Professor Fred Watson: Hi there.
Andrew Dunkley: Thanks again for joining us. This is Space
Nuts. My name is Andrew Dunkley and every
week we talk astronomy and space science
and we answer audience questions in our
alternative show, which, uh, happens,
um, well, wherever you are. I mean, we
release it on a Monday, but that doesn't mean
you listen to it on a Monday. Uh, coming up
today we've got, uh, a couple of
nuclear explosive storeys. Uh,
SpaceX is involved in one of those and
the other storey is about, uh, blowing things
up with atomic weapons from space.
Yes, highly guaranteed. Very, very, uh,
effective as well. Uh, but I think there's
probably a reason not to. We'll look at all
of that. Uh, we're also going to talk about
where Earth's, uh, dust came from. Quite a
bit of it, which might come as a bit of a
surprise. Uh, you just have to look under
just about every bed and kitchen table in the
world to find as much dust as there is in the
world. But we'll see where that, uh, is
headed. And our galaxy, uh, reaches
out further than we thought. Apparently, uh,
there's some interesting science behind that.
We'll talk about it all on this edition of
space nuts.
Professor Fred Watson: 15 seconds. Guidance is internal.
10, 9. Ignition
sequence start.
Professor Fred Watson: Space nuts.
Professor Fred Watson: 5, 4, 3, 2. 1, 2, 3, 4,
5, 5, 4, 3, 2, 1.
Andrew Dunkley: Space nuts.
Professor Fred Watson: Astronauts report it feels good.
Andrew Dunkley: And joining us again to talk about all of
that and more is Professor Fred Watson
Watson, astronomer at large. Hello,
Fred Watson.
Professor Fred Watson: Hello, Andrew. Good to see you. Good to see
you. Yes.
We sort of missed a few days, haven't we?
Yes.
Andrew Dunkley: Uh, you've been off conferencing.
Professor Fred Watson: Yes. So the annual science meeting,
as it's called, of the National Astronomy
Society, the Astronomical Society of
Australia, it's where all the professional
astronomers get together and, uh, talk about
what they've been doing, their research. Uh,
it was a big meeting. There were, I would
have guessed, maybe a couple of hundred
people there altogether. Uh, that's quite big
for astronomers in a country that's only got
700 astronomers in it.
Professor Fred Watson: Yeah.
Professor Fred Watson: Uh, but, um, what was interesting and
what was very, I think,
heartening for me was the number of
youngsters that were there. I call them
youngsters, you know, people under 50
people, um, the new generation of
astronomers, uh, most of them whom I didn't
know and they've no idea who I am, and that's
fine. Uh, that all was okay. It
just contrasts with a few years ago. So when
I was the astronomer in charge of the
observatory at, uh, Coonabarabran, uh,
we were kind of the Shopkeepers. So all these
astronomers used to come through, stay in the
lodge and do their research using the
telescope. So I knew a large fraction of
the astronomical population of Australia. But
that's changed, uh, because my job,
that job is no longer mine. Uh,
and so I don't see people the same way. But
it was very nice to meet a lot of new faces
and catch up with some very old faces as
well, some even older than mine. Um, and we
also discussed matters such as the future
of Australian astronomy because that's
uh, in a interesting
state at the moment. With the government
having declined, uh, to
engage in membership with the European
Southern Observatory. We are now working on
plan B. Uh, and um. Well, it looks
promising.
Andrew Dunkley: Yes, fingers crossed. A lot going on.
Okay, um, we should probably get
stuck into these storeys because there's a
lot to discuss. The first storey is a double
banger about nuclear, um, energy and
atomic weapons.
Uh, we'll start off with the storey about
SpaceX. And
um, they're looking at nuclear power
in space, nuclear powered satellites. What's
the storey here?
Professor Fred Watson: It's a test launch, really. A launch of
a cubesat basically that um,
has not a nuclear reactor inside but
um, basically a capsule of something called
tritium which is sometimes called heavy
hydrogen. It's hydrogen with two
electrons in it as well as the proton at uh,
its centre. And it's radioactive. Uh,
tritium is um, I suppose you'd call it
mildly radioactive. Um, we used to
use tritium standard lamps at the
observatory when I was working there, which
was a little capsule of tritium with some
phosphor on it. Um, and
um, basically the electrons released by the
tritium lit up the phosphor and
gave a very constant glow so we could use it
to calibrate other, other instruments.
So I've been close up and personal with um,
a little nuclear power source a bit like
that, but it was just making faint light.
This one is one that's been uh,
developed by a private company. Um,
and it's uh, basically a
company called City Labs, uh, in the United
States. Uh, they've built
um, a little, as I said, it's
effectively a cubesat which has this um,
little nuclear, not nuclear
reactor, but nuclear power source inside a
tritium, uh, source that I've just been
talking about, which doesn't actually convert
the electrons into light, it
converts them directly into electricity.
So they've got these panels on the side of it
that take the electrons that come from the
tritium and turn them straight into
um, electricity. Ah, it's
Called Bohr B O H R, uh, which is
a bit of a play on words because Niels Bohr
was one of the great founders of quantum
theory. Same spelling, um
Danish one, A uh, Danish uh
scientist, uh and it stands for
Beta Voltaic. And a
Beta Voltaic is taking the beta particles,
which are otherwise known as electrons, uh
turning them into electricity. So it's Beta
Voltaic orbital high reliability
spacecraft. That's where you get the Bohr
from and it's been launched. Uh,
so SpaceX's part in this storey is just to
provide the taxi, uh up into um, up
into orbit. It's a transporter, uh
mission, um, basically
one of uh, SpaceX's taxi rides to get stuff
up and down from uh, or up to orbit,
coming down to different storey and most of
them just burn up.
Professor Fred Watson: Yes.
Professor Fred Watson: Uh, but it is uh, probably the
first CubeSat to include a nuclear
power system. Uh and
maybe, just maybe we'll sort of illuminate
the way for a new generation of uh,
spacecraft which are equipped with uh,
these nuclear power sources.
Andrew Dunkley: I suppose they have to look at alternatives
because we've been reliant, fairly
reliant anyway on solar energy in
space, um particularly with our uh, orbiting
satellites, but also with um, the
International Space Station and others. Um,
but the time will come where we are
in places where there won't be that
much sunlight and
in some places there won't be any at all. And
solar panels are going to be useless.
Professor Fred Watson: Uh, that's correct. And we've seen already
um, the use of these UH RTGs,
radioisotope thermoelectric
generators, uh which are carried by both
the Curiosity and the uh
Perseverance rovers, uh as well as
spacecraft in deep space like uh,
Voyager 1, Voyager 2, Pioneers. I think
they've got them as well. And these are
spacecraft that are so far from the sun that
you get very little light from the sun,
uh in terms of um, you know, using it to
generate electricity. So they've, they've had
their nuclear power sources for a long time.
They are quite different though from what
we're talking about here. There are, I think
it's 13 kilogrammes if I remember rightly, is
the amount in a canister of plutonium
dioxide, uh which is
decaying all the time and getting very hot as
it does that and that heat is then used
to generate electricity, uh and
it actually dies away as time goes on. So
these nuclear uh, RTGs, the
radioisotope thermoelectric generators
gradually lose their power, um, and that's
why we hear from time to time and we usually
report this on space nuts. We hear of
uh, uh instruments on board Voyager 1
being turned off to save the power.
Andrew Dunkley: Yeah. And that happened again not so long
ago.
Professor Fred Watson: I think that's correct. Yes it did.
There was one turned off uh quite recently
but perhaps more to the point and
uh, what you've just said about there being
some places that have no sunlight whatsoever,
uh that applies to uh, those deep
craters near the moon's south pole
and that's where we're thinking of exploring.
So it may be that um, these
beta voltaic arrays
uh uh, or devices might well
be the future of power generation
near the moon's south pole because you're in
places where there's no light whatsoever from
the sun.
Andrew Dunkley: That's absolutely true. Darn cold too. It is.
Professor Fred Watson: It is always cold there. Yes, yes
indeed.
Andrew Dunkley: Uh, uh that's a really interesting storey and
we're obviously in the early phases of
finding these alternatives. Is um, tritium
safe?
Professor Fred Watson: Uh, it's probably something regarded
uh, treated carefully.
It is generally safe. I mean we never took
any real precautions with the device that we
had on the telescope. Maybe we should
have done. Although uh, most of
us are still around and in fairly good
health. But um, yes they are
releasing electrons, uh beta radiation,
uh, it's um, uh if you had a
high level though of tritium, if you had a
significant amount of it then you would have
to be careful about how you handled it and
where it was put and if it needed shielding
and things of that sort.
Andrew Dunkley: Yeah. So uh, don't sprinkle it on your
cornflakes or anything like that.
Professor Fred Watson: Yes, that's right. It's best to avoid it if
you can.
Andrew Dunkley: Yeah. Sugar's damaging enough already.
Professor Fred Watson: It is. Tell my dentist about it.
Andrew Dunkley: If you'd like to um, read up on that storey
about the uh, the launch of the cubesat with
the tritium nuclear ah power device
they're testing. Uh you can read about
it@dailygalaxy.com.
um, let's keep on this theme
Fred Watson, because that's the good news.
Uh the bad news is um,
the the problem of exploding nuclear
devices in space or firing nuclear
devices from space to targets on Earth.
That's, that's a real issue. I know.
Um, was it back in the 80s the
Star wars um
um push was uh, all the rage in the news
at the time and uh, that got shut down pretty
quickly.
Professor Fred Watson: Star wars was um, a
Reagan era initiative. Yes, I think it was, I
think it was um, uh basically
electromagnetic Radiation to zap your
satellites. It wasn't nuclear though, uh,
because nuclear weapons are in space, are
prohibited by the outer Space Treaty
1967.
Andrew Dunkley: So what's happening?
Professor Fred Watson: They're not allowed. But,
um, there may be some there
launched by powers that
stretch um, the envelope, if I can put it
that way. Governments that stretch the
envelope. And uh, we don't know. We don't
know if there are any. You know, they're
banned by the uh, Outer Space Treaty. So
there shouldn't be any nuclear weapons in
space. But that's all very well.
Professor Fred Watson: Um.
Professor Fred Watson: There's a lot of things that shouldn't happen
but do happen. And um. So it may be
that perhaps there are nuclear weapons in
space. So the question is,
um, how do you detect them if there are,
ah, these weapons? Um,
and um, that's
where this piece of research, uh, from
the Massachusetts Institute of Technology
has come from. It's um, a um, person
whose name is Areg Dana
Gulian. Sounds uh, like an Armenian name.
Does that usually I a n on the end. Armenian.
An associate professor of nuclear science and
engineering at the Massachusetts Institute of
Technology. And he has
um, essentially
thought of a neat way,
uh, of building a device that
you could fly in the vicinity
of a satellite to detect whether
it is carrying nuclear weapons.
Um, and it's all about the subatomic
particles, uh, that um, you know,
that, that nuclear um,
weapons are all about. It's all about uh,
neutrons and uh, you know, the nuclear
nuclei of atoms. That's where it all comes
from. Um, so
what he has suggested, and I might
quote, um,
I might quote from uh, Dr. Dana
Gulian's work. Uh
the risk is that
if you did explode a nuclear weapon in
low Earth orbit, then you basically wreck low
Earth orbit for everybody. It's not the
blast, it's just the subatomic particles that
do it. Uh, and so what he goes on to say
is this danger is compounded by the lack
of a verification mechanism for the Outer
Space Treaty. Um,
there's no detection methodologies that have
been proposed in the scientific literature.
So what he's saying is here's a concept and
feasibility study, um, for
verifying a satellite's compliance
to the Outer Space Treaty by observing
the neutrons induced by spallation
from the approximately
giga electron volt protons in the
Innovant Allen radiation belts, which is
a slightly complicated and technical way of
saying, uh, you've already got subatomic
particles in the radiation belts around
our planet. Um, if you can,
um, basically watch the way,
um, a satellite responds
to those protons that are in the radiation
belts. Um, if for example that uh,
bombardment of protons from the radiation
belts causes neutron neutrons to be
uh, emitted then you can
have a fair degree of
um, confidence that there might be a nuclear
weapon on board or a lot of nuclear fissile
material, heavy elements like uranium.
That's the kind of thing that this is all
about. And so um,
uh, what this is all
about is building uh, a
satellite that can detect
uh, neutrons uh, coming
from radioactive material. And
he's basically suggesting a
detector, uh, uh, uh, what
he calls an inspector satellite that flies
by, uh, the satellite that you're
interested in finding out whether it's got
nuclear weapons. And it's got these detectors
uh, which are almost like X ray detectors.
The kind of things that you see now when you
go for an X ray, a chest X ray. They're
electronic, they're not photograph they used
to be back in the day. Um, and they've got
what are called neutron sensors, uh they're
called scintillators. And uh, you
put those in a special arrangement with
other basically other detectors.
Uh, and um, if you do that then
you can apparently sort out the
neutrons from the other natural
subatomic particles that are floating around
near the radiation belts. And the neutrons
come from radioactive material and you can
also see the direct direction that they're
coming from. So you can sort of point this
thing towards your target satellite, uh, the
one that you suspect might have nuclear
weapons and it will give you the direction of
where it's coming from. Um, and
so uh, just a quote,
um again from Dr. Dana
Gulian. Um, the calculations show
that a nine unit cubesat size
detection platform, that's something the size
of, what's that, about three loaves of bread?
Something of that sort size. It's quite
small. Um, it can identify a
thermonuclear weapon from a distance of
four kilometres in approximately one
week of observation. Now that's quite a long
time but uh, apparently
if you could get it to within one kilometre
it would take you about an hour to detect a
weapon. And that's
promising. That's one flyby, that's you know,
an hour of proximity, uh, you could do that
as you go past the
suspect satell. If you got an hour in
close uh, contact with it or close uh,
proximity to it within a
kilometre, uh, then you might well
detect a nuclear weapon on board. And of
course you could improve that if you had more
than one of these inspector satellites. If
you multiplied them up, then you could get,
uh, quite significant improvements in that
performance. So it's really quite
interesting. Um, uh, one
quote that I really liked, um,
and I'm going to read, uh,
from, uh. Universe Today has a very nice
article on this. The last sentence is, right
now, nations like the USA and Russia rely on
intelligence to know what the other is doing.
And as we know from history, intelligence can
get things wrong. You can fake intelligence,
said Dr. Dana Gulian, but you can't fake
physics. I like that. Yeah, it's true. So
you could do it by physics. Yeah.
Andrew Dunkley: They do, uh, mention in this particular
article that there's one suspect satellite
that seems to have been launched by Russia.
And the bottom line is that it's
been put in an orbit that is very strange
and very hostile in terms
of its radiation, uh, in that area.
And the question is asked. Well, it says no
one puts satellites there because it's highly
radioactive. Why would you put a satellite in
that orbit? So that's one they've already.
They haven't identified as maybe carrying a
nuclear weapon, but they've certainly
identified it as suspicious.
Professor Fred Watson: Yes, that's correct. And so, um.
Yes, highlighting that, I think, you know,
puts this article in context. It
tells you that this is a real issue and, um,
we kind of need to work on how you might
detect, uh, nuclear weapons in space.
Andrew Dunkley: Of course, the other side of it is if you do
identify a satellite that's carrying a
nuclear weapon, what do you do next?
It's like trying to teach people not to
overtake emerging lanes, isn't it?
Professor Fred Watson: Uh, yes. Uh, but,
uh, it's worse than that really, because. A
little bit, yeah, you know, we have
nations that completely disregard
international law. They invade other
countries without so much as a,
you know, a sniff of the,
um, um. Of the, um.
All the international treaties, they just,
Just run amok among them and away they go.
Uh, and yes, so that's the possibility that,
uh, we might already have them.
There is a kind of
corollary of this which I was thinking of
when I read this, Storey. Um, and
that is that back in the 70s,
uh, gamma ray
satellites were launched,
satellites that detect gamma radiation. And
that was to detect any in
atmosphere nuclear tests, uh, conducted on,
uh. Because there was a test ban treaty that
was signed, uh, all the signatories
said, no, we won't test nuclear, uh, weapons
in the atmosphere. Uh, but they had to
verify it. And so the verification process
involved, uh, a number of satellites being
launched that could detect gamma rays which
would be emitted by a nuclear bomb being
detonated in the atmosphere. Uh,
now none were. But those
satellites are what detected gamma ray
bursts. These um, you know, fascinating
pulses of radiation that come from, uh, from
explosions deep in space. Yeah, of course,
man made explosions, but natural ones. Yes.
Andrew Dunkley: Because if they do start detecting nuclear,
uh, weapons in space, then the
parties involved, uh, they won't say, oh,
sorry, sorry, we'll take them all down.
They'll find ways of hiding them.
Professor Fred Watson: Probably. Yes, that's probably right.
Andrew Dunkley: Gosh, it's tough, isn't it?
Professor Fred Watson: Uh, tough world we live in.
Andrew Dunkley: Indeed. Uh, and beyond it in some
respects. Uh, you can read that
storey@universetoday.com. this
is space Nuts with Andrew Dunkley and
Professor Fred Watson Watson.
Space Nuts.
Uh, next storey, Fred Watson, uh, is
looking at, uh, all the dust on Earth
and where it might have come from. Now I was
thinking cats because
they do shed. Uh, but it's uh, a bit
more involved than that. And what
is really interesting about this storey is
they think a heck of a lot of it came from
one source.
Professor Fred Watson: That's right. And it's a mysterious one as
well. Um, so this is
quite a nice storey, uh, from publishing, uh,
Science Adventures. Um, it's
about, uh, the
micrometeorites that bombard the Earth.
And it's a bit surprising, this
stuff. Uh, you know, we think of meteorites
as big chunks of rock that come through the
atmosphere, they have a blaze of glory and
then land on the Earth somewhere. And
what we've got there is um, a
free sample of extraterrestrial
material. But there are also these
micrometeorites which rain on the Earth's
atmosphere and they're dust particles, as
you've kind of hinted. Uh,
um, and they're sort of always
falling on Earth. Uh, and that,
uh, is again, it's a free gift from space.
Um, I think. So I was sort of
vaguely involved with this stuff probably 50
years ago, back in the 70s. I think they
were then called Brownlee particles. Um.
Oh, that sounds familiar. We're talking
about. Yeah. Uh, but they're now,
I think, called cosmic spherules. Uh, I
should cheque whether Brownlee particles and
cosmic spherules are the same thing, but
basically what they are
is bits of meteor that have
melted as they come down through the
Earth's atmosphere, but
they actually survive into the inner
atmosphere and they cool down and they form a
little sphere because the um, basically the
surface tension of molten material brings
them into a sphere. Uh, and that
uh, is the storey so far
because that um, heating
that you, that they experience as
the sort of parent Body, the meteor. Meteor
or meteorite, as it comes through the
atmosphere, it, um,
kind of destroys their chemical
structure, you know, the minerals in it. It
get metamorphosed, they get changed because
they've been subject to very high
temperatures. Um, but there is
a technique, uh, that allows you
to look at, uh, some
of the characteristics of these
objects that is not destroyed by
heat. And it's the oxygen
isotope signature, uh, which we've
talked about before. We've talked about
isotopes and how they, uh, you know, how we
distinguish between heavy water and normal
water and all of that sort, sort of thing.
That's. So it's basically the. The number of,
uh, neutrons in an atom. Um,
so you've got these oxygen
signatures, uh, that,
um, essentially, uh, let you,
ah, group these cosmic
spherules, the Brownlee particles, if that's
what they are. Um, and it turns out
that so, so people do, you know, they do
population census statistics on these objects
to find out, uh, what
relationships they bear with one another.
About 10% of them of these
ferals that have been identified and
analysed collect in a group
that has got the wonderful name of Group
four, uh, which presumably means
there's another three as well. Yeah. Um,
and it's, uh, the. Again, what
makes them stand out in this group is the
oxygen isotope signature that I just
mentioned before. It's depleted in, uh, an
isotope called oxygen 16.
But here's where the storey gets very
interesting because, um,
no known meteorites have
that same oxygen isotope signature.
And you'd expect, uh, if these
things were common, that there would be
meteorites, uh, that match them in their
composition. Uh, and often with
meteorites we can get an idea where they've
come from. Uh, most of them come from the
asteroid belt from collisions between
asteroids. Uh, so, uh,
um, that is a bit mysterious
that we've got these subatomic, sorry, these
small spherules of material that have come
down through the atmosphere, uh, and got that
globular shape. Um, it's
mysterious that we don't know. We don't see
any meteorites that match their
composition.
Andrew Dunkley: Weird.
Professor Fred Watson: It is weird, yes. Uh, and so what
they're suggesting is that, um,
it's basically something that
comes from an asteroid, uh,
whose characteristics are unusual, uh,
that we have not, uh, yet, um,
identified it.
Andrew Dunkley: Wow. Okay, so we're
still looking.
Professor Fred Watson: We're still looking. There's a sort of sub
mystery as well because, um,
a detailed analysis of this, you can break
that Group 4 stuff down into other smaller
groups. And, uh, some of them
Basically show signs of having had two
different, uh, minerals in
them before they entered the Earth's
atmosphere. And, um,
one would be typical of,
uh, well known types of asteroids. And the
other, as I said, doesn't correspond to any
kind of known, um, group of, uh,
um, cosmic spherules or meteorites.
Uh, and it's really quite
remarkable that this, you know, we're being
bombarded by dust particles that come from
somewhere which we haven't identified.
Professor Fred Watson: Yeah.
Andrew Dunkley: Wow. Um, could that mean they're from
beyond our system or it's just a part of the
system that we.
Professor Fred Watson: I think it's.
Andrew Dunkley: I don't know.
Professor Fred Watson: Yeah, I think it's the other way around. Um,
because the m. The team who've done the
research on this, a very, very thorough piece
of research, they've basically,
um, as you would, you've used, uh,
simulations, computer simulations
to, to essentially work out
what conditions these things formed in when
they, um, melted coming through the Earth's
atmosphere. And it suggested that the best
fit they get to what they see, the sort of
textures that are in the material fit
with relatively low
velocities, uh, 14 to 17 kilometres
per second. Uh, which is
pretty speedy when you think of it on Earth.
But, um, uh, in space, that's a
fairly modest, uh, space speed for a
meteorite that typically will be more like 30
kilometres per second. And so that
low value, uh, suggests
that possibly those
particles originated in near
Earth asteroids, um, ones
that are, um, following a similar path
through space to the Earth. And that
might mean that we've got some sort of,
um, in the Earth's environment, some
sort of unusual asteroid
that is not, not matched by all the ones that
we know already.
Professor Fred Watson: Wow.
Andrew Dunkley: That'd be something, uh, that's probably
gonna be hard to track down though.
Professor Fred Watson: Yes, yes, that's probably right. And
especially since it might not exist anymore,
it may have collided and formed little bits
that have basically rained down on the Earth.
Andrew Dunkley: Yeah. Now, it wasn't Thea. Rusty just.
Professor Fred Watson: No, it wasn't Thea. That's right. Yeah.
Thanks, Rusty. It's not Thea.
Andrew Dunkley: Um, for the record, Brownlee particles and
cosmic spherules are closely related, but
they are not exactly the same thing.
Professor Fred Watson: Okay.
Andrew Dunkley: They represent two different ages or types
of micrometeorites.
Professor Fred Watson: There you go. Thank you for checking that.
Yes, that's all right.
Andrew Dunkley: Um, yeah, they're very close, but they're
not, not the same.
Professor Fred Watson: So I was on the right track.
Andrew Dunkley: You were, yes.
And you can read all about that at, uh,
the AstroDailyPod Galaxy website. Um, and
the article Was published where,
Fred Watson, I've lost the science advances.
That's right, yes. Want to read the whole
thing before bed so you sleep well?
Professor Fred Watson: Yep.
Professor Fred Watson: Yeah.
Andrew Dunkley: This is Space Nuts with Andrew Dunkley and
Professor Fred Watson Watson.
Professor Fred Watson: We choose to go to the moon in this decade
and do the other things, not because they are
easy, but because they are hard, these nuts.
Andrew Dunkley: Our, ah, final storey today takes us
to the edge of our galaxy. Well, it takes us
from the centre of our galaxy right out to
the edge of our galaxy because we're talking
about the whole thing lock, stock and barrel.
And it appears, Fred Watson, with some very
clever scientific brains in action,
that, uh, our galaxy stretches out further
than we thought.
Professor Fred Watson: Uh, it does. It looks as though the spiral
arms are longer than we thought they were.
And I think this is a very nice piece of
work, uh, as, uh, I hinted before,
uh, partly because it uses a technique that I
think is really extraordinary. It's a very
powerful technique, uh, using what we call
light echoes. Um,
so the storey, basically, to set this in
context, it's very hard for us to
produce a map of what our own galaxy looks
like. And that's because we're embedded in
one of the spiral arms. Uh, the
stars that we see when we look at the Milky
Way. They're stars that, uh, fellow
travellers in the spiral arms with our, uh,
sun and solar system. But they only go out to
1000 light years or so because the spiral
arms are so dusty that you can't really
penetrate much beyond that. Um,
and if you were relying only on visible
light, uh, it would be
like trying to draw a map
of the whole of Dubbo from
standing outside Dubbo jail there on, um,
uh, forgotten. Is that Macquarie Street?
Andrew Dunkley: Macquarie street, yeah.
Professor Fred Watson: Yes, yes.
Andrew Dunkley: Oh, for the record, they're putting a, um,
they've taken down the public building in
front of the old Dubbo jail.
Professor Fred Watson: Oh, there you go.
Andrew Dunkley: Now they're turning it into a public
common. Common.
Professor Fred Watson: I, uh, like that idea.
Andrew Dunkley: That's going to look very nice when it's
done.
Professor Fred Watson: So that would improve your view of the city
of Dubbo, but it still might not let you make
a map of Dubbo from just there. Uh,
and that's how we are in our galaxy. If
you're relying on visible light observations,
uh, all you're seeing when you look
is the neighbourhood of, uh, our
spiral arm, a local spiral arm. You don't get
any hint or inclination of the structure of
the galaxy, uh, beyond that. And in
particular, you know, if we see
a thousand light years or so, there's another
Hundred thousand that we're not seeing
because that's about the diameter of, ah, our
galaxy. So, um, ah, the
situation improves when you use infrared, uh,
radiation. You can sort of penetrate, uh,
through the dust and see actually the centre,
towards the centre of our galaxy. That's how
we know about the black hole in the centre of
our galaxy, because we could see stars
orbiting around it. Um, but
it improves even more on a broader scale if
you can use radio telescopes, because you can
plot, um, where the clouds of
hydrogen gas called hydrogen, uh, which
radiates in, uh, radio waves, uh, with a
wavelength of 21 centimetres, uh, that you
can plot out. But if you're going to try and
draw a map, you do need to do some modelling
with that. You've got to assume things about
the rotation of the galaxy so it doesn't just
give you a direct map, map. And that could
be wrong. We could have that little bit of it
wrong, uh, you know, uh, the stuff that comes
from the radio observations. So
what's happened now is it's a
team, uh, I think they're based in Italy,
uh, and what they've done
is used, um,
a direct method of kind of
setting up a standard ruler. Uh, because if
you've got a standard ruler and you can see
it in deep space, then you know how far away
it is because you can measure how long it
appears to be. And if you know how long it
is, which is what a standard ruler is, then
you know how far away it is. And that's
what they're doing. They have. And it goes
back to something we mentioned earlier in the
show, gamma ray bursts. These bursts of gamma
radiation, those
bursts, uh, don't just directly come to
us, they also bounce off or are
reflected by clouds of dust in our
spiral arms. And, uh, so
by timing how long,
uh, it takes for these echoes, as
they're called, light echoes, even though
it's gamma radiation, uh, to what
the delay is between a light
echo and the, uh, source itself,
which is the gamma ray burst, I should say
they probably come from collapsing
massive stars or merger of neutron
stars, uh, very energetic events
because they're bright in gamma radiation.
But if you look at a light echo from a gamma
ray burst, it gives you a scale to this,
you know, um, how far.
Basically, uh, it gives you a standard ruler,
um, because you can time it accurately, you
know that 300,000 kilometres per second is
the speed of gamma rays through space. And,
you know, if you know how far away it's gone
in that time, then that gives you a distance
measure. So you've got a standard ruler. Uh,
it's a very, very nice way of doing this.
And, um, using that, uh, these,
uh, scientists, um, as I
said, uh, at least the lead author is, uh,
certainly in Italy at ENAF in Milano,
uh, uh, they've done this work
looking at these gamma ray bursts with their
light echoes, and that allows them to
calculate basically the size of our, uh,
spiral arms without relying on any kind of
modelling. And so
they think that the new
observations indicate that, uh, our spiral
arms are something like 10%
longer than we thought they were. Wow,
that's, uh.
Professor Fred Watson: A lot.
Professor Fred Watson: Yes. That's significant, isn't it? It's
really, um. You know, this is. As I said,
this is very nice, uh, nice astronomy.
Andrew Dunkley: It is indeed. Yeah. Um, of
course, as you say, we can't really look at
our galaxy. We don't know exactly what it
looks like. Um, there's a lot of science that
they've put together to try and create
the image of it. And even in this particular
storey, uh, which is in the Universe Today
dot com, they've got an artist's impression
of what this new, uh, look is like.
Professor Fred Watson: Yes. That's all you can do.
Andrew Dunkley: Reminds me of an upside down snail.
Professor Fred Watson: It does, yes, that's right. I see what you
mean. Yes, yes.
Andrew Dunkley: Or a squid. Could be a squid.
Professor Fred Watson: Could be a squid, yeah.
Andrew Dunkley: Uh, but in real terms we just have
to. It's an edge. Very, very educated
guess, I suppose.
Professor Fred Watson: Um, yes, it is. It's a measurement.
So you're right,
it's an artist's impression. That's really
the only way we can depict the Milky Way.
Some of the depictions are very, very good
and they rely on the very best radio and
infrared observations that have been made.
But this is going to modify it a little bit
by our new knowledge of the spiral arms. And
I should say, um, this, the, um.
It's the Chandra satellite, uh, which is a,
ah, an X ray observatory, um,
by. Operated by NASA, uh,
that has been used to make the measurements.
And I do like the headline on a little, uh,
NASA video that there is Here, which is
NASA's Chandra examines Milky Way at
Arm's Length.
Andrew Dunkley: Yeah, nice. Um, very
well done.
Professor Fred Watson: Clever, clever. Yeah, they are.
There's some good people there.
Andrew Dunkley: Uh, so the articles in Universe Today, but
you can read it in a deeper form
through the NASA website or the, uh,
Astronomy and Astrophysics Journal, I think,
has published, uh, the full paper, which is.
Professor Fred Watson: Yeah, that's the European journal.
Andrew Dunkley: Lots of numbers in it. Yeah, lots and
lots of numbers. Numbers that are too big
for my brain.
All right, uh, that's where we end the show.
Fred Watson, thank you very much.
Professor Fred Watson: Much.
Professor Fred Watson: Oh, a pleasure. Uh, as you said at the
beginning, some nice storeys there.
Andrew Dunkley: Yeah. I'm very glad to be able to
Professor Fred Watson: share them with you.
Andrew Dunkley: Indeed. Uh, we'll catch you real soon. Thank
you, Fred Watson.
Professor Fred Watson: No worries. Thanks, Andrew.
Andrew Dunkley: Professor Fred Watson Watson, astronomer at
large, and, uh, as I say, between episodes,
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Uh, thanks for your company. We'll catch you
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