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

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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

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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

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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

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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

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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.

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Andrew Dunkley here with Professor Fred Watson. Okay, we take a space nuts.

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Moving right along, Fred. Our
next question comes from a regular contributor

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who we will call Martin. Hello, Space Nuts, Martin Berman, Gorvine

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here, writer extraordinaire many genres from
Potomac, Maryland, USA. And I've

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been busy launching glycine elephants at the
Moon Titan and putting them on comets,

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of course, and well believe me, at tychy getting those elephants on the

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those comments. Now the elephant not
in the comet, I'll never know.

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But my annoying frenemy, Egon Rusk, wants to know what kind of has

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what are the major hazards to his
lights near white speed spacecraft as it approaches

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the major hazards to the traveling humans
and the biosphere. Can't wait for me

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answer, Berman Gorvine over and out. Thanks Martin. I'm assuming he's referring

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to a science fiction novel in that
first part. I think so. Yes,

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I think that's right, which is
probably simultaneously in many genres. Yeah,

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that's yes, interesting possibly so indeed, yes, But the question was

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hidden in there somewhere about now.
I'm trying to think of it. My

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brain's not working well today. This
question, it's all about what what are

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the difficulties of something as you approach
the speed of life you're a space as

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traveler, Yeah, what are the
space hazards? And actually, interestingly we

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had a similar question last time.
I think, well one of them,

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so questioners are whether you need to
streamline your spacecraft when you're traveling at relativistic

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velocities so that you don't get too
much dragged from the interstellar medium. That's

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right, we did too, and
that was a couple of weeks ago.

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Yeah, But one correlation of that
was that as you approach the speed of

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light, you're talking about particle accelerator
speed, and so you know, if

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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,

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or if you're in the Solar System, the interplanetary medium would be at such

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high energies that you would get nuclear
interactions in the walls of your spacecraft.

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So you know, you hit hit
us something particle nearly the space of light,

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and you get all these you get
the collision that generates sub atomic particles

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of different species. It's how that
things like the large Hatter and collider work

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and some of those might be some
of those might be quite dangerous. You

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know, there might be gamma radiation
comes off or something of that sort.

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So I'm speculating here wildly rather than
basing this on from scientific knowledge. But

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there could be dangers from radiation because
because of the effects of the interaction of

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your your spacecraft with the with the
basically the solar wind, the interstellar medium,

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the interplanetary medium. So yeah,
just watch out for that, especially

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if you're carrying elephants with you.
That could, you know, really make

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it a tricky business. And they've
got pretty thick heart though I think that's

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true. They may mean natural radiation
shields, who knows. Yeah, and

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they were already packed because they're carrying
a trunk. I like that one.

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I like that. I had to
do it. I had to do it.

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But my first thought when I listened
to Martin's question in rehearsal the other

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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

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the Moon just by being on the
Moon. It's a hazard. On Mars.

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You can't live on the surface unprotected. So traveling in space, especially

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at those relativistic speeds, opens up
all sorts of possibilities. Yeah, it's

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one thing to talk about reaching the
speed of light in terms of travel,

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but you've got to think about the
consequences of doing it, not only warping

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time, but waking up things that
ought not to be playing with. I

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think, yeah, maybe so maybe
so. Thank you Martin. Always good

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to hear from you. And our
final question comes from Ryan Here, guys,

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it's Ryan from town Zen, Delaware. Again. I had a question

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about the James Web Space Telescope.
I know that it has a limited amount

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of fuel and limited lifespan, but
did they design in anything that would allow

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a secondary craft to come out and
top up the tanks and keep it going.

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Thanks as always, keep up the
good work. Well, we know

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that after Hubble was launched they were
able to send a Space Shuttle up there

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to fix a problem with I think
it was the lens or the focus or

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something. There was a problem there. But I think when you and I

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started talking about James Web it was
all about getting it exactly right, straight

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up, because once it was out
there, that was it. All bets

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were off. Oh that's great,
that's right, And that's because of where

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it is. So you're right,
Andrew. The Hubble mirror was the most

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perfect mirror ever made, but made
to the wrong prescription because of an accident

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in testing. We understood in the
end what had happened, and that was

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corrected at least partially by means of
a little correcting lens system that was sent

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up and as you say, it
was repaired. It was repaired again late

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in the shuttle's career, this Shuttle
system's career, with new gyros being provided

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for it. Because that's the problem. Yeah, I remember that. Yeah,

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that was probably around twenty eleven when
the Shuttle program was winding down.

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The reason for that was the Shuttle
was the only spacecraft able to reach the

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altitude of the Hubble telescope, which
I think is six hundred kilometers or maybe

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seven hundred, and the Shuttle could
do that, but the other spacecraft available,

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which was actually principal science capsules,
couldn't. I'm not sure where we

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are now with that actually, whether
it's something like the Blowing star Liner,

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which we're still waiting for its test
launch first one with astronauts, or the

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crew Dragon spacecraft, whether that would
be capable of reaching the Hubble's altitude,

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but I think that's unlikely. I
think the next thing that might rendezvous with

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the Hubble will be a robotic spacecraft
that will be designed to bring it down,

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maybe probably in a no controlled it's
sorry, a control burn up into

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the atmosphere. The original plan with
the Hubble was it was going to be

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brought back to the Earth by Space
Shuttle and put in a museum. Yeah,

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but with the Space Shuttle being retired
in twenty eleven, that option has

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gone. At the moment, I
haven't got anything big enough to bring it

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back, although in the end maybe
Elon Musk's Starship might have a cargo version

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that would let you do that.
So I don't know the answer to that

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anyway, making cargo versions of Tesla's
these days, so why not. Yeah,

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that's right. We saw one actually
when we're in the US. One

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of his forgot what it's called.
It's got a funny name, yeah,

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the truck. It's a truck.
Yes, it's it's like a ute with

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kind of science fiction name which it
loses me at the moment. But anyway,

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Yeah, someone in Garuda in Texas
I usually called Greene. Interesting side

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note, the interesting side note that
a lot of Australians would be aware of,

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but maybe not too many others.
The ute, the utility was an

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Australian invention. There you go.
Yeah, But getting to the point of

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Ryan's question, uh, the point
the thing about the and you've put it

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in a nutshell already, Andrew.
The James Webspace Telescope sits at the L

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two point, the Earth's second lagraunge
point in relation to the Sun, which

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means it's one point five million kilometers
on the side of the Earth away from

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the Sun, and certainly with present
technology, is unreachable by humans. Whether

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you could mount a robotic mission to
refuel or repair is an economics question,

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and certainly the thinking at the beginning
of the James Webb's mission was that it

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would cost more to certainly set up
a mission to repair it or to put

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you know, put extra fuel in
the tanks of which we think is about

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twenty years worth, by the way, and this is to maneuver it,

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to keep it pointing in the right
direction. It will be more expensive to

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do that than to just build another
one and you know, send that up

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into orbit. So the normal philosophy
on the web is that if anything goes

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wrong, that's the end of the
story, and you think about what comes

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next. Yeah, which makes me
wonder. Obviously, it carries fuel twenty

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years worth to keep it in position. So when it runs out of fuel,

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what will happen to it? Will
it just sort of get flung around

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a bit or just spin off into
oblivion? And how will that affect it?

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So it will, yes, so
it's orbit. Will it's currently in

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orbit around an imaginary point in orbit's
the l two point, the stable point

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caused by the balance of the Earth
and the Sun's gravity and the motion around

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the Sun. So what would happen
will be it would just kind of drift

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off away from where you want it. It will be subject to gravitational forces

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of the planets, principally Jupiter,
which will disturb its orbit, and so

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it will kind of hang around.
The risk is that it's uncontrol. There's

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several other bits of hardware or two
points, including the Plank spacecraft which measured

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the cosmic wife for their background radiation, so that would be then seen as

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a hazard to shipping. You might
want to boost it into what's called the

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graveyard orbit, which is somewhere where
it is out of the way and isn't

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going to interfere with anything. So
yes, so it's maybe they built that

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into the planning. Probably, Yeah, I'm sure that's true. Sure,

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that's true. Well, there is
a requirement these days, isn't it that

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if you put something into space,
it's your responsibility to bring it down safely

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or deal with it according to those
parades. I don't know if it would

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apply to James Webb because it's not
in orbit around the planet, but I

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would assume. So, okay,
thank you, Ryan. The answer is

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another one that we've we've got it. We've got a few hard nos this

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this week, some of the questions, but that happens from time to time.

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But yeah, no no way of
refueling or fixing the proof of valve

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if it if it breaks, it's
all on its own out there. And

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thanks to everybody who contributed this week
to space Nuts Q and A. Really

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appreciate your questions. We've just received
a new batch, so we'll be going

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through those and we'll have plenty to
talk about in forward episodes. But don't

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let that discourage you from sending questions
in via our website, Space nuts podcast

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00:28:34.799 --> 00:28:41.079
dot com or space nuts dot io. And have a look around while you're

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00:28:41.079 --> 00:28:44.480
there. Buy a couple of books
from Fred. He needs the money for

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00:28:44.559 --> 00:28:51.240
his landscaping and and all of that. Thank you, Fredd. As usual,

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it's always great fun. It's a
pleasure. Andrew, there's a big

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hesitation there. I'm not sure.
No, it's a pleasure. Just trying

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to juggle a few things at once
here and I can only do it one

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00:29:03.960 --> 00:29:07.160
thing at the time. That's the
problem. Yeah, me too, and

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thinking it's not one of them that
ever, that's right, that's right,

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see your friend, Thank you,
cheer just for now talk so bye bye.

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Fred Wat's an astronomer at large,
and Hugh in the studio who send

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00:29:19.799 --> 00:29:23.000
us those questions. We're going to
have to do a bit more vetting here.

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I think that's too hard. And
from me Andrew uncle you thanks for

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00:29:26.519 --> 00:29:30.680
your company again. We'll catch you
on the next episode of Space Nuts.

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By bye. You'll be listening to
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00:29:37.839 --> 00:29:42.559
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