Heidi Campo: Welcome back to another fun, exciting
Q and A episode of space
nuts.
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Heidi Campo: I am your substitute host for this episode,
Heidi Campo. And joining us is professor
Fred Watson, astronomer at large.
How are you doing today, Fred?
Professor Fred Watson: Um, I'm very well, thanks, Heidi, and great to see you, as
always. And I hope you're well and I hope you're surviving the
thunderstorm that apparently is going on around you at the moment.
Heidi Campo: It is. You know, like I just said,
would I would rather have a thunderstorm than a
hurricane? Because I am here in Space Center Houston, not m.
Space Center, Space City. I'm not in the
Space Center. I'm in Space City. Um, we did have a
hurricane last year that was not fun. Um,
I was alone. My husband was traveling at the time for work, and
I had a broken foot. My neighbor's tree.
The trunk didn't fall, but almost all of the big
branches did. So I was out there with a
broken foot brace on my leg crutches and
a chainsaw trying to chop up these
branches and deal with it. Dealing with my
first hurricane. And then we didn't have power
for nine days. It was awful. In the middle
of July. Oh, whoa, whoa.
Professor Fred Watson: That's awful.
Heidi Campo: So those are. I guess
I just. Just sheer will, I
guess. But those of you who live, um,
in climates where you don't get hurricanes,
enjoy those.
M. Speaking of,
looks like our first question today is from
Jakob or Jacob. If I'm saying that right,
I think it's Jakob from Norway.
Uh, they do not get any hurricanes there. You are safe from
hurricanes, and you get to enjoy the auroras.
Jakob's, uh, question is,
um. Hi, this is Jakob from Norway. I'm working on a
presentation about planet nine for my school,
where I will be comparing the mathematical
prediction of the nine planet
with Urbian. Lee
Verriners. You'll have to correct me on that,
Fred. Um, work to finding
Neptune. In 1864, Lee
Varenner saw that something was wrong with the
orbit of Uranus and figured out that it was getting
pulled on by another planet. He told astronomers
exactly where to look for this planet. And surely
enough, they found Neptune on the first night
of looking. What are the odds of that? Now, almost
200 years later, scientists see something wrong with some
objects in the Jupiter belt and say that,
excuse me, say that another planet may be causing these strange
orbital paths. My question is,
why can't we predict exactly where
Planet Nine is like Lee Varenner did in
1864. Have we gotten worse at
maths? Thank you for the great podcast
and.
Professor Fred Watson: Thank you for the great question Jakob because
um, you know you've hit the nail on the head there. You're
quite right about uh, the discovery of
Neptune. Um um it's
usually said that Neptune was the first planet
discovered with the point of a pen
because it was calculations by Le Verrier
and also um, actually a
British ah, astronomer,
uh, I think his name was Adams, I might be misremembering that
uh, who did the calculations at the same time
and also predicted the existence of another planet.
But he couldn't get anybody in England interested in
actually following up on it. Le Verrier
um, basically was fortunate
in having the director of the Berlin Observatory
um, uh, to help him out. And
that was when Neptune was discovered exactly where it was
predicted. Now Planet nine, uh, you're
absolutely right. There's a nice link
there between um, 1846 and the
early 2000s because it was back in
2016 that two American astronomers
figured out that there was something about
the orbits of uh, objects
as you mentioned in the Kuiper Belt, uh,
which are uh, aligned in a way that
suggested that there's another planet out there,
uh, that's pulling them all into uh,
this alignment, this orbital alignment,
um, but we haven't found it yet and
some suggest that, that it doesn't exist at all.
And the difference between the discovery
of Neptune and the search for Planet nine
is that Neptune, uh the prediction of
Neptune's existence was based on very
accurate observations of one object which was the planet
Uranus uh in the outer solar system. And
it was what we call perturbations in the orbit of
Uranus, Uh but that means
it's being pulled out of
what you'd normally expect to see. And it's that pulling
that was attributed Neptune. And you can then because
you're only looking at well three objects, the Sun,
Uranus and the other, whatever mystery
body it is which turned out to be Uranus. You can do the
calculation and predict pretty exactly where you're going
to find the as ah, yet unknown object. And that's
what happened. It's a great story uh, with lots of
twists and turns. It's a bit different with
Planet nine. What we're seeing is uh, the
suggestion uh, that some of the orbits of these
Kuiper Belt objects are aligned in a way that
uh, means that they're being pulled uh, out of
a uh, different orbit by a hidden planet.
But you're now talking about not accurate
positions of gravitational pulls. You're talking about
statistical, uh, uh, discussions
because you're talking about many objects,
uh, and you're talking about many orbits. And
one of the reasons why, uh, this is such
a difficult problem is that if there was an
object pulling these, uh, Kuiper Belt
objects into their elongated orbits, into their
aligned orbits, uh, it would be a very long way
away from the sun. It would be very faint and very
difficult to see. But the other thing is
you can't be sure that you're not
seeing a statistical fluke. And a
number of scientists have pointed this out that
maybe the Kuiper Belt objects, these icy
asteroids beyond the orbit of Neptune, uh,
those objects are uh, just a small sound
of what is a bigger sample that we have not yet
discovered. And if we could see the whole sample, there
wouldn't be an issue. There would be no preferred alignment.
Uh, so it's what we would call a selection effect. It's a
statistical fluke. So that's the bottom
line with this. It's a statistical business
rather than a, ah, direct gravitational
um, calculation which is what it was for Neptune.
So we haven't yet found planet nine. A lot of people are still looking.
I'm kind of hopeful that we will do. But the latest
results suggests that maybe it's not there at all.
Heidi Campo: Sounds like, um, machine learning may be
a very beneficial asset in
discovering these statistics and
advanced, advanced formulas to find this.
Professor Fred Watson: That's right. I'm sure people are throwing
AI at uh, this problem. Uh,
there's only so much you can do though because you're limited
with the data set that you've got to
start with, which is something like, I don't know, I think they're about
10 of these, uh, asteroids which are
particularly aligned that suggest the existence of planet
nine.
Heidi Campo: This is true. This is true.
Well, our next question is from
Enrique and this is an audio question that we will
play for you now.
Henrique: Hello, I'm, um, Henrique from
Portugal. Thank you for
answering my last question about space
time. I have another one.
How do black holes have density
if the singularity doesn't have
volume? Thank you.
Bye.
Heidi Campo: It's always so sweet to hear from Enrique.
Um, you said he was, uh, what did we say
his last email said he was six.
So. Is that right, Fred? I think when they emailed us before
he said he was 6 years old.
Professor Fred Watson: Yes, that's correct.
Heidi Campo: Something like that, yeah. No Enrique, so cute.
He's so smart too. I'm like, man, I was not thinking about
this stuff when I was his age.
Professor Fred Watson: Yeah, me neither. Sorry.
Um, uh, just to let our listeners
know that we are improvising here, we're listening
separately to, uh, it might be
Henrik rather than Enrique. Anyway, it's
um, Henrik by the sound of it, from Portugal.
And I was listening slightly after you, so
I could. So that's why you, you didn't get a
response from me to your question, which I'm sure Huw
will tidy up when he edits this whole
thing. Um, his question was, um,
how can you have.
How can an object have density when it's got zero
volume? I, uh, think I'm paraphrasing that
correctly. And, uh, Henrik has
gone straight to the nub of the matter
with a black hole because a black hole is
effectively defined as a point in space which
has infinite density. Uh,
now black holes have mass and we can measure
different masses for black holes. Some are supermassive black holes,
uh, which have masses millions or even billions of
times the mass of the sun. Uh, some are
stellar, uh, mass black holes, which are similar in
mass to the sun. Uh, but they all have mass.
If they don't have volume, though, uh, you'll
remember. Maybe you don't know this formula,
Henrique. I, uh, don't think I did when I was 6.
But density is mass divided by
volum. If volume is zero, and that's the
way we think a black hole is, then the density is
infinite. Uh, because if you divide something
by zero, the answer you get is infinity. Two very
odd mathematical quirks. So,
um, it's possible that
real black holes don't have infinite density, but
their densities are very, very high because a black
hole by definition is either
zero volume or at least a very, very small
volume. Uh, so it's a great question and
what you is, you've basically gone to the heart of what
defines a black hole. Well done.
Heidi Campo: And we absolutely need more young people interested
in this stuff. I saw. Um, I'm
actually. Oh, I'm gonna brag for a second. I am a brand new aunt for the
first time. I had my first nephew. So
shout out to baby Roman. So excited you're here.
But I was looking through baby books and I guess they have the
cutest little baby books these days. You can get quantum, um,
physics for babies, astronomy, um, for babies,
um, math for babies. They have all sorts of cute little book
and I am so excited because I'm going to buy him all the science books in
the world because their brains are little
sponges and they can learn so much so fast. And
I'm like, you know what we should do is we should have little kids
solving these problems because they would probably come up with the
answer faster than an adult
would.0G.
Professor Fred Watson: And I feel fine.
Heidi Campo: Space Nuts. Well, our uh, next question.
Professor Fred Watson: Congratulations on your um, on being an
aunt.
Heidi Campo: Thank you so much. Oh, I'm so excited. He's so cute.
Um, our next question is from Ben.
Um, Ben, looks like you're emailing us from
Northwestern University. Ben says
I don't know how common it is, but I do know
for certain. I do know for certain things like
gravitational wave detections, many
observations will drop or uh, many
observatories will drop what they're doing to
attempt to observe the source of the waves.
I have four questions about this.
One, is it common for
observatories to do this? Two,
for what sort of events do
observatories do this? Three,
are there any sort of observations
which are immune to these interruptions?
And four, my understanding is that
observing time is quite constricted, highly
scheduled and difficult to obtain. So
how do they compensate for these interruptions?
Do they just move the entire schedule schedule back? Do they
just find a different slot for the observations that were
interrupted while keeping most
observations unimpacted or something else?
Professor Fred Watson: Thanks Heidi and Ben. That's um, a question that I
don't think we've ever been asked before on Space Nuts.
And it's a really good question because it's part and
parcel of the work of
your average observatory. Uh,
and so the first of your four questions, is it common
for observatories to do this? And the answer is
yes. Uh, these are
effectively what we call target of opportunity
observations where uh, you know
the scheduled use of a telescope. And you're
absolutely right, those schedules are ah,
laid down months in advance. People
have applied for telescope time,
sweat, blood and tears to actually uh,
get their applications in and succeed in winning the
telescope time. I used to do this quite a lot back in the day.
Um, typically uh, on the Anglo Australian telescope, which
is the one I used most, uh, the biggest visible uh,
light telescope in Australia. Uh,
typically for every night uh, of available
observing time there will be three to four different
groups wanting to use it. So that's the level of
competition that there is. And of course only one
wins out. And the result of that is you might be allocated
two or three nights and four
occasionally got fauna allocations where
you're at the mercy of the weather, uh, and at the mercy
of all the instruments working but you've worked so hard to get that
time. Uh, the last thing you want is for
somebody to come along and say, oh, there's been,
uh, X, Y or Z happening in the space. We're going to grab
your telescope. But, um, it is,
uh, sort of built into most observatories
that, that is a potential way of
operating. I guess some don't. Uh,
but certainly at the Anglo Australian Telescop,
uh, these target of
opportunity observations were made. Um,
so, uh, Ben, your second question is for what sort of
events do observatories do this? Well, as you
said, uh, it's, you know, some of the gravitational wave
detections in recent months of, um,
neutron star collisions where there might be
a radio or optical counterpart, in other
words, a flash either in the radio spectrum or the
visible light spectrum. Uh, then you would
that the target of opportunity rules would kick
in because there would have to be rules about this.
Um, it works, I think, for radio telescopes as well. I
don't have any direct experience of observing on
radio, um, telescopes, but I do know about the other kind, the
optical telescopes. And yes, your time
will be taken over. So neutron star
collisions, um, supernovae is the most common
one. If you've got a bright supernova, uh,
and you have a telescope that's got the right equipment on it,
you will probably turn to that to detect,
uh, the supernova explosion and measure its
spectrum at the peak of its intensity. Uh,
that's happened a lot. Gamma ray bursts,
the visible light counterparts of things that are detected
by gamma ray satellites. That's happened
too. Uh, so these things are, um. You
know, there are several transient, what we call transient
phenomena for which this kind of, um,
uh, observation would be made. Uh, number three, are there
any sorts of observations that are immune to these interruptions?
Well, that be. Would. Would depend, I think, on the
policies of the particular observatory in question. There might
well be, um, certainly at the aat,
uh, there weren't. We did a lot of
routine survey work where we were building up large
catalogues of information on things. And that would
be very much, uh, something that could be
interrupted by, uh, a target of
opportunity observation. Uh, and four, my
understanding is that observing time is quite constrained, highly
scheduled and difficult to obtain. Indeed it is.
So how do they compensate for those interruptions? Uh,
do they just move the entire schedule back? No, they don't.
Uh, what they do is the
astronomers who've lost the time
really, uh, have to face the fact that they've lost the time.
Um, and that might be, you know, one of the
conditions under which they accept the time, the telescope
time in the first place. Um, often
though, there will be, uh,
you know, there will be moves to try and
compensate, uh, for that loss
of time. And that's the last part of your
question. Do they just find a different slot for the
observations that were interrupted while keeping most
observations unimpacted? That's basically the way it
works. Uh, and in the case of the
Anglo Australian telescope, we had,
uh, time. There was a small amount of time that was not
allocated to users. We called it director's time
because it was at the director's discretion
to allocate that time, whether it was for hardware
improvements or whatever tests, things of that sort.
Uh, but, um, that is what normally would
happen. The director would try and allocate some
of his director's time to compensate for somebody who
had lost time because of a target opportunity
observation. The great question. Thanks very much,
Ben.
Heidi Campo: Yeah, and I can attest to that. My good
friend, um, Dr. Allison McGraw, she's a planetary
scientist over at the Lunar and Planetary Institute,
and she is always competing to get the best
telescope time. Um, she was just in Hawaii not
too long ago and she was so excited because it was perfect,
perfect conditions and she got everything she wanted.
Professor Fred Watson: Very good.
Generic: Three, two, one.
Heidi Campo: Space nuts.
All right, so this brings us to our very last question for the
evening, which is from Fenton. And this is
an audio question that I will
play for you now. I'll give Fred just a second
to get synced up with me.
Professor Fred Watson: Synced up with me.
Heidi Campo: And then we can, we can both hit play
at the same time and listen to Fenton's question, which
you will hear now.
Fenton: Hey, Fred and Andrew, this is Fenton from St. Paul,
Minnesota, in the U.S. uh, I
understand you guys need some questions, so here's one for you to think
about. I really like, by the way, uh,
everything that you do with the questions, whether they're good
or bad, you always do a good job of coming
up with something interesting on them. So
you guys talk a lot about gravity
waves. And I ask
myself, can you compare a gravity
wave to a geometrical wave that
is a sinusoidal wave or a sine wave
that's going to have regular minima and
maxima to it? So what do you think of that? Does
that make any sense? Um, and
then if that were the case, I thought,
can two gravity waves interact?
Can they either double their intensity or
nullify each other?
Can they be in phase or out of phase is another way of looking at
it. And then if we want
to continue this classical analogy
of, um, speed is equal,
uh, to wavelength divided by
time. Can one gravity have a
wavelength that, for example, would be one
half that of the others? In other words, you'd have
a sort of phase shifting there, maybe.
I'd love to hear what you think about it. I hope you like the question. Cue
up the good job and stay, uh,
warm down there. Bye now.
Heidi Campo: Well, that was a very nice question. Thank
you so much, Fenton. I will stay warm.
It's nothing but warm here in Houston in the summertime for us.
Professor Fred Watson: Yes, I can imagine. So, Fenton,
that's a, uh, good set of questions. And the answer
to most of your questions in there is yes,
uh, the, um, gravitational
waves, ah, are, uh, waves.
They're basically vibrations of space. Uh,
and you probably know that, um,
the waves that we're normally familiar with, like
sound waves, are what are called longitudinal waves.
The molecules of air move backwards and forwards
as the wave progresses. Whereas, uh,
light waves are transverse, uh, waves.
Which are a vibration of the
magnetic and electric fields, uh, which
are, uh, you know, existent at any given time. So,
uh, they are. They are sinusoidal
is the way you describe them. Gravitational
waves are something different. They're called quadrupole waves.
And they're a bit like sine waves,
but they've got a sort of rotational component to
them as well. So they are not,
um, exactly like, uh, a light
wave. But they are similar, uh, in
broad characteristics. And in particular,
they are similar in that, yes, they can interfere
with one another. That's the phenomenon that you were talking about,
uh, where, uh, light waves can either
cancel out or add. Uh, to give you these,
what we call fringe patterns, uh, gravitational
waves can do that as well. Uh, the quadrupole waves
can interfere with one another. And you're also
right that they come in different
wavelengths. We normally think of it as different
frequencies. Uh, so gravitational waves
caused by different phenomena. Have a
very, very wide, uh, variation in
frequency. Uh, some are, uh, what we call,
uh. Well, let me just tell you the ones
that we've observed so far. And that's because the
particular gravitational wave detectors that we have.
Are tuned effectively to these frequencies.
They're the ones that come from colliding
neutron stars, colliding black holes, all of that sort of thing we were just
talking about a few minutes ago. Uh, and
they are more or less in the, um, audio
frequency spectrum. Uh, so if you amplified
them enough, you could hear them. They're, uh, a few
hundred hertz. One hertz is one cycle
per second. But some of the bigger
phenomena in the universe. And I'm thinking now of things
like the Big Bang or the epoch of inflation
times in the universe when things were very different from what they are
now. They generate what we call
nanohertz waves, where the frequencies,
uh, are, uh, measured in, uh,
billionths of a hertz rather than
a few hundred hertz, uh,
uh, so they would be detected in a
completely different way. And in fact, we think. I think one of the ways of detecting
them might be from the cosmic microwave background
radiation, the flash of the Big Bang that we can still see.
So you're right on the money, uh, with all of those
questions. Yes, gravitational waves do behave
almost in an analogous way to light. They certainly travel at
the same speed of light. They can interfere, and they
do come in widely different frequencies.
Heidi Campo: Well, excellent. Thank you. Thank you so much, Fred. These have
been wonderful answers to some
wonderful questions. And thank you so much to everybody
who has written in. Um, we
really do have some of the best
listeners here. I mean, this podcast, we
have such an amazing, engaged
audience. I mean, you guys are half of the show, really.
Your questions are half of the show. Um, so
please stay curious. Keep sending in
your wonderful questions. Uh, it's
certainly so fun for me to hear Fred, um,
answer them and, ah, it's a good time.
Um, Fred, do you have anything else you want to say
before we sign off for today?
Professor Fred Watson: No, just keep the questions coming in, folks, because this is
the thing that makes SpaceNut special. We've got such a
wide audience all over the world. We love
hearing from you and we cover your questions,
tricky ones or non tricky ones alike.
Thank you. And thanks to you, Heidi, too.
Heidi Campo: Oh, thank you, Fred. You're so sweet.
All right, well, this has been, um, another Q and A
episode of Space Nuts. We are,
Heidi and Fred, signing off.
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