The Supermassive Podcast - 37: BONUS - The Supermassive Mailbox

Episode Date: February 11, 2023

You spoke. We listened. We're releasing more episodes! Izzie, Dr Becky and Robert answer your questions in this first bonus episode of The Supermassive Podcast.  How hard is life for an astronomer that's a morning person? How do we know if a star is really red or just red-shifted? And more.  To add your questions, photos, messages to The Supermassive Mailbox then email [e-mail], tweet @RoyalAstroSoc or find us on Instagram @SupermassivePod. 

Hello and welcome to our first ever bonus episode of the Supermassive podcast from the Royal Astronomical Society. With me, science journalist Izzy Clark and astrophysicist Dr. Becky Smethurst. You asked, we listened. We'll be bringing you more from the Supermassive mailbox in between our main episodes. Because let's be honest, our mailbox is now supermassive officially classified because there are so many questions that have been sent in so whether that's just fun emails that we'll be reading out your questions or any other exciting space news this is the place where we'll get it covered yes and so if you want to add to the supermassive mailbox then email podcast at ras.ac.uk, tweet at Royal Astro Sock.

And we're also on Instagram at Supermassive Pod. So Becky, Robert, are you ready? Born ready at this point, is he? Yes, obviously. So a nice, easy one to start us off. Renee Horn emailed to say, I'm not sure if any of you would be able to answer this question, but how hard is life for an

astronomer that's a morning person hard that is me actually um winter is your friend let's put it that way because you can you can observe like early evening and not into the night time and not be grumpy in the morning it's not a problem weirdly for if you're a professional astronomer so like when i go to telescopes to use them for my own observing you know you just have to change your time zone essentially to 12 hours opposite whatever time zone you're in so if you're flying to hawaii from the uk it's great because you basically just stay on uk time and then you know you're everybody's friend when you're the person that's really chirpy at like 8pm and everyone else is still like really jet lagged. What about you, Robert? I'm so not a morning person, you know, no, I'm really not. If I didn't

have a daughter, I honestly think I'd start work at 11 at the earliest. So it's been good for my professional life, you know, having kids because I have to get up. But I did get up a few early a few times this month before dawn, which isn't like me at all, to look at the comet. And lots of coffee really helps. So there's a mix of us on there, really. Yeah, I think when I was younger, I was much even even less of a morning person than now. But Beck is right. If you're working on it professionally, actually, most of the time you're not observing. Unless I guess you're one of the support astronomers at an observatory or something like that. And so it's it's not a massive issue because and also with remote remote observing as well you might be connecting to an observatory on the other

side of the world so you could be you know becky could be sitting in cambridge and connecting to an observatory in hawaii and it would all be not too bad okay so becky we've got a question for you here which is from david chevenet who emailed to ask a question about dark matter he says in the bullet cluster images i think you can see dark matter being smacked and that is actually how he spelt it and i really enjoy that smacked out of some galaxies or more actually two galaxies being smacked out of their surrounding clouds of dark matter it looks like the dark matter blobs kept going forward after the collision and the galaxies also kept going, but at a lower speed.

Maybe we're going to see the blobs of dark matter far right and far left continue and each would be a galaxy of dark matter. Is that right? Wouldn't that be the coolest thing ever? Unfortunately, that's not quite right, David. So it's not two galaxies that are colliding in the bullet cluster. It's two clusters of galaxies. So essentially a load of galaxies all bound together by their gravity in one big clump. And there's two of those things

that have collided together. Now in a cluster, you've got three things. You've got the galaxy of stars or the galaxies of stars dotting around the cluster. You've then got the dark matter that then essentially surrounds all of those galaxies and basically binds them all together in what we call a halo of dark matter. gas, so like hydrogen gas that also pervades the space in between those galaxies in the cluster that could, you know, sort of eventually fall onto a galaxy, cool down and be used to make more stars, something like that. Now in the collision of these two clusters, those three components have all acted differently. So the first thing is that the galaxies of stars, none of those have actually collided, they've just sort of gone straight through each other and out the other side. So has the dark matter that pervades all of the space in between those galaxies. The dark matter traces where the galaxies are now, and we can see that in the big

mass map, and that's what's either side. The hot gas in the middle that pervaded all that space, though, collided in the center. So all the molecules just collided in on each other and have been left behind sort of in the wreckage of that cluster collision in the middle. And that's how we know they've collided and gone through each other. So what that tells us about dark matter is that it acts more like stars than it does gas. So in essence, when you think about it, like molecules of gas, stars, you think it's just a different scale. So in essence, when you think about it, like molecules of gas, stars, you think it's just a different scale. But in reality, it tells us about, you know, if there is particles that makes up dark matter, then what it means is that it's something that

we call collisionless. So it's very, very unlikely that like if dark matter is a particle, that those two particles ever collide like molecules of gas do when gas comes together and collides. So at least we almost know one property of dark matter by looking at the bullet cluster. And that's what it tells us. It doesn't mean unfortunately there's just like galaxies of dark matter alone. I mean, there are probably dark matter halos out there that don't have galaxies of stars in the middle of them. We we've seen that when we simulate the universe so perhaps they could exist but in the bullet cluster that's not what we have here well thanks for sorting that one out then becky robert andrew jones on twitter has a question about space telescopes and he says does increasing the size of a space telescope mirror give ever

increasing improvements or is there a point where the returns start to diminish? Would a theoretical space telescope with a 650 metre mirror be 100 times better than Jane's work? Well, it wasn't something I've thought about before, just because, you know, we'll take bigger and bigger telescopes. Yes, please, if they're on offer, Andrew. Now, on the ground, there would be a limit because you have real difficulties structural engineering and very large structures and suspending them and even though very large mirrors are segmented it's a tough thing to do there was a proposal for something called the overwhelmingly large telescope built by ESO the European Southern Observatory but

instead and that was going to be 100 meter mirror that was probably getting close to the maximum but instead we had to put up with a mere 40-meter mirror from the European Extremely Large Telescope. That was the decision that was made. And yes, everything you're going to say about the names until they get better. But in space, then, obviously, a telescope could be a lot bigger. You don't have the issues of gravity causing major issues in engineering and structural engineering and so on in quite the same way.

And you would get ever sharper images if you're able to make it bigger and bigger and bigger and bigger and there are plans for say louvois with this which i mentioned in the episode 15 meters mirror across so that's that's big but the problem with doing it on a huge scale is i think more it's a structural one it's you have to take all those components to space and probably find an automated process for assembling the telescope that's going to be incredibly hard to do and if you think of the 300 or whatever it was points of failure for JWST and imagine doing that for a telescope 100 times bigger you can see it would be a big ask but in theory if someone is up for this, then yes,

there would be really, really good returns with a mirror 100 metres, 100 times better than James Webb. What's that going to be? 65 kilometres. Yeah, not bad at all. Yeah. But I doubt astronomers will object if there is a trillionaire out there that wants to support this. I just think of the points of failure and I'm like,

I know scientists all around the world just sweating like oh god no it's yeah absolutely you you definitely grow old managing that project i mean i suppose it would be so big you could then i think actually to get to see things like details on earth like planets around other stars they have to be even bigger they have to be sort of the equivalent of a telescope that's the size of a continent so it's it's incredibly hard to do you can sort of simulate it with separated telescopes but that's that's really quite tough with visible light yeah yeah okay becky i've got another question for you as our queen of black holes man's on instagram wants to know when a star collapses how long does it take for it to form a black hole is it

instantaneous almost instantaneous because the speed of gravity we now know is the speed of light thanks to our detections of gravitational waves and we think about the sort of the way you phrase that question once collapse you know collapse means there is nothing stopping gravity pulling everything inwards anymore so yes when you reach collapse stage it's pretty much instantaneous that that sort of creation of a black hole does happen we've even seen some stars that skip supernova entirely and they're there one day and then they've winked out the next and presumably just collapsed straight down into a black hole that we still don't quite know how to describe. We don't know why necessarily that they've skipped that process of throwing off the outer layers in a supernova

and only the core collapsing down straight into a black hole. In terms of how long does it take to go from when you run out of hydrogen to fuse into helium and then you start doing all of the helium fusing into heavier elements and then carbon and oxygen, nitrogen and and so that runaway fusion of heavier elements until there's nothing left to do but to collapse down. It depends on the size of the star, like the mass of the star, how long that actually takes. But roughly you're looking at something like one to two million years worth of helium burning and then you know maybe a few thousand years of like carbon burning before you then get to sort of full-on collapse stage so in terms of

like you know lifetimes of stars i mean even the most masses of stars only lived hundreds of thousands of years you're looking at even shorter time scales than that um in terms of the lifetimes of stars it's pretty short but it's not as instantaneous almost as the collapse down when there's finally nothing left to to stop gravity from pulling inwards anymore okay and finally robert jamie on twitter asks how do astronomers know if a star is really red or just red shifted or both How do astronomers see blue stars that are red shifted? Yeah, the stars we see nearby, they're not very shifted because they don't tend to be moving very quickly away towards or away from us.

So you don't get a very strong red shift when it's moving away or a very strong blue shift when it's coming towards us. So the colour that the eye sees, it's not going to be a big shift. But when you've got very distant objects that's different and because the galaxies they're in are moving away with the expansion of the universe so that's when you get these very very high apparent speeds and it's usually very hard to see individual stars in those galaxies but there are some exceptions and one of which is the star erindel which is magnified by a gravitational lens and that that's 28 billion light years away, and the light's taken 13 billion years to reach us

because in the interim time the universe has expanded. That has a redshift of 6.2, so the wavelength of its spectrum has changed by a factor of 7. And what that means is that that's enough to make quite a blue star pretty infrared, so it's really shifted it through. And the way we confirm that, though, if you're looking at a random star in our galaxy and you apply the same process to all the objects in the universe is you look in their spectra you look at say an element like hydrogen which has a pattern of lines

associated with it that we can see and measure in a lab on earth and we measure them in this on the star or the galaxy and we check them against them and that's how we measure the redshift and it's enough to tell us that the any kind of apparent color that say comes up through measuring it with different filters which is one way of determining the colors of stars to look at how much light they give out in each color we can check it against that and we know that it's genuinely redshifted can i add to that as well yeah go for it this is something that i do in my research all the time so we when we talk about redshift we're really talking about galaxies mostly, as Robert said. So when I study galaxies, I actually measure the color of them.

We put a number on it and say, okay, how much red light did we detect? How much blue light did we detect? Take one from the other. And then if you get a negative number, you know it's more blue, et cetera, et cetera. And so what we deal with when we talk about colors is we have to be very careful. Whether we're saying, yes, it's very red, or if it's very blue, that we've shifted those to what we call rest frame rather than the red shifted light that we're detecting. So rest frame would be like if the galaxy wasn't moving away from us, what would that color actually be? And so we have to be very careful.

Like we're like, oh, it's, you know, optical color here is this. Oh, but it's not rest frame. like oh it's you know optical color here is this oh but it's not rest frame um or the rest frame color that we've corrected you know from the amount of light that we've actually received in when we you know split the light into a spectra we can then work out uh the rest frame color usually nice well jamie i hope that answers your question and i think that's pretty much it for our first bonus episode thank you everyone do keep the coming. I'll put in the description of this episode how you can get in touch. And yeah, keep growing the Supermassive Mailbox.

The fear, the fear is there. Yeah, well, eventually we'll get down to inbox red zero. Maybe. You guys really do have like the best questions. So please do keep sending them in. We'll be back in a few weeks time with an episode about gravitational waves. But until then, everybody, happy stargazing.