TAQueries: Nearing Andromeda

First of all, the questioner hadn’t used the TAQueries hashtag in the question. I’d like to ask everyone to please use the hashtag, otherwise I won’t be able to answer the question here on my blog. Thanks. Okay, so here goes the question:

Universal expansion, as the name obviously suggests, is the expansion of the universe itself. First discovered through observations by Edwin Hubble, it has been the subject of many studies ever since. When Edwin measured the relative velocities of galaxies, he realised that they’re all moving away from us. Not only that, he also found that the farther away galaxies were, the faster they were moving away from us. This has become to be known as the “Hubble’s Law”. Now we know that these weren’t the galaxies themselves moving away from us, but rather, it was the space in between those galaxies that was expanding. Space, nothingness itself, can warp and stretch! If that doesn’t make your brain go into overdrive, I honestly don’t know what will.


Though all galaxies seem to be moving away from us, there are exceptions. Andromeda, our nearest galactic neighbor if you don’t count the tiny galaxies orbiting the Milky Way, is moving towards us at roughly 396,000 kilometers per hour. If all galaxies are moving away from us, why isn’t Andromeda? It all comes down to the gravitational attraction between Andromeda and the Milky Way. The rate at which the space between Andromeda and Milky Way is expanding is not quite enough to overcome the powerful gravitational attraction between the two.

Imagine a trampoline. If you were to put two people on opposite sides of the trampoline and give each of them one of two ends of a rope to hold on to, then magically started expanding the the trampoline while the rope kept getting shorter, you wouldn’t be able to expand the trampoline fast enough and the rope would eventually pull the two people into a single point. Okay… I’ll admit that is a pretty bad analogy. But I think it does the job. So if the expansion of the trampoline represents the expansion of space and the contraction of the rope represents the gravitational pull of Andromeda and the Milky Way, just like the people on the trampoline, both of the galaxies will eventually end up being pulled together which in turn will cause them to collide. This will give birth to an entirely new galaxy. You can call it “Milkomeda” if you like. In the process of the collision, Earth’s sky will look something like this:

Nighttime Sky View of Future Galaxy Merger: 3.85-3.9 Billion Years
Nighttime Sky View of Future Galaxy Merger: 3.85-3.9 Billion Years Credit: NASA, ESA, Z. Levay and R. van der Marel (STScI), T. Hallas, and A. Mellinger


But that won’t be the end of it. Another collision will take place roughly 2 billion years after the creation of Milkomeda. The combined mass of the Milky Way and Andromeda will attract the next nearest neighbor. The Triangulum Galaxy. Once Milkomeda collides with the Triangulum Galaxy, the total number of stars in the resulting colossal galaxy will be about 1.14×1012. That’s 1,140,000,000,000 or 1.14 trillion stars in total. Now that… is what I call astronomical.

Not quite the answer you were looking for? Be sure to let me know via email: theastrophysicist@hotmail.com or by tweeting at me @ThomasMoszczuk


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