Andrew Dunkley: Hello there. Thanks for joining us. This is
Space Nuts, where we talk astronomy and
space science. My name is Andrew Dunkley.
Great to have your company on this, the
600 millionth episode. Maybe not that many,
but we've done quite a few. What is it,
643 we're up to? Blimey.
All right, uh, what are we talking about?
We're talking about, um, an old clapped out,
uh, telescope. Fred Watson happens to be its
patron. He's old and clapped out too. Uh,
we're also going to look, uh, at
a new black hole discovery which was made
after, um, two black holes
collided and they recorded the loudest crash
of gravitational waves ever. So
what's it going to tell us? Also, uh, China
is going to upgrade its space station and
launch a new space telescope. And a
star that got close to our sun
may have caused a bit of a disturbance in the
force. We'll tell you all about it on this
episode of space nuts.
Professor Fred Watson: 15 seconds. Guidance is internal.
10, 9. Ignition
sequence.
Andrew Dunkley: Star.
Professor Fred Watson: Uh, space nuts. 5, 4, 3, 2. 1.
2, 3, 4, 5, 5, 4, 3, 2,
1.
Andrew Dunkley: Space nuts. Astronauts report it feels
good. And he's back again. As always,
it's Professor Fred Watson Watson, astronomer
at large. Hello, Fred Watson.
Professor Fred Watson: Hello, Andrew. Hello. Uh, thank you for that
nice introduction. It's, uh,
nice to hear welcome like that.
Andrew Dunkley: You know, I know I only said it a few seconds
ago, but I forgot what I said. And then it
dawned on me that I'd actually insulted.
Professor Fred Watson: Yes. Oh, forget about that. Yeah, no, that's
all right, that's all right. You're right.
Andrew Dunkley: Last week.
Professor Fred Watson: I am old and clapped out. There's no question
about that.
Andrew Dunkley: Aren't we all, Aren't we all?
Um, now, um, before we get into, uh,
today's storeys, um, the old clapped out
telescope I referred to is actually a, uh,
wonderful device, uh, that I've actually seen
in person when we were down in Melbourne a
few years ago. Uh, it's the
Melbourne telescope. Dates back to
1869. And you're its patron because you
were there when they put the first screw in
it. Got you again.
Professor Fred Watson: Yeah. So the link and the reason why I'm.
Well, there's a number of reasons why this
telescope is very close to my heart. One is
that, uh, I was
still at school when I found a picture of it
in Henry King's History of the Telescope, a
very famous book, uh, on the history of
telescopes, published, I think in 1955.
Had a copy of that in the school library. And
there's this telescope there, the Great
Melbourne Telescope. And I thought that is.
That is a telescope. That's what I want one
like looks.
Andrew Dunkley: It just looks like you'd expect one to
look, doesn't it?
Professor Fred Watson: You can tell it's a telescope. It's got um.
With decorative bits like the latticework
tube, which is uh, very unusual, almost
unique. Anyway, that was my first
um, encounter with it. Uh, and as
sort of followed up as much as I could. A
didn't realise that by then it was actually
uh, in Canberra at Matt Stromlo. It had been
refurbished, um, having left Melbourne in
1944. But, uh,
100 years
exactly after work started on
the manufacture of that telescope in
1867, 100 years later I
joined the company that built it.
So it was uh, its 20th
century equivalent. It was uh, Howard
Grubb, Dublin when, uh, the telescope was
built. By the time I got there it was sir,
uh, Howard Grubb Parsons Co. Ltd. But
it was basically the same company amalgamated
in 1926 with the Parsons company. So,
um, I continued my kinship with that
telescope and uh, uh, of course when I came
to Australia, was interested to see it at
stromlo. Then in 2003,
uh, the Stromlo Observatory had that terrible
fire, bush fire that went through, destroyed
all the heritage buildings, including the one
that uh, that telescope sat in,
uh, and basically melted a lot of
the. Well, melted the dome onto the
telescope. The dome was aluminium, uh, and
the telescope was wrecked, its mirror was
smashed and all the rest of it. Uh, so I,
When I. So I wrote a book on the history of
telescopes which was published I think
just after that fire because,
um, I wrote at the end I had a whole chapter
on this telescope and I wrote something to
the effect that uh. The best we could hope to
see would for it to be a static
exhibit in a museum, just the remnants.
Uh, but it was for a while. Well it wasn't.
No, it stayed put in Stromlo. And it was five
years after the fire, 2008, when this
consortium of museums, uh, Victoria,
the Astronomical Society of Victoria, uh,
Royal Botanic Gardens, Melbourne, because
that's where it started its career. Uh,
uh, and uh. I think the Bureau of Meteorology
were involved as well. Uh, and they
got together a plan to basically
restore it. Uh, and
so I uh, did play a role in that. In
2015 we actually held
a workshop which I chaired, which was about
how you could update the optics of the
telescope because the mechanical stuff could
be refurbished. Uh, but the
optics were a different matter. Uh, and a uh,
sort of optical prescription was drawn up.
Now Those optics are still in the process of
being manufactured. Uh, but
the telescope itself is now
essentially mechanically complete. It is
as complete as it was when it was built.
And the work that's been done, more than 100
volunteers and staff from Museums
Victoria and the Astronomical Society of
Victoria, well over a hundred have worked on
it. And so last, uh, week there was a little
party to celebrate that. And,
uh, some of the museum's dignitary said a few
words, I said a few words. The chap who's
been leading the project, Simon Brink over
the last few years, he said a few words. He's
actually coming to lunch with us on Saturday.
Oh, lovely. Even though he's in Melbourne,
he's coming up, um, which is nice.
Um, so we had a celebration and, uh,
to be honest, what they've done is nothing
short of miraculous because there weren't any
diagrams of all the bits and pieces of this
telescope. There were engineering diagrams of
the thing complete. They were published in a
journal. But the individual parts and
probably thousands of
components, screws, washers,
uh, pulleys, cog wheels of various
different sized, all of that. No
idea what they looked like. And by
scouring photographs of the telescope, uh,
from many sources and
working out things like the numbers of teeth
you need on a cogwheel to make the things
work properly, uh, they've done a great job
with all that. And now it's in basically in
perfect working order, except it doesn't have
its main mirror yet that's being fabricated.
Um, it's at the moment still at
Scienceworks, which is the Science M Museum
in Victoria. And it's a big exhibit which is
Andrew Dunkley: worth a visit, especially with the kids.
Professor Fred Watson: Yeah, it's a great place to go. Uh, and
anybody, uh, who does go to Melbourne and
sees scienceworks definitely have a look at
the great Melbourne telescope. The hope is
that one day it will be in its original
building, which still exists in the Royal
Botanic Gardens. Uh, but, um, there's quite a
bit of work needs to be done to make
that, uh, oh, s. Uh,
satisfactory for 2026
or whenever it happens, compared with
the, um, you know, the health and safety
regulations in 1869 when people came and
went, um, just had a look through the
telescope. That's the idea that it will
eventually be a working telescope for the
public for people to come and look through.
Andrew Dunkley: Wonderful. And, uh, if you can't get down to
see it in Melbourne, uh, just do a search for
the Melbourne telescope online and have a
look at it and you'll know what we're talking
about, um, the lattice work is just
beautiful. It is a glorious piece of
equipment. And I stumbled across it. I
didn't even know it was at Science Works when
we went there. And we just went for a wander
and found it. And I went, oh, Fred Watson
will love this. And then it turns out you
were the patron, so.
Professor Fred Watson: Yes, that's right. Yeah. Yeah. It's um,
it is, uh, it's quite staggering.
It's how big it is, isn't it? When you.
Andrew Dunkley: Oh yeah.
Professor Fred Watson: Just when you.
Andrew Dunkley: It blows your mind.
Professor Fred Watson: Yes.
Andrew Dunkley: You just stand there in awe.
Professor Fred Watson: Telescope. It was the biggest fully
steerable telescope in the world at the time
when, um, it was built. It wasn't the
biggest, but it was. Biggest telescope in the
world. But it wasn't far off.
Andrew Dunkley: Yeah. As a good friend of mine often says,
it's a great piece of kit.
Professor Fred Watson: It was a great piece of kit. And hopefully it
will be again one day.
Andrew Dunkley: Fingers crossed.
All right, uh, moving on. We're talking black
holes. Very unusual. We don't usually talk
things like this, but, uh, this, this is an
interesting one because they, They've uh,
made it a bit of a discovery. They've.
They've recorded the loudest crash of
gravitational waves ever heard. And it was
because of two black holes that
decided, uh, to play billiards with each
other and boom. Uh, but
it's what they've discovered from the. In the
aftermath of all this that's getting
interesting.
Professor Fred Watson: Uh, yes, it is. Um, so,
yep, we black, um, gravitational waves
from colliding objects have been detectable
by humans since 2015,
um, with uh, the LIGO
Laser Interferometer Gravitational Wave
Observatory in America. And that now works
with, uh, virgo, which is an
Italian, uh, uh, gravitational wave
observatory, and kagra, which is the
Kamioka Gravitational Wave Detector in
Japan. So those three telescopes work
together to pick up the vibrations of space,
uh, which are, uh, transmitted from very
distant collisions usually. And it's usually
neutron stars and black holes, uh, with
collisions between either neutron stars and
neutron stars or black holes and black holes,
or neutron stars and black holes. Um,
those all produce gravitational wave signals
that are actually in the frequency range
detectable by uh, these telescopes.
Because that's a key part of it. The amount
of energy that's involved tells, uh, you what
the frequency of the gravitational waves is
going to be. And as we've noted
before, Andrew, it's curious that, um,
the gravitational waves that these telescopes
are sensitive to are actually in the audio
frequency regime. They're basically. If you
just amplified them, uh, you would have an
audio signal. And that's basically what they
do, except they're doing it in a very much
more sophisticated way. Um,
um. The amount of, um,
shaking of space that they can
detect is
absolutely infinitesimal. Uh, but
these things are sensitive enough that they
can measure a distance that is a
thousandth, I think it's a 10,000th actually,
of the diameter of a proton. Uh, that's
the accuracy with which they can measure the
distance between two mirrors, which is how
you do all this sort of thing. So that's the
backstory. Uh, the up storey,
the forward storey. Is that
an object or you don't have an object,
you have a gravitational wave signal. Uh, it
rejoices in the name of
GW25014.
Uh, that tells you that it was picked up, um,
in January, uh, 2025. Uh,
that's where the 25011 comes
from. Um. Uh, and it,
uh, basically, uh, on
analysis, um, has
been, uh, detected to be
a collision between two black holes, each
of which had, uh, around 32 times the
mass of the sun until they collided. And
that set, uh, you know, set the
gravitational waves on their way because it
basically disturbed space, it rippled space.
So what's happened is. And this, as you
mentioned at the beginning, is the loudest
gravitational wave signal that's been
detected, or certainly the most, uh,
intense. The, um, highest amplitude one.
Andrew Dunkley: Yeah.
Professor Fred Watson: Um, so what has happened
is, uh, that researchers, uh, have
analysed the audio signal,
um, and they found in it, um,
basically that it's been described as a
feature, uh, which is uh, something
called a direct wave. It's
a component of the signal, uh,
and it's a direct wave, uh, that
has not. That's been seen before,
but hasn't. Nobody's worked out what it
is, but apparently it
is a feature that
essentially, uh. In
the gravitational wave structure that comes
from this event, you can tell this
direct wave is to do with
the event horizon of the combined
black holes. So you've got two black
holes, each of which has got its own event
horizon. They're spinning around one another,
getting ever closer, as we've seen that sort
of thing before. And the frequency goes up of
the gravitational waves, um, and then
suddenly it all stops because they've
collided and there's no more accelerations,
which is what you need, uh, to set up
gravitational waves. Um, but,
uh, at that point the two, um,
gravitate, sorry, the two event horizons
merge.
Uh, now, a recap on event horizons. That's
the point of no return. Basically,
it's the distance from the black hole,
uh, where the escape velocity
uh, is more than the speed of
light. And so nothing can escape from
within the event horizon. Uh, and in
particular light can't escape. So the event
horizon is black. It's a sphere around the
black hole, uh, through which you can't see
because nothing escapes, including light.
So um, that is what the event horizon
is. In a sense it's imaginary. Uh, uh,
Andrew, you know it's not a real surface,
it's an imaginary surface because it's just
the boundary between what's visible and
what's not visible.
Now we know when black holes
collide. Uh, I don't know that
much about the details of these things but
there is a period immediately after
they've merged which is called the ring down.
And it's a time when they sort of
consolidate as one black hole. And that
means their event horizons also consolidate.
And I think this direct wave that has been
detected is basically
uh, an artefact of that ring
down. Uh, and so um,
what I guess is uh, perhaps the
takeaway message from this work is not
that we've learned something miraculous
and new about the event horizon
but that we've learned that there might be a
way of, in future
gravitational wave events uh, might be
a way of analysing these direct waves to give
us more information on the black hole
event horizon. Because at the moment we don't
know much about it. We've seen them
in the telescopes, you know the
um, observations from the Event Horizon
Telescope that um, amalgam of many radio
telescopes, an Earth sized array,
uh, which has been used to look at the black
holes in centre of our own galaxy. And in
M57 I think it was uh, with um,
uh fairly high degree of
precision. What we've seen is the black
shadow of the event horizon. Um
but perhaps with these gravitational waves,
these direct waves there might be a ah,
way of teasing out even more detail from
these distant and highly enigmatic
objects.
Andrew Dunkley: Yes, indeed. And uh, another interesting
thing that comes out of this storey is that
um, they're suggesting uh, the
measurements that uh, that they've
made could be a step towards
future um, tests of general relativity
using direct waves. So you know there's all
sorts of potential by the sound of it.
Professor Fred Watson: That's right, yeah. I mean exactly. And uh,
of course this is one of the holy grails of
science generally actually certainly physics
to find chinks in general relativity
because uh, at the moment it behaves
exactly as predicted. Everything that we've
seen in the universe Follows, uh,
the rules and regulations of general
relativity, uh, in a perfect way.
So maybe, uh, direct waves will, as you
said, uh, give us a way of testing general
relativity. If we find, um, things
that don't work in general relativity, then
that could be an opening into new physics,
which is certainly a hot topic at the moment.
Andrew Dunkley: Indeed it is. Uh, well, uh, everyone,
including Einstein, thinks something's wrong
with it. They just. Yes, they just can't find
anything at the moment. It keeps coming up
aces every time they test it.
Professor Fred Watson: Yeah, they think something's wrong with it
because it doesn't sit with quantum
mechanics. The two are incompatible and they
both work perfectly well, but they're
incompatible.
Andrew Dunkley: Weird, isn't it?
Professor Fred Watson: Yes, that's very weird. Yeah.
Andrew Dunkley: The other thing that I find fascinating about
this Storey, is that from something as simple
as a, as a gravitational wave,
they're able to break it down and find
information that is
really just. You can't
see any of this. It's all just data, isn't
it?
Professor Fred Watson: Yeah, yeah, that's correct. That's right.
But, uh, the physics is well understood
because general relativity is such a reliable
tool for people to use to analyse these
things. Um, that's how we can make these
statements about it. And yes, um, if we can
find flaws with general relativity, it will
be very exciting indeed it will.
Andrew Dunkley: And you can read all about it@the space.com
website. Uh, they publish their research,
uh, in the journal Nature. This
is Space Nuts with Andrew Dunkley and
Professor Fred Watson Watson.
Professor Fred Watson: I believe that this nation should commit
Andrew Dunkley: itself to achieving the goal,
before this decade is out, of landing a
man
Professor Fred Watson: on the moon and returning him safely to the
Earth.
Andrew Dunkley: These nuts.
Now, Fred Watson, we turn our, uh, attention
towards China. Uh, of course, they've got a
very active space station in operation
at the moment. Uh, the latest news though is
that they intend to, uh, make it
bigger and at the same time they're going to
put a new space telescope into, uh, into
orbit as well. So, uh, they're really going
ahead in leaps and bounds, aren't they?
Professor Fred Watson: They are, yes. Uh, it's, um. You know, this
is part of the Chinese. It's not the China
national, uh, Space Agency.
Uh, I think it's that they've got a separate
space agency for human space flight.
Uh, and that's the organisation that
operates the Tiangong, uh, space Station,
which has been up there since 2021, I think
was when, uh, we started seeing it being
assembled. It was assembled in a very similar
manner to the International Space Station by
building sort of modules that you can stick
together like Lego, uh, up once
uh, these modules are in orbit.
Andrew Dunkley: Yeah. And at the moment it's the China
National Space Administration which handles
the programmes, and the China Manned Space
Agency which um, oversees human
spaceflight.
Professor Fred Watson: That's right. I knew there were two
organisations involved. Thank you for that.
Andrew Dunkley: That's all right.
Professor Fred Watson: Um, so, uh,
yes, so uh, at the moment the,
the Tiangong consists of three
modules and they're arranged in a sort of T
shape, uh, with um.
Uh, two, three. The, the three
end points of the modules if you like,
coming, coming together in a, in a sort of
vestibule where you can uh, tunnel your way
from one to the, to the other with these
uh, basically entry and exit hatches. That
uh, is the way things work on the
International Space Station as well. But as
you've said, uh, what they're now planning to
do is to add three more
modules. Um and the reason they
want to do that is because uh,
they want to do more research up there,
uh, and make more frequent crew and
cargo changes. Um, so they're
actually, I think the way to deal
with that is to make the space station
bigger. Um, and so it's going to be
what they're calling a double T shape, which
I think is probably an H shape
if I can put it that way. Um, well that's
what it.
Andrew Dunkley: Yeah, it would turn into that, wouldn't it?
Professor Fred Watson: You'd expect so. Yes, that's right. Unless
they do something clever, uh, like turn
one of the T's round, uh right angles to the
other one. Anyway, we don't know what's going
to happen there. But um, there is a new
multipurpose um, module and two
new experimental modules that are planned
uh, to um, essentially uh,
you know, allow Chinese
uh, space exploration in low Earth
orbit to continue and be extended.
Um, um, we understand from
um, some of the researchers in China
that uh, it's always been
uh, an expectation that this
would take place, that there'd be this
extension. Uh, and what it will do in
terms of the mass of the um, space
station is take it up from its current 90
tonnes, uh up to
180 tonnes or thereabouts. And there's a
yardstick, if I remember rightly, and you
might be able to correct me here Andrew, but
I think the International Space station is
about 400 tonnes in terms of its mass.
I think that is the case. So uh,
that's uh, the plan and
alongside that, as you've already mentioned
Andrew, is the idea of a new
um, space observatory, an optical
Telescope quite similar in some
ways to the Hubble Space Telescope. A
slightly smaller mirror, 2 metres rather than
2.3 metres,
um, and also with a much wider
field of view. The Hubble has quite a narrow
field of view. Uh, and in fact the Nancy
Grace Roman telescope, which is also very
similar to the Hubble, will have a much wider
field of view than Hubble. That's being
launched later this year, I hope.
Um, this, uh, Chinese
telescope, uh, which has a name, Shuntian,
I think, is probably how it's
pronounced in my,
um, poor Chinese, uh, poor
Mandarin and poor Chinese.
Um, it's got a much bigger field of view and
will actually give new, uh,
surveys to Chinese, uh,
astronomers. We'll see a lot more
information about the universe coming from
this telescope. The more telescopes you've
got on the universe, the better. And, uh,
Shuntian will be one of those, uh,
features when it is launched and actually
commissioned, uh, that will, we hope, um,
really bring new insights into our knowledge
of space.
Andrew Dunkley: Yeah. Apparently its field of view
is going to be massive compared to
Hubble at 300 times.
Professor Fred Watson: Correct? Yes, that's right. So it's a wide
angle telescope rather than the sort of
pinpoint view of the Hubble.
Andrew Dunkley: Yeah, quite incredible. Uh, you were right
about the International space station. Uh,
419,700 kilogrammes
is its mass, or say 420,
um, tonnes. Yes, indeed. Um, the
other interesting thing that China's working
on, uh, is a new,
um, um, delivery system for their. They
call them taika nauts, don't they?
Professor Fred Watson: Yes, they do, yeah.
Andrew Dunkley: Uh, they want to. They want to develop a
rocket system that will send seven up at a
time.
Professor Fred Watson: Yes, yeah, seven up.
Andrew Dunkley: No, I'm joking. But, um, again, yeah, that's
what they're looking at doing at the moment.
They can only send up three at a time.
Professor Fred Watson: Yes. So the Chinese, um,
uh, orbital
vehicle for getting astronauts up,
Taikonauts up there. And
I'm ashamed that I can't remember what it's
called. Uh, is it Shenzhou?
Shenzhou, I can't remember. Um,
but that is basically an adaptation
of the old Soyuts Russian
spacecraft which is still in service in the
International Space Station. Developed in the
1960s. A, uh, three person,
uh, module. Uh, I think I'm right in
saying that the crew Dragon can take up to
seven astronauts as well.
Andrew Dunkley: Interesting. Shenzhou.
Professor Fred Watson: Shenzhou, yeah.
Andrew Dunkley: Is the, um, is the system they
Professor Fred Watson: used at the moment.
You did m. So, uh,
yes. So that will go from three to seven.
It's understandable, you know, if you Want to
keep the crews coming and going. I think this
is a really important development because,
um, if nothing else, it's going to, I
think, spur, uh,
the private sector, um, to pick up the
baton of what you might call Western
International Space Stations or the Western
International Space Station, because that's
scheduled at the moment to be decommissioned
in 2030. That might change. But
it's a possibility that we will lose the ISS
in 2030. And we've seen problems
with the leakage that we had in one of the
modules a couple of weeks ago where the
crew was evacuated, not evacuated, but
moved. The American crew,
uh, the NASA end of the spacecraft
were moved into a crew Dragon capsule
to uh, just be certain that
nothing untoward was going to happen, uh,
if there was a catastrophic
leak, uh, when the Roscosmos,
cosmonauts, they were actually trying to fix
the leak, uh, they moved the other crew,
um, into the crew Dragon capsule for safety.
Andrew Dunkley: Yeah, uh, in terms of replacing the iss,
there are no firm plans at the moment, but
they're kind of thinking about,
um, I think you mentioned it, the commercial
sector getting involved.
And that's probably logical.
I'm pretty sure that, uh, Elon would be
pretty keen to put a space station into orbit
and a few others probably.
There's plenty of people around with uh,
megabucks to do it.
Professor Fred Watson: Yes, that's right. Um, um, but, uh, you
know, you might think, have to think
carefully about whether you, uh, take
over the old, uh, the old tired
and quite dodgy old, uh,
International Space Station or whether you
build something new. Um, and uh, of course
the technology's moved on enormously since
the 1990s when that was put together.
It's been continuously occupied since
2000. Uh, that's 26
years of, um, tenants coming and going. It's
probably taken a fair beating inside.
Andrew Dunkley: Yeah, I'm sure they've had a few parties.
Yeah, no doubt about it.
Uh, if you want to uh, read all about, uh,
China's plans, you can do
that@space.com. uh, this is
Space Nuts with Andrew Dunkley and Professor
Fred Watson Watson.
Space Nuts, our final
storey. Fred Watson takes us close to home.
And this is really quite a fascinating storey
because it talks about a star, not
our sun. Ah, another star that got
up close and personal, um, with
our particular, uh, sun, um, a
little while ago. But the
effects of that interaction,
uh, seem to still exist,
which is very odd.
Professor Fred Watson: Yeah, well, that's right. Uh, yes, it is,
it's an interesting storey. It covers two
quite different bits of astronomy here that
come together to sort of work out what was
going on. So this star in question,
it's got the glorious name of
HD7977. HD
stands for Henry Draper. It's one of the
early star catalogues, uh, from the 19th
century I think, uh, the Henry Draper
catalogue. Uh, and it's a relatively
near star, similar to the
sun. Uh, it's currently in the constellation
of Cassiopeia, which is um, one of my
favourite northern constellations. Actually.
It's one that we don't see from down here in
Australia. Uh, so,
um, how do we know that
HD7977 had um,
a near miss with our solar system?
And the answer is with the Gaia mission.
So Gaia is a spacecraft. Uh,
it sits at the um, uh,
sun, Earth, uh, L2 point, that's
the Lagrange point, on the opposite side of
the Earth from the sun. Um, it's been
working for, I think, certainly more than a
decade. And what it's done is measured
star positions with absolutely
exquisite precision. Uh, you're talking
about, I think it's sort of some
accuracies in the region of 100 millionths of
an arc second. These are phenomenal
accuracies. And an arc second of course is
1-3600th of a degree, uh,
the size of a, here In Australia, a $1 coin
held up at five kilometres. It's a tiny
angle, but this thing's measuring
millionths of that basically, or 100
millions. Uh, and what that does is it
allows you, if you make these measurements at
different times, it allows you to plot the
motions of stars,
uh, not just in our own galaxy and in our own
neighbourhood, but also in the Two
Magellanic Clouds, uh, the two
nearest neighbour dwarf galaxies, the big
ones, Large and Small Magellanic Clouds
165 and 200,000 light
years away respectively. Uh, those,
uh, you can detect the motions of stars in
those galaxies. And even in the Andromeda
galaxy, about 2 1/2 million light years away,
you can see evidence of what we call lateral
motion on the sky, sideways motion of things.
And if you can measure the radial velocity,
that's the velocity along the line of sight,
which is actually much easier if you can do
that as well. You've got, um, the three
dimensional motion of objects in space. And
that is how, uh,
HD7977 was picked
up as having passed close to the sun
about two and a half million years ago.
As both these stars, The sun and
HD7977, as they both orbit around the
centre of our galaxy. Uh, we still
don't know exactly how close. Uh, the data
from Gaia suggests It was between
4,000 and 25,000
astronomical units. And as we've mentioned
before, an astronomical unit is the distance
between the Earth and the sun. Um, convenient
measure it is uh, 150 million kilometres.
Um, they may have
um, we might be able to
tie that close approach down though by other
methods. And the methods in question
have been employed by uh, some
scientists at the University of
Bordeaux. Uh, and basically
what they have done is looked not
at Gaia data to try and refine
uh, this sort of look back in
time as to when these two stars were close
together. They've looked at long period
comets, comets that uh, come in
from the very furthest reaches of the solar
system where we think there is a
reservoir of comets. We call it the Oort
Cloud. Uh, and it turns out that
if you look at long period comets,
uh, which have been measured over the
past hundred years I guess, um, then
you get uh, an idea
of the distribution of their orbits.
And basically there's a quote here
from one of the authors uh, of
the paper that we're talking about uh, who
says the distribution of comet orbits
suggests we living through an unusual time
where HD 7977 has
dominated the generation of new comets
and not the larger gravitational field of the
Milky Way as it usually would. This would
also mean we're living through the late
stages of a pretty rare and powerful
comet shower. And so what they've done
is made computer simulations of uh,
how comet orbits might behave
as a result of being tipped out of the Oort
cloud by the passage of this star HD
7977. They've kicked out the Oort cloud
and heading towards the sun. Uh, they've
measured uh, basically the details of
112 long period comets. Actually they've
chosen ones that have only been observed in
recent years, since 1989 because
that's when we could detect comets coming
from uh, any part of the sky. Uh,
if you only limit yourself to one part of the
sky then you've got uh, as visible for
example by a single observatory, uh, or even
as visible by the Northern Hemisphere
observatory. You're missing uh,
half the objects that you want to see. And
since what you're doing is looking at the
statistical distribution of these things, you
can't afford to um, eliminate
things that way. It's what would be called a
selection effect. Um, so yes these
long period comets they've got very elongated
Orbits, uh, and the suggestion is that the
distribution of those orbits in relation to
the direction that we know
HD7977 went through the solar system or
went close to the solar system. Uh, that's
why they believe, uh, that the two
events, uh, um, the close
passage of 7977, uh,
tipped up the comets and caused a lot more of
these comets to come in. And if you
accept uh, their hypothesis,
um, then what it does is,
ties down rather
better the distance that we estimate
HD7977, uh,
approach the sun at somewhere
between 6,000 and 10,000 astronomical units.
A tighter window compared with the 4,000 to
25,000 astronomical units that Gaia
suggests. Yes, uh, so, uh, it's a nice
tightening up of our uh, understanding of
this hypothesised but probably
real event 2 1/2 million years ago.
Andrew Dunkley: And just to give people a bit of an idea of
the distance, so somewhere between 6 and
10,000 AU is where
HD7977 and kind
of grazed our uh, solar system.
Professor Fred Watson: Yes.
Andrew Dunkley: Voyager 1 is 170
AU from Earth. So
we're talking a fair way out.
Professor Fred Watson: It's a long way off. That's right.
Andrew Dunkley: You're talking probably getting into the
vicinity of the Oort cloud, which makes sense
given what they're hypothesising in
this paper.
Professor Fred Watson: Exactly right. So a star passing nearby the
Oort cloud would definitely upset it and
send stuff in towards the, the inner solar
system. Yes, it's actually um, it's a theory
that, uh, that general mechanism
was proposed by colleagues of mine in the
Royal Observatory in Edinburgh, Victor Klub
and Bill Napier, back in the late 1970s.
The idea that they were suggesting it might
have needed a bit more mass than a single
star to disturb the Oort cloud. And uh, they
suggested the passage nearby, passage of
something called a giant molecular cloud, uh,
a kind of stellar birthplace. If one of those
goes past the solar system, they were
inferring it would disturb the Oort cloud to
the extent that you would get bombardment of
the inner solar system by comets and that
might be visible in the geological record on
Earth. That was basically um, uh,
their principal line of attack. Uh, really
very interesting science. Uh, so this is not
a new idea, but this is new research
that suggests that um, perhaps we can learn
more by pursuing it.
Andrew Dunkley: Indeed, yes. Um, the paper by the way,
has been accepted by the Planetary Science
Journal and is available at the moment,
moment on the Arxiv Preprint server.
You can also read about it at phys.org, p h
y s.org Fred Watson,
that brings us to the end of the show.
Thank you so much.
Professor Fred Watson: Well, that went very quickly. Uh, what a good
time we had.
Andrew Dunkley: We did indeed. Yes. We'll catch you on the
next one.
Professor Fred Watson: Sounds great.
Andrew Dunkley: Thank you very much, Professor Fred Watson
Watson, astronomer at large. And don't forget
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thanks to Huw in the studio who, uh, couldn't
be with us today because he saw a passing
star and chased her down for an autograph.
And from and from me, Andrew Dunkley. Thanks
for your company. We'll see you on the next
episode of Space Nuts. Bye. Bye.
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