Andromeda On Collision Course With the Milky Way 217
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.'"
And this is news how? (Score:1, Informative)
Oh, you got me to click on the story. Got me again, you ad-whoring editors!
don't panic, it's just the end of the world (Score:5, Informative)
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:Watch video of simulation of this collision (Score:3, Informative)
Andromeda-Milky Way collision starts at 2:54, before that is a recap of the Fermi architecture.
Re:And this is news how? (Score:5, Informative)
There is a better article from NASA:
http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html [nasa.gov]
Re:And this is news how? (Score:1, Informative)
It's news because we didn't know if Andromeda and the Milky Way were orbiting each other or on a collision course without the transverse velocity of Andromeda. Now we know. Well, we think we know. It's going to be a little while until we can actually observe the outcome.
No, it's not news. I heard it 10-15 years ago. (Could be more, hard to keep track.)
Re:770,000 parsecs? (Score:5, Informative)
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 [wikipedia.org]
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:Watch video of simulation of this collision (Score:4, Informative)
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.
Re:770,000 parsecs? (Score:4, Informative)
Re:And this is news how? (Score:5, Informative)
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.
Re:Imagine (Score:4, Informative)
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.