Andrew Dunkley: Hello again and thank you for joining us on
another episode of Space Nuts. This is a Q
and A edition where we take audience
questions. We put them on paper and then we
put them on a roll that goes on a little
thing in a bathroom. Or we could
answer them. We can do that. Uh, coming up
today we have questions, uh, uh,
from John about Martian days. The length
of a Martian day. It's close, but is it
close enough to Earth standard? We'll discuss
that. Uh, the growth of a black
hole has been, uh, brought up again.
Uh, we've got a, um, a question, uh,
from an 11 year old named Thomas. Hi, Thomas.
He wants to talk about the galactic centre.
And Paul is asking our, uh, about
our galactic location. So we'll deal with
all of that today on this episode 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. Space
Nuts astronauts report it feels good.
Andrew Dunkley: Joining us again to sort all that out is
Professor Fred Watson Watson, astronomer at
large. Hello, Fred Watson.
Professor Fred Watson: Hello, Andrew. Good to see you again.
Andrew Dunkley: Uh, good to see you too.
Professor Fred Watson: Yes. Despite the hole in my head.
Andrew Dunkley: Yeah, yeah. It doesn't look any better than
last time.
Professor Fred Watson: It doesn't, does it?
Andrew Dunkley: No, I mean, you know, it's only been
minutes. You'd think it would have improved
by now.
Professor Fred Watson: That's what happens when you walk into a,
when you walk into a closed screen door.
Andrew Dunkley: Yeah.
Professor Fred Watson: In the dark it hurts.
Andrew Dunkley: Now that's why they have stuff, um, on,
on glass sliding doors, you know,
uh, that, that's a standard safety standard
required these days so that, you know, the
door is there.
Professor Fred Watson: Yeah.
Andrew Dunkley: But when it's nighttime and it's a screen
door. Not, not many excuses left there,
Fred Watson.
Professor Fred Watson: Really only stupidity, I think is the,
is the last one. But that's, that's
my excuse many, many times.
Andrew Dunkley: Yeah, well, we've all done it.
Shall we try and answer these questions?
Professor Fred Watson: We should.
Andrew Dunkley: Okay, let's go to question one. This one
comes from John.
Uh, we know that the Martian Day is 39
minutes longer than an Earth Day. That's
about four and a half hours a week. Uh, when
and if Mars is populated with humans,
how would we work with the longer
day, week? Would human
biology tend to keep to the 24 hour
day or would we adapt to a longer day,
Night. Cycle. Cycle. Thanks. Love the show
and have been a listener since you started.
Wow, you've got a lot of spare time, John.
Thank you so much, uh, for sending your
question in and hope all is well. Uh,
I love this question because
you've got a planet that is close enough for
us to get to in the not too distant future.
Probably not a
permanent settlement, but a rotating
settlement of some kind will be the initial
stages of humans being on Mars.
And yet you've got an extra 39
minutes a day to deal with what
is going to be the impact.
Professor Fred Watson: Um, I think we've already, we have
um, a lot of data on this
Andrew Dunkley: because the, we've already talked about this
once before in the deep dark past. Quite a
lot came up again.
Professor Fred Watson: Yeah, yeah, because of the, the um,
rover, um, drivers, they,
the people who are uh, in command of,
if I can put it that way, because they don't
actually drive them directly but in command
of the rovers on Mars and the two active
NASA ones at the moment are Curiosity. Uh,
and perseverance. Uh, they
Adapt to uh,
24 hours, 39 minutes day,
and do it quite successfully
as far as I've been able to work out.
Andrew Dunkley: Well I hope so, yeah.
Professor Fred Watson: Otherwise there might be a pile up on Mars.
Um, and in fact the reason why I said they
don't actually drive them is because the
rovers themselves have got to be to some
extent autonomous because of the delay
in signal time to get between Mars and
the Earth. You can't have video coming back
from your rover and a steering wheel so that
you respond to that because you'd have a sort
of 20 or 30 minute delay probably before
uh, before um, you turn, before
the wheels turned on the rover.
Andrew Dunkley: I would imagine that the manual
driving of a rover from Earth
on Mars would be damn near impossible because
even your images would be out of sync with.
Professor Fred Watson: Everything's out of sync. That's right.
Andrew Dunkley: So you say, oh, there's a rock coming up.
That was 40 minutes ago, I'll turn
left now.
Martin Berman Gorvine: Oops.
Andrew Dunkley: Yeah.
Professor Fred Watson: Ah, um,
so the rovers drive themselves basically,
uh, with a lot of assistance, um,
and monitoring from Earth, uh, in order
to see what's coming up and see what
the onboard computers are doing in terms of
what route they're taking through the rocks
and debris on Mars. Ah, uh,
um, but those people, as I understand
it, do go on to uh, this 24
hours and 39 minutes day length.
Uh, I think it's nearing enough to our 24
hours that I think they adapt quite quickly.
From my recollection of our previous
conversation about this Andrew.
Andrew Dunkley: Yeah, if I remember rightly, we were talking
about the fact that if you're going to stay
on Mars long term you would
have to adapt.
Um, you wouldn't adapt naturally
at all you'd have to take catnaps
or something like that to catch up. Um,
or something to that effect.
Professor Fred Watson: Well, yes. So your circadian rhythms
would, they'd be under stress, they'd change
and I suppose you'd have a permanent feeling
of jet lag. Probably what it feels like.
Andrew Dunkley: It would be tough. I read an article, uh,
last weekend which I found fascinating
and it was, um, detailing how
the eight hour night cycle
that humans have, like going to bed for eight
hours, is a myth.
Professor Fred Watson: Yes.
Andrew Dunkley: And that, um, it was actually
something invented by a mattress company back
in 1938. Have you heard this?
Professor Fred Watson: No. Yes, I do know that
we used to sleep twice in the night.
Andrew Dunkley: That's right. So you go to bed at like 9 o'
clock and you'd sleep for four hours
and then you'd get up for two hours and you'd
do stuff like, stuff we can't talk about on
this podcast, but other stuff like,
um, they cited a couple of,
um, famous people, um, whose names have
dropped straight out of my head. Um,
William Shakespeare apparently wrote
a lot of his famous works between
1 and 3 in the morning when he got up and
then he'd go back to bed for four hours. And,
uh, Beethoven did the same thing with some of
his symphonies. He wrote some of the
best works that he ever created
at 3 o' clock in the morning, um,
during his wake time between his two sleeps.
So the eight hour sleep
that we have at night was an invention
apparently, to sell mattresses. That's
what I'm told. Look, I haven't confirmed or
denied that, but it seems
possible, I suppose.
Professor Fred Watson: Well, yes, I think we have,
uh, I think, um, there's been evidence
from the earliest times,
uh, the times when people truly were ancient
peoples back thousands of years ago,
uh, that that's how they lived their lives.
Exactly as you've said. And maybe the last
vestiges of that were keeping
going in Shakespeare's time and then in
Beethoven's time. Um, there
weren't that many clocks around then. There
were some, but not that many. It wasn't like
you had a smart watch by your bedside or
anything like that. So, uh, it would be a
natural rhythm that they would use, uh,
to sleep and wake up.
Andrew Dunkley: Yes. Modernization certainly
messed us up, hasn't it?
Professor Fred Watson: Yeah, yeah, that's right. I think in that
case it has.
Andrew Dunkley: And I think, uh, on Mars, um,
it will be a pretty difficult thing,
Professor Fred Watson: I imagine it may be.
So maybe I can just sidestep here slightly,
Andrew, um, because I would very much like to
know uh, what
answer one of our listeners would give to
that, and that's Dr. Heidi DeBlock who's
I think based in Houston, if I remember
rightly, who is basically a space medic.
Uh, and um, uh, it will be very interesting
to hear her take on how humans will adapt
to that. And if I may, she was in touch with
us recently to comment on one of our earlier
questions. Would it be all right if I. Yeah.
Andrew Dunkley: And that was when we were talking about how
people deal with um, gravity when they
get back on Earth after being out in space
for a while, correct?
Professor Fred Watson: Yes, that's right. Uh, she
says, um, I just finished the July
5th space nuts and wanted to help answer the
question about how the astronauts feel when
they land back on Earth. Of course I haven't
experienced it in person, but have worked
with plenty of astronauts at landing. In
particular, all of our, uh, physiology
changes in space as we are designed for
1G. Some astronauts are pretty good when
they land, especially those who are on the
shuttle and in space. For short time.
Sorry, for a short time. Some had significant
problems. They stemmed from the orthostatic
hypotension as a result from the
cardiovascular changes, some of the changes
in the inner ear with balance and knowing
where you physically are, some mild
weaknesses, et cetera. These changes are more
exaggerated with long duration flight in the
International Space Station. The vision
problems are called SANS S A N S
which is an acronym for Spaceflight
Associated Neuro Ocular
Syndrome. Our lab is studying that
as well. That's a whole other fascinating
issue. I could tell you some
fun storeys about astronauts and how weird
some of them feel when they get back. Maybe
we need to get Heidi on the show. Maybe we
do. Yeah, no, that's um,
uh, she has another interesting comment
actually about the, about the uh,
Voyager Golden Record. But we might talk
about that another time. Fair enough.
Andrew Dunkley: Yeah. All right. Thank you, Heidi. That was
fascinating.
Professor Fred Watson: Yeah.
Andrew Dunkley: Um, what an amazing job working with all
those incredible people trying to
figure out how to deal with the zero G
problem. But uh, on Mars the gravity will
also be an issue. So, um, there's
a heck of a lot that needs to be sorted out
before we um, put people down
there. Because it's such a long trip to
get there. It's not like you can go, uh, ah,
no, this is no good and come straight back.
Professor Fred Watson: It's not going to be that simple. That's
right. Once you're on your way. On your way.
And the only way back is to keep going.
Andrew Dunkley: Yeah, exactly. Thanks for the question, John.
Uh, well asked. And yeah, it's not
going to be a snack, that's for sure. Let's,
uh, move on to our, uh, next question from
Dan.
Martin Berman Gorvine: Hello gentlemen. Dan from the Gold coast
here. Uh, now I know you've been
asked a million questions about black holes,
uh, but I do have a quick two parter and I'm
hoping that's something you've never had to
answer before. Really quickly, from the
point when a black hole is born,
birth, created, whatever you want to call it,
uh, how quickly is that growing to become a,
let's say, supermassive black hole or just
something a lot bigger? Um,
or is that not how black holes work and I'm
not understanding it properly? Two,
Hypothetically, uh, if there's no matter or
energy or anything surrounding
the black hole to take in and let's say
eat, uh, is the black hole still going to
grow? Is there more to the black hole growing
than I understand?
Um, yeah. Hopefully that made sense and
hopefully it's worth answering. Love the
show. Love you guys. Work. Cheers,
bye.
Andrew Dunkley: Thank you, Dan. Uh, nice to hear from you.
Uh, yeah, a couple of questions in that one.
Um, we never talk about black holes, but we
will today. Ah, speed of growth.
Um, that's an interesting one. Um,
given that we're starting to think that there
were some absolutely
enormous, um, black holes in the
early universe. Um,
and, and they're looking
for more and more evidence to see what was
going on early on. Um, but we've got some
gargantuan ones still around. Uh,
so how fast did they get that big? And
I, um, I'm starting to think, Fred Watson,
it wouldn't be a stock standard approach.
Professor Fred Watson: Maybe not, maybe not. Uh, but I mean,
Dan's asking, uh, one of the
fundamental questions of astrophysics at the
moment. This is a very hot topic. Uh, and
what set the cat among the pigeons and made
it a hot topic is the James Webb Space
Telescope. Because, um, until
that came along, the idea was
that as basically as Daniel suggests,
black holes were formed in
the early universe by exploding stars that,
um, collapsed at the end of their lives
to form a black hole. The core would collapse
to a black hole and that then
over billions of years that black hole would
grow. And eventually in our own epoch
today, 13.8 billion years after the
Big Bang, uh, you have supermassive black
holes at the centre of every galaxy. That
was the old wisdom. But the James Webb
telescope has turned that completely on its
head because we have serious
evidence of supermassive black holes
within the first 500 million years
of the universe's existence. And that's
too quick for, or too
short a time for this, um, you
know, this slow accretion of
stuff, uh, as being the, um,
the growth mechanism for black holes. Uh,
it's too short a time for that to be the
case. Uh, so
either our ideas of how fast they gobble
up matter is wrong. And they
gobble up matter a lot faster than we
thought. And we actually covered a storey on
this, I think, about four or five episodes
ago, because there are some scientists who
came to conclusion that one of the things
that we thought limited how fast a
black hole can gobble stuff up, uh, was
actually invalid under certain circumstances.
So that's that one avenue of
research that's come from the James Webb
Telescope showing us that, ah, we've got
these supermassive black holes in the early
universe. But the other one is the idea of
the little pink dots or the little red dots
as they're called. And these are thought to
be, uh, basically just
clouds of gas, hydrogen gas,
which are directly feeding a black hole
that may have been formed in the Big Bang. In
other words, you didn't have to have star
formation and then stars blowing up to
create black holes in order to kick this
process off. The Big Bang itself might have
kicked off the process of black hole
formation by producing these things that we
call primordial black holes. Um, and
they may have turned out to be able
to grow very quickly, um, by
immersing themselves simply in big
clouds of hydrogen and gobbling it all up.
Andrew Dunkley: Yeah, of course, um,
when they run out of stuff, they can't grow.
Is that right?
Professor Fred Watson: That's right. So that's part two of, uh,
Dan's question. Uh, what happens when
there's nothing there for them to eat and
they become what we call quiescent black
holes? They don't do anything. They're
there, uh, and they're still, uh,
things that, um, if a cloud of hydrogen
strayed by, they might seize it
by their own gravity and pull it in. But,
um, they're not going to go out,
um, roaming through the universe looking for
stuff to accrete. In other words, looking for
a snack.
Professor Fred Watson: Yeah.
Andrew Dunkley: Ah, I used to work with a guy whose nickname
was quiescent black hole. He was there, but
he didn't do anything.
Professor Fred Watson: Yes, I think I know who you mean.
Yeah. Anyway, quiescent black holes, uh, are,
uh, basically what, uh, Dan has
described. But the first part of his question
is absolutely asking the same questions
that today's astrophysicists are. Uh, it's
one whose answer we don't know. But the
consensus will emerge over the next. Probably
not very long because we're getting so much
data from the James Webb telescope that I
think it'll be quite soon before this whole
issue is resolved, I would think. Sorry,
I was just going to say when, when there is
hard evidence of a primordial black hole
being discovered, one that was created in the
Big Bang, then that'll be Nobel
Prize winning science when we get to that
stage. But it won't be us.
Andrew Dunkley: Indeed, I was going to suggest that black um,
holes are probably like humans. Consumption
will decide how big they get.
Professor Fred Watson: Maybe that's right, yeah, yeah, we'll have
Andrew Dunkley: to wait and see. All right Dan. Hopefully uh,
we covered that for you adequately. Thanks
for sending in the question. This is Space
Nuts with Andrew Dunkley and Professor
Fred Watson Watson.
Professor Fred Watson: Three, two, one.
Andrew Dunkley: Space Nuts.
Our next question, Fred Watson, comes from
Thomas Reid. Thomas is 11 years old.
He says something has been troubling me. In
books I've read they say that the centres of
galaxies are very big black holes and I
have a few questions about them but uh, I'm
only an 11 year old kid so the questions
might sound silly but here they are. Now
we've got five questions Fred Watson, so we
can be brief on on them. Unless you wanted to
sit here for another couple of hours. Um, if
Jonty was here we would be a couple of hours.
Um, can the galactic centre swallow all the
stars and planets in the galaxy? How big are
the galactic centres or do we not know,
uh, if they can swallow up all the stars and
planets. Is there a limit? If there is a
limit, what is it? And if there is a
limit happens when the limit is reached.
Thank you for taking the time to read this
and I would love it if you could reply. Well
we are going to reply right now Thomas. Um,
yeah, it's great that somebody, uh, so
young is taking a keen interest in something
so mysterious as a black hole. Uh,
we want to start at the top. Can the galactic
centre swallow all the stars and planets in
the galaxy?
Professor Fred Watson: Well so the answer is no. Um, so the
galaxies are very big. Ours is about 100,000
light years across. Uh, black holes
have ah, a kind of sphere of
influence um, which gravitationally
stretches to the edge of the galaxy. But by
the time you get there the gravity of the
black hole is very, very weak indeed. And
so it's only in the central region of a
galaxy where you could get material
being swallowed up uh, to create this
activity that we talk about when we Talk
about active black holes, uh, where
there's, uh, an accretion disc, a disc of
material swirling around it. And these jets,
uh, point basically at right angles to the
accretion disc, jets of material travelling
at nearly the speed of light. Quite
extraordinary. So, um, that's all
great and black holes, like a factory or a
furnace doing that, but its stretch is not
very far. Uh, it's measured
in light years, but not in hundreds of
thousands of light years, which would have to
be to grab everything in the galaxy. So the
answer is no. The, uh, galactic centre, uh,
black hole cannot swallow all the stars and
planets in the galaxy.
Andrew Dunkley: Uh, so Thomas can sleep well tonight. Um, how
big are the galactic centres? Do we know how
big?
Professor Fred Watson: M. We do. Yes, we do, because
we can measure the speed
of rotation of stuff
swirling around a black hole, if it's an
active one. And that directly tells you
the mass of the black hole. Um, because
the bigger the black hole, the faster the
stuff is going. And so, um, in terms
of if, the if by
big, Thomas means what's their mass?
Uh, we can measure them quite accurately
now because we can measure their mass. We can
also work out their event horizon
diameter or radius. The event horizon
is that sort of imaginary sphere around a
black hole beyond which light cannot
escape. And so it would appear as a dark
sphere. So the event horizon is the
point of no return for anything going into a
black hole. And it's also the point of no
escape for light waves. Uh,
so we can, knowing the mass of a black hole,
we can calculate how big that event
horizon would be. And some of the
supermassive ones, ah, are really very big.
They're measured in light years, tens of
light years, perhaps for the supermassive
black holes.
Andrew Dunkley: Yeah. It's a level of enormity
that you just struggle to get your head
around.
Professor Fred Watson: Yeah, yeah, I suppose.
Andrew Dunkley: In terms of the rest of Thomas's questions,
you've basically answered it with the answer
to first question, because he's asking if
they can swallow up all the stars and
planets. Is there a limit? If there is a
limit, what is it? Uh, and if there is a
limit, what happens when the limit is
reached? Well, the limit is probably
the local area of the centre of the galaxy
and what's available to eat.
Professor Fred Watson: Yes, that's right. So the limiting factor,
uh, is, um,
basically what you might call the grasp of
the black hole, how far it can reach to
pull something in. And that is
dependent on how fast the objects are moving.
So you can have some stars and there are
some. We've observed them, uh, with infrared
radiation that are comfortably in
orbit, uh, around
the black hole at the centre of our own
galaxy, which are not being pulled in,
they're orbiting. And that's because their
speed is enough to keep them out of the grasp
of the black hole. Um, their distances from
the black hole are measured in not two
dissimilar units from the solar system. Sort
of half a light day or something like that,
you know, light day, that's
the sort of measures that we're talking
about. Um, which probably
denies what I just said a few minutes ago
about, um, some black hole event horizons
being tens of light years. I don't think they
are. I think they're smaller than that.
Joe: Okay.
Andrew Dunkley: I thought of a way to explain it to Thomas.
So, uh, Thomas, you've won a competition
kitchen and you can go to
McDonald's and eat everything you want.
Absolutely. Just keep eating until, you know,
the cows come home. However, you aren't
allowed to move from wherever you're standing
and you can only eat what's within reach.
Once you run out of food, you stop
growing. And you're the black hole, by the
way. How's that for an analogy?
Professor Fred Watson: It's a nice one. I like it. Yes. Yeah,
because your reach is the sort of
gravitational force that you can exert. It's
a good way of putting it.
Professor Fred Watson: It.
Andrew Dunkley: Andrew, well done.
Professor Fred Watson: You should be on the I try
Andrew Dunkley: to think on 11 year old level, but I'm
thinking Thomas was probably much brighter at
11 than I was struggle
Professor Fred Watson: to get to 11. So do I.
Andrew Dunkley: Yes, thanks Thomas. That was really terrific.
Thanks for sending it in and uh, keep on
listening.
Professor Fred Watson: Tranquilly Base here. The eagle has landed.
Professor Fred Watson: Space nets.
Andrew Dunkley: Final question, Fred Watson, comes from Paul.
Joe: Hello, Space Nights. Paul here from
Sunnybris, Vegas, where it's currently
bucketing down in what is being described
as a rare rain occurrence.
Anyway, I
am currently looking through a very old book
of mine. Guess it's old compared to
these students I teach. It was published back
in 1978. I think I got it in 1980 from
uh, an uncle of mine, Uncle Jim. Thank you
very much. It's called Stars and Planets and
it's probably what got me into
the whole field of astronomy in the first
place. At least my interest in astronomy.
Obviously
Andrew Dunkley: very, uh, very grateful.
Joe: I'm on the page where it's talking about
how the American astronomer Carlo
Shapley used
the 1.5 metre reflector on
top of Matt Wilson in California
to work out that our sun is
not at the centre of our galaxy. As was
previously thought, but is about two thirds
of the way to the edge. Could you
please give us some idea how
he actually managed to do that?
Was it something about the
density of stars? I mean, how many
stars in the field of view?
Andrew Dunkley: Uh, when you point it one way
Joe: compared to the other other. How did you do
it? I'm really curious and I know I could
Google it, but I'd rather hear it from you
guys. So thanks in advance. Love
the show and dare I
say, keep up the good work. Cheers.
Professor Fred Watson: Cheers.
Andrew Dunkley: Paul, thanks for sending that in. Uh,
sending the question in and uh, we don't know
the answer, so. But
we're going to Google it. No, um, uh,
1978, stars and planets. Uh,
I tried to look it up. There are umpteen
books named Stars and Planets.
Professor Fred Watson: Yeah.
Andrew Dunkley: So I haven't been able to, you know,
distinguish one from the other as yet. So,
um. Uh, yeah, you'll have to do some
fishing to find the book that, uh, Paul was
talking about.
But he wanted to know about
the man who decided or
discovered that the sun was not the centre of
everything. Uh, which was a common
belief back in the day.
Professor Fred Watson: It was, um, it was actually 1919 when that
discovery was made.
Andrew Dunkley: Was it that recent?
Professor Fred Watson: Yeah. Wow. Uh, it's one of my favourite
astronomical discoveries, which is why I
didn't need to go to Google to look it up.
Um, so it goes back to the time
of William Herschel, uh, who was
a German turned British
astronomer, worked late in
the 18th century and early in the 19th
century, discovered the planet Uranus in
1780. But what he was doing when
he discovered Uranus was actually mapping the
Milky Way. He was observing, um,
the Milky Way in a very systematic way with a
relatively small telescope. So sort of
counting stars in the
field of view of his telescope and then
moving the telescope a bit further along the
Milky Way, counting stars again, how many he
could see in the field of view and doing that
and doing it. He couldn't do it all the way
around the Milky Way. Cause there's parts of
it that he could never see because they're in
the southern hemisphere. But he'd got round
most of it. And what he discovered was that
the star counts are pretty even all the way
around. And so that led
him to build the hypothesis that
the stars are in a sort of flattened disc,
which is correct. Uh, but that we're very
near the middle, which is not correct.
And the reason why he got that
erroneous answer was that, uh, when you look
through, I think it was a 7 inch telescope,
if I remember right, a telescope of that
size at, uh, the Milky Way, the stars that
you see are all relatively
nearby. They're perhaps 1000
light years away or something like that,
maybe a bit more, maybe a couple of thousand
light years away in the plane of the Milky
Way. And, uh, that's partly because the Milky
Way is very dusty. Uh, there's a lot of dust
everywhere. It's probably better described as
smoke, but we call it dust in the world of
astronomy. And so that dust limits how far
you can see. And so when you look at the
Milky Way, it does look generally relatively
even. There's one bit in the constellation of
Sagittarius where it's brighter and that's
because you are looking towards, as we now
know, the galactic centre. But, um, Herschel,
um, he couldn't see that very well from the
Northern hemisphere anyway. But he did sort
of discount that. Uh, he said, by and large,
it's the same count all the way around, so we
must be in the middle, uh, roll
on the years. And in 1919, Harlow
Shapley, a very gifted American astronomer,
although he did get one thing, one big thing
wrong, uh, but what he did was
he was interested in objects that we call
globular clusters. And so these are, uh, in
fact they were named by William Herschel. He
gave them that name. Uh, clusters of stars
that appear like a globe. Uh, and
Harlow Shapley was, uh,
he was interested in globular clusters. He
noticed there were a lot of them in our, uh,
skies. Uh, they tended
to be different sizes. Uh,
and he didn't know whether that was because
they were all the same size and some were
nearer than others or whether they were
intrinsically different sizes. But what he
did notice was that there's a concentration
of them in the southern
hemisphere sky. Uh, he was
observing from California, so he could see,
see a fair swath of the southern hemisphere
sky. But he noticed that they were
concentrated in that direction and that made
him wonder if that
was where the centre of the galaxy lay,
rather than us being near the centre. Uh,
but then his other step was that he
recognised that within these globular
clusters was something called, they
called them cluster variables, stars that
varied in a certain way with a
periodicity of about a day. Uh, today
we call them RR liry variables. And I
actually started my astronomical research
back in the 70s studying these things,
uh, RR variables. Uh, and
they are good because they've
got basically a known distance.
Uh, if you can see an RR
variable and identify it as one, you know how
intrinsically bright it is, uh, and then from
that you can work out how far away it is.
And so he found these variable stars in the
globular clusters and recognised that he
could draw a chart with the globular
clusters all at their correct distance on it,
make a kind of three dimensional map of the
sky and sure enough, um, they
concentrated around the galactic
centre around a point. Uh, he actually got
the answer wrong because his magnitude, his
brightness that he had for the, uh, cluster
variables was incorrect. And I can't remember
what answer he got, but in my modern PARLANCE
it's about 25,000 light years.
The globular clusters themselves cluster
around a point about 25,000 light years
away, which is deeply hidden by the dust
clouds in Sagittarius. So he
figured out that that's where the centre of
the galaxy was. A brilliant piece of
detective work. We know he was right. Uh,
what he was wrong about was, uh, he had a big
discussion, I think in 1923,
just before Hubble recogn that
galaxies were big things a long way away. Uh,
Shapley was arguing that galaxies lie within
our own Milky Way, that they're small objects
in our own Milky Way. And he was, um,
arguing. It was a public debate actually,
between Shapley and a guy called Heber
Curtis. Uh, Curtis had the answer right. He
said they're big and a long way off. Uh,
Shapley said, no, they're small and nearby.
And it was very soon after that that Hubble
produced that they're big and a long way. Uh,
uh, proved that they're big and a long way
off. So Shapley was wrong in that, but he was
right about galactic centre.
Andrew Dunkley: Fantastic. Gee whiz. Um, great
question, Paul. And, um, yeah, uh,
if people are looking for that, uh, book
Stars and Planets, uh, it is out there. Uh,
look, I've found a couple that were actually
published around that time that Paul
mentioned, but not, um, sure if they're the
ones. I can't remember the author now, um,
that he said, but I don't think
Professor Fred Watson: anyway, mentioned an author.
Andrew Dunkley: I thought he did, but, uh, he might have
mentioned it.
Joe: Uncle.
Professor Fred Watson: It was his uncle he mentioned.
Andrew Dunkley: Uncle.
Professor Fred Watson: Uncle Jim.
Andrew Dunkley: Right. But, um,
um, so, yeah, thanks, Paul. Thanks for the
question. And, um, yeah, it's a fascinating,
um, history in astronomy as we discover these
things. I think one of my favourite
moments, I suppose, in astronomical history
was when they discovered that our sun was a
star.
Professor Fred Watson: M. That was a long time ago. Yeah,
yeah.
Andrew Dunkley: But for a while there we didn't think of It.
Professor Fred Watson: I thought it was something else. That's
right. Something a bit special. Yeah.
Andrew Dunkley: Um, and I saw that on a BBC documentary
many years ago and I sat there and went,
wow. I never thought about that because I've
always known it to be a star, but for
generations they didn't.
Quite intriguing. And why would you. It
doesn't look like a star.
Professor Fred Watson: That's right. Uh, uh, it's
clearly quite different from a star. Uh,
Andrew Dunkley: incredible.
Thanks, Paul. Thanks for sending that in. And
if you have a question for. Thanks to all our
sender innerers, I've always wanted to say
that, uh, for their questions. And if you
would like to send a question, go to our
website, spacenutspodcast.com or
spacenuts IO and there's a little
AMA M tab at the top, which stands for Ask
me anything. Not me personally, it's the
rookie royal me. And, um,
just put your, uh, question in there. It can
be text or audio. Don't forget to tell us who
you are and where you're from and have a look
around. While you're there, don't forget to
leave a review at your favourite podcasting
platform. We're all done. Thanks,
Fred Watson.
Professor Fred Watson: A great pleasure, Andrew. Um, we, uh,
continue to get great questions from great
listeners and long may it continue. Thank
you.
Andrew Dunkley: Yes, indeed, we continue to solve and evolve.
Um, maybe not.
Professor Fred Watson: I'm not evolving.
Andrew Dunkley: Once you reach a certain age, evolving
just is not part of the programme. That's
right.
Professor Fred Watson: Yeah.
Andrew Dunkley: Ask my mum on the Internet. Uh, thanks,
Fred Watson. We'll see you soon.
Professor Fred Watson: Sounds great. Thanks, Andrea.
Andrew Dunkley: Professor Fred Watson Watson, astronomer at
large. And thanks to Huw in the studio. He's
just turned up. Um, we started 39
minutes ago and, um, Huw set his
clock to a Martian day, so that's why he's
39 minutes late.
Professor Fred Watson: Boom, boom.
Andrew Dunkley: And from me, Andrew Dunkley, thanks for your
company. We'll see you on the next episode of
Space Nuts.
Professor Fred Watson: Bye. Bye.
Joe: You've been listening to the Space Nuts
Andrew Dunkley: podcast, available at
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