#422: Dim Lights & Dark Matter: Cosmic Questions Answered

Hi there, Andrew Dunkley here. Thanks for joining us on Space Nuts Q and a good to have your company coming up. Were doing a bit of homework. You might remember a couple of episodes ago Allen was asking about the detectability of light at one candle power of an led in space. Fred has done so for you, Allan. We're also going to be looking at bolometric luminosity, hawking radiation, major space hazards, and what do you do if you need to fix something on the James Webb space Telescope. We will tackle all of those questions on this episode of Space Nuts fifteen. Second guidance is Internal ten nine Ignition siquench Space Nuts NI four three two one Space Nuts. As when I reported Bill's good and he's back again, it's Professor Fred Watson, astronomer at LARCHI. Hello Andrew, fancy seeing you here behind you? Yes, yeah, you can see that. Yeah, it's pointing up at the sky right now, which is blocked by a big roof useless although I don't know if you notice, but it's got a sun filter on it. Yes, I did say that. Yeah. I went out the other day and I had a bit of a squize at at the disk of the Sun and I could actually see little sunspots. Amazing, amazing. Yeah, it is. It's going to be very careful when you're looking at the Sun. Actually, I did have the filter off at one stage and I just must have passed my face over the eyepiece and I just found that a streak of heat crossing you would you caught me quite off guard. I'm glad I didn't bought my eye over the eyepiece at that point in time. Fred, we have a bit of homework for you to deal with. Alan contacted has the other day about the detectability of light at one candle power of an LED in space, and we, I mean, we discussed the fact that light travels basically forever, and Allen's question was more about how far would be too far not to be able to see it that y I've got a feeling Alan mentioned the Hubble telescope as well. Maybe not, that might be my imagination, but the bottom line is, so, well, let me rephrase the question, then, how far how far away could you see a one candle power LED with the Hubble telescope. I think it was something like that in Allen's question, and so you've got to basically make a few assumptions on this, and I made some very rough and ready ones. But checking the the literature, checking the you know, the interweb, got the impression that you would be able to see with the naked eye and good eyesight. You know, you're talking now top class eye sight of a young person, not an old gimmer like me. The the the detectability of a one a one candle power led with your unaided eye would be I've seen suggestions up to two kilometers, but I think, you know, I think that's pretty optimistic. So I settled on a kilometer, and that makes life very much easier for the rest of the calculation. So if you could see, if you could just see this candle at a distance of one kilometer or this one candle power led that if you can just see it, that means it's got the magnitude of a sixth magnitude star. You remember, we in the trade measure star brightness in magnitude, and the numbers go the wrong way. So first magnitude star is a bright one. Jordie likes, Jordi likes first magnitude stars. You can taste absolutely some even this goes back to the ancient Greeks, actually stars of the first magnitude. But we now, having set up a measuring system for that, we know that there are some stars that have negative magnitudes. Like the brightest star in the sky serious, if I remember rightly, is minus one point eight or thereabouts. I think it's a very bright object. But typically the faintest thing you could see with the unadid eye would with the sixth magnitude. Now assuming that the faintest thing that Hubble telescope can see is about the thirtieth magnitude, and I think that's in the right ballpark. Doing some rough and ready calculations, which I might have got completely wrong because I did them this morning while I was thinking about breakfast, the answer I got was that the Hubble telescope would be able to detect It's not as far as you might think. Actually, it will be able to detect a one candle power lamp at the at a distance of sixty three thousand kilometers. Wow, yeah, I thought it would be more than that. Yeah, it's and that's about what is it a sixth of the distance of the Moon, So you would not be able to see a one candle power led at the distance of the Moon even with the Hubble telescope. You might do it with the web. Actually I should have done the calculation for the web as well. Anyway, that's the book line. I hope I've done that calculation correctly. Yeah, it's not as far as you might think. No, no, not at all all right, and hopefully that solves your little puzzle things for sitting there in the other day. Let's go to some audio questions. Now, this one comes from Night Hey guys, Nate from the Glasshouse Mountains in Queensland here. I've been listening for about a year now. I love the podcast. I'm currently doing a postgrad in astronomy. It's Swindburne and recently we were discussing bolometric luminosity, which is the stellar measurement of wave links across the entire electromagna spectrum, not just the visible portion. Now we have an equation for this, and it got me wondering whether there's some sort of a bolometric standard for when a star goes through a major change. I'm not quite sure I know the right words to phrase the question properly, but an example might be is there an equation or standardized way to predict the bolometric luminosity of let's say, a supernova before the super giant explodes, or is it completely dependent upon the classification or stage of life of the star beforehand? And then on the flip side of that, is there such a thing as bolometric decay so I guess using the same example as before, or to certain wavelengths that arise from something like a supernova decay at different rates compared to others. Or again, is it just completely depending on the classification or stage of life at the star before it goes back? I hope that made sense. Keep up the great work, guys, and thanks for giving my questions ago. Thanks Nate didn't make sense. Next question. Honestly, that one really was a mind bender for me. I hope, I hope. I'm pretty sure you've got a bit of better idea of what he was talking about. Friend. Yes, it's a great question, a highly technical question that they're a bit of a bit of unpicking me if they will excuse me while I talk about the background to this and that is that bolometric brightness is the brightness of something measured over its whole spectrum. So it goes from you know, the the gamma ray spectrum right out to the long wavelength radio spectrum. So if you're making a bolometric measure, you're measuring all the radiation. And there's a machine that does that, or a device that does that. It's called a bolometer. And bilometers in principle are very simple. It's a bit of metal with a wire attached, cooled down to nearly absolute zero. They're used principally in microwave telescopes, telescopes like the James Kirk Clark Maxwell Telescope in Hawaii, like Alma the Attakama Large Millimeter Array telescope. So and there's a reason for that. Even though a bilometer in principle could be used across the whole spectrum, it turns out that excuse me, it turns out that if you want to measure, you know, the brightness of light or the brightness of X rays or anything, there are far more sensitive methods of doing that than using a bolometer. But in the microwave region of the spectrum is all you've got and that's the best way to do it. So that's just sort of discussing a little bit about where blometry comes in. I was honestly I've got to tell you that a bolometer sounds like something Monty Python made up. Well, it's funny you should say that because the you know, the original paper for bilometers was CLEAs et al. I'm kidding, I'm kidding, making up as you go along. That was that was well delivered, though, I'm that wouldn't be hard. No, anyway. Yeah, it's a strange word, that's right. I should check its origins. It's probably Greek in origin, it's but but it basically means you're measuring the whole the whole spectrum, and so you can, yes, you can say that molometric equations and things of that sort as mentions. Now, similarly to what I've just said about there being better ways than looking at the bolometric system to measure the brightness of styles and things of that sort, using different kinds of detectors, I think it's probably true that in the situation that is talking about, where you've got a star that's kind of not very far off going super and over and has symptoms in its light, what you'd be doing you would be looking at the spectrum analysis. You'd really be looking in detail, probably the visible spectrum, because that's the richest region of the spectrum. In diagnostic features, the atomic and molecular lines are what we call absorption lines. There the fingerprint of different elements and molecules that kind of barcode that we see across the spectrum of a star or galaxy. That would be a much more telling way of looking at where the star is evolving. Then it's sort of bolometric magnitude. And I'm not sure whether I'm answering the question that Nate is expounding or postulating, but I think that will be the answer anyway, that you would always look for much more sensitive symptoms or fingerprints. Something was going to happen in a star, highly evolved star, one near the end of its life that's about to go soup and over, I think you would be thinking about the ratios of elements and things of that sort, rather than looking at the bolometric equation. I hope that the question. Yeah, he also asked about bolometric decay. Is this such a thing? Well, yes, so there probably is. But I think there are other markers that will be much more sensitive than bolometric decay, if I can put it that way right fair enough, And bolometric comes from the Greek bowl ray anyway, right, bowl ray i metric. I think I've lost it now, word origin bowl from the Greek bowl ray bolometric a yeah, and it's there's all sorts of variations on it. So bolometer is the English word of the Greek. And I keep getting pop ups. Yeah, bull of metric, bolometrically, bollerlemetry from the Greek bowl, ray of light, stroke from balin to throw plus a minus meter. That didn't make any sense to me whatsoever. I just quoted that straight from the Collins dictionary. Yeah, well, okay, yeah, anyway, it's Greek origin. That's all we really wanted to figure out. So boll is the Greek word for a ray. That what I'm never gonna find it again. Yeah, it's here somewhere, all right. Well it's written in Greek, so I can't tell you what it is. It's all Greek to me. Andrew. Yeah, yeah, let's let's let's leave everybody to look it up themselves. Someone send us a note because I'm done with that. Yeah, it's hurting my brain. Thank you, Nate. Great question, really deep, and my pharmacist will be selling me something to fix my head after listening to that one. Let's let's go next to David. Hi, guys, David from Melbourne Here. Stephen Hawking theorize the existence of Hawking radiation, and I've been wondering has this could this have anything to do with dark matter or dark energy? Anyway? Love the show, Thanks great, Thanks David. We get this one a lot, don't we. Is Hawking radiation anything to do with dark matter dark energy? What's the usual answer? Maybe maybe not? The usual answer will be no, because it's very you know, Hawking radiation is it just kind of seeps out of black holes with with not really much energy. It's electromagnetic radiation probably if you need a belobita to look at it, but so slow and so low intensity that it's hard to imagine that Hawking radiation as such would contribute to dark energy. But we have had this this research done recently that you and I spoke about Andrew, that does link black holes to dark energy. And I have to say, I can't remember the mechanism which was being proposed in that, but I don't think it involved her hooking radiation. I think it was something well, that's a simple answer. It was gravitational decay. Yeah, so the answer is no. But black holes may play a part in dark energy. M Okay, there you go, David, simple one, big n O or maybe a little one. Because this is astronomy. Sometimes we've got a definite idea of something that turns out to be not the right answer, in the completely wrong. But at this stage, no, at this stage, no, Yes, this is space nuts. Andrew Dunkley here with Professor Fred Watson. Okay, we take a space nuts. Moving right along, Fred. Our next question comes from a regular contributor who we will call Martin. Hello, Space Nuts, Martin Berman, Gorvine here, writer extraordinaire many genres from Potomac, Maryland, USA. And I've been busy launching glycine elephants at the Moon Titan and putting them on comets, of course, and well believe me, at tychy getting those elephants on the those comments. Now the elephant not in the comet, I'll never know. But my annoying frenemy, Egon Rusk, wants to know what kind of has what are the major hazards to his lights near white speed spacecraft as it approaches the major hazards to the traveling humans and the biosphere. Can't wait for me answer, Berman Gorvine over and out. Thanks Martin. I'm assuming he's referring to a science fiction novel in that first part. I think so. Yes, I think that's right, which is probably simultaneously in many genres. Yeah, that's yes, interesting possibly so indeed, yes, But the question was hidden in there somewhere about now. I'm trying to think of it. My brain's not working well today. This question, it's all about what what are the difficulties of something as you approach the speed of life you're a space as traveler, Yeah, what are the space hazards? And actually, interestingly we had a similar question last time. I think, well one of them, so questioners are whether you need to streamline your spacecraft when you're traveling at relativistic velocities so that you don't get too much dragged from the interstellar medium. That's right, we did too, and that was a couple of weeks ago. Yeah, But one correlation of that was that as you approach the speed of light, you're talking about particle accelerator speed, and so you know, if you think of your spacecraft traveling near the speed of light, this is for Martin, maybe what would happen is the particle content of the interstellar medium, or if you're in the Solar System, the interplanetary medium would be at such high energies that you would get nuclear interactions in the walls of your spacecraft. So you know, you hit hit us something particle nearly the space of light, and you get all these you get the collision that generates sub atomic particles of different species. It's how that things like the large Hatter and collider work and some of those might be some of those might be quite dangerous. You know, there might be gamma radiation comes off or something of that sort. So I'm speculating here wildly rather than basing this on from scientific knowledge. But there could be dangers from radiation because because of the effects of the interaction of your your spacecraft with the with the basically the solar wind, the interstellar medium, the interplanetary medium. So yeah, just watch out for that, especially if you're carrying elephants with you. That could, you know, really make it a tricky business. And they've got pretty thick heart though I think that's true. They may mean natural radiation shields, who knows. Yeah, and they were already packed because they're carrying a trunk. I like that one. I like that. I had to do it. I had to do it. But my first thought when I listened to Martin's question in rehearsal the other day was radiation. My first thought was radiation. So there you go. You're on the body. It could be yes, could well. I'd say it's one of the major hazards regardless in space. I mean it has on the Moon just by being on the Moon. It's a hazard. On Mars. You can't live on the surface unprotected. So traveling in space, especially at those relativistic speeds, opens up all sorts of possibilities. Yeah, it's one thing to talk about reaching the speed of light in terms of travel, but you've got to think about the consequences of doing it, not only warping time, but waking up things that ought not to be playing with. I think, yeah, maybe so maybe so. Thank you Martin. Always good to hear from you. And our final question comes from Ryan Here, guys, it's Ryan from town Zen, Delaware. Again. I had a question about the James Web Space Telescope. I know that it has a limited amount of fuel and limited lifespan, but did they design in anything that would allow a secondary craft to come out and top up the tanks and keep it going. Thanks as always, keep up the good work. Well, we know that after Hubble was launched they were able to send a Space Shuttle up there to fix a problem with I think it was the lens or the focus or something. There was a problem there. But I think when you and I started talking about James Web it was all about getting it exactly right, straight up, because once it was out there, that was it. All bets were off. Oh that's great, that's right, And that's because of where it is. So you're right, Andrew. The Hubble mirror was the most perfect mirror ever made, but made to the wrong prescription because of an accident in testing. We understood in the end what had happened, and that was corrected at least partially by means of a little correcting lens system that was sent up and as you say, it was repaired. It was repaired again late in the shuttle's career, this Shuttle system's career, with new gyros being provided for it. Because that's the problem. Yeah, I remember that. Yeah, that was probably around twenty eleven when the Shuttle program was winding down. The reason for that was the Shuttle was the only spacecraft able to reach the altitude of the Hubble telescope, which I think is six hundred kilometers or maybe seven hundred, and the Shuttle could do that, but the other spacecraft available, which was actually principal science capsules, couldn't. I'm not sure where we are now with that actually, whether it's something like the Blowing star Liner, which we're still waiting for its test launch first one with astronauts, or the crew Dragon spacecraft, whether that would be capable of reaching the Hubble's altitude, but I think that's unlikely. I think the next thing that might rendezvous with the Hubble will be a robotic spacecraft that will be designed to bring it down, maybe probably in a no controlled it's sorry, a control burn up into the atmosphere. The original plan with the Hubble was it was going to be brought back to the Earth by Space Shuttle and put in a museum. Yeah, but with the Space Shuttle being retired in twenty eleven, that option has gone. At the moment, I haven't got anything big enough to bring it back, although in the end maybe Elon Musk's Starship might have a cargo version that would let you do that. So I don't know the answer to that anyway, making cargo versions of Tesla's these days, so why not. Yeah, that's right. We saw one actually when we're in the US. One of his forgot what it's called. It's got a funny name, yeah, the truck. It's a truck. Yes, it's it's like a ute with kind of science fiction name which it loses me at the moment. But anyway, Yeah, someone in Garuda in Texas I usually called Greene. Interesting side note, the interesting side note that a lot of Australians would be aware of, but maybe not too many others. The ute, the utility was an Australian invention. There you go. Yeah, But getting to the point of Ryan's question, uh, the point the thing about the and you've put it in a nutshell already, Andrew. The James Webspace Telescope sits at the L two point, the Earth's second lagraunge point in relation to the Sun, which means it's one point five million kilometers on the side of the Earth away from the Sun, and certainly with present technology, is unreachable by humans. Whether you could mount a robotic mission to refuel or repair is an economics question, and certainly the thinking at the beginning of the James Webb's mission was that it would cost more to certainly set up a mission to repair it or to put you know, put extra fuel in the tanks of which we think is about twenty years worth, by the way, and this is to maneuver it, to keep it pointing in the right direction. It will be more expensive to do that than to just build another one and you know, send that up into orbit. So the normal philosophy on the web is that if anything goes wrong, that's the end of the story, and you think about what comes next. Yeah, which makes me wonder. Obviously, it carries fuel twenty years worth to keep it in position. So when it runs out of fuel, what will happen to it? Will it just sort of get flung around a bit or just spin off into oblivion? And how will that affect it? So it will, yes, so it's orbit. Will it's currently in orbit around an imaginary point in orbit's the l two point, the stable point caused by the balance of the Earth and the Sun's gravity and the motion around the Sun. So what would happen will be it would just kind of drift off away from where you want it. It will be subject to gravitational forces of the planets, principally Jupiter, which will disturb its orbit, and so it will kind of hang around. The risk is that it's uncontrol. There's several other bits of hardware or two points, including the Plank spacecraft which measured the cosmic wife for their background radiation, so that would be then seen as a hazard to shipping. You might want to boost it into what's called the graveyard orbit, which is somewhere where it is out of the way and isn't going to interfere with anything. So yes, so it's maybe they built that into the planning. Probably, Yeah, I'm sure that's true. Sure, that's true. Well, there is a requirement these days, isn't it that if you put something into space, it's your responsibility to bring it down safely or deal with it according to those parades. I don't know if it would apply to James Webb because it's not in orbit around the planet, but I would assume. So, okay, thank you, Ryan. The answer is another one that we've we've got it. We've got a few hard nos this this week, some of the questions, but that happens from time to time. But yeah, no no way of refueling or fixing the proof of valve if it if it breaks, it's all on its own out there. And thanks to everybody who contributed this week to space Nuts Q and A. Really appreciate your questions. We've just received a new batch, so we'll be going through those and we'll have plenty to talk about in forward episodes. But don't let that discourage you from sending questions in via our website, Space nuts podcast dot com or space nuts dot io. And have a look around while you're there. Buy a couple of books from Fred. He needs the money for his landscaping and and all of that. Thank you, Fredd. As usual, it's always great fun. It's a pleasure. Andrew, there's a big hesitation there. I'm not sure. No, it's a pleasure. Just trying to juggle a few things at once here and I can only do it one thing at the time. That's the problem. Yeah, me too, and thinking it's not one of them that ever, that's right, that's right, see your friend, Thank you, cheer just for now talk so bye bye. Fred Wat's an astronomer at large, and Hugh in the studio who send us those questions. We're going to have to do a bit more vetting here. I think that's too hard. And from me Andrew uncle you thanks for your company again. We'll catch you on the next episode of Space Nuts. By bye. You'll be listening to the Space Nuts podcast available at Apple Podcasts, Spotify, iHeart Radio, or your favorite podcast player. You can also stream on demand at bites dot com. 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