The Supermassive Podcast - 27: How to Build a Galaxy

Episode Date: March 25, 2022

Izzie and Dr Becky are attempting to tackle the massive subject of building a galaxy.  Professor Mike Merrifield from The University of Nottingham explains how galaxies form and our very own galaxy expert, Dr Becky, tells us why they come in different shapes and sizes. Plus, Dr Robert Massey has his top tips for stargazing in spring.  Thank you to Brilliant for sponsoring this episode.  Head to brilliant.org/supermassive to start free courses in maths, science, and computer science. The first 200 subscribers will get 20% off. Explore the Galaxy Zoo here: https://www.zooniverse.org/projects/zookeeper/galaxy-zoo/ Space Book Club recommendations... Back to Earth - Nicole Stott The End of Astronauts - Donald Goldsmith & Martin Rees The Disordered Cosmos - Chanda Prescod-Weinstein "A Year In Space" by The Supermassive Team will be out on Oct 13th 2022. Pre-order here: https://www.amazon.co.uk/Year-Space-Supermassive-Podcast-Astronomical/dp/1472299507/ref=sr_1_3?crid=1O3PS3QUCPP2A&keywords=the+year+in+space&qid=1650904438&s=books&sprefix=the+year+in+space%2Cstripbooks%2C94&sr=1-3 The Supermassive Podcast is a Boffin Media Production by Izzie Clarke and Richard Hollingham. Editing this month is by Sarah Moore.

We are absolutely thrilled to say that Brilliant is sponsoring this episode of the Supermassive podcast. There's no denying that podcasts are a great tool for learning, but so are videos. You know I love a video. Brilliant is an interactive STEM learning platform that helps you to truly understand concepts in maths, science and computer science by guiding you through engaging hands-on courses. You have got to see these courses. The visuals are incredible and they're a great way to get an overview and learn the basics of lots of different topics.

And ultimately, it's fun. And this might sound odd, but I genuinely found working through calculations during my degree quite relaxing. So I've got my eye on the new everyday math course that's just gone up this month. And also, Izzy, if you get stuck, Brilliant provides these in-depth explanations

to like break down the material for you even more so that it stays fun. Yeah, I'm probably going to need that. Head to brilliant.org slash supermassive to get started for free and the first 200 subscribers will get 20% off. Although space is very empty, it turns out galaxies aren't actually that far apart from each other typically.

The blueprint is that yes, there's a supermassive black hole at the centre of every galaxy. If you look at it from one side, it'll look like it's going clockwise and if you look at it from the other, it'll be anticlockwise. Hello and welcome to the Supermassive podcast from the Royal Astronomical Society. With me, science journalist Izzy Clark and astrophysicist Dr Becky Smothers. Yeah, this month we're attempting to tackle the massive subject of galaxies. Also happens to be my favourite subject as well. It's so convenient.

This topic is actually so big that we're going to be doing two episodes all about galaxies. Yep. So first up, I chat with Professor Mike Merrifield from the University of Nottingham about how galaxies form. And, you know, let's use Becky here. She is our galaxy expert. So Becky will be telling us all about the different shapes and sizes that galaxies come in. Plus, Dr. Robert Massey is here, obviously, the Deputy Director of the Royal Astronomical Society. So there are a lot of galaxies, but let's look at our own one. You know, how much do we know about the Milky Way? Well, a lot of galaxies is definitely an understatement, isn't it? Yeah. And I bow to Betty's expertise in much of this. Well, I mean,

we know quite a bit about our own galaxy, but I guess the difference is that unlike all the others, we don't have an external view. So we've had to piece together how it looks from the inside, which is a curious and intriguing thing to do. And there are disciplines like galactic archaeology that gives us a clue to that. So we look at the way that stars moves now

and we try and understand its history through that process. And from that kind of work and other things like understand its history through that process and from that kind of work and other things like understanding the age of stars and so on we think the galaxy has been there you know it was among the earliest to form it's probably about 13.6 billion years old so a bit 200 million years after the big bang and it's huge it's got spiral arms stretching out from this central bar the whole thing is depending on how you measure it 200 000 light years across possibly bigger if you include all this halo around it and you mean we need to update the song we do exactly 100 000 light years side to side monty python told me that's how i remember

and as many as 400 billion stars so really really big numbers and then of course you know the mind-blowing thing is always that this is just one of many billions of galaxies just in the universe that we can see it's like questions like this where you're like my life is so insignificant i am just a speck no no no is he the other way i like to think about it is that there are infinite possibilities out there and infinite places you could go and infinite things that you could be that's how you look at it right the universe is so big and the earth is very special within that yeah we live it but it's also a really nice place okay um and peter hennis on twitter has actually asked a question and says how do we know the shape and size of our galaxy it's like guessing the size and

shape of a city without ever leaving your bedroom is that accurate yeah yeah it is it's exactly like that i remember a long time ago having a great lecture actually where someone was saying if you stood on your roof at night and looked at lights in a city you'd start to work out the size and shape of the city by studying and things like traffic lights having similar frequencies and that kind of thing you know so it's not all that easy to answer but we can tell something about its shape even with our eye because if you see the inside of our galaxy, the Milky Way at night on a clear, dark night, and the winter and summer months are best for that. And there's no moon in the sky and all of those things. You see this band stretching across it.

So that tells you, once you even pick up a pair of binoculars and look at that band, you can see it's made up of lots of stars. It tells you the stars are concentrated in particular directions. So it tells you something about the shape of the galaxy we're living in. And our first president, William Herschel, the first president of the Royal Astronomical Society, was one of the people who tried to map it. And he came up with a disk shape with the sun at the centre. So, you know, not understanding the different types of stars so well, that was a good starting point. But then in the 20th century, because we knew more about

different stars and how bright they really were, if you see a star in the sky and it's faint, it might actually be genuinely faint or it might be far away. Those are the things you need to understand when you're trying to understand the shape of the galaxies. And then with radio observatories from the 1950s onwards, we looked at things like hydrogen gas and we could see the spiral structure of the galaxy we're in so when you look out to external galaxies a lot of those are spirals so that was consistent you know the milky way is one like that and with things like infrared astronomy now we can see through dust so we can see you know further than we could before and measure more of those stars and then brilliant amazing missions like gaia which have mapped so many

stars, getting up for a billion stars. We've got extraordinarily good maps now. So it's a lot better than it used to be. But it was a tricky thing to do. And if you didn't have those tools, you know, all you would probably know is that this is banned in the sky. And before, you know, before we had that work as well, you know, there's a lot of uncertainty before the larger telescopes were developed about what these fuzzy objects that we now know or other galaxies actually are too yeah and that's what i study so i'm glad they resolved those fuzzy blobs so robert we'll catch up with you later in the show to take on some listener questions but is he now i hear you've got a special guest this week as someone who used to be my boss i'm like should i

be quick in my boot well he used to be my former lecturer as well like, should I be quick in my boots? Well, he used to be my former lecturer as well. So we've covered what we know about the Milky Way so far. But as I've said, there are a few more galaxies out there. So I got in touch with Professor Mike Merrifield from the University of Nottingham to answer one of the biggest questions on my mind, which is how does a galaxy form? Obviously, in the very early universe, there weren't any galaxies at all. But the raw material, the gas that would come together to form the galaxies, the dark matter that would come together to form the galaxies was all there. And so we just had to kind of get it all into one place, or at least for each galaxy all into one

place. And there the force that helps us out is gravity. If you just have a little bit of a density enhancement somewhere, that's going to attract material from around it and that will then in turn attract more material and so you have a kind of runaway process. So you end up pulling the material together, the gas that's being pulled in will start turning into stars and there you've made a galaxy. Actually, we had an interesting question from a listener

which was saying, what sort of starts first? You have all of that matter that pulls together and you sort of have this rough galaxy and then stars start appearing. Or are the stars made first and then you get bigger and bigger and you've got a galaxy, a cluster of stars? Well, the short answer is we really don't know yet. And it's one of those things that we're kind of pushing towards. It's hopefully that one of the next things we're going to discover. But almost certainly the first stars, when they formed, they didn't form in complete isolation.

Stars tend to form in clusters in the universe today, and almost certainly that was the case in the past, that you'd have a particularly high-density material, region of material where the stars would start to form. And so probably, you know, at the very least, the first thing that formed would have been a cluster of stars. Now, how big a cluster of stars has to be before you call it a galaxy is kind of slightly a matter of semantics, I guess. And so then what happens? What is the next step in that galaxy formation?

So when people first started thinking about galaxy formation, it was pretty much that was the whole process, right? You would just have this what was called the monolithic collapse. You'd have this kind of collapse of gas and more and more and more stuff would get added to it. Over time, the galaxy would grow bigger and bigger and bigger and would turn ultimately into something like the Milky Way. The kind of missing part of that story is that galaxies don't actually form in complete isolation. They tend to form, you know, the galaxies tend to have neighbours. They tend to have other galaxies around them. Although space is very empty, it turns out galaxies aren't actually that far apart from each other typically. And so that means that there is a

non-zero chance that they'll just crash into each other. So the other big part of the way you make a galaxy, as well as this kind of ongoing process of material just falling in, is that adjacent galaxies just collide with one another and end up forming a galaxy which is twice as big. So the other way a galaxy can grow is through this kind of merger process as well as through the secretion process. In the case of the Milky Way, we can kind of see the partially digested remains of probably half a dozen smaller galaxies. The biggest galaxies we find, they're probably about 10 times the mass of the Milky Way. So there are galaxies a lot bigger than the Milky Way, but there aren't any galaxies out there that are 100 times the mass of the Milky Way. Why don't galaxies just keep growing? As well as these processes that kind of enhance

galaxies that make them grow, there is also sort of negative feedback processes that stop galaxies from growing. And the two processes that really stop galaxies from growing are the explosions of stars, so supernovae, and when they blow up, they actually tend to blow the gas out of the galaxy. So for fairly small galaxies, that's a very efficient way of actually stopping them from forming and limiting their number. For very big galaxies, there's an alternative kind of feedback process, which is one of the components we haven't talked about so far is that there's this supermassive black hole at the centre of galaxies.

And that supermassive black hole, if it starts accreting material itself, it becomes very, very very energetic starts throwing out light and material itself and that can be so energetic that it can blow the material out and just to clarify this isn't something that stops the making stars full stop at least in the short term it really can shut it down completely you really can make a galaxy stop forming stars entirely just by blowing out all the material that it would have used to make the next generation of stars of course then you've got a galaxy that's just sitting there and it's still got a pull of gravity. So it will start pulling more material into it.

So you could actually have it, you know, stop its star formation. And then maybe at a later date, it can sort of come back to life again as more material falls in. I mean, individual galaxies really can have quite complicated stories to tell. So there's lots of that weather type thing going on for each individual galaxy. But there's kind of the climate thing of how did the galaxies overall form as well. Right. And so when we talk about when they started, you know, how far after the Big Bang are we talking about here? We honestly, at this point, we don't know, at least observationally, we don't know because we haven't been able to push back that far, you know, with the telescopes that we're looking at the universe with. But it really is very early. So, you know, with the universe

that's 14 billion years old, certainly within hundreds of millions of years to that first billion years, it was already happening. But again, we get back into this semantic thing of when those first stars formed, is that a galaxy already? So it really depends on when you want to say this is a galaxy and that wasn't as to when you actually say that galaxies started to form.

I see. And so I guess this leads on to a question of how do we know any of this? I mean, I guess the good news from my perspective is that we don't, or at least we don't in all the detail yet. Otherwise I'd be kind of out of business at this point. But we have a variety of tools that we can kind of bring to bear on this. The first is that you can observe the universe and there are sort of two approaches to observing the universe to learn about how galaxies form. One is that you could just look very, very far away. And of course, as you look to great distances, because light's travelling at a finite speed, you're seeing galaxies as they were in the past. So already we compare to galaxies

to a point where the universe was only a billion years old. And we can see when we look at the universe when it was only a billion years old, that the galaxies back then were different from the ones we see today. They were smaller, for example, they were less massive typically. And actually their structure was different as well. They were more chaotic looking, they were more complicated looking structures. So there's this sort of direct approach of peering back in time. The snags with that are firstly that when you're looking at those very distant objects, they're very small, very faint. And so it's hard to see much detail. And the second thing is you only get kind of the snapshot view, right? We can see what galaxies look like when the

universe was a billion years old or 3 billion years old or 7 billion years old, but we can't kind of join the dots and say that galaxy turned into this galaxy turned into this galaxy. So the alternative and kind of my end of studying galaxy evolution is you can kind of look at the finished products the galaxies in the very nearby universe and kind of try and do the archaeology of how did this thing get put together and the advantage of that approach is that we know what the finished product is because that's what we're looking at the downside is that as with any kind of archaeology you only have kind of fragmentary information you don't get the whole picture in the same way that you do with a snapshot view. So in principle, they're kind of complementary to each other,

and you'd hope they ultimately would give the same answer. And then the final aspect is that instead of doing the tedious thing of using a telescope and all that, you can actually be a bit grander and say, tell you what, I'm going to make my own universe and make my own galaxies. Yes, I had a feeling it was leading to this point. And so there were the simulators who at this point, you know, you can actually put the entire universe into a computer or at least the laws of physics and say, OK, I'm going to start with what I think the universe was like

and just turn the handle and see if I may end up making things that look like the galaxies we see around us today. What would you say are the next big things that we need to do in order to further study galaxy formation? There's lots of incremental things in the sense that, for example, from those simulation ends of things, you know, the quality of the simulations, the resolution, the detail that we can study within them is increasing all the time. From the observational end, I guess the thing that astronomers are most excited about at the moment is the James Webb Space Telescope. We can push back where we observed, you know, the first galaxies to form, the first stars that forming to, you know, maybe a billion

years after the Big Bang. With JWST, we're going to be able to push that quite a bit further. And so that question about, you know, which form first, was it stars that form first? Was it galaxies that form first? What kind of environment were those first stars forming in? What did those first galaxies really look like? The hope is that with with JWST we really will be able to push back far enough to be able to answer those kinds of questions oh I cannot wait for the first James Webb image oh god we've said it was and I'll keep saying it until they arrive thank you so much to Mike Merrifield from the University of Nottingham yeah and we literally just saw like the first properly focused image from james webb last week as well and oh my i'm just i'm like i got asked how how do scientists feel about seeing this and i was like we're giddy it's the only word for it is

that we're absolutely giddy james webb is working at the peak that the laws of physics will allow it to work at you know if anything had gone wrong i either fold out or anything like that we could have ended up with something that was you know we had to you know have a work around to have it still keep working and maybe would have got less performance than we expected but that image just showed that it's amazing like the resolution so for everyone else it's an alignment test there is this incredible sort of ready hue and right in the center is this flash of really clear light and when you compare that to what was you know the most accurate picture until this point of that part of the sky yeah exactly you're just like oh my god yeah everything goes from just like pixelated fuzzy blobs to crystal clear shapes of galaxies that's what's so amazing is that this is a calibration image and it almost looks like

it's like the hubble ultra deep field it's ridiculous i know i always message you i was like no i'm speaking to her tomorrow we will talk about this on the podcast and the one the one big question that i've been asked over and over again i know our listeners might be listening if they've seen it is what's with the weird sort of spiky shape on the james webb images you have this sort of six pointed star with then two extra spikes coming out the side and we're not really used to seeing that because with hubble images we get these four pointed stars essentially and it's all to do with what happens the light as it goes through the optic systems, the mirrors. So because James Webb has a hexagonal shaped mirror on something that's round, like Hubble, you get these six points that are like 60 degrees separate, separated, like the angles in a

hexagon, right? So it's very, very regular. But then also because you have this giant big boom holding up the secondary mirror, it's like 25 meters away. You also get these extra two horizontal spikes as well that are due to that. And it's all to just do with the setup of the system. the secondary mirror that's like 25 meters away you also get these extra two horizontal spikes as well that are due to that and it's all to just do with the setup of the system ah well now we know james webb detour i'm here for it always always if i said picture a galaxy what do you think of i think most of us would resort to some sort of spiral galaxy sprinkled with stars and perhaps some sort of central bulge but there is a lot more to it unfortunately for us this is very much becky's bag

so becky for the listeners just explain what do you actually research so my research is on the processes that affect galaxies through their lifetimes. So that could be any process that might affect a galaxy's shape, or might even somehow prevent it from forming more stars. Because stars can go supernova all the time, and they can make new stars out of the gas that's left over, but if you somehow remove that gas or heat it up so that it can't collapse under gravity, then you've somehow affected that galaxy. And so essentially when we look at a galaxy shape the shape can actually tell us what processes a

galaxy has been through like how hard of a life has it had really and that could be anything from an external process you know like say an interaction a flyby with another galaxy or even a full-on merge like a collision of two galaxies or it could be a process that's internal to a galaxy itself so the galaxy is literally shaping itself by funneling gas and moving gas around it either down those beautiful spiral arms that we see in some galaxies or along these big bar structures sometimes as well and you can kind of think of it as like this idea that we've stolen from biology right of nature versus nurture you know you have the very nature of a galaxy shaping itself but you

can also be nurtured depending on what environment you find it in if it's in sort of an empty environment or surrounded by other galaxies okay and so let's look at that a bit more so what are the different shapes that a galaxy can be well how long's a piece of string um you can have all of them now innumerable shapes right and my favorite category of galaxy is the miscellaneous category where we put things that look like penguins and mice and dolphins and all sorts into this random category but essentially there are two main types first type is that there's like a flat disc structure right like the milky way is um and that could have spiral structure maybe it could have a ring of stars in it it could also have this sort of long thin structure that we call a bar as well and

again sort of that would be like anything that's essentially featured right the Milky Way falls into that or you could have sort of a roundish blobbish featureless boring thing I shouldn't say boring I think they're boring but a lot of people devote their entire lives to something so no offense sorry yeah take that with Becky not yeah sorry but I think they're very boring um but essentially that can then tell us about whether it's a spiral shape or whether it's a blobish that can tell us what galaxy's been through essentially okay and so what actually gives us those spirals that we might see or whether it is that bar structure through the center you know what's going on there to give us that sort of structure yeah so essentially that's what the field of galaxy evolution is trying to explain right so obviously all these different fields in

astrophysics from exoplanets to cosmology to galaxy evolution this is what we're talking about here and essentially what that's trying to explain is how did we go from you know the soup of hydrogen after the big bang like where mike was talking about to all the shapes that we see today like what has shaped all of these things and so we think galaxy start life is sort of just like little clumps of stars essentially that are sort of in this embedded in this sort of gas that could be spinning that could then form this gas disc that you then form more stars out of and then you've obviously got this flat structure and then okay how do spiral structures form out of that how do bar structures form out of that if you have what's called an instability in this gas disc if it buckles slightly does that send like a wave

moving through the disc and therefore you can clump stars together and when we think about spiral structure it's also like is it an actual structure in the galaxy or is it like a wave in the same way that like traffic on a road is a wave right like you know how a mexican wave is a wave but actually it's only people moving up and down but the wave is moving around the stadium that's kind of what we think about it like sometimes in terms of spiral structure is it actually a structure or is it a transient thing that's moving around that just happens to be clumping stars into these spiral structures and stuff like that and we still don't really know which one of those is the case there's a lot of argument about how you even get spiral structure what it even is as

well but you can also destroy that spiral structure so if you have a lot of mergers of two galaxies essentially you completely rearrange everything in a merger right you tear it up and you you start afresh essentially and what happens is that you end up with instead of stars all orbiting a galaxy in the same plane like the solar system of the planets right you end up with stars orbiting in lots of different planes all chaotically kind of like a beehive right they're just right going in whatever direction they want to and that's what happens with the merger and it's how we end up with these huge big giant spherical blobs but that i call beehives that are i think they're very boring because they're very featureless but it's because they can disrupt that shape so we have very confident

that we know how the blobs form but the spiral structure is the more interesting and yet we still don't really understand it and i think a term that people will often hear about when we talk about galaxies are these elliptical galaxies yeah um those are the blobs the elliptical is probably the the more scientific term for it but i prefer the word blob because i hear rowan atkinson saying it in my head every time i say it but essentially that's what an elliptical galaxy is elliptical because obviously a circle is just a very special form of an ellipse right which is like an oval shape so we call them elliptical because they're not necessarily perfectly spherical they might be what we call triaxial because you can chop it along the z-axis, the y-axis and the

x-axis and you get three different shapes. So can you just talk us through the different regions within a galaxy? You know, for example, where are stars mostly formed? What are the different parts of a galaxy essentially? Yeah, I feel like we split galaxies into two main parts anyway no matter what kind of overall very detailed structure they have so really we have the disk and then what we call the bulge and the bulge you can kind of think of as like a mini elliptical galaxy so if you don't have what's called a major merger where you have two galaxies of the same size coming together that will probably completely destroy spiral structure and make an elliptical but if you have something like a smaller galaxy merging with a larger galaxy say something that's maybe like 10 of the size or the mass of the other

galaxy then you won't completely destroy all the spiral structure but all those stars from the little galaxy coming in will probably sink to the center and will form like a bulge so i like to think of it as like an egg yolk in a fried egg right that's essentially what you should picture the disc is the white and the bulge is the yolk in the middle right and galaxies essentially are then a blend of how big the yolk is and how big the white is right and so an elliptical galaxy is like one which is all yolk essentially and so where you form the stars in that structure is essentially then where the gas is and so there's a lot of gas out in the disk it's very calm very cold out there so a lot of stars form because

cold gas can be brought together under gravity because the molecules don't have that much energy you know flying around whereas hot gas which has usually been heated up by like a merger or something will sink to the center and you necessarily form many stars there and so we actually see this dichotomy when you look at galaxies that the disks look blue because there's lots of hot young stars formed there and they're a lot bluer in color whereas the bulge will look redder because that's all sort of the the older cooler stars that are like the dying embers of a fire and so you know kind of this reddish color but we also do see fully red spiraled galaxies and we see you know maybe a smaller fraction but still some blue elliptical galaxies

though as well that are you know still forming stars so these processes which transition a galaxy from forming stars to not forming stars can also affect the shape but not always so it's really difficult to disentangle and this is what i look at especially how the supermassive black hole plays a role in this so we think that the center of every galaxy so you've got disc you've got bulge and then right at the center there's also a supermassive black hole as well and and this is something that i want to talk about you know just how common is that is that like blueprint you've got a galaxy it's gonna have a black hole supermassive black hole in the center we think so

yeah that's like the leading hypothesis at the minute there's a couple of dwarf galaxies that might be challenging that but maybe it's just because we can't spot an intermediate mass black hole okay um and stuff like this but the blueprint is that yes it's a supermassive black hole at the center of every galaxy um and so if you've got gas for star formation that could be used by the black hole instead to grow bigger and as a black hole grows it gets what we call an accretion disc around it so a disc of this swirling material that's slowly sort of going to make its way into the black hole but then that starts to glow and so then that exerts this pressure due to light outwards of gas coming in

and so you can get these sort of gas coming in turned around by the pressure outwards from the light and then that puts energy back into the galaxy again can churn up the gas and stop it from star forming and so we know one of we know that growing a black hole is a process that can maybe stop stars from forming theoretically anyway but like finding it observationally is really difficult and disentangling it from all the processes that could have affected a galaxy in the past is really really difficult you know it's i like to say that it's this sort of like conspiracy of what we call quenching mechanisms quenching being like stopping a galaxy from forming stars they're all working together and picking out which one was responsible for the change in shape or the drop in star formation is really difficult

and perhaps this is something for next month but how does the black hole get there just answer that little one for me um we don't know um i like to joke that this is the astrophysics equivalent of a chicken or the egg did the galaxy of stars form first one of them go in supernova become a black hole sink to the center and then eventually grow from there to be the supermassive black hole as the galaxy formed and evolved over 13 million years or did a cloud of gas in the early universe collapse to form a not quite super massive a massive black hole and then a galaxy of stars form around that we don't honestly know well it's really handy having a galaxy expert on the team thanks so much becky you're very welcome i should say a lot of this information comes from

the galaxy zoo project online as well so this website that gets people to classify the shapes of galaxies because to do this kind of work we need huge statistical knowledge to do it and so you know we need classifications of over a million images of galaxies which is still something that computer struggles to do it can do the easy ones we still need humans to look at them so if you've ever classified on galaxy zoo thank you my phd and the research i do right now is possible thanks to you but also you know it's still got data on that it still needs classifying if you want to help out looking at pretty pictures of space and telling us what shape they are amazing we'll put that in the episode description so you can find it this is the super massive podcast from the royal astronomical

society with me astrophysicist dr becky smethurst and with science journalist izzy clark as promised we're doing space book club yes so what have we got gang uh okay so i have been reading um nicole stott's back to earth um nicole is a retired astronaut and so she's written about what life in space has taught her but also like what we as humanity can learn from it to solve you know the big problems still playing us you know like climate change for example like that and it's just it's a fascinating insight into the feelings and emotions and the headspace of an astronaut while they're on board the international space station which i'm fascinated by just that feeling of isolation but connectivity at the same time that you get i think it's fantastic and it's just really thought-provoking i could highly recommend

as well the audiobook which is narrated by nicole herself as well which i don't know it just gives i love when audiobooks are written by the authors especially with something like this it really just helps you feel more connected to it oh that is a good one okay yeah i really need to find that not finished it yet but enjoying it so robert what have you got well i haven't finished this book either and in contrast i've got a book by donald goldsmith i know donald goldsmith and martin reese which is called the end of astronauts which has just come out so i know i mean martin reese the astronomer royal you know i like him a lot i I also like Nicole Stott, actually, and her husband, Chris, you know,

who I went off to see in a book. Who you can hear on our episode. Oh, yeah, of course. Exactly. Why did I make that connection? They were both out trying to see the eclipse. So anyway, the end of Astronauts is, Martin Rees is quite keen on this theme,

and he argues that as robotic explorers get ever more sophisticated, that the need for humans to do some of that work declines and then it becomes more of a kind of adventuring and private adventuring thing that it is about you know government sending people into space but it is also very thought-provoking i mean he goes through the kind of arguments and says you know well is there a sort of genetic predisposition to explore you know probably not that's more driven by circumstances and those kind of things than we might imagine so i do recommend it and you know if only even if you're a great fan of people going into space just to challenge your ideas a bit and

you know presumably if you don't like the idea of people going in space it will validate those too but i think it's a good thing to read you know as we think about how much we uh send people up into space in the coming decades and you know whether we ever get anybody to mars or not yeah because i always hear these sort of like you know like competitions to become the next mars astronaut or whatever what was the name of that oh mars one yeah and you're just like disappeared without a trace oh yeah i think it's just i think honestly i think it's a little bit point unless there's a scientific reason for a human to go i'm so in favor of just sending a probe yeah i always think i've always been asked about this by journalists and i always think well actually you know if we could get there in a few days right then we'd be doing it now etc etc and

we could absolutely i'm convinced sure if governments around the world uh collaborated which admittedly is rather difficult moment but if they were to get together you know and you pulled tens of billions of dollars into this hundreds of billions you could absolutely send people to mars and back but it's a long journey two years it's fraught with risk and you know is that just that quick there and back thing enough for what you want to do for this scientific return when you can have rovers exploring the surface for more than a decade and more and we can and we can get a sample return back so i think it's even little drones that fly around the city well exactly helicopters yeah well yeah it's a really important debate to have because you know i think

we should should ask those questions you know if we want to send people it might not be about the science it might be about something else and that's yeah that's fine if people decide to do it and maybe i'm breaking the rules a bit this month because because you're not halfway through because i'm not even halfway i haven't even even started. But it's a book that a really close friend of mine has given me. And I'm five pages in. But I'm really enjoying those five pages. But anyway, it's called The Disordered Cosmos by Dr. Chandra Prescott Weinstein. Nice.

And for those who are not familiar with her work she is a theoretical physicist and it's it's for those if okay it's niche i'll just warn you but it's really interesting it's for anyone that's interested in astrophysics social justice and i guess that intersection between humanities and sciences and it's all about exploring physics and astronomy and how that is tied to human identity and history nice um that sounds fascinating yeah like she talks a lot about this kind of stuff on twitter as well so i've been a long twitter follower of tanya i think she's incredible but like you've i mean you often have to remind people like science is done by people we can't do science without people so and i think it just gets swept under the rug a lot of this stuff and so the fact that she's written i'm

gonna so pick up this book because it just sounds fascinating yeah i'm really excited to get to properly get stuck in and i've got a few weeks off soon and this is number one on my list so i'll give you an update of like actually yeah i'll add it to my tbr but who knows picking it up and in some very exciting news we'd like to announce that we're also bringing out a book this year as well it is called the year in space and it will be like an annual everyone remember having annuals as kids i love them i collected them so much i mean annual format book which highlights the best space news over the past 12 months and also looks ahead to the 12 months to come i'm so excited because one i'm excited that we've got a book but two i'm going to finally be joining the authors club that the rest of you lot are already a part of so it should be coming out in autumn and

we'll of course keep you posted for any keen beans that might want to pre-order that. I'm sure you'll be hearing more and more about it as the year goes on. But that's not the only good news that we've got. Becky's also got some good news of her own. Yes, I do. I'm delighted to say I am off the academic job market. Those who are familiar with it know that it is fraught with stresses. I essentially have funding

to carry on doing my research for the next three years and it is coming from the Royal Astronomical Society. I have been awarded the Royal Astronomical Society's Fellowship for 2022 and I will be spending

three more years in Oxford continuing my research on galaxies and supermassive black holes. And to say I'm excited is a huge understatement. I had no hand in the decision by the way yeah but hang on a second fair process i promise yeah interview panel and everything very very nerve-wracking and um yeah all these sort of like research proposals to say what you want to do a cv list of publications all this kind of stuff very competitive process and um yeah i'm

just delighted to say that i was awarded it oh well congratulations well done everyone right so i think we should get on to some listeners questions and i know that i say this every month but for this topic in particular there was like double the amount of yeah even i noticed that i was like so thank you so much maybe we, even I noticed that. I was like, oh. So thank you so much. Maybe we can carry some of those over to next month's topic. We'll see how it works. But Robert, we have this question from Gabby from Texas.

Hi, Gabby. Hello. And she asks, do all galaxies spin in the same direction? If not, what determines the direction of the spin? Well, hi, Gabby, for me as well we're so happy to see how much you like astronomy when we look at galaxies as you might expect about half turning appear to be turning in one direction clockwise and the other half anti-clockwise and what that says really is that you know you're looking out and things are averaging out it's

what you'd expect by chance so if you imagine looking at say a wheel or i was thinking actually about my daughter's fidget spinner for those of you with young children if you look at it from one side it'll look like it's going clockwise and if you look at it from the other it'll be anti-clockwise so it isn't surprising that on average you see that spread out neatly and it'll be very very weird indeed if that wasn't the case and as for how they actually rotate this goes back to what uh becky was saying earlier on about spirals and the way they turn and you typically have the arms trailing the rotation but not always and they're not like it's not like string winding around the center that's the thing to understand that you know that's why we talk about these this idea of waves of forming stars moving around over

millions of years and i think this is right isn't it becky that you get some situations where it's not like that where there might have been a recent collision or absorption of a galaxy and the rotation isn't quite what we'd expect yeah you can get counter rotating discs which is really strange like the gas going in opposite directions to the stars which is really really weird yeah yeah it's so so odd we can't really describe them apart from with emergent. Other than they're weird. Okay. Yeah.

Okay, Becky. Alex S says, is there a limit to the size of a galaxy? Also, why do we have a bunch of galaxies instead of one huge galaxy if everything was so close together after the Big Bang? Yeah. Okay. So I'll start with that one first.

So I don't know if people have heard of this idea of inflation. So there was the Big Bang, but then there was this period of incredibly rapid expansion you know more rapid than anything we see today that essentially imprinted whatever tiny quantum fluctuations there were right after the big bang because there will have been some fluctuations yes there's just a big soup of hydrogen but there would have been like oh slightly more clumped together over here or slightly less clumped together over here and then that was inflated massively until you get this sort of imprint across the universe of more hydrogen over here and less hydrogen over here and we actually see those imprints in what's called the cosmic microwave background if people have seen that picture of the splotchy blue and yellow red

stuff across you know sort of the sky but essentially yeah those splotches essentially tell us where more galaxies are going to have eventually formed in the universe because that's where there was more hydrogen or less hydrogen. And so that's why we don't end up with one giant big galaxy is because we ended up with this very patchy universe, essentially, and then that's just been expanding

since then, taking the galaxies even further apart, unless they were, you know, in clusters or something like that. In terms of like the most massive a galaxy can be at we actually think that that's limited by growing the black hole so actually when we look at the mass of a galaxy and the mass of a black hole the two are really correlated and we think it's because you know if you if you end up feeding the black hole you're not feeding the galaxy and then you get this feedback effect where the black hole can put energy back into a

galaxy and stop it forming more stars so we actually do see this big drop off of the amount of galaxies at very large sizes which we think is due to that process so i think the most massive that we sort of get to is around about a trillion times the mass of the sun but that's like pushing it for how big you can you can really get in terms of a galaxy. Thanks, Becky. And Robert Peet has sent this in and he asks, when we look at the oldest galaxies we can see, is there reason to believe they formed or behaved any differently than the newer ones we observe? Yeah, this is again astronomy as a kind of time machine. So if you look at things a very, very long way away, then you're seeing them as they were a very long time in the past. And in the case of the most distant galaxies, that's 13 billion years ago and more. So what you're looking at there is almost like the ancestors of the

galaxies we see around us today. So they haven't settled into the kind of shapes that we see today. They're not, you know, the characteristic spirals and ellipticals and so on. They tend to be a lot smaller, clumpier, as Becky was mentioning earlier. And with this sort of baby boom of stars going on, you know, absolutely starts forming incredibly rapidly as the universe takes shape. So those sort of spirals develop later on, you know, again, as Becky mentioned earlier on, and we see the kind of big galaxies we see today are ones that have absorbed and collided with neighbours to develop their shape. So it's more like, yes, they're different, but that's because there are ancestors. There aren't galaxies like this around in the same way today

because it was a very different epoch in the universe. It also is, for me, a really neat way of proving the Big Bang theory as well, actually, that the universe was definitely very different in the past because the galaxies look so different. So the old idea that it was something you know the steady state idea that it was eternal and so on was really i think demolished finally by those observations with the hubble space telescope that showed that the universe had changed over time brilliant well thank you for that and if you're listening and you think i've got questions for the team then send it in for a future episode you can email

podcast at ras.ac.uk or pile in on our monthly thread on twitter it's at royal astro sock so that's almost everything for this month but robert what can people see this month you know spring is here almost oh spring is here sitting here recording in the sunshine it's fantastic astronomical spring is here okay so it's um on the downside it's not a great time for planets in the sunshine it's fantastic astronomical spring okay so it's um on the downside it's not a great time for planets in the northern hemisphere although if you're in the southern hemisphere you get a reasonable view of quite a few of them in the morning sky but the moon's still really good uh you know this is one of the best times to look out for

craters and features on the moon because when it's visible in the evening sky when it's a crescent going through to first quarter it's brilliant and that's from about the week after the 3rd of April will be will be good for us but what I'd really recommend if you don't have a telescope particularly is doing things like learning the spring constellations you can easily see Leo the lion it's really high up in the evening sky after sunset and later on you can look up at the plow or if you prefer as a major the great bear and if you look at the tail of the bear or the handle of the plow if you, you can trail that down to Arcturus, the fourth brightest star in the sky, in the constellation of Boötes. And then you can go

down to Spica in Virgo. So these are classic spring constellations to look out for. And in that same region of the sky, connecting nicely with this episode, it's actually quite a good time to look for galaxies as well. Now, I should should stress you won't see any of these without a pair of binoculars at the very least probably a reasonably good size ones or ideally a small telescope but it is a time to look for them if you have access to those if you're in a dark enough sky you can just about make out andromeda you can indeed yeah yeah it's uh that That's very true, but it's more of an autumn object. And I think now, you know, this time of year, I'm not sure if any of the spring galaxies are bright enough to see with the eye.

Probably not, no. Some of them are bright enough if you've got a pair of binoculars, absolutely. And it's very hard to describe exactly where they are in an audio podcast, but quite a few of them are in Ursa Major, they're nearby. So if you look up some of the brighter Messier catalogue ones, like M81 is a nice spiral, M82 is a regular beyond the bowl of the plough, M101 is above the handle of the plough or the bear's tail. And then lower down, M51 was one that was a classic pinwheel shape, so one of the classic spiral ones with a very large telescope. But all of these should be fairly okay to spot with binoculars if you're in a doubt on a dark night and then lower down underneath the Ursa Major is the wonderfully named Coma Berenicis the

Berenice's hair and that's underneath Ursa Major in our hemisphere and the bowl of Virgo beneath it you can then see that's where a large cluster of galaxies is and you won't see most of them there are thousands of them but if you have a pair of binoculars you won't see most of them there are thousands of them but if you have a pair of binoculars you might spot a few of the brighter ones or a small telescope more still and bear in mind though in all of this you'll be looking at something which looks like fuzzes unresolved fuzzes unlike the stuff that becky gets to see but if you do spot them in some cases you're looking at massive systems of stars more than 50 million light years away so if you spot them think on that as you see even if it looks like this small fuzz and i know there are loads of

astro images out there who produce phenomenal results of these things and they really do look like stonky great galaxies too but with the eye with the periphanocytus that tends to be what you're looking at but it's just perhaps a moment of reflection there when you look at this and you realize you're looking at something that's quite so distant. Oh, amazing. I can't wait to get out there now. Yeah, because it's sort of the time to do it. Exactly.

Because it's like 12-hour nights, it's 12-hour days, right? It's perfect balance. But then also they're slightly warmer than nights as well. They're not quite as like the crisp, cold winter nights that give you the clearest views, obviously, but it just means that you're not quite as like, you know, shaking as you try to hold the binoculars shaking as you try well i think that is it for this month so we'll be back in april with our part two on galaxies and we're also going to take a deeper dive into black holes and thank you to brilliant for sponsoring this episode and don't forget to tweet us if you have any questions

it's at Royal Astro Sock on Twitter or you can email podcast at ras.ac.uk and we'll try and cover them in a future episode but until then everybody happy stargazing