Galactic collisions

Collision of the Milky Way Galaxy with Andromeda (forming "Milkomeda")

Galactic collisions

Discussion and questions for this video
Wow, what an amazing and beautiful video! I'm struggling with one thing though - if everything is moving away from everything, how could be collide with another galaxy? Have the galaxies been orbiting around something bigger and are crossing paths? Is the Milky Way traveling faster than the Andromeda galaxy? What exactly makes this possible?
If you're close enough then gravity pulls you together a lot faster than the universal expansion spreads you apart. Just think about you and the Earth... technically, every instant the expansion of the universe makes you a little bit further from the center of the Earth, but your gravitational attraction to the Earth is a LOT stronger and keeps moving you back toward it.
Are there any pictures of galaxies that are halfway through colliding? i mean with 200-300 billion galaxies there have got to be some.
hi! Please clarify for me: our galaxies are set on a collision course of some sort yet our distance is substantial enough for the Hubble's law equation? Just confused a little bit regarding this collision and the notion of all objects moving away relative to us.
Someone else answered this already in a different question, but yeah -- everything is moving away from everything because of expansion, but gravity is a stronger force when you have enough mass at a small distance (which is why, among other things, we individual people are not expanding away from the earth). So these galaxies have become close enough to be attracted to each other gravitationally. Does that help?
But wouldn't the black holes burn out like other stars over that time?
Black holes take time scales much longer than that to burn out. The video spans maybe 2,000,000,000 years. The average stellar black hole will take 10^66 years or 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 years to decay. A supermassive black hole (like the ones at the centers of the galaxies) will take 10^92 years to decay.
If we do collide with Andromeda, and lets say our sun did hit another star what would happen? Also what if a farther away star say Beetlejuice collided with another star? 3rd question. Would we on Earth not really feel anything from such a huge collision? Not even an increase in some radiation or something?
If our sun hit another star when the galaxy clashes with the Andromeda, then we're dead. You might think this is a stupid answer, but this is basically the simplest answer. If a star clashes with the sun, there would have been something like a mega nuclear explosion because of major nuclear fusion interruption. If that didn't kill us, the cold would have. And if a star like Betelgeuse (not Beetlejuice) hit another star, there would have been an incredibly large explosion, that even we would have been affected, the speed of the Earth would have been increased, which is major (at least by a day).
To be fair, Sal didn't make it up, it is the already made name for the future galaxy.
if there where people in a galaxy that collides with another what would happen to those people
It's worth noting that since galaxies are mostly empty space, the chances of a colloision are astronomically slim.
Are there any other known galaxies that are predicted to collide in the future?
I think the Milky Way and Andromeda collision is the only one astronomers have predicted so far, but there are a number of galaxies that are "currently" in the process of colliding. Here are two sources that have images, simulations, and descriptions of them: and the Notable Interacting Galaxies portion from I hope that helps!
If we were to collide with another galaxy right now, would this galaxy or at least a part of it be destroyed?
And some million stars and planets will be hurled off into intergalactic space.
Why don't the galaxcies explode when they collide?
Why would they? Most of the stars or planets do not collide. The "matter" that could collide is only a very small fraction of the "space" that galaxies make up. There is a slim chance that any two object could collide and maybe explode.
How can this work? if we are in the middle of the milky way, how would we know what this would look like from so far out. how do we even know what the milky way looks like?
We can tell by A: studying other galaxies and B: observing that there are almost no Pop I stars (stars with higher metal concentrations) in the bulge of the galaxy, and that there is a very high number of Pop II stars (stars with no metals, old dim red stars) in the bulge. This observation tells us that the bulge of the galaxy is most likely red while the spiral arms (the disk) is very blue. In other words, we think the Milky Way looks a lot like the Andromeda.
Surely in three - five billion years, the current supermassive black holes in the center of the galaxies will be, as it is commonly termed "evaporated", also will the gravitational pull effect the galxy and even the solar system in the future, such as M81 and M82 (Bode's Galaxy and Cigar Galaxy), just a thought.
The supermassive black holes will not evaporate for about 10^99 years, way more than the 3 to 5 billion years. The gravitational pull of Andromeda will distort the Milky Way, but it will not do much to the solar system. The greatest thing we will have to worry about is the sun will be dying at around the same time.
If two or three black holes collide, would it create a super massive black hole? Or is it possible that when they are nearby each other that they pull each other into just a bunch of matter floating in space?
From the
It is possible for two black holes to collide. Once they come so close that they cannot escape each other's gravity, they will merge to become one bigger black hole. Such an event would be extremely violent. Even when simulating this event on powerful computers, we cannot fully understand it. However, we do know that a black hole merger would produce tremendous energy and send massive ripples through the space-time fabric of the Universe. These ripples are called gravitational waves.

Nobody has witnessed a collision of black holes yet. However, there are many black holes in the Universe and it is not preposterous to assume that they might collide. In fact, we know of galaxies in which two supermassive black holes move dangerously close to each other. Theoretical models predict that these black holes will spiral toward each other until they eventually collide.

Gravitational waves have never been directly observed. However, they are a fundamental prediction of Einstein's theory of general relativity. Detecting them would provide an important test of our understanding of gravity. It would also provide important new insights into the physics of black holes. Large instruments capable of detecting gravitational waves from outer space have been built in recent years. Even more powerful instruments are under construction. The moment they detect their first gravitational wave, you are sure to hear about it!
Does anyone know the mass of Andromeda's supermassive black hole? In order for quasars to happen, the supermassive black hole has to be in between 10^7 and 10^8 solar masses, so If it is less than 6 million solar masses, then Milkomeda (Andromeda Way) would not be bright enough a quasar.
You are right that size doesn't matter, however mass does, the brightest quasars come from galactic nuclei that have in between 10^7 and 10^8 solar masses. I think that since the overall mass of the Andromeda Galaxy (including Dark Matter) is less than the Milky Way's, Andromeda's nuclei won't have enough mass to reach the Quasar sweet spot.
When the galaxies collide, wouldn't both of the super massive black holes in the center of the galaxies become quasars, because they'd be sucking up a bunch of stars?
It really depends on how the collision occurs. If we assume that the two black holes do come close enough to be captured in each other gravitational fields sInce most of a galaxy is empty space most of the stars just pass through each other. The supermassive black hole in our galaxy is estimated to be about about twice the diameter of the orbit of Uranus, about 0.000001297219% the diameter of the Milky Way. So it could encounter stars along the way and pull them in but it would a small number of them.

There would be a fair amount of disruption of the orbits of the stars and the galaxy may become active again if enough matter is pulled to the center of mass.

The two black holes would start or orbit each other and over a long time come together and merge.
What happens when the 2 black holes at the center of each galaxy collide at 2:37? do they both collide to make a big black hole, or does one black hole eat the other?
The two blackholes will orbit each other until their gravity draws one into the other, forming a gigantic blackhole.
what I dont understand is why is the black hole dosent suck things up because i thought black holes always did that and dose anybody agree with me that the video was beautiful
Black holes do suck things up! But only those things which have not enough angular momentum to keep in orbit around a black hole. I guess if you give it enough time, each orbiting object will lose their momentum and slowly orbit into the blackhole. So everything is sucked up, but some objects very slowly thanks to their angular momentum.

About the event horizon: this is only the border of which light can not escape. If you are far from the event horizon, it could very much be that the gravity is way to much for YOU to escape, but light still can. Beyond the event horizon, even light can not escape! That's where everything becomes black. The actual material of the black hole can be somewhere inside the dark sphere of the event horizon.
Have I understood things right?
Space expands, but the mass of the centre of a galaxy is so massive, that galaxies that are relatively close to each other, are being attracted because of the gravitational pull of the centre of the galaxy?

In other words: the Milky way and the Andromeda galaxy are attracted to each other, because of the incredible gravitational pull of the centre of both of the galaxies.. Is that why the Milky way and the Andromeda galaxy do not red shift away from each other?
Can someone answer my questions?
Okay #1 We know the Moon drifts away from the Earth but only by so much, if its drifting away from the Earth, is its gravity strong enough to nudge Earth out of its normal orbit?
#2 Which event will happen first? The death of the sun or the Andromeda galaxy colliding with Earth?
1. The moons gravity is getting weaker as it moves farther away.
2. Andromeda will collide with us in 2-3 billion years while the Sun will become a white dwarf in 5-6 billion years. Andromeda will hit us first.
Whoa FREAKING AWSOME :O ..... that was the best animation that ive ever saw .... sal really is a blessing to people who want to learn Every Where its good to learn from someone who knows what there talking about!
Don't forget that NASA did the video. Sal gets credit for being aware of it and putting it into the set of Khan Academy videos. But most of the credit goes to NASA for this one! Sal was careful to give credit to where the credit was due.
2:45, Sal says that the Milky Way and the Andromeda galaxies will merge, but is it into a new galaxy, or something else? I mean, would they destroy each other?
Their collision will fling countless stars out of both galaxies but they will merge into a large elliptical galaxy.
Will the overall mass of the galaxy formed after the collision of the Milky Way and Andromeda be more or less than the present mass of the Milky Way ?
How could the mass of two not be bigger than the mass of one?
I seriously wonder how the stuff of the galaxies can fade so much, when the velocity they slide into each other is so extremely low?!
The velocity at which galaxies collide with each other is very fast indeed. We are talking in thousands of kilometres per second. It only appears slow since we're seeing them on such a large scale.
if galaxies can collide can black holes too? what would happen if so would they suck each other in?
if black holes are real they could suck parts of the galaxy?
Black holes are real. We are aware of a few of them. They however are about as capable of sucking in parts of the galaxy as stars are. The typical black hole is about 20 solar masses which means that it has the gravity of a 20 solar mass star. For instance, if the Sun were to become a black hole right now, Earth's orbit would not be affected at all. Since the Sun's mass never changed (it just got much denser), its gravity wouldn't change.
The middle of a galaxy is a super massive black hole. These were huge stars that managed to collapse to an infinitely dense point. Normally you couldn't see it, but its accretion disk (All the objects orbiting it fast enough and close enough to burn and create this light) is having some light escape, so you can see the accretion disk. Watch the super massive black hole video for more info.
Does this conflict with the theories of Hubble's Law?
No, the gravity between Andromeda and the milky way is pulling them together.
i've saw a picture of the entire branch of space. Even if we did have our *cavemen traveling into space* would we know what else is out there? Outer space is sooo vast and now, us humans have so much technology, can we find out if we do have interalactic neighbors?
The Andromeda Galaxy, which is essentially the closest galaxy to ours, is a spiral galaxy approximately 2.5 million light-years away from our galaxy. If we had an intergalactic neighbor in the Andromeda galaxy who had an unbelievable amount of energy available, and they decided to send a “hello” signal out to the universe, it would take 2.5 million years for their “hello” to get to us. And then we wouldn’t know if we [now] have an intergalactic neighbor, just that we had a neighbor 2.5 million years ago. Who knows if they are still our neighbor? A lot could have happened to them over the last 2.5 million years!
We are observing galaxy collisions right now. Look up the Antennae Galaxies.
What a beautiful video. Couple questions:
1) Isn't everything in the universe moving away from everything else? So how is this collision possible?
2) Was a quasar formed at the end of the video, or was it just a super-dense galaxy?
No, everything is not moving away from everything else. Your fingers were moving toward your keyboard when you typed. You moved toward your desk to type. You are not drifting upward from the surface of the earth.

There are forces in the universe that attract things to one another. Gravity is the most relevant one in this particular instance. Galaxies that are relatively close to one another will experience an attractive force that creates much greater "local" motion than would be seen by the relatively small amount of spatial expansion between them.

The expansion rate of space becomes very meaningful only over vast, vast distances. The further away from each other two objects are, the more space between them there is to expand, so objects that are very, very far apart do move noticeably away from one another, sometimes at very high speeds, even speeds greater than the speed of light.
Humans would be living in other planets at a long time , if the collision happen ( and it will!) would the humans survive since there different part of other solar systems in the milky way?
This collision will do little to affect the stars or planets themselves since the distances between the stars of both galaxies is so vast. We should be safe on earth.
We are not exactly sure how dark matter interacts with anything. The only force that affects it appears to be gravity, it might have other forces acting on it that we are not aware of. we do not know how dark matter interacts with other dark matter.
How is that possible?The Milky Way and Andromeda, aren't they growing apart from each other?How could they collide?
I know it seems confusing. The Big Bang means that on a large scale, space is expanding so all galaxies are getting more far apart from each other. But on a local scale, you can have two or more galaxies that, due to the reciprocal gravitational pull, start to get closer together, like our galaxy and Andromeda.
When galaxies collide, all the mass orbiting the two central black holes are disrupted by the gravity of the other black hole. With their orbits destabilized, all the matter starts to fall into either hole as the two holes merge. this material is to much for the new black hole to swallow so two bipolar jets of matter are formed near the black holes emitting light, this is called a quasar.
What happens when two neutron stars collide/merge? Do they create a supernova? A gammaburst? A black hole, or gravitational waves? Or something completely different?

Hopefully someone can help me!
You would either get a larger neutron star, or a black hole.
Why are there galactic collisions and when did they first begin?
No I don't think quasars are being taken into account in this simulation. What I think you see here are millions or maybe even billions of stars and solar systems being thrown away by the acceleration. Like when you would tie a rock to a human hair, hold it in your hand and start spinning around really fast. The outward force will become too big, the hair will break and the rock will fly away. In this analogy the hair is the gravitational pull, but due to the huge accelaration and spinning those stars are "thrown away". They break loose of the gravitational pull and orbits.

It looks like dust, because they're just millions or maybe even billions of stars together.
If every single particles holds so many stars, how many particles are there? It would be awesome to know how many stars were in that video. I'm guessing 6,000,000,000.
Since it's NASA doing the computations on a very expensive supercomputer you can assume they took the actual numbers of stars in the respective galaxies, which are the Milky Way and the Andromeda Galaxy.

Milky Way: 200-400 billion stars (wikipedia)
Andromeda Galaxy: +- 1 trillion stars (spitzer telescope, wikipedia)

So the total number of stars would be about 1.2 - 1.4 triillion stars.
But what if the sun gets thrown off but not the earth?
it wouldnt because we are so close to the sun that we are permanent orbit some of the smaller planets that are far out like Pluto or Neptune or Uranus but they would float to another star and we might get some extra plantes too
When we colide galaxies in billions of years, will the solar system be thrown into space, or will the solar system be ripped appart by the newly formed supermassive black hole?
I know galaxies collide because the universe expands, but if the univese didn't expand, or contract, would the result be a major catastrophi?
When 2 galaxies merge do their supermassive black holes get bigger or do they just remain the same size?
And what is the probability that Andromeda will suck in the milky way galaxy?
When two galaxies collide, often the supermassive black holes fuse together into a single one larger than either of them originally.

Nothing is going to suck in anything, our galaxy is moving towards the Andromeda galaxy and will eventually collide.
Here is the URL for the NASA video. You must also look at the illustrations at the bottom of the page showing what the night sky will look in in the future, especially the sky in 3.75 billion years. Absolutely mind-blowing!