Andromeda On Collision Course With the Milky Way

ananyo writes "From the Nature story: 'The Andromeda galaxy will collide with the Milky Way about 4 billion years from now, astronomers announced today. Although the Sun and other stars will remain intact, the titanic tumult is likely to shove the Solar System to the outskirts of the merged galaxies. Researchers came to that conclusion after using the Hubble Space Telescope between 2002 and 2010 to painstakingly track the motion of Andromeda as it inched along the sky. Andromeda, roughly 770,000 parsecs (2.5 million light years) away, is the nearest large spiral galaxy to the Milky Way.'"

Comments

770,000 parsecs?

[Anonymous Coward]

I thought parsecs was a unit of time though? So 770,000 parsecs is about 4 billion years?

So 12 parsecs is about 20 hours?

Re:770,000 parsecs?

[Jappus]

So. A measure of both distance and time, depending on your context.

No. A parsec is "a distance corresponding to a parallax of one second". But here, "second" does not refer to the unit of time "second" but to an "arc-second", a specific angular value. If you have a circle, and you divide it into 360 parts, a single slice covers an angle of exactly one "degree" (do note that this in turn also does not refer to temperature). If you divide that slice into 60 parts, each slice covers an angle of 1 arc-minute. If you divide such a slice into another 60 parts, you get an angle that covers 1 arc-second.

http://en.wikipedia.org/wiki/Arcsecond#Symbols_and_abbreviations

As for what a parallax is, please read the link provided by the grandparent.

But even if you had used a unit of time to define the parsec -- like in the light-year -- what you actually define is a pure length. Do note that you can define a light-year as both "the distance light crosses in an absolute vacuum in one solar year" or "9.4605284 x 10^15 meters". See how the latter does not include any reference to time? You could even express the light-year as the distance you can drive an object of a certain mass and shape when you accelerate it with a certain energy through a perfectly uniform medium of a certain density (thus slowing down the object eventually to a standstill).

You can define a length with the help of a unit of time, but you don't need to. That is also why the 1 astronomical unit distance used in the parsec is also not a unit of time; as the fact that it derives from the rotation of the earth around the sun is unimportant as long as the ultimately defined value remains a pure time.

Re:770,000 parsecs?

[witherstaff]

It was explained in a later SW expanded universe book that Kessle is surrounded by black holes so the shortest route is also the most dangerous. All things considered I thought it was a pretty good explanation.

Re:770,000 parsecs?

[Anonymous Coward]

The WHOOSH is strong with this one.

Re:770,000 parsecs?

[Ol Biscuitbarrel]

A bigger question is where will the /. editors find room to store all of these geek cards?

oh noews!

[j-stroy]

can't we launch a mission to deflect it ? !

Re:oh noews!

[Anonymous Coward]

Eh, the Sun itself only has about 4.5 billion years left in it...So Andromeda slamming into us might be a welcome change by then.

Re:oh noews!

[Anonymous Coward]

Nope, this event is clearly unavoidable. There is no way we have enough time to relocate or divert it.

What if we used a crack team of roughnecks?

Don't Panic

[stms]

Stop Panicking!!! This is no time to panic... Though if you do panic try to hold on to that feeling because it is the proper response to being told that your galaxy is on a collision course with another galaxy.

Re:And this is news how?

[Anonymous Coward]

This may not be news to you, but I'm thankful to know so I could cancel my tickets to The Book Of Mormon while they're still refundable.

Watch video of simulation of this collision

[gupg]

NVIDIA showed a simulation of this collision running on their latest Tesla GPGPU based on the "Kepler" architecture

Starts at around 1:00 on this video with a great explanation of the collision itself.
http://www.youtube.com/watch?v=aByz-mxOXJM&feature=relmfu

Sumit
(NVIDIA employee)

Re:Watch video of simulation of this collision

[Anonymous Coward]

Andromeda-Milky Way collision starts at 2:54, before that is a recap of the Fermi architecture.

Re:Watch video of simulation of this collision

[flimflammer]

You can right click a video at any time and select "Copy link at current time"

When you do that, which he likely did, it uses seconds.

don't panic, it's just the end of the world

[FatLittleMonkey]

It's been known for a long time that Andromeda had a velocity towards the Milky Way (easily measured by its blue-shift), but no one could tell what its lateral velocity was, therefore whether it was going to actually collide or whether it was in an eccentric orbit. Actually measuring such a tiny side-shift, against more distant galaxies, of a source which is not actually a single defined object, where every part of it is in separate motion, in just 8 years, is pretty fucking impressive.

Re:don't panic, it's just the end of the world

[Anonymous Coward]

In real-time?

Did the computation really take 4 billion years?

Re:don't panic, it's just the end of the world

[Hognoxious]

Yep, it was written in Java.

The first billion went while they were waiting for Eclipse to open.

Re:And this is news how?

[Jeremiah Cornelius]

Well, just in time to warn our Great^12 Grandchildren.

Maybe we could embed the message in some giant, black humming monolith, or something...

Oh no! Not the Galaxy!

[Cyberllama]

That's where I keep all my stuff!

Re:And this is news how?

[Extremus]

There is a better article from NASA:

http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html

Re:Red Giant Sol?

[toruonu]

If after 3-4 billion years we're still stuck on this rock we deserve to burn up...

Imagine

[allcoolnameswheretak]

Imagine how awesome the sky would look once Andromeda is near enough to dominate the view.

Imagine how awesome the sky would look with two galaxies, one of them much larger than our own, sprawling around it.

Imagine how such a view might affect the belief systems and cultures of all the advanced life forms that might be able to perceive it.

Hopefully, I will be there, billions of years in the future, and be able to experience it.

Re:Imagine

[NormalVisual]

Imagine how awesome the sky would look once Andromeda is near enough to dominate the view.

Andromeda is already that big in the sky - it's over four times the size of the full Moon as seen from Earth right now. It's *extremely* diffuse though (and will continue to get more diffuse as it gets closer), so it's quite dim and generally isn't visible except from relatively dark sites.

Not an unexpected result

[Michael Woodhams]

Isolated clusters of galaxies (such as the local group) are expected to have low total angular momentum (basically because the initial condition has low angular momentum, and in the absence of large mass anisotropy nearby, there is nothing to change this.) The mass of the local group is dominated by Andromeda and us, and hence so is the angular momentum. If the us/Andromeda pair has low angular momentum about their centre of mass (and given the pair is gravitationally bound), they will both pass close to that centre of mass - i.e., they will collide.

Of course, having an actual measurment is much more satisfying than having a theory.

Also - although they can be spectacular from outside, galactic collisions aren't expected to have bad results for life living on their planets. The biggest effect is that colliding dust clouds trigger a burst of star formation, so the night sky will be pretty.

It has been a few decades since I studied this, so I hope this is all accurate.

Re:And this is news how?

[buchner.johannes]

The point is, people knew Andromeda was coming towards us at x km/s. But that is only the tangential component (towards us). It might have also flown at x km/s to the right at the same time, going 45 past us.

Now people observed the speed of Andromeda on the sky (a painstaking measurement). As it turns out, Andromeda will not miss our Galaxy. That was kind of expected from the masses of galaxies in our local group -- Andromeda and the Milky Way have the same mass and are much larger than all the others, so they should attract each other most.