# What percentage of stars collide when two galaxy’s collide?
**URL:** https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993
**Category:** Factual Questions
**Created:** [February 18, 2003, 11:20pm UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993 "2003-02-18T23:20:44Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@ready29003](https://boards.straightdope.com/u/ready29003)
#### Post date: [February 18, 2003, 11:20pm UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993/1 "2003-02-18T23:20:44Z")
My understanding is that when two galaxy’s collide, typically, “very few” stars actually collide, because there is so much space inbetween stars.
Do any astronomers or physicists or probability experts out there have an approximate % range?
is it around 1-5% collide or what?
Just curious.
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### Author:  [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)
#### Post date: [February 18, 2003, 11:44pm UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993/2 "2003-02-18T23:44:12Z")
I think even less than that but the gravity effects of the stars on each other can cause a lot of havoc.
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### Author:  [@ready29003](https://boards.straightdope.com/u/ready29003)
#### Post date: [February 18, 2003, 11:45pm UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993/3 "2003-02-18T23:45:58Z")
Ok then maybe 2 questions:
What percentage of the stars would collide?
and
What percentage of the stars would be effected enough to totally mess up/destroy life on any orbiting planets?
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [February 18, 2003, 11:53pm UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993/4 "2003-02-18T23:53:22Z")
Almost no stars actually collide when galaxies pass through one another. With light-years separating individual stars, there is a huge amount of empty space in a typical galaxy, so collisions between stars are statistically insignificant. It would be impossible to estimate how many life-bearing planets would be affected, though, since we have no idea how common life is in the universe, or even in our own galaxy. Assuming, say, one star in a million has a planet which supports life, I’d say again the odds of one being affected to the point of destroying all life on it are miniscule. This would probably only happen if the planet in question were to be ejected from it’s parent star system.
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### Author:  [@Ice\_Wolf](https://boards.straightdope.com/u/Ice_Wolf)
#### Post date: [February 19, 2003, 12:03am UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993/5 "2003-02-19T00:03:38Z")
I agree with **Q.E.D.** – but the number of new star formations appearing in the [Antennae Galaxies](http://csep10.phys.utk.edu/astr162/lect/galaxies/colliding.html) certainly makes you wonder about overall radiation levels and just what might have been destroyed to create the new starstuff.
BTW, the above link has a computer simulation movie on how the present state of the Antennae Galaxies might have been come about during the collision.
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### Author:  [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)
#### Post date: [February 19, 2003, 3:42am UTC](https://boards.straightdope.com/t/what-percentage-of-stars-collide-when-two-galaxy-s-collide/155993/6 "2003-02-19T03:42:11Z")
There are more collisions that are due to infall spiralling of binaries than due to the two galaxies colliding by an inordinate number of orders of magnitude. And the number of events of spiralling binaries infall spiralling is somewhere near 1 per century per 1000 galaxies or so.