Explore the inevitable collision between the Milky Way and Andromeda galaxies and the violent nature of galactic collisions.

Video of the day December 31st 2019


How Does A Galaxy Collide

I’m sure you’re thinking, “wait a minute, what do you mean inevitable collision?” On a cosmic scale, it might seem hard to think that galaxies would actually collide with one another, especially when you consider that galaxies aren’t a singular object, but a collection or millions, or even billions of tinier objects.

All of which are caught within the gravity of certain massive objects. So how exactly does a galaxy “collide” with another? Well to be fair, it’s not your typical type of “collision”.

Because when you think about a collision, you’re likely thinking about a car crash, or you’re thinking about two people running into each other, you think of a physical confrontation that leaves both sides wounded in the aftermath, which is fine!

But that’s not exactly what’s going on here.

When two galaxies “collide”, it’s more about them getting so close to one another that their gravities start to fight one another.

What Happens When A Galaxy Collides

It can get physical, but not in the sense of planets running into one another, or stars absorbing one another, that kind of thing. It technically can happen that way, but it’s an extreme rarity. Rather, what usually happens (based on how we’ve observed the universe, including seeing some smaller galaxies colliding) is that there is a bigger galaxy, and a smaller galaxy, and over time, they drift closer and closer to one another. Eventually, the gravities of one of them reach the other, and when that happens the “collision” begins. Usually by the larger galaxy ripping apart what is on the edge of the smaller galaxy. They’ll move closer and closer together, entities like planets, moons, stars and more will be ripped from their orbits and find themselves getting “settled” in the newer galaxy.

At times, the force of the opposing orbits will force planets or stars to actually be THROWN out of the galaxy itself, becoming a wondering entity among the stars. Other times the placement of things like black holes will devour certain things in the young galaxy depending on their position. Needless to say, it’s a rather violent affair. To the extent that when all is said and done, there is typically only one galaxy remaining, and that galaxy is much bigger and full of entities than it was before. It’s not quick, but it is all-consuming, and so you can see why people are afraid of the Andromeda galaxy absorbing us, especially when you hear that this particular galaxy…has swallowed up other galaxies before.

“Andromeda has a much bigger and more complex stellar halo than the Milky Way, which indicates that it has cannibalized many more galaxies, possibly larger ones.” notes one scientist “Wait, what?

The Andromeda Galaxy has taken out other galaxies before?” Oh yeah, it has, many times in fact. You see, many acknowledge that Andromeda is a rather large galaxy, which is another reason that many fear it colliding with the Milky Way galaxy, but as they observed Andromeda over the years they noticed something. Streams of stars that was within its “galactic halo“. Meaning that they were remnants of the stars that it’s gobbled up and eaten over the long time of its life. Though we can’t confirm this officially (as we don’t have a map of the universe from the beginning up to now), based on these star streams, it would appear that the Andromeda galaxy has devoured numerous galaxies over billions of years, and that is what led it to becoming the monster galaxy we have now.

The Andromeda Monster

The reason for its “cannibal’ nature may have been more of a circumstance than anything else. By that, we mean that at one point in time the Andromeda Galaxy was large…but not as large is it now. To that end, it was surrounded by smaller galaxies that inevitably drifted into the path of the Andromeda Galaxy. So eventually, they got eaten, Andromeda grew bigger, and then it would eat another galaxy, and another, and another and on and on it went until Andromeda was one of the biggest galaxies in the known universe. For the record, the Andromeda Galaxy is 110,000 light years across. It’s REALLY big. But some of the galaxies that it’s eaten can be large contributed to that size. One such one was M32p, which at one time in the universe was the third-largest galaxy within it, but Andromeda ate it up and thus gained a massive amount of…well…mass.

Scientists have been very interested in how Andromeda not only does this, but continues How Andromeda Eats to do this: “By tracing the faint remains of these smaller galaxies with embedded star clusters, we’ve been able to recreate the way Andromeda drew them in and ultimately enveloped them at the different times,” said Dougal Mackey, author of the new study at the Australian National University’s Research School of Astronomy and Astrophysics. But wait, there’s a twist, while scientist have been able to figure out which galaxies (for the most part) Andromeda has “collected”, the positions of them have raised an unusual

The Cosmic Web Question.

Mainly, even with the expanded size of Andromeda, the galaxies it gobbled up came from variousdirections and not just on one path. So how did it pull that off? “This is very weird and suggests that the extragalactic meals are fed from what’s known as the ‘cosmic web’ of matter that threads the universe,” said Geraint Lewis, study co-author and professor at the Sydney Institute for Astronomy and University of Sydney School of Physics. “More surprising is the discovery that the direction of the ancient feeding is the same as the bizarre ‘plane of satellites’, an unexpected alignment of dwarf galaxies orbiting Andromeda.” So yeah, Andromeda has quite the appetite, don’t you think? But here’s another twist for you, the Milky Way Galaxy is also a cannibal of other galaxies, and in fact, it’s doing some “eating” right now”.

That way you don’t miss any of our weekly videos! “Hold on!” you cry out, “If we’re combining with another galaxy right now, wouldn’t we know about it? You know, wouldn’t we feel the other galaxy combining with us?” Well…yes and no.

milky way

Dwarf galaxies

If the circumstances were right, and our place in our solar system was directly in the path of the galaxy that we were absorbing…then yes, we would feel it. Do you hear the “but” coming? You see, while it’s true that the Milky Way is absorbing some galaxies right now, they’re not anywhere close to the scale of our own. In fact, they’re specifically called “Dwarf Galaxies” because of their size. If you’re curious, one of them is known as the Sagittarius Dwarf Spheroidal Galaxy. And it is indeed merging with us right now and will help expand the mass of the Milky Way.

Galaxies colliding is something that scientists have observed for some time, and in fact, they happen much more often than you think. The raindrops all hit the window in equal measure, some bigger and some smaller, but they’re all their own entity. But, as they drift down the window (not unlike galaxies drifting in the universe) they eventually collide with other droplets, and become bigger. Whether it’s the Milky Way, Andromeda, or another galaxy that is out there, this is the fate they face. And that includes the Milky Way and Andromeda colliding. But…before that “clash of the titans”, the Milky Way has a date with another entity known as the Large Magellanic Cloud. If you don’t know, the Large Magellanic Cloud is another satellite galaxy, and one of the biggest in the sky currently. I wasn’t supposed to be near us, but about 1.5 billion years ago it came to our corner of the universe.

When it did, it held a course that would keep it away from us. That is, until something happened within it that caused it to lose energy, and when it did, it headed towards the Milky Way. At present, it’s about 163,000 Light Years away, which is not as far away as you might think. Sure, it’ll take 2 billion years for the two galaxies to collide, but when it does, it will be bad. Very bad in fact. “The destruction of the Large Magellanic Cloud, as it is devoured by the Milky Way, will wreak havoc with our galaxy, waking up the black hole that lives at its center and turning Will we survive our galaxy into an ‘active galactic nucleus’ or quasar,” said Marius Cautun, study author and postdoctoral fellow at Durham University’s Institute for Computational Cosmology, in a statement.

Will we survive that epic fusion? It’s honestly hard to say. There are a lot of factors that go into massive galaxies fusing together in a somewhat natural yet entirely violent, way. But, if we DO survive, we’re going to have something to see… “Barring any disasters, like a major disturbance to the Solar System, our descendants, if any, are in for a treat: a spectacular display of cosmic fireworks as the newly awakened supermassive black hole at the center of our galaxy reacts by emitting jets of extremely bright energetic radiation,” said Carlos Frenk, study co-author and director for the Durham University’s Institute for Computational Cosmology, in a statement. But I guess we have been dodging the main question…haven’t we? When will the Andromeda Galaxy hit us.

So when exactly will the Andromeda Galaxy hit us?

Well, that’s the good news believe it or not: “The Milky Way is on a collision course with Andromeda in about four billion years. So, knowing what kind of a monster our galaxy is up against is useful in finding out the Milky Way’s ultimate fate,” said Dougal Mackey, So take heart! Not only will you be long gone before that epic clash happens, most of your descendants will likely be gone as well! Not to mention the fact that if humanity is alive at all, we’ll likely be across the stars, possibly in another galaxy!

Heck, we may even be IN the Andromeda Galaxy when it tries to absorb the Milky Way! 4 billion years is a long time! You never know! Does that mean Earth is doomed, well…it’s likely…but maybe not in the way you think: “I think it’s unlikely the Earth will be physically destroyed by the collision with Andromeda,” Mackey said. “It’s not out of the question, but in general the stars in galaxies are spaced sufficiently sparsely that direct collisions between stars are rare.

If you got lost

However, it’s possible that the Sun could be thrown out of the merged Andromeda and Milky Way system by the collision, into intergalactic space, and/or a nearby close passage with another star could perturb the Earth’s orbit such that the Earth can no longer support life.” If you got lost in what he was saying, I’ll explain. He’s stating how it’s incredibly improbable that the Earth itself would be destroyed in the collision of the galaxies. But, when it comes to the larger scope of it all, the sun that we have would likely lose its position in our galaxy via being pulled away by a stronger gravity. And when that happens, we’d lose our tether in the solar system.

We would either be flung away into another part of the galaxy until we got caught by another galaxy, or, we’d be left alone in an atypical orbit with no sun. Either way, the Earth would basically be screwed because of the fact that we have the perfect balance of light and heat with our sun right now that if it was disrupted, even momentarily, it would cause a lot of problems for the Earth. But again, it’s 4 billion years into the future, so we technically don’t need to worry about it right now. But it is something to think about, and that is why the notion of the two galaxies colliding is a big deal to some scientists. You see, it’s easy for us right here to think that the events of 4 billion years from now don’t matter, and in a certain way that’s true.

Why should we care We’re NOT going to feel the effects of what happen at that point, so why should we care? Why should anyone care? The answer is information. The notion of galaxies colliding with one another isn’t new, but it’s not exactly as fresh in terms of its discovery as you might think. It wasn’t until 1992 that scientists realized they could calculate the distance of the galaxies and how fast they’re moving with their natural momentum. That was a huge discovery, and it helped them understand how and when previous galaxies were devoured. Information is very important, and it helps lead people to conclusions that we didn’t know about before.


So while it’s true that knowing that the Milky Way Galaxy will be “gone” in about 4 billion years doesn’t affect us right now, that doesn’t mean it’s not important. The universe at large remains one of the biggest mysteries in the history our lives. In fact, many scientists are trying to learn about the Andromeda Galaxy and how it came to be in order to learn more about the Milky Way Galaxy. Because since we live in it, it’s harder to observe from our position. But if we see similarities between the two galaxies, it can teach us a lot. So yeah, there’s a very violent collision coming our way in a time when we won’t see it, but that doesn’t mean that the event can’t teach us things right now.

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