 Okay, hello and welcome everyone to today's Mount Storm though outreach talk on life story of the galaxy Now if some of you are wondering what the galaxy is the galaxy is basically a collection of lots and lots of stars and Sometimes if you have been If you have been at night and you have seen a huge stream of gas and dust in the night sky where it is dark When you're in our camping or somewhere where there's very less ambient light like here you would have seen this massive lean-up first gas and Stars and this is our very own galaxy, which is called the Milky Way In this picture, we also see two other galaxies which are part of our local group of galaxies which basically go around the Milky Way and There are they are here this fuzzy thing here and the second fuzzy thing here These are called the small and large Magellanic clouds and they're also galaxies today We will be talking about Milky Way and many other galaxies how they are first their life story And all that in today's talk it'll go on for 20 minutes if you have any questions Please put them in the comment section and I will get back to them after the end of this talk Okay So before we go into galaxies, let's first go about who I am, right? So I am Radh Sikar. I'm a PhD student from India and I work at the astronomy department at A&E And other than that I have how much which are Motorcycling hiking and today I will be talking to you about life story of the galaxy So to get a sense of how big galaxies really I will start zooming out from a building and we'll be zooming out at a constant rate And then in that we'll reach Milky Way and the other two galaxies that I showed you in the first picture Okay. Now here we are zooming out from a building. Now we have slowly reached Europe then Earth and Now we are called the moon Then the Sun our big bright yellow Sun and as you zoom out further and further into lots of stars and dust away There's a Milky Way, right? so we Got to Europe in around seven seconds. We got to Earth in around eight seconds we got to Sun around 15 seconds and And to Milky Way in around 24 seconds So that gives you an idea about if you're zooming out almost uniformly How big the galaxy actually is we have so many so many stars in it Now if this is an estimate of how the Milky Way may look like because we Can't really look at it from outside. So we can only estimate how it may look like otherwise So this this is the center of the Milky Way and we are and it has a big bar here And it has spiral arms With lots and lots of stars in the spirals and we the Sun in the solar system lie in one of the spiral arms around two-thirds out The Sun is 25,000 light years away from the center of the Milky Way Now if you are wondering what a light is a light is a unit of distance It's basically how far light travels in one whole year and it's almost equal to 10 trillion kilometers That's one with 13 zeros after it now. What's a typical galaxy made up of so again here's a picture of the Milky Way And you see there's a lot of bright things here which are stars then you see a lot of dark patches which are dust and of course We already know that stars are basically made up of gas So a typical galaxy is made up of gas dust Billions of stars in a disc. You see it's all very flat and circular. Okay, and Most galaxies have a big black hole in the center and We have something invisible in a galaxy as well not dust. It's dark matter. So Just to motivate dark matter in a short way It's if you look at how fast the stars are going around the center of the galaxy and Then you calculate how much total mass is there including all the stars in the big black hole in the center That mass together cannot Pull the sun or any other star to keep on rotating around the center at the speed Which it is going. It's like if you swing something too fast Then it should the tug of force gravity which is pulling you towards the center should give up And the star should be flood outwards But then that doesn't happen because there's some invisible matter Which is a lot of boss and it attracts the stars and gives them from flying out of the galaxy If you have more questions about dark matter, I can take them up later on in the talk or after Okay, now Milky Way is a spiral galaxy, but galaxies come in many different shapes They come look at me like ellipses Or they can look like pinwheels Like a ring Like a barred spiral You see here you have a bar in the center and spirals going around And Really exotic shapes like jellyfish Now this is a system in which galaxies are classified Based on how they look. Okay, you have different kinds of spirals and then where you just have yeah You have spider shapes and then you have bars plus spirals Milky Way is one of the bars plus spirals kind and you have ellipses This is something known as the Hubble fork Now how are galaxies formed? Now here in this title boom means big bang and then after a lot of time we had galaxies So after the big bang you see in the left bottom insert here You have a lot of dark matter and gas that is distributed around in a web Okay, it's it's like a spider's web and all these webs they start falling together to the center in the form of oops Yeah, the matter and gas start falling towards the center and They all get together and form really really dense clumps and once you have lots of gas and dark matter Some of this gas can fuse together to make stars so And the stars and a lot of these systems of stars and dark matter come together and start making a big spinning disk Like you see here This figure here, you see we have made our own galaxy by just putting dark matter and gas in through this cosmic web and then Center of it center at one of the nodes of these cosmic webs we form galaxies Okay, what happens? As galaxies age, how do they do they look any different? So young galaxies are often blue and they Are more in the shape of a disk that either parts of spirals or part spirals. They basically have a very big disk component Okay, and they look very blue. Whereas older galaxies Look red. Okay. This is because When galaxies make stars they make all sorts of stars starting from blue red yellow like a sun all sorts of stars But the blue stars they Are the brightest and the biggest whereas the red stars are the smaller ones and They are some more dimmer. So the blue when the galaxies are young. They have a lot of blue stars and these are really bright now By the time you By the time the problem with blue stars is they burn so bright and they have lots of miles But they also burn really fast and they are gone. They die within a few million years Whereas the red stars which are tiny, but they burn very slowly They can last up to billions or even I think trillions of years So because of that as a galaxy becomes older and older only the red stars survive. Whereas the blue stars die off Okay, now we also saw some spirals and bars in the galaxy is uh structures that we saw but Is it always the same stars that make up the spiral or is it different ones? So to explain that I have this small video In which you see if you follow the spiral you see that Stars are leaving and new stars are entering the spiral. Whereas the pattern remains the same So this is similar to a traffic jam. Whereas when your one car slows down and then the five cars behind it slow down But then the first car can always speed up and leave and then this jam that is there in the road It just keeps on getting refreshed. So new cars which join behind start slowing down which is in this case stars and the old Ones which were part of the traffic jam. They start speeding away so The spiral arms or bars are basically like traffic jams in a galaxy galaxies have some of the prettiest weddings in the universe Now I'll show you a few pictures of that and you would totally believe me. I think so here are mice galaxies. You see And then there's ngc 3921 Yes, another pretty picture of the galaxy wedding and then here we have a flying v of galaxies It's amazing how beautiful galaxy weddings can look and This is a simulation from way back in 1995 which shows two spiral galaxies merging and then it compares it to real-world observations Of galaxy mergers. So you see at different times You can see that the we are in different stages of the galaxy mergers. So if you pause it here You see that we see this image in the sky, which is basically at this stage of the galaxy merger. And then Yeah, here You have this one And because there are discs here and they can be in any possible orientation will basically see galaxy mergers from all possible different Now galaxies can also sometimes look like rings like this one with a big yellow center It's called the whole subject And a big outside radius of stars and gas or it can even look like a cartwheel with Spokes running out from the center Now how ring galaxies form There's one theory that she says that you have a galaxy merger again So one galaxy comes it passes through the center of the other galaxy Now that sends a shock wave outward which basically sends All this gas out what and as the gas travels out it the galaxy starts making new stars in this gas around it So that's how a ring galaxy is formed Now galaxies also like living in big huge families with thousands of other galaxies They're called galaxy clusters. Sometimes they also live in smaller groups and they're called galaxy groups Okay, here is this is called pandora's cluster It's because this is like when you look at this image It's like opening a pandora's box full of galaxies and so many interesting physics things that we can learn from this Just this picture. So if you Galaxy families are not just composed of galaxies, but they also have a lot of dark matter And a lot of hot gas the hot gas is called Intra cluster gas, which is basically the gas between galaxies in a cluster and this gas can be really really hot It can be as hot as a few million kelvins Now In this picture you see in red that you see this very hot gas And in blue you see how much dark matter. So this is an example of where you have the nodes of the cosmic web You have lots and lots of dark matter. You have lots of galaxy in there They like to live in big families And they also have lots of hot gas between them Now this is another one, uh, really pretty galaxy cluster Uh, which looks like it's smiling Now it is really interesting why this galaxy cluster looks like it's smiling. It's because of something called gravitational lensing If you want to know more about gravitational lensing drop a question in the comment section and I will Try to explain it further during the questions Of course, yeah, this does look like a happy family Now coming to cosmic jellyfishism. I shortly talk told you about this beautiful jellyfish galaxy So how does this, uh How do you how does the galaxy end up looking like a jellyfish? You see here? We are developing a deal of this jellyfish galaxy, right? So if you look at this picture in x-ray again You see that it has a humongous state in x-ray Now what has happened is this galaxy wanted to be a part of a big galaxy cluster It wanted to join a family But what happened is the family already had lots and lots of hot gas So when the galaxy tried to come in and become part of the family It had to get rid of many much of its gas and stars. So they got shredded out Basically got rid of a lot of its gas uh For comparison you can think of going really fast on a hot day in a convertible So if you have your windows down and your roof open All the hot air just comes in and takes out whatever air was originally inside your car So it's basically the same as a hot wind Blowing out the gas that was already part of the galaxy Now here now galaxies are not always very nice They can also bully some smaller galaxies around them If you remember this picture from the first slide here, we have a milky way and Here we have our two satellite galaxies. So these galaxies just go around the milky way like the moon goes around our earth These are the Magellanic clouds small and large Magellanic clouds now you should look at the Around or milky way in uh, let's say radio in radio frequencies basically see a lot of gas that emits These lines and that's shown in red. What is happening is milky way is pulling these tiny satellite galaxies into giving up their gas And you can see that so in this video we have the small and large Magellanic clouds So they are the satellite galaxies that are going around earth And as they're going around milky way is tripping them off the gas. You see all the red gas that is forming At this point. So this is almost exactly the same as the stream here, which we see now So this gas was originally part of these two tiny galaxies But our milky way bullied them into giving up their own galaxies See their own gas So your galaxies can sometimes not be that nice. You can bully other galaxies now Death of a galaxy. So how do galaxies die? This is a short poem written by myse So it basically summarizes How galaxies die Now, uh, what happens is Galaxies, uh, they need gas to keep on making stars. Okay As you as galaxies grow older and older they start using up almost all the gas And ultimately they have no gas left to make no new stars But and also most of the blue stars start dying faster First and then you are green yellow. All those starts are dying off. Then you're left with the tiny red stars Which are not that bright and then uh, you basically form no new star with the red stars You run for millions of years. So In the end you are left with lots and lots of tiny red stars and that's basically the death of the galaxy So what have we learned today? Young galaxies, which are first picture They are blue because there are lots of young blue stars And which are the brightest There are lots of gas and stars and they are making stars continuously. They make lots and lots new stars Then galaxy marriages, according to me, they are the prettiest weddings in the universe Galaxy families, they contain thousands of galaxies and they make happy families And old galaxies They are red and old stars and they're basically almost all of gas Okay, so we have reached the end of this Questions as uh, sorry the uh main presentation. So now I can start answering questions Okay, first question is is our galaxy a pinwheel So I can go back to the relevant slide in which I show the approximate structure of the milky way Yeah, so the milky way is more like a small bar Plus the spider it's not exactly a pinwheel pinwheel means all of these arms start right from the center That was the Inwheel galaxy You see it doesn't have a bar. It's a spiral galaxy with a small bar in the center Uh galaxies are generally measured in kilo par 6 So for one par 6 is basically like three light years Uh par 6 are more relevant as an astronomical uh unit because uh one par 6 basically means you look at the angular So basically we divide this kind of different angles and then we try to look at the same object six months apart then we See oh this object is now this much just Angular It's at a different angular position now compared to six months back. Basically you're on the opposite side of the sun Six months after and then if they're separated by one second, we call it uh parsing So it's much more important if you're using a telescope to observe, uh these galaxies It's easier to And estimate distances in terms of par 6 Okay Now the third question is so the milky way would be a young adult middle-aged I would say it's middle age going into old age, but the milky way will Still has a lot of galaxies around it. It's going to ban Andromeda galaxy it's going to merge with andromeda galaxy So when two galaxies merge they get a lot of new star and they start making lots of lots and lots of new stars But then after that they also become old and uh start dying Okay, uh How fast do galaxies travel must take a very long time for one to pass through another That's true galaxies can travel up to thousands of kilometers per second or maybe even faster. I have to Check that actually I can get back to you in the comments later It must take a very long time to pass each other Yeah, it can take up to billions or even sometimes billions of years for galaxies to pass each other But when you're talking about astronomical timescales given that the universe universe from 13 billions 13 billion years back 100 million or even a billion years doesn't seem like that long a time Could a hypernova destroy galaxy? I am assuming you are talking about supernova So supernovae are basically big stars that explode in spectacular And it's basically a really nice spectacular. You gives out lots of light. In fact supernovae can outshine the entire galaxy when they explode and Uh, but they can't really destroy a galaxy if many many supernovae go off together at the same time What they can do is they can send all the gas in their own region They're like a bomb exploding in the galaxy So what they can do is they can send all the gas around them out of the galaxy But that's as much as they can do they can't really destroy galaxy Speaking of colliding galaxies Is our galaxy going to collide with others in future? Okay for this I actually have the right slide. I have a video of what it may look like when Milky Way and andromeda collide to make uh, either we can call it milco meta or or milk dromedar Let's go to that video And here it is. Yes So this is milky way and then we have andromeda and when Start colliding or they have a spectacular marriage. They first pass through in the comeback and collide and Then they make a bigger galaxy and they look red Also when get big galaxies collide the big big black holes in the center They also merge to make an even bigger black hole in the center Okay, the next question is At the very beginning, what comes first dust gas or dark matter? Where do the dust gas or dark matter come from or start from? Okay, this is a very good question This is a really good question. So uh basically dark matter dark matters from this Cosmic waves of gas city of There are these cosmic waves of dark matter and then galaxy follows the dark matter because dark matter is a lot more important So they form the biggest part of they basically attract all the gas And then as the gas starts falling in and then they form small galaxy, let's say some small proto galaxies and then Once they start these some small proto galaxies will start merging to make a proper galaxy with the gas gas and Dark matter and then they start they have lots and stars and then these stars They basically start making the dust so the dust comes much later So first you have dark matter then the gas comes in and Then comes the dust If a galaxy sling slotted another galaxies gases Couldn't the gas combine to become a jam start? That's again a really good question Yes, uh, if galaxy is slingshot another galaxies gases It generally leads to an explosion of star for me sometimes Some almost dead galaxies if one they collide with another galaxy What happens is all that gas that they had sometimes can come together and start making new and new stars But then it will only be short lasting because that gas will finish out really quickly Now there's another question. Are there such things as cologne of us? Yes, there are and if you want to have a look at some of our older videos Georgie Taylor, uh, wanna See did an outreach talk about supernovae if you weeks back So you could have a look at that and yes cologne always exist So this has been a really fun round of questions. There are some really good questions Okay, I will wait for one moment. Uh, there are more questions Or you can end the talk Okay, so there's a question. What would happen if black hole t o n six one eight replace tragedy as a So I don't really know what's the mass of t o n six one eight, but then so the major gravity Force of gravitation comes from the dark matter in the galaxy So the central supermassive black hole has almost no function even if it was not there We would still be rotating around the center of our galaxy at almost the same speed So the major amount of mass is not in the black hole, but in the dark matter So it doesn't really matter if the center black hole was replaced by some other black hole Next question is where do the dust in galaxy formation Rise from because there are no planets or asteroids yet, right? Yes, that's true That's basically it comes from stars and stars explored. Uh, they Basically clear so stars use to make new and new elements. So initially when uh, like after the big bang And then when you started forming the first stars and galaxies We only had hydrogen and helium and then as more and more stars Started fusing these different elements together and then they started exploding We started making the newer elements. Uh, and we started making dust okay, and then Once we had your newer and new and then what happens is when these starts explode they try to mix all these Uh new elements that are formed. Uh, they get mixed up together and if the stars explode then that's really good because all these different elements from different parts of the local matter come together and then Yeah, they come together and uh, basically then they can Make another new generation of stars which would have more dust in them now Dusty stars are different from normal stars And also the area around the stars you can start making planets, uh, and asteroids around them So they come in like the second or third generation of stars. They're more likely to come in the second or third generation of stars Planets that are stored are a much later thing. They won't be there in the early universe Okay, now There's another question on uh, is there bigger things than kilonovers? Yes, there are bigger things than kilonovers. There are super novice, but uh for this again I would refer you to a really good talk by Giorgi Who talked about many different schemes of explosion in space. So you could have much more detailed answer Once you watch her talk or if you have further questions, you can again comment in the same link And I will reply to you at a later time Do we know what causes stop matter? So scientists When they don't know what something is they try naming it as dark matter or dark energy Dark and we cannot understand it. So there are some theories regarding what causes dark matter, but we Don't really know What it actually is Now that's another question. Does dark energy have a part to play in galaxy formation I would say dark energy would prevent galaxies or new galaxies from forming because what it's trying to do is right now The entire universe is expanding faster and faster due to dark energy. So what is happening is All the galaxies that were Earlier closer to each other now moving farther and farther the farther you look if you look at a distant galaxy It is accelerating away from you. It's not just Moving at a constant speed. It's moving away faster and faster. So Dark energy is expanding the universe so fast that after So a few billion years what can happen is the milky way will have no chance of Going close to any other galaxy outside its local group So all the galaxies near milky way can merge and then make another new galaxy, but Because of dark energy the universe would have expanded so much that we'll be away from everything else Now that's the question. Do universes come before galaxies? Yes, universes come before galaxies first the universe form through the big bang then we had After sometime so first everything was hot then everything cooled down and once everything cooled down they started and there were some There was some asymmetry because of which we had these dark matter webs and in these webs you had gas cold gas pollen Along these webs and we started making stars where there was lots of gas and then slowly these small areas of stars and dark matter came in together and We had lots of gas and lots of dark matter in areas called galaxies and that's how the first galaxies came in Okay, any more questions? If so, please type them in the comment section And I'll get back to you as soon as I can or if you have a question Later as well, uh, you can still put it in the comment section and uh, we will try to get back to them And we'll wait for one more minute for questions meanwhile, we can all watch a pretty video of zooming out from A building to a galaxy. How big is the biggest galaxy in the universe? Well, we may not have detected the biggest galaxy in the universe yet, but galaxies Unlike us, let's say don't have just one man merger. They have many many many mergers So as a galaxy grows older and older many of these galaxies nearby it start merging and they make Really really big galaxies. But the thing is they don't Make new stars after some time because after some time they just get rid of all the gas So they can be really big galaxies, but they will only have red and They will only have red stars So the biggest galaxies can also occur in the center of galaxy clusters So we look at these big happy families of galaxies You find that Yes, so in the centers of these big galaxy clusters, you have uh, the biggest galaxies in the universe They are called vcgs or brightest cluster galaxies. So they are really big giant elliptical galaxies And they've come in the center of big clusters Well, thank you everyone, uh for listening in and we had really good questions in the end Please be online for our next talk. We'll keep on doing such online outreach events Thank you all for listening again. Bye