting to meet at all.
However, galaxies tell a different story. Galaxies have a wider array of stars, But let’s take the Milky Way as a guide. The diameter of the Milky Way is approximately 100,000 light-years (10 to the power of 5 light years). But how far is it from its nearest galaxy? Andromeda is the closest galaxy to the Milky Way at a distance of approximately 2.5 million light years or 10 to the power of 6 light years.
Now do the same calculations for stars and divide the size of the mass by the distance between it and its neighbouring mass. For stars, the number 0.0000001 was obtained, which is a tiny number. When we do these calculations for galaxies, we arrive at a figure of 0.1.
Unlike stars, galaxies size and distance ratio is not that small. It can be said that two galaxies can find each other and collide more easily and this will happen to the Milky Way and Andromeda in the next 5 billion years. Galaxies often collide with each other and the consequences of such collisions can be impressive; it not only changes the shape of the galaxy; but It also affects its ability to form new stars.
Other galactic assessments
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It should be noted that there is a vital role in this story. Stars born near each other as binary or triple systems may merge over time. Also, in the densest parts of the galaxy, stars gradually approach each other and stellar collisions may occur.
We must say that your point of view is important. In the next step, the initial velocities should be considered; Because it shows how fast objects move in distances. Also, force fields such as gravity must be considered in the interaction of objects. In galactic collisions, a single star feels the gravitational effect of all celestials, including stars within the galaxy.
However, on average, stars never collide; But galaxy collisions are common, and as we said, we need two numbers to know the answer: size and distance.