# Our collision with Andromeda
**URL:** https://boards.straightdope.com/t/our-collision-with-andromeda/689358
**Category:** Factual Questions
**Created:** [May 27, 2014, 9:26am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358 "2014-05-27T09:26:38Z")
**Posts on this page:** 16
**Page:** 1
### Author:  [@panache45](https://boards.straightdope.com/u/panache45)
#### Post date: [May 27, 2014, 9:26am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/1 "2014-05-27T09:26:38Z")
As we all know, in about 4 billion years, Andromeda and the Milky Way will collide. And because of the massive distance between stars, stellar collisions will be few, if any.
Assuming that we still have descendants on Earth, and our solar system is intact, people will see a night sky that’s radically different than now. We’ll see both galaxies as they converge, and the number of local start will increase. What I’m wondering is: How long would a person have to live, to see changes in the night sky, without instrumentation? Would it look like the Milky Way stars would remain in their usual locations (over a person’s lifetime), while the Andromeda stars would pass among them?
And of course this depends whether the centers of the gallaxies collide, as opposed to an “off-center” collision. Is this something we already know?
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 27, 2014, 1:51pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/2 "2014-05-27T13:51:20Z")
First off, we don’t know that they’re going to collide. We know that we’re getting closer together, but we don’t know how much perpendicular velocity we have. For comparison, when you’re driving you often see cars in the other lane which are getting closer to you, but those cars almost never collide with you.
That said: Even if we do collide, it’s a very slow process. At no point will the skies look detectably different after a single human lifespan. At any given moment it would of course look very different from how it does now, but people then won’t remember what it looks like now.
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### Author:  [@Johanna](https://boards.straightdope.com/u/Johanna)
#### Post date: [May 27, 2014, 2:13pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/3 "2014-05-27T14:13:06Z")
The end result will be all the pretty spiral arms on both galaxies getting messed up and leaving just a big blob. Ugh.
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### Author:  [@billfish678](https://boards.straightdope.com/u/billfish678)
#### Post date: [May 27, 2014, 3:02pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/4 "2014-05-27T15:02:43Z")
Well, the local density of stars should increase.
So, if the outer part of the Andromeda galaxy passes through our area, as a rough measure the number of stars in the sky would double compared to what it typically is.
If the areas closer to the core of the Andromeda passes through our local area, the amount of stars in our sky is going to go up. Way up.
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### Author:  [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)
#### Post date: [May 27, 2014, 3:11pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/5 "2014-05-27T15:11:27Z")
So what happens? Do they just pass through each other and proceed on their merry way or will they be inextricably mingled and form a larger galaxy?
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### Author:  [@Grey](https://boards.straightdope.com/u/Grey)
#### Post date: [May 27, 2014, 3:27pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/6 "2014-05-27T15:27:02Z")
Pass through, circle back and ultimately combine.
[http://isc.astro.cornell.edu/~spoon/crashcourse/collisions.html](http://isc.astro.cornell.edu/~spoon/crashcourse/collisions.html) has an Andromeda/Milky Way simulation.
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### Author:  [@Learjeff](https://boards.straightdope.com/u/Learjeff)
#### Post date: [May 27, 2014, 3:38pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/7 "2014-05-27T15:38:07Z")
> [@Johanna](#):
>
> The end result will be all the pretty spiral arms on both galaxies getting messed up and leaving just a big blob. Ugh.
Yeah, won’t THAT suck! I’m glad I won’t be here to see it!
But imagine how lovely the night sky might be as Andromeda approaches and we can see it clearly. Just before Sol goes red-giant, that is, after which we see nothing unless we got off-planet.
> [@Grey](#):
>
> Pass through, circle back and ultimately combine.
>
> [WebHome \< IRS \< IRS](http://isc.astro.cornell.edu/~spoon/crashcourse/collisions.html) has an Andromeda/Milky Way simulation.
Love those simulations. Thanks for sharing!
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### Author:  [@danhanegan](https://boards.straightdope.com/u/danhanegan)
#### Post date: [May 28, 2014, 7:28am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/8 "2014-05-28T07:28:39Z")
Both Andromeda and the Milky Way have supermassive black holes at their centers. I read somewhere that if those should collide the result will be a quasar, releasing enough radiation to exterminate all life on pretty much every planet in either galaxy. So the changes in the night sky may be moot.
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [May 28, 2014, 8:20am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/9 "2014-05-28T08:20:08Z")
> [@danhanegan](#):
>
> Both Andromeda and the Milky Way have supermassive black holes at their centers. I read somewhere that if those should collide the result will be a quasar, releasing enough radiation to exterminate all life on pretty much every planet in either galaxy. So the changes in the night sky may be moot.
If that rids the galaxy of Klingons, it will all be worth it.
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### Author:  [@mandala](https://boards.straightdope.com/u/mandala)
#### Post date: [May 28, 2014, 9:51am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/10 "2014-05-28T09:51:10Z")
> [@danhanegan](#):
>
> Both Andromeda and the Milky Way have supermassive black holes at their centers. I read somewhere that if those should collide the result will be a quasar, releasing enough radiation to exterminate all life on pretty much every planet in either galaxy. So the changes in the night sky may be moot.
Cite? I doubt if a quasar can radiate so much that all life will be destroyed. I am pretty certain, though, that the galactic habitable zone will move outward from the new core - be it a quasar core or not. If we find ourselves flung away from the core into the new HZ, life might go on as usual. If we are flung inward, depending on the distance from the core, we might just evolve to withstand a higher radiation flux.
ETA: Besides, the Milky Way’s black hole is puny in comparison to Andromeda’s. So the fireworks may not be so pronounced.
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### Author:  [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)
#### Post date: [May 28, 2014, 9:53am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/11 "2014-05-28T09:53:49Z")
> [@Learjeff](#):
>
> But imagine how lovely the night sky might be as Andromeda approaches and we can see it clearly.
\*Would \*we be able to see it clearly? After all, we are inside the Milky Way, and you have to get well away from city lights before that’s even visible.
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### Author:  [@Ken001](https://boards.straightdope.com/u/Ken001)
#### Post date: [May 28, 2014, 10:12am UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/12 "2014-05-28T10:12:27Z")
We are living in a galactic collision right now. The small Sagittarius Dwarf Spheroidal Galaxy runs through the Milky Way on a sharp angle and is being torn apart.
One interesting theory is this small galaxy has dragged our Solar System onto a 60 degree angle relative to the plane of the Milky Way. That explains why the MW crosses our sky on an angle instead of being straight across.
Or our System could even be part of the Sagittarius Dwarf.
> **[Sagittarius Dwarf Spheroidal Galaxy](https://en.wikipedia.org/wiki/Sagittarius_Dwarf_Spheroidal_Galaxy)**
>
> The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in its main body, with the brightest of them – NGC 6715 (M54) – being known well before the discovery of the galaxy itself in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit (an or Of...
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### Author:  [@Dana\_Scully](https://boards.straightdope.com/u/Dana_Scully)
#### Post date: [May 28, 2014, 1:10pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/13 "2014-05-28T13:10:57Z")
[quote=“Chronos, post:2, topic:689358”]
First off, we don’t know that they’re going to collide. We know that we’re getting closer together, but we don’t know how much perpendicular velocity we have. For comparison, when you’re driving you often see cars in the other lane which are getting closer to you, but those cars almost never collide with you.
That said: Even if we do collide, it’s a very slow process. At no point will the skies look detectably different after a single human lifespan. At any given moment it would of course look very different from how it does now, \*\*but people then won’t remember what it looks like now.[/\*\*QUOTE] 😕
But of course they WILL–haven’t you heard of photography???
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### Author:  [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)
#### Post date: [May 28, 2014, 2:01pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/14 "2014-05-28T14:01:59Z")
> [@Dana\_Scully](#):
>
> But of course they WILL–haven’t you heard of photography???
I suspect he means that no data recording mechanism currently in existence is likely to survive for 4 billion years.
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### Author:  [@Pixel\_Dent](https://boards.straightdope.com/u/Pixel_Dent)
#### Post date: [May 28, 2014, 2:02pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/15 "2014-05-28T14:02:24Z")
> [@Dana\_Scully](#):
>
> But of course they WILL–haven’t you heard of photography???
But they won’t be able to find a USB cable to connect photography datatesseract to the sentient AI even though they’re sure they saw one here just last week when they didn’t need it.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 28, 2014, 3:41pm UTC](https://boards.straightdope.com/t/our-collision-with-andromeda/689358/16 "2014-05-28T15:41:17Z")
The OP was talking about changes visible without instrumentation, over a person’s lifespan. That rules out photography.