Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / #422: Dim Lights & Dark Matter: Cosmic Questions Answered

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#422: Dim Lights & Dark Matter: Cosmic Questions Answered · Space Nuts: Astronomy Insights & Cosmic Discoveries

0:00
Hi there, Andrew Dunkley here. Thanks for joining us on Space Nuts Q
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and a good to have your company coming up. Were doing a bit of
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homework. You might remember a couple of episodes ago Allen was asking about the
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detectability of light at one candle power of an led in space. Fred has
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done so for you, Allan. We're also going to be looking at bolometric
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luminosity, hawking radiation, major space hazards, and what do you do if
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you need to fix something on the James Webb space Telescope. We will tackle
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all of those questions on this episode of Space Nuts fifteen. Second guidance is
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Internal ten nine Ignition siquench Space Nuts NI four three two one Space Nuts.
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As when I reported Bill's good and he's back again, it's Professor Fred Watson,
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astronomer at LARCHI. Hello Andrew, fancy seeing you here behind you?
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Yes, yeah, you can see that. Yeah, it's pointing up at
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the sky right now, which is blocked by a big roof useless although I
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don't know if you notice, but it's got a sun filter on it.
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Yes, I did say that. Yeah. I went out the other day
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and I had a bit of a squize at at the disk of the Sun
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and I could actually see little sunspots. Amazing, amazing. Yeah, it
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is. It's going to be very careful when you're looking at the Sun.
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Actually, I did have the filter off at one stage and I just must
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have passed my face over the eyepiece and I just found that a streak of
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heat crossing you would you caught me quite off guard. I'm glad I didn't
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bought my eye over the eyepiece at that point in time. Fred, we
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have a bit of homework for you to deal with. Alan contacted has the
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other day about the detectability of light at one candle power of an LED in
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space, and we, I mean, we discussed the fact that light travels
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basically forever, and Allen's question was more about how far would be too far
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not to be able to see it that y I've got a feeling Alan mentioned
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the Hubble telescope as well. Maybe not, that might be my imagination,
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but the bottom line is, so, well, let me rephrase the question,
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then, how far how far away could you see a one candle power
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LED with the Hubble telescope. I think it was something like that in Allen's
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question, and so you've got to basically make a few assumptions on this,
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and I made some very rough and ready ones. But checking the the literature,
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checking the you know, the interweb, got the impression that you would
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be able to see with the naked eye and good eyesight. You know,
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you're talking now top class eye sight of a young person, not an old
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gimmer like me. The the the detectability of a one a one candle power
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led with your unaided eye would be I've seen suggestions up to two kilometers,
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but I think, you know, I think that's pretty optimistic. So I
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settled on a kilometer, and that makes life very much easier for the rest
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of the calculation. So if you could see, if you could just see
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this candle at a distance of one kilometer or this one candle power led that
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if you can just see it, that means it's got the magnitude of a
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sixth magnitude star. You remember, we in the trade measure star brightness in
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magnitude, and the numbers go the wrong way. So first magnitude star is
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a bright one. Jordie likes, Jordi likes first magnitude stars. You can
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taste absolutely some even this goes back to the ancient Greeks, actually stars of
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the first magnitude. But we now, having set up a measuring system for
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that, we know that there are some stars that have negative magnitudes. Like
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the brightest star in the sky serious, if I remember rightly, is minus
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one point eight or thereabouts. I think it's a very bright object. But
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typically the faintest thing you could see with the unadid eye would with the sixth
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magnitude. Now assuming that the faintest thing that Hubble telescope can see is about
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the thirtieth magnitude, and I think that's in the right ballpark. Doing some
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rough and ready calculations, which I might have got completely wrong because I did
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them this morning while I was thinking about breakfast, the answer I got was
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that the Hubble telescope would be able to detect It's not as far as you
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might think. Actually, it will be able to detect a one candle power
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lamp at the at a distance of sixty three thousand kilometers. Wow, yeah,
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I thought it would be more than that. Yeah, it's and that's
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about what is it a sixth of the distance of the Moon, So you
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would not be able to see a one candle power led at the distance of
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the Moon even with the Hubble telescope. You might do it with the web.
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Actually I should have done the calculation for the web as well. Anyway,
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that's the book line. I hope I've done that calculation correctly. Yeah,
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it's not as far as you might think. No, no, not
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at all all right, and hopefully that solves your little puzzle things for sitting
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there in the other day. Let's go to some audio questions. Now,
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this one comes from Night Hey guys, Nate from the Glasshouse Mountains in Queensland
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here. I've been listening for about a year now. I love the podcast.
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I'm currently doing a postgrad in astronomy. It's Swindburne and recently we were
6:14
discussing bolometric luminosity, which is the stellar measurement of wave links across the entire
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electromagna spectrum, not just the visible portion. Now we have an equation for
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this, and it got me wondering whether there's some sort of a bolometric standard
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for when a star goes through a major change. I'm not quite sure I
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know the right words to phrase the question properly, but an example might be
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is there an equation or standardized way to predict the bolometric luminosity of let's say,
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a supernova before the super giant explodes, or is it completely dependent upon
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the classification or stage of life of the star beforehand? And then on the
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flip side of that, is there such a thing as bolometric decay so I
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guess using the same example as before, or to certain wavelengths that arise from
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something like a supernova decay at different rates compared to others. Or again,
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is it just completely depending on the classification or stage of life at the star
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before it goes back? I hope that made sense. Keep up the great
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work, guys, and thanks for giving my questions ago. Thanks Nate didn't
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make sense. Next question. Honestly, that one really was a mind bender
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for me. I hope, I hope. I'm pretty sure you've got a
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bit of better idea of what he was talking about. Friend. Yes,
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it's a great question, a highly technical question that they're a bit of a
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bit of unpicking me if they will excuse me while I talk about the background
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to this and that is that bolometric brightness is the brightness of something measured over
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its whole spectrum. So it goes from you know, the the gamma ray
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spectrum right out to the long wavelength radio spectrum. So if you're making a
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bolometric measure, you're measuring all the radiation. And there's a machine that does
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that, or a device that does that. It's called a bolometer. And
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bilometers in principle are very simple. It's a bit of metal with a wire
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attached, cooled down to nearly absolute zero. They're used principally in microwave telescopes,
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telescopes like the James Kirk Clark Maxwell Telescope in Hawaii, like Alma the
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Attakama Large Millimeter Array telescope. So and there's a reason for that. Even
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though a bilometer in principle could be used across the whole spectrum, it turns
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out that excuse me, it turns out that if you want to measure,
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you know, the brightness of light or the brightness of X rays or anything,
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there are far more sensitive methods of doing that than using a bolometer.
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But in the microwave region of the spectrum is all you've got and that's the
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best way to do it. So that's just sort of discussing a little bit
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about where blometry comes in. I was honestly I've got to tell you that
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a bolometer sounds like something Monty Python made up. Well, it's funny you
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should say that because the you know, the original paper for bilometers was CLEAs
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et al. I'm kidding, I'm kidding, making up as you go along.
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That was that was well delivered, though, I'm that wouldn't be hard.
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No, anyway. Yeah, it's a strange word, that's right.
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I should check its origins. It's probably Greek in origin, it's but but
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it basically means you're measuring the whole the whole spectrum, and so you can,
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yes, you can say that molometric equations and things of that sort as
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mentions. Now, similarly to what I've just said about there being better ways
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than looking at the bolometric system to measure the brightness of styles and things of
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that sort, using different kinds of detectors, I think it's probably true that
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in the situation that is talking about, where you've got a star that's kind
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of not very far off going super and over and has symptoms in its light,
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what you'd be doing you would be looking at the spectrum analysis. You'd
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really be looking in detail, probably the visible spectrum, because that's the richest
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region of the spectrum. In diagnostic features, the atomic and molecular lines are
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what we call absorption lines. There the fingerprint of different elements and molecules that
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kind of barcode that we see across the spectrum of a star or galaxy.
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That would be a much more telling way of looking at where the star is
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evolving. Then it's sort of bolometric magnitude. And I'm not sure whether I'm
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answering the question that Nate is expounding or postulating, but I think that will
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be the answer anyway, that you would always look for much more sensitive symptoms
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or fingerprints. Something was going to happen in a star, highly evolved star,
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one near the end of its life that's about to go soup and over,
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I think you would be thinking about the ratios of elements and things of
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that sort, rather than looking at the bolometric equation. I hope that the
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question. Yeah, he also asked about bolometric decay. Is this such a
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thing? Well, yes, so there probably is. But I think there
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are other markers that will be much more sensitive than bolometric decay, if I
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can put it that way right fair enough, And bolometric comes from the Greek
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bowl ray anyway, right, bowl ray i metric. I think I've lost
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it now, word origin bowl from the Greek bowl ray bolometric a yeah,
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and it's there's all sorts of variations on it. So bolometer is the English
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word of the Greek. And I keep getting pop ups. Yeah, bull
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of metric, bolometrically, bollerlemetry from the Greek bowl, ray of light,
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stroke from balin to throw plus a minus meter. That didn't make any sense
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to me whatsoever. I just quoted that straight from the Collins dictionary. Yeah,
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well, okay, yeah, anyway, it's Greek origin. That's all
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we really wanted to figure out. So boll is the Greek word for a
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ray. That what I'm never gonna find it again. Yeah, it's here
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somewhere, all right. Well it's written in Greek, so I can't tell
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you what it is. It's all Greek to me. Andrew. Yeah,
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yeah, let's let's let's leave everybody to look it up themselves. Someone send
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us a note because I'm done with that. Yeah, it's hurting my brain.
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Thank you, Nate. Great question, really deep, and my pharmacist
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will be selling me something to fix my head after listening to that one.
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Let's let's go next to David. Hi, guys, David from Melbourne Here.
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Stephen Hawking theorize the existence of Hawking radiation, and I've been wondering has
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this could this have anything to do with dark matter or dark energy? Anyway?
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Love the show, Thanks great, Thanks David. We get this one
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a lot, don't we. Is Hawking radiation anything to do with dark matter
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dark energy? What's the usual answer? Maybe maybe not? The usual answer
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will be no, because it's very you know, Hawking radiation is it just
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kind of seeps out of black holes with with not really much energy. It's
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electromagnetic radiation probably if you need a belobita to look at it, but so
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slow and so low intensity that it's hard to imagine that Hawking radiation as such
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would contribute to dark energy. But we have had this this research done recently
14:54
that you and I spoke about Andrew, that does link black holes to dark
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energy. And I have to say, I can't remember the mechanism which was
15:05
being proposed in that, but I don't think it involved her hooking radiation.
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I think it was something well, that's a simple answer. It was gravitational
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decay. Yeah, so the answer is no. But black holes may play
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a part in dark energy. M Okay, there you go, David,
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simple one, big n O or maybe a little one. Because this is
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astronomy. Sometimes we've got a definite idea of something that turns out to be
15:31
not the right answer, in the completely wrong. But at this stage,
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no, at this stage, no, Yes, this is space nuts.
15:43
Andrew Dunkley here with Professor Fred Watson. Okay, we take a space nuts.
15:52
Moving right along, Fred. Our next question comes from a regular contributor
15:58
who we will call Martin. Hello, Space Nuts, Martin Berman, Gorvine
16:06
here, writer extraordinaire many genres from Potomac, Maryland, USA. And I've
16:17
been busy launching glycine elephants at the Moon Titan and putting them on comets,
16:26
of course, and well believe me, at tychy getting those elephants on the
16:33
those comments. Now the elephant not in the comet, I'll never know.
16:37
But my annoying frenemy, Egon Rusk, wants to know what kind of has
16:48
what are the major hazards to his lights near white speed spacecraft as it approaches
17:00
the major hazards to the traveling humans and the biosphere. Can't wait for me
17:06
answer, Berman Gorvine over and out. Thanks Martin. I'm assuming he's referring
17:14
to a science fiction novel in that first part. I think so. Yes,
17:18
I think that's right, which is probably simultaneously in many genres. Yeah,
17:22
that's yes, interesting possibly so indeed, yes, But the question was
17:27
hidden in there somewhere about now. I'm trying to think of it. My
17:36
brain's not working well today. This question, it's all about what what are
17:41
the difficulties of something as you approach the speed of life you're a space as
17:45
traveler, Yeah, what are the space hazards? And actually, interestingly we
17:51
had a similar question last time. I think, well one of them,
17:57
so questioners are whether you need to streamline your spacecraft when you're traveling at relativistic
18:06
velocities so that you don't get too much dragged from the interstellar medium. That's
18:11
right, we did too, and that was a couple of weeks ago.
18:15
Yeah, But one correlation of that was that as you approach the speed of
18:18
light, you're talking about particle accelerator speed, and so you know, if
18:26
you think of your spacecraft traveling near the speed of light, this is for
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Martin, maybe what would happen is the particle content of the interstellar medium,
18:41
or if you're in the Solar System, the interplanetary medium would be at such
18:47
high energies that you would get nuclear interactions in the walls of your spacecraft.
18:55
So you know, you hit hit us something particle nearly the space of light,
19:00
and you get all these you get the collision that generates sub atomic particles
19:06
of different species. It's how that things like the large Hatter and collider work
19:11
and some of those might be some of those might be quite dangerous. You
19:15
know, there might be gamma radiation comes off or something of that sort.
19:19
So I'm speculating here wildly rather than basing this on from scientific knowledge. But
19:27
there could be dangers from radiation because because of the effects of the interaction of
19:33
your your spacecraft with the with the basically the solar wind, the interstellar medium,
19:40
the interplanetary medium. So yeah, just watch out for that, especially
19:45
if you're carrying elephants with you. That could, you know, really make
19:47
it a tricky business. And they've got pretty thick heart though I think that's
19:52
true. They may mean natural radiation shields, who knows. Yeah, and
20:00
they were already packed because they're carrying a trunk. I like that one.
20:06
I like that. I had to do it. I had to do it.
20:10
But my first thought when I listened to Martin's question in rehearsal the other
20:17
day was radiation. My first thought was radiation. So there you go.
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You're on the body. It could be yes, could well. I'd say
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it's one of the major hazards regardless in space. I mean it has on
20:27
the Moon just by being on the Moon. It's a hazard. On Mars.
20:32
You can't live on the surface unprotected. So traveling in space, especially
20:37
at those relativistic speeds, opens up all sorts of possibilities. Yeah, it's
20:45
one thing to talk about reaching the speed of light in terms of travel,
20:48
but you've got to think about the consequences of doing it, not only warping
20:52
time, but waking up things that ought not to be playing with. I
20:59
think, yeah, maybe so maybe so. Thank you Martin. Always good
21:04
to hear from you. And our final question comes from Ryan Here, guys,
21:11
it's Ryan from town Zen, Delaware. Again. I had a question
21:14
about the James Web Space Telescope. I know that it has a limited amount
21:18
of fuel and limited lifespan, but did they design in anything that would allow
21:26
a secondary craft to come out and top up the tanks and keep it going.
21:30
Thanks as always, keep up the good work. Well, we know
21:34
that after Hubble was launched they were able to send a Space Shuttle up there
21:38
to fix a problem with I think it was the lens or the focus or
21:42
something. There was a problem there. But I think when you and I
21:47
started talking about James Web it was all about getting it exactly right, straight
21:52
up, because once it was out there, that was it. All bets
21:56
were off. Oh that's great, that's right, And that's because of where
22:00
it is. So you're right, Andrew. The Hubble mirror was the most
22:06
perfect mirror ever made, but made to the wrong prescription because of an accident
22:11
in testing. We understood in the end what had happened, and that was
22:15
corrected at least partially by means of a little correcting lens system that was sent
22:22
up and as you say, it was repaired. It was repaired again late
22:27
in the shuttle's career, this Shuttle system's career, with new gyros being provided
22:34
for it. Because that's the problem. Yeah, I remember that. Yeah,
22:37
that was probably around twenty eleven when the Shuttle program was winding down.
22:41
The reason for that was the Shuttle was the only spacecraft able to reach the
22:45
altitude of the Hubble telescope, which I think is six hundred kilometers or maybe
22:51
seven hundred, and the Shuttle could do that, but the other spacecraft available,
22:56
which was actually principal science capsules, couldn't. I'm not sure where we
23:00
are now with that actually, whether it's something like the Blowing star Liner,
23:04
which we're still waiting for its test launch first one with astronauts, or the
23:11
crew Dragon spacecraft, whether that would be capable of reaching the Hubble's altitude,
23:17
but I think that's unlikely. I think the next thing that might rendezvous with
23:22
the Hubble will be a robotic spacecraft that will be designed to bring it down,
23:27
maybe probably in a no controlled it's sorry, a control burn up into
23:33
the atmosphere. The original plan with the Hubble was it was going to be
23:37
brought back to the Earth by Space Shuttle and put in a museum. Yeah,
23:44
but with the Space Shuttle being retired in twenty eleven, that option has
23:48
gone. At the moment, I haven't got anything big enough to bring it
23:52
back, although in the end maybe Elon Musk's Starship might have a cargo version
23:59
that would let you do that. So I don't know the answer to that
24:02
anyway, making cargo versions of Tesla's these days, so why not. Yeah,
24:06
that's right. We saw one actually when we're in the US. One
24:07
of his forgot what it's called. It's got a funny name, yeah,
24:12
the truck. It's a truck. Yes, it's it's like a ute with
24:19
kind of science fiction name which it loses me at the moment. But anyway,
24:22
Yeah, someone in Garuda in Texas I usually called Greene. Interesting side
24:33
note, the interesting side note that a lot of Australians would be aware of,
24:37
but maybe not too many others. The ute, the utility was an
24:40
Australian invention. There you go. Yeah, But getting to the point of
24:45
Ryan's question, uh, the point the thing about the and you've put it
24:51
in a nutshell already, Andrew. The James Webspace Telescope sits at the L
24:59
two point, the Earth's second lagraunge point in relation to the Sun, which
25:03
means it's one point five million kilometers on the side of the Earth away from
25:07
the Sun, and certainly with present technology, is unreachable by humans. Whether
25:18
you could mount a robotic mission to refuel or repair is an economics question,
25:26
and certainly the thinking at the beginning of the James Webb's mission was that it
25:33
would cost more to certainly set up a mission to repair it or to put
25:40
you know, put extra fuel in the tanks of which we think is about
25:44
twenty years worth, by the way, and this is to maneuver it,
25:47
to keep it pointing in the right direction. It will be more expensive to
25:51
do that than to just build another one and you know, send that up
25:55
into orbit. So the normal philosophy on the web is that if anything goes
26:02
wrong, that's the end of the story, and you think about what comes
26:04
next. Yeah, which makes me wonder. Obviously, it carries fuel twenty
26:11
years worth to keep it in position. So when it runs out of fuel,
26:17
what will happen to it? Will it just sort of get flung around
26:21
a bit or just spin off into oblivion? And how will that affect it?
26:26
So it will, yes, so it's orbit. Will it's currently in
26:30
orbit around an imaginary point in orbit's the l two point, the stable point
26:37
caused by the balance of the Earth and the Sun's gravity and the motion around
26:41
the Sun. So what would happen will be it would just kind of drift
26:45
off away from where you want it. It will be subject to gravitational forces
26:52
of the planets, principally Jupiter, which will disturb its orbit, and so
26:57
it will kind of hang around. The risk is that it's uncontrol. There's
27:03
several other bits of hardware or two points, including the Plank spacecraft which measured
27:08
the cosmic wife for their background radiation, so that would be then seen as
27:14
a hazard to shipping. You might want to boost it into what's called the
27:18
graveyard orbit, which is somewhere where it is out of the way and isn't
27:22
going to interfere with anything. So yes, so it's maybe they built that
27:30
into the planning. Probably, Yeah, I'm sure that's true. Sure,
27:33
that's true. Well, there is a requirement these days, isn't it that
27:38
if you put something into space, it's your responsibility to bring it down safely
27:42
or deal with it according to those parades. I don't know if it would
27:48
apply to James Webb because it's not in orbit around the planet, but I
27:52
would assume. So, okay, thank you, Ryan. The answer is
27:57
another one that we've we've got it. We've got a few hard nos this
28:03
this week, some of the questions, but that happens from time to time.
28:06
But yeah, no no way of refueling or fixing the proof of valve
28:11
if it if it breaks, it's all on its own out there. And
28:17
thanks to everybody who contributed this week to space Nuts Q and A. Really
28:22
appreciate your questions. We've just received a new batch, so we'll be going
28:26
through those and we'll have plenty to talk about in forward episodes. But don't
28:30
let that discourage you from sending questions in via our website, Space nuts podcast
28:34
dot com or space nuts dot io. And have a look around while you're
28:41
there. Buy a couple of books from Fred. He needs the money for
28:44
his landscaping and and all of that. Thank you, Fredd. As usual,
28:51
it's always great fun. It's a pleasure. Andrew, there's a big
28:56
hesitation there. I'm not sure. No, it's a pleasure. Just trying
29:02
to juggle a few things at once here and I can only do it one
29:03
thing at the time. That's the problem. Yeah, me too, and
29:07
thinking it's not one of them that ever, that's right, that's right,
29:11
see your friend, Thank you, cheer just for now talk so bye bye.
29:15
Fred Wat's an astronomer at large, and Hugh in the studio who send
29:19
us those questions. We're going to have to do a bit more vetting here.
29:23
I think that's too hard. And from me Andrew uncle you thanks for
29:26
your company again. We'll catch you on the next episode of Space Nuts.
29:30
By bye. You'll be listening to the Space Nuts podcast available at Apple Podcasts,
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