# Will the Milky Way actually collide with the Andromeda galaxy?!

## Метаданные

- **Канал:** Dr. Becky
- **YouTube:** https://www.youtube.com/watch?v=BxylLJj5y4s
- **Дата:** 26.06.2025
- **Длительность:** 14:29
- **Просмотры:** 92,971
- **Источник:** https://ekstraktznaniy.ru/video/15157

## Описание

AD - Get an exclusive 15% discount on Saily data plans! Use code DRBECKY at checkout. Download the  Saily app or go to https://saily.com/drbecky | Will our Milky Way galaxy, our island in the universe of 100 billion stars, one day collide with our neighbour the Andromeda galaxy? Because when we observe the light from Andromeda, we see that unique features from light given off by the elements like hydrogen and oxygen are doppler shifted; the light from Andromeda is squashed as it moves towards us, and we see that as a shift of the light to bluer colours: a blueshift. From that we know how fast Andromeda is moving relative to us at 301 km/s towards us - so that means a collision with the Milky Way must be imminent in 2.5 billion years or so once we close the 10 billion billion km gap, right? Turns out, maybe not. A paper by Sawala et al. was published earlier this month claiming there’s actually only a 50% chance that the Milky Way and Andromeda will merge in the next 10 billion years. A

## Транскрипт

### Introduction []

One of the first things that I learned about our universe that really hooked me and made me want to become an astrophysicist was that our galaxy, the Milky Way, our island in the universe of a 100 billion stars, will one day collide and merge with our neighbor, the Andromeda galaxy. From then on, I was hooked. I found Andromeda in the sky and looked at it with binoculars and a telescope and I read everything that I could about how we know that this is going to happen in the next few billion years. Because when we observe the light from Andromeda, we see that unique features from that light given off by elements like hydrogen and oxygen are Doppler shifted. A doppel shift is probably something you experience if not on a daily basis, at least a weekly basis. For example, when an ambulance races past you and you hear the siren get higher pitch as it moves towards you and lower pitch as it races away from you because the sound waves are squashed and stretched by the movement of the ambulance. The light from Andromeda is actually squashed because it is moving towards us and we see that as a squashing or a shift of the light to bluer colors. So a color change rather than a pitch change like it is for sound. And from that we can measure that the Andromeda galaxy is moving relative to us here in the Milky Way at 301 km/s towards us. So that means a collision with the Milky Way must be imminent in around two and a half billion years or so once we close that 10 billion km gap between us, right? Turns out maybe not. This paper by Sabala and collaborators was published earlier this month claiming there's actually only a 50% chance that the Milky Way and Andromeda will merge in the next 10 billion years. And it all seems to depend not on Andromeda, but on some of our closest other neighbor galaxies, the large Melanic cloud and the triangulum galaxy. So, in this video, we're going to dive into all the details on this study. First, about the galactic members of our backyard group of the universe. Second, the simulations that were run by Sabala and collaborators. And finally, what has the biggest influence on whether the Milky Way and Andromeda will merge. Now, while we might not be traveling to Andromeda anytime soon, you might be taking a trip this summer, either for fun or for work, like me on the classic academic summer conference circuit. Now, if you have ever badly needed an internet connection while you're in a foreign country, you know, for work or because, let's face it, you're just lost in a city somewhere, you'll know how annoying it is when you just don't have access to your data like normal and the huge difference that just having a local like SIM card can actually make. But buying and swapping out those like physical tiny little SIM cards constantly with every new country is just so inconvenient. That's why I love the convenience of SLY, the sponsor of this week's video. Sy is a simple eSIM app that helps you stay connected in over 200 places around the world. An eSIM is just like a digital SIM card that works exactly the same, but without the faf of having to swap out a physical SIM card all the time. All you have to do with SY is download the app, choose a data plan and install it on your phone and that's it. You're all set. You'll then have internet wherever you go without any of the dreaded expensive roaming fees, saving you time and money and also saving you the panic when you then can't find your normal home SIM card when you get back. Because let's face it, those things are just tiny. And if you're planning on visiting several countries during your next trip, sail can help you save even more because if you get a global or a regional plan, say for Europe as a whole, you can travel with the same eim plan and not have to worry with every new country. So if you head to s. com/dbecky or if you just use the code Dr. Becky at checkout, you'll get 15% off all of SY's data plans. So download the app before your next trip and thank me later. So a big thanks to SY for sponsoring this video. And now let's dive in and chat

### The members of our galactic backyard of the Universe [3:56]

first about the galactic members of our backyard of the universe. So first of all, the sun is just one star of over 100 billion stars in our galaxy, the Milky Way, which is a flat frisbee shape. We are out on the edge of the galaxy in a spiral arm. The whole galaxy itself is about 90,000 lighty years across. Meaning it takes light traveling at just under 300,000 km a second 90,000 years to go from one side of the galaxy to the other. In everyday units, that's around 950,000 billion km. But then the Milky Way also has a bunch of much smaller galaxies known as dwarf galaxies in orbit around it. That includes the small and large melenic clouds, which you can actually see from a dark sky in the southern hemisphere. The large melanic cloud is 32,000 lighty years wide with 30 billion stars. So around about a third of the size of the Milky Way, and it's around about 163,000 lighty years away. And all of these dwarf galaxies in the Milky Way are part of what's known as the local group of galaxies, a clump of galaxies that are closer together than what you would typically see. So much so that they are gravitationally bound together. Meaning their movements are more dominated by the gravitational forces between them than they are by the expansion of space that's happening between them. Now, the Milky Way is not the biggest galaxy in our local group of galaxies. That title goes to the Andromeda galaxy, also known as Messier 31 or M31. It's 150,000 lighty years across with around a trillion stars, but it is 2. 5 million light years away. It too has a lot of dwarf galaxies in orbit around it, including M32, which is not a spiral galaxy. It's instead a dwarf soreroidal galaxy where all the stars are like bunched together in a sphere. So unlike you know the planets in the solar system going around the sun in the center and unlike you know the stars in the Milky Way or Andromeda which are all going around in like one flat plane with this nice ordered rotation, the stars are all still orbiting the center, but they're doing so kind of like a beehive. Just lots of chaos, lots of different planes of orbit, and that's sort of what builds up that spheroid shape. We think those kind of galaxies form when galaxies collide and merge together. The gravitational forces between all the stars in the merger scramble at their orbits, turning spirals into big blobby spheres. And then last but not least, the third biggest member of our local group of galaxies is Messier 33 or M33, the triangulum galaxy, which is about 3 million lighty years away, 60,000 lighty years wide, and contains around 40 billion stars. So that's around about 40% of the size of Andromeda, which it's thought to be a satellite of. on the rebound after having a close flyby a few billion years ago. So when we think about okay well the Milky Way and Andromeda might collide in the next few billion years what you don't have is just you know the Milky Way and Andromeda pulling on each other. Every single galaxy in the local group is exerting a force on every other single galaxy. Obviously the bigger the galaxy the greater that force will be. So, if you're trying to run a simulation where you sort of like press fast forward on time to see what happens in the future, to see if the Milky Way and Andromeda merge and see what happens to all the other galaxies in the local group, it's not just like a twobody problem between the Milky Way and Andromeda. It's more of an 80body problem if you include all the galaxies. Which brings me to part two, the simulations that

### The simulations run by Sawala and collaborators [7:36]

Savalar and collaborators ran. So to do this, to run these kind of simulations where you're like pressing fast forward on time, Savalar and collaborators first had to get the most precise and accurate measurements available for each galaxy's mass and position and velocity, but also you know how their stars are distributed and spread out around the galaxy, whether they're more centrally concentrated like for Andromeda versus more diffuse like for the large melanic cloud. And thanks to efforts with the Hubble Space Telescope and with the European Space Ay's Gaia mission, we have that data for these galaxies, albeit with some measurement uncertainty, but we can then use those as input to the simulation to press play and fast forward and then see what happens as those forces on the galaxies change over time as well. Not to mention the sheer amount of computing power that would be needed to do that. Savala and collaborators just focused on the four largest members of the local group. So, Andromeda, the Milky Way, M33, and the large melenic cloud since those are going to have the largest effect, and you just assume that the pools from the smaller dwarf galaxies are negligible. That's a very, very big assumption, but given current computing constraints, that's how you make progress in this field. Now, due to the measurement error on each of these 22 different parameters that are needed as starting points, as inputs to this simulation to describe the masses and velocities and positions of these four galaxies, the ever so slightest difference in the inputs, because of these uncertainties, because of like a range of values that these could have then lead to much bigger differences billions of years later in the simulation. So Savala and collaborators ran 50,000 simulations of this fourbody problem with the Milky Way to see what happened in the slight variations of starting points 10 billion years later and say when you left out certain galaxies from the simulation. So what was the impact of putting M33 in the simulation versus leaving it out and for the large melaninic cloud as well. So here you can compare the position. So where the Milky Way and Andromeda ended up in space after 10 billion years when you leave out M33 and the LMC on the left hand side and include them in your simulations on the right hand side. This plot just shows 100 different possibilities which are drawn randomly from all of the simulations that were run and the white dots show the situations where a merger between the Milky Way and Andromeda actually happened. That exact same data is also in this plot as well that shows the distance between the Milky Way and Andromeda on the Y-axis in the same two scenarios again with these little white triangles at the bottom showing the simulations where the merger actually happened. So you can pick a track and follow it through time and see either the two galaxies will come close together and then fling back out again or perhaps come close and then swoop back in for the merger or have a few close passes before the merger eventually happens. These percentage values in the bottom left corners tell you how many simulations actually ended up with the Milky Way and Andromeda merging before the 10 billion years was up. With just the twobody problem is only 44%. So just under a 50/50 chance that the two galaxies will actually collide. But including all of the four heaviest galaxies in the local group, that number goes up to 54%. Which brings me to part three. what has

### What has the biggest influence on whether the Milky Way and Andromeda will merge? [10:58]

the biggest influence on whether the Milky Way and Andromeda will actually merge? Because Savala and collaborators also ran their simulations to test what would happen if you put in M33 but left out the large melaninic cloud or you put in but left out M33. And you can see that by adding M33, the percent chance that the Milky Way and Andromeda will merge goes up to 63%. whereas adding the large melanic cloud but leaving out M33 drops the chance to just 37%. So what is going on here? So once again collaborators looked at sort of like the positions in space that the Milky Way and Andromeda would be in this scenario where you put one of these smaller galaxies in but leave the other out. And as expected M33 doesn't have much of an effect on the position of the Milky Way because it's so much further away at 3 billion lightyear. But the large melaninic cloud changes things a lot more. Conversely, if you look at the position of Andromeda, the LMC doesn't affect Andromeda that much, but Andromeda is affected by the much closer M33, which again just makes things a little bit more chaotic in its path. And in particular, what's going on here is that the effect that M33 is having on Andromeda is that it is slowing it down with respect to the Milky Way. Whereas the LMC is actually speeding up the Milky Way relative to Andromeda. And this is what affects the chance of the merger. Speed up their relative velocities and they'll absolutely fly past each other and are less likely to merge. But slow down their relative velocities, then gravity's got a much better chance of being able to slosh them together so that they eventually merge. And it's also worth saying that all four will eventually become one galaxies cuz Spar and collaborators find that LMC is likely to merge with the Milky Way and M33 with Andromeda before any Milky Way Andromeda merger happens. So what does this all mean for that thing that I feel like a lot of us just take for granted, this statement of the Milky Way will merge with Andromeda one day? I think at the minute there's just too many sources of uncertainty in our data to say for sure. As better data comes out from the Gaia mission tracking the positions and velocities of stars in the Milky Way and the large melaninic cloud and with even more observations of M33 and Andromeda with the Hubble Space Telescope and Jbus T and maybe even Roman once that launches, we can hopefully reduce those uncertainties to reduce the uncertainties later on we run the simulations and get a clearer picture for what could happen. But a substantial amount of work is needed before we get to that point. And as Savar and collaborators put it, as it stands, proclamations of the impending demise of our galaxy seem greatly exaggerated.

### Bloopers [13:56]

exaggerated. One of the first things that I learned about our universe that really hooked me and made me want to become an astrophysics astrophysics. Makes no sense. You know what I say, space is hard, words are harder. So to do this, to run these kind of simulations where you press fast, press fast forward, press fast forward and JT and maybe even Reuben once that launches, not Reuben. And maybe but Reuben, I meant what did I mean? Uh Roman, that's what I meant.