# Galaxies colliding
**URL:** https://boards.straightdope.com/t/galaxies-colliding/438963
**Category:** Factual Questions
**Created:** [February 24, 2008, 4:57pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963 "2008-02-24T16:57:42Z")
**Posts on this page:** 12
**Page:** 1
### Author:  [@KlondikeGeoff](https://boards.straightdope.com/u/KlondikeGeoff)
#### Post date: [February 24, 2008, 4:57pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/1 "2008-02-24T16:57:42Z")
Beautiful pictureof colliding galaxies [here](http://antwrp.gsfc.nasa.gov/apod/astropix.html).
This will happen to us eventually when the Andromeda Galaxy hits us. Just something else to worry about. đ
Actually, what does happen to the stars, and any planets, when this happens?
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [February 24, 2008, 5:04pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/2 "2008-02-24T17:04:13Z")
[QUOTE=KlondikeGeoff]
This will happen to us eventually when the Andromeda Galaxy hits us.
[/QUOTE]
This is far from a certainty. We can readily measure the relative motion of Andromeda towards us by observing the red/blue shift, but we lack the sensitivity to accurately measure the lateral motion component in the relative.y short time weâve been observing it. The likelihood is that Andromeda is simply on its way in to swing around us, to complete yet another mutual orbit.
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### Author:  [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)
#### Post date: [February 24, 2008, 5:55pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/3 "2008-02-24T17:55:23Z")
Very little will happen to the stars and planets when and if the Milky Way and the Andromeda Galaxies collide:
> **[AndromedaâMilky Way collision](https://en.wikipedia.org/wiki/Andromeda-Milky_Way_collision)**
>
> The AndromedaâMilky Way collision is a galactic collision predicted to occur in about 4.5 billion years between the two largest galaxies in the Local Groupâthe Milky Way (which contains the Solar System and Earth) and the Andromeda Galaxy. The stars involved are sufficiently far apart that it is improbable that any of them will individually collide, though some stars will be ejected.\[self-published source\]
> The Andromeda Galaxy is approaching the Milky Way at about 300 km/s (186.411 miles per sec...
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### Author:  [@jjimm](https://boards.straightdope.com/u/jjimm)
#### Post date: [February 24, 2008, 6:00pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/4 "2008-02-24T18:00:14Z")
The vastness of the distances involved in that picture is giving me a âmomentâ. It makes me feel weird and not a little insignificant.
Am I right in guessing that actual star-to-star collisions would be quite unlikely, despite the galaxiesâ interaction? Anyone ever seen such a thing through a telescope.
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [February 24, 2008, 6:26pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/5 "2008-02-24T18:26:43Z")
AFAIK, individual stars almost never collide - they are simply too far apart. The collision also takes place over millions of years, so nobody will ever âseeâ it happening. Hereâs a website that will let you smack your own galaxies together:[http://burro.astr.cwru.edu/JavaLab/GalCrashWeb/main.html](http://burro.astr.cwru.edu/JavaLab/GalCrashWeb/main.html)
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [February 24, 2008, 6:34pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/6 "2008-02-24T18:34:30Z")
[QUOTE=beowulff]
AFAIK, individual stars almost never collide - they are simply too far apart.
[/QUOTE]
Impacts do occur within globular clusters, but the stellar density inside a cluster is huge:
[Two Stars Collide; A New Star Is Born](http://query.nytimes.com/gst/fullpage.html?res=9C05E4DB143EF930A25755C0A9669C8B63)
> [@](#):
>
> Within the star groups, known as globular clusters, the clouds of gas and dust that give birth to stars had been exhausted billions of years ago, which raised the question: where did these young blue stars come from?
>
> At first, some astronomers speculated that these ââblue stragglerââ stars had somehow conserved their fuel, but with the help of the Hubble Space Telescope, astronomers have concluded that a blue straggler star is actually two small, old stars that combined to form a rejuvenated blue star.
>
> Collisions are more frequent in globular clusters, because there are many more stars. In the outer region of the galaxy where our solar system lies, the density of stars is about one per 10 cubic light-years. In a globular cluster, there may be several hundred thousand stars in that same space.
>
> Dr. Sharaâs estimate of several hundred collisions per hour may seem frequent, but with 100 billion galaxies in the observable universe and each galaxy containing, on average, 30 globular clusters, most of the collisions occur far away and out of view.
>
> According to his calculations, over the 10 billion-year lifetime of the Milky Way, Earthâs home galaxy, there have been at least one million collisions within globular clusters â or about one every 10,000 years.
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### Author:  [@Napier](https://boards.straightdope.com/u/Napier)
#### Post date: [February 24, 2008, 7:23pm UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/7 "2008-02-24T19:23:38Z")
\>Actually, what does happen to the stars, and any planets, when this happens?
Nothing happens to them. The way you know that you are in a galactic collision is that astronomers studying star motion figure out one must have been happening. An intellegent civilization that never cared about astronomy would never know.
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### Author:  [@MikeS](https://boards.straightdope.com/u/MikeS)
#### Post date: [February 25, 2008, 12:12am UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/8 "2008-02-25T00:12:06Z")
[QUOTE=jjimm]
Am I right in guessing that actual star-to-star collisions would be quite unlikely, despite the galaxiesâ interaction?
[/QUOTE]
Iâve heard estimates (but canât find a cite right now, sorry) that the number of actual star-to-star collisions one would expect if Andromeda actually collided with our Galaxy is around a few dozen. Considering how many stars there are in each Galaxy, it would be an incredibly rare phenomenon.
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### Author:  [@shelbo](https://boards.straightdope.com/u/shelbo)
#### Post date: [February 25, 2008, 12:43am UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/9 "2008-02-25T00:43:29Z")
[QUOTE=jjimm]
The vastness of the distances involved in that picture is giving me a âmomentâ. It makes me feel weird and not a little insignificant.
[/QUOTE]
Me too. Those deep field Hubble shots scare the crap out of me.
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### Author:  [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)
#### Post date: [February 25, 2008, 12:43am UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/10 "2008-02-25T00:43:46Z")
Iâd guess that comets and such in Oort clouds around many stars would have their orbits disturbed, leading to an increased chance of cometary impacts on planets. Wouldnât affect the planets themselves much, but any life on them would be.
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### Author:  [@asterion](https://boards.straightdope.com/u/asterion)
#### Post date: [February 25, 2008, 1:31am UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/11 "2008-02-25T01:31:01Z")
How about near-misses, close enough to change or completely throw a planet out of its current orbit? Wouldnât the odds be much higher than an actual star-star collision?
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [February 25, 2008, 1:45am UTC](https://boards.straightdope.com/t/galaxies-colliding/438963/12 "2008-02-25T01:45:44Z")
[QUOTE=asterion]
How about near-misses, close enough to change or completely throw a planet out of its current orbit?
[/QUOTE]
Ignoring gravitational effects, the superposition of two galaxies will result in a doubling of stellar density. So in earthâs neighborhood weâd have 2 stars per 10 cubic light years rather than one star. The average distance between those stars would be 2.15 light years. Thatâs a _lot_ of room for noninteracting cometary haloes.