Find out here: howfarawayisandromeda.neocities.org
The Andromeda Galaxy (aka Messier 31) has been estimated to be somewhere around 2.5 million lightyears away from us here on Earth. Due to its relative size and proximity to the Milky Way, Andromeda can actually be observed with the naked eye in the night sky.
Also because of its blueshift we can determine that it is approaching our galaxy at around 110 kilometers per second.
That means that in around 4 to 6 billion years (or 4 to 6 gigayears, if you want to be cool), Andromeda and the Milky Way will collide (or rather merge) with each other, forming a giant elliptical galaxy often referred to as Milkdromeda.
This is just something I did for fun. Is there actually a name for something like this? Like these sort of answering-exactly-one-specific-question-and-nothing-else sites?
Now, while I took a lot of effort and care in researching this, I would in no way say that this site a reliable countdown to the Milkdromeda merger. The problem is there are just too many variables and uncertainties to take into account. I'll just try and talk about a few of them here.
First of all, as the current distance to Andromeda I took an average of some of the more recent measurements which range from around 2.51 to 2.57 × 10^6 ly. As a starting point of my countdown I took May of 2012 (which in reality does not really matter much, with hunderts of thousands of lightyears possible deviation in distance it hardly matters wheater I start in 2012 or 1970). So there's already quite a big margin for error there.
As for the speed, that's the part I'm most unsure about. 110 km/s was the most common figure I could find, based on doppler effect measurements. I believe The M31 Velocity Vector. III. also uses a figure between 100 and 150 km/s in their simulation model. Of course this is the speed relative to the Milky Way and not relative to our sun / solar system which is also moving around in the Milky Way! If we take the speed between our sun and Andromeda I believe it would be around 300 km/s currently. And later as our sun would circle further around the galactic center, our systems relative approach to Andromeda would persistently change.
On top of that, on a much larger timescale, you would also have to take into account that the galaxies would speed up as they approach their orbital pericenter and then slow down again at the apocenters, bouncing back and forth and slowly getting closer each time (Again, the paper mentioned above shows this quite nicely in graph-form, Figure 4).
And I'm not sure on it, but I would bet that over time the accelerating expansion of the universe would also factor into the approach.
And all that aside, when does Milkdromeda actually form, or when does Andromeda collide with us? Is it in 4 billion years when the first pericenter occurs at around 31 kiloparsecs? Or in 7 billion years when the elliptical galaxy is fully formed? When does Andromeda stop being a seperate thing distant from the Milky Way and both start being part of each other?
As you can see, there are a lot of things that make calculating this really complicated. And since I don't want and can't do a n-body simulation in your browser I feel like this code is enough for what I wanted to achieve.
Contributing and using this code
You are free to use my code in any way you want. And since it's probably not that super, I hope you consider improving and contribution to it.
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