Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / Europa's Ocean Secrets, Gravitational Waves & Black Hole Mysteries

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Europa's Ocean Secrets, Gravitational Waves & Black Hole Mysteries · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: Hi, Andrew Dunkley here. Fred and I are
• 0:02
  taking a little bit of a break over the
• 0:04
  Christmas New Year period just to catch our
• 0:06
  breath. We'll be back, uh, sometime around
• 0:09
  mid January. In the meantime, we've been
• 0:11
  digging through the archives at some of the
• 0:14
  most perplexing and popular
• 0:16
  episodes that we've done in recent times. So
• 0:19
  sit back and enjoy. 15
• 0:22
  seconds. Guidance is internal.
• 0:24
  Professor Fred Watson: 10, 9. Ignition
• 0:27
  sequence start. Space nets.
• 0:29
  Andrew Dunkley: 5, 4, 3.
• 0:30
  Professor Fred Watson: 2. 1, 2, 3, 4, 5, 5, 4, 3,
• 0:33
  2, 1.
• 0:34
  Andrew Dunkley: Space nuts astronauts report it feels
• 0:37
  good. Hi there and thanks for joining us on
• 0:40
  the Space Nuts podcast. My name's Andrew
• 0:42
  Dunkley, your host. And joining me, uh, as
• 0:45
  always, Professor Fred Watson, Astronomer at
• 0:48
  Large from the department of Da da da da da
• 0:51
  da da. It's a pretty long title. That's what
• 0:53
  we'll call it from now on. G', day, Fred.
• 0:55
  Professor Fred Watson: You could call me the Aaliyah.
• 0:58
  Andrew Dunkley: Aal.
• 0:58
  Professor Fred Watson: Yeah, when I was Astronomer in Charge, I was
• 1:01
  aic. Um, the only trouble is
• 1:04
  AAL actually has another significant
• 1:06
  meaning in Australian astronomy because it
• 1:09
  doesn't only stand for Astronomer at Large,
• 1:10
  it also stands for Astronomy Australia
• 1:13
  Limited. So, uh, just throw that idea out.
• 1:16
  That's a rubbish idea. I'll just be
• 1:17
  astronomer.
• 1:18
  Andrew Dunkley: Yeah, I was once given the title urrs.
• 1:21
  But anyway, um,
• 1:25
  some people will understand that.
• 1:27
  Professor Fred Watson: Yeah, you've got lovely friends, haven't you?
• 1:29
  Andrew Dunkley: I've got a lot of good friends, yes.
• 1:31
  Now today we're going to talk about some very
• 1:34
  exciting things. It looks like black holes
• 1:36
  are still in people's minds. So we're going
• 1:38
  to be talking about, um, a couple of
• 1:40
  questions that have come in from people about
• 1:42
  infinite density. Uh, density. I
• 1:45
  keep getting it mixed up with destiny. I
• 1:47
  don't know why. Might have been a Back to the
• 1:49
  Future movie that confused me on that front.
• 1:51
  Uh, uh, and issues, uh, photographing a black
• 1:54
  hole. Why were they issues at all? And uh,
• 1:56
  another question about space travel and uh,
• 1:59
  near light speed travel. Uh, we're also
• 2:02
  going to, uh, look at,
• 2:04
  um, the cause of a gravitational
• 2:07
  wave that was detected recently. This is
• 2:09
  exciting because they think they've
• 2:10
  pinpointed, uh, an actual cause.
• 2:13
  And we're going to start off today.
• 2:15
  Professor Fred Watson: Fred, by talking about, uh, this rather.
• 2:17
  Andrew Dunkley: Exciting mission that's one step closer to
• 2:19
  happening. A mission to Jupiter's ice
• 2:22
  moon Europa. And that's what we'll start
• 2:25
  with. This, uh, well, this afternoon, this
• 2:27
  morning, tonight, this evening, yesterday.
• 2:30
  Professor Fred Watson: Whenever. Whenever it is. Yeah, it's,
• 2:33
  yeah. So look, a terrific story. Very good
• 2:36
  news from uh, NASA that they,
• 2:39
  um, the powers that be within NASA have uh,
• 2:42
  given the go ahead um, for a
• 2:45
  mission called Europa Clipper, which is, is
• 2:47
  one of the uh, missions that's been
• 2:50
  uh, postulated or sorry proposed is a better
• 2:53
  word for um, exploring the moons of the outer
• 2:56
  planets. There are a number that are kind of
• 2:58
  on the, on the table at the moment, some
• 3:00
  further advanced than others. But Europa
• 3:02
  Clipper is pretty well advanced and
• 3:05
  as you can tell its target, its main target
• 3:08
  is Jupiter's moon Europa, which is one of
• 3:11
  these um, ocean moons. Ice, uh,
• 3:14
  ocean moons. Uh, we believe it has
• 3:17
  a covering of ice and we don't know whether
• 3:19
  it's thin ice or thick ice. So that would be
• 3:21
  one of the things that Europa Clipper would
• 3:23
  find out. Um, and an ocean underneath it
• 3:26
  and a rocky core. Uh, so
• 3:29
  Europa Clipper, I think they are
• 3:31
  talking about having it ready for launch in
• 3:34
  2023 which is
• 3:36
  um, you know, fantastic if they can
• 3:39
  do that. That's right. Uh, but apparently
• 3:42
  um, that's the
• 3:45
  baseline commitment as it's called, supports
• 3:48
  a launch readiness date by 2025.
• 3:51
  Um, it's all being done at ah, the Propulsion
• 3:53
  Laboratory in Pasadena. That's where the
• 3:56
  spacecraft will be built. So they've got the
• 3:58
  go ahead, um, it's
• 4:01
  got the next step,
• 4:04
  uh, in approval from NASA, which
• 4:07
  I think is a pretty solid one. So I
• 4:10
  think you and I, back in 2025
• 4:13
  we'll be talking a lot about Europa Clipper.
• 4:16
  Andrew Dunkley: Maybe what will be the
• 4:19
  basis of the mission? Are they just going
• 4:21
  there to have a look?
• 4:22
  Professor Fred Watson: Because it is a bit like uh, but it's
• 4:25
  a very good look. Um, so it's not going to
• 4:27
  land on Europa. It is a proposal to go into
• 4:30
  orbit around Europe, actually to go into
• 4:32
  orbit around Jupiter. Uh and of course
• 4:35
  orbiting Jupiter is always hazardous because
• 4:37
  of um, the
• 4:40
  intense uh, radiation belts that Jupiter
• 4:43
  has. It's got a magnetic field thousands of
• 4:45
  times bigger than the Earth and has these
• 4:47
  high energy radiation belts around it that
• 4:50
  threaten to melt the innards of spacecraft.
• 4:53
  Uh, so like the uh, Juno mission which
• 4:56
  is currently in orbit around Jupiter, this
• 4:59
  uh, Europa Clipper will go into a very
• 5:02
  elongated uh, orbit, um, which
• 5:05
  will uh, give it 45
• 5:08
  flybys of Europa. Uh and
• 5:11
  their altitudes will vary from
• 5:13
  2700km to 25km.
• 5:16
  So it will really be skimming over the
• 5:17
  surface. Oh well, and it's got this huge
• 5:20
  science package with all the kind of,
• 5:23
  you know, the gubbins that you would expect
• 5:24
  to find on board something like that,
• 5:28
  a mass spectrometer, uh, which
• 5:31
  basically measures, you know the weights
• 5:34
  of atoms, as you might guess. Uh,
• 5:37
  it, um, that is interesting because
• 5:40
  Europa, like Saturn's moon Enceladus,
• 5:43
  is thought to have, although it hasn't really
• 5:44
  been properly confirmed, but thought to have
• 5:47
  ice, uh, fountains coming out of
• 5:50
  it, um, which are water that's
• 5:52
  squirting up through its, uh, through its icy
• 5:55
  shell and instantly freezing. It's not
• 5:57
  frozen. But if you fly through it, as
• 6:00
  Cassini did with Enceladus, then you can
• 6:02
  sample what the atomic makeup is. And so
• 6:05
  the mass spectrometer will help with that.
• 6:08
  Uh, and also, um, it's got this ground
• 6:11
  penetrating radar and that's going to be
• 6:14
  crucial in characterizing
• 6:17
  Europa's crust, um, and
• 6:19
  revealing how much of, you know, the
• 6:22
  potential water within is oceanic, as
• 6:25
  is expected, uh, or whether it is just
• 6:27
  pockets of water as we find in Antarctica
• 6:30
  and indeed around the South Pole of Mars.
• 6:32
  Andrew Dunkley: Will they be able to tell what kind of water
• 6:34
  it is?
• 6:36
  Professor Fred Watson: Um, uh, to some
• 6:38
  extent they will. Um, it may
• 6:41
  require a bit of, you know,
• 6:44
  inference from other measurements, but if
• 6:46
  you've got, uh, samples of ice crystals,
• 6:49
  uh, then you can do exactly that. You can,
• 6:52
  you know, you can uh, basically
• 6:56
  tell whether it's saline water or fresh water
• 6:59
  because you can see the, you can measure the
• 7:01
  salt content of it.
• 7:02
  Andrew Dunkley: It.
• 7:02
  Professor Fred Watson: So like um, Saturn's moon
• 7:05
  Enceladus, uh, which is actually quite
• 7:08
  rich in minerals and it's the silicates in
• 7:10
  that that tells you that this water was once
• 7:12
  in contact with rock. Uh, I think
• 7:15
  the Europa Clipper will be able to sample
• 7:18
  exactly those things too. Assuming these
• 7:20
  plumes are real, because they're not
• 7:23
  well observed. There is evidence. I've seen
• 7:25
  images that seem to show these plumes
• 7:28
  coming from Europa. Uh, assuming they're real
• 7:31
  when they fly through, um, hopefully we will
• 7:33
  be able to tell what kind of water it is.
• 7:35
  Exactly.
• 7:35
  Andrew Dunkley: And will they be able to tell how much
• 7:38
  water there is underneath the surface?
• 7:40
  Professor Fred Watson: Yes they will because that will very
• 7:43
  much be revealed by the um, the ground
• 7:46
  penetrating radar in exactly the way
• 7:48
  that, um, um, one of the spacecraft in orbit
• 7:51
  around Mars, I think it was the, I think it
• 7:53
  was, might even have been Mars Reconnaissance
• 7:55
  Orbiter, I'm not sure, detected this
• 7:57
  lake of liquid water underneath the ice cap
• 8:00
  of the southern ice cap of Mars about a year
• 8:03
  ago you and I spoke about it. Um, and
• 8:06
  they can tell exactly how much there is there
• 8:08
  because you can see the boundary with this
• 8:11
  sort of radar. You can see the boundary
• 8:12
  between an ice surface and a water surface.
• 8:14
  And that's crucial to doing this so.
• 8:17
  Andrew Dunkley: This mission won't actually be looking
• 8:20
  for life, but it will be looking
• 8:23
  for, uh, the potential for life
• 8:25
  to perhaps exist on a moon
• 8:28
  like this.
• 8:30
  Professor Fred Watson: Exactly. So as the blurb,
• 8:33
  um, on the NASA website says, uh, it
• 8:36
  will help scientists investigate the chemical
• 8:38
  makeup of Europa's potentially habitable
• 8:40
  environment while minimizing the need to
• 8:43
  drill through layers of ice so that what
• 8:45
  they're going to try and do is as much as
• 8:47
  they can from orbit. Um, and
• 8:50
  then if there's like, if they find
• 8:52
  lipids and amino acids and all this sort of
• 8:55
  thing, uh, in the plumes of ice coming,
• 8:58
  coming from Europa, then clearly the next
• 9:00
  step will be a lander, uh, that starts
• 9:02
  digging holes in the ice.
• 9:03
  Andrew Dunkley: Yes.
• 9:04
  Professor Fred Watson: I mean, you know, before you do that, the
• 9:06
  first thing you need to know is how thick the
• 9:08
  ice is. Yes.
• 9:09
  Andrew Dunkley: If it's a couple of miles thick.
• 9:12
  Professor Fred Watson: Well, actually, a couple of miles
• 9:15
  is better than what they're expecting.
• 9:17
  Andrew Dunkley: Oh, is that right?
• 9:18
  Professor Fred Watson: More like 25 or 30 miles
• 9:20
  or kilometers. M. That's right. Choose your
• 9:23
  units. Um, yes. So, yes,
• 9:26
  a thinner layer of ice will be
• 9:29
  pretty, pretty, um, good to, you know, to
• 9:31
  cope with. You could probably do that. I mean
• 9:33
  by thin, I mean less than a kilometer,
• 9:35
  probably. Yes.
• 9:36
  Andrew Dunkley: But the likelihood, uh, is it's, it's
• 9:39
  probably more, but I guess we'll, we'll have
• 9:40
  to wait and see.
• 9:43
  Professor Fred Watson: Um, Europa's covered in all these cracks that
• 9:45
  are, that are brownish in color.
• 9:46
  Andrew Dunkley: Yes.
• 9:47
  Professor Fred Watson: That's thought to be the effect of sunlight
• 9:49
  on brine, on basically on salt water. So
• 9:52
  you've already got a hint there that, uh,
• 9:55
  it's probably a salty ocean underneath the
• 9:57
  surface.
• 9:58
  Andrew Dunkley: Well, salt's probably not that uncommon in
• 10:00
  the universe really.
• 10:01
  Professor Fred Watson: Um, that's right. It's not.
• 10:03
  Andrew Dunkley: It's one of, one of the base materials, isn't
• 10:06
  it? Uh, of course, this doesn't guarantee
• 10:08
  they're actually going to go. This is just
• 10:10
  another step forward in the approval process.
• 10:12
  Professor Fred Watson: It does, it does.
• 10:14
  Andrew Dunkley: Very longitudinal process and they have to
• 10:17
  get over a lot of hurdles before they
• 10:18
  actually hit the launch button. So, uh,
• 10:21
  hopefully they're, um, they're going to get
• 10:23
  there and um, it's. It's a long trip too.
• 10:26
  Professor Fred Watson: Yes, it is. That's the other thing.
• 10:27
  Andrew Dunkley: So they've got to time it right. They've got
• 10:29
  to get in the right place at the right time.
• 10:30
  Professor Fred Watson: Exactly. All of the above. That's right. So,
• 10:34
  uh, at least what it, you know, at least, uh,
• 10:36
  it's not a knockback. That's the good news.
• 10:39
  Andrew Dunkley: Indeed. All right, well, we'll keep an eye on
• 10:40
  this story because I'm sure there'll be more
• 10:42
  to report in the not too distant future about
• 10:45
  uh, a mission to Europa. You're listening
• 10:48
  to Space Nuts with Andrew Dunkley and Fred
• 10:51
  Watson.
• 10:53
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• 12:48
  Professor Fred Watson: Space Nuts.
• 12:49
  Andrew Dunkley: Now Fred, we've uh, discussed
• 12:51
  uh, gravitational waves before and
• 12:54
  uh, a few of those have been detected in
• 12:56
  recent times. The problem with them
• 12:59
  is what is the cause?
• 13:02
  And now in a recently detected
• 13:05
  gravitational wave they think they've got a
• 13:08
  candidate.
• 13:09
  Professor Fred Watson: That's, that's right. This is so this is, you
• 13:11
  know, it's a, an ongoing story. Uh,
• 13:14
  what I like about this story is it's got a
• 13:16
  nice Australian component because there is
• 13:18
  um, there's a, basically
• 13:21
  a collaboration here in Australia which is
• 13:24
  called osgrav, uh, which is about
• 13:26
  gravitational waves. It's a kind of fairly
• 13:29
  predictable name but um, it includes people
• 13:31
  from the Australian National University and
• 13:34
  I think University of Western Australia Other
• 13:36
  places which are strong in gravitational wave
• 13:38
  astronomy. So, um, it's very nice
• 13:41
  that it's. It has this Australian component.
• 13:43
  So what's the story? Well, uh, the large.
• 13:47
  Sorry, uh, the Laser Interferometer
• 13:49
  Gravitational Wave Observatory, Otherwise
• 13:51
  known as LIGO, um, has been operating
• 13:55
  since, uh, 2015 in its
• 13:58
  sort of current state. It's actually
• 14:00
  technically called Advanced LIGO because I
• 14:02
  think it took 15 years of development to get
• 14:05
  to this stage. But they have,
• 14:08
  uh, now, not quite regularly, but at, uh,
• 14:11
  fairly infrequent intervals. Sorry,
• 14:13
  fairly moderately moderate intervals.
• 14:16
  Let me put it that way. They've been
• 14:18
  detecting gravitational wave events. And for
• 14:21
  the last couple of years they've had an
• 14:22
  additional string to their bow. Remember,
• 14:24
  there are two of these detectors at opposite
• 14:26
  corners of the United States,
• 14:28
  um, which, um, you need because,
• 14:31
  uh, otherwise you've got no idea where these
• 14:34
  things come from or even if they're real. You
• 14:36
  need to see the gravitational wave pass one
• 14:38
  and then the other with the right kind of
• 14:40
  time interval in between. Um, but they've
• 14:43
  been joined in the last few years by
• 14:44
  something called, uh, uh, Virgo, which,
• 14:47
  uh. In fact, I think it's called Advanced
• 14:49
  Virgo. Like Advanced ligo. Virgo is an
• 14:51
  Italian gravitational wave detector. And of
• 14:54
  course, having three detectors widely spread
• 14:57
  over the surface of the Earth, uh, means you
• 14:59
  can pinpoint things much more accurately in
• 15:01
  terms of the direction in which these
• 15:03
  gravitational waves come in.
• 15:04
  Andrew Dunkley: From triangulating the signal.
• 15:07
  Professor Fred Watson: Exactly. That's exactly what it is.
• 15:09
  Um, what's interesting about this one though,
• 15:12
  is that the signal seems to be
• 15:15
  from a black hole absorbing
• 15:18
  a neutron star.
• 15:21
  Um, we actually had a false alarm on
• 15:24
  this, which is embarrassing because, um, my
• 15:27
  book has just gone to the printer saying,
• 15:29
  yes, we've observed a neutron star being
• 15:31
  absorbed by a black hole. Um, and
• 15:34
  that I think disappeared because it turned
• 15:36
  out to be, um, terrestrial noise. It was
• 15:39
  sort of, you know. So I don't know whether it
• 15:41
  was a train going underneath oven probably,
• 15:44
  or. Yeah, something like that. That's the
• 15:46
  usual story, isn't it? A microwave oven. Um,
• 15:48
  that was earlier this year. And that,
• 15:51
  um, has now gone away. But it looks as
• 15:54
  though this one might actually be the
• 15:57
  real thing. A black hole and a neutron star.
• 16:00
  We've had two black holes merging. Uh,
• 16:03
  that's probably been the commonest source of,
• 16:06
  uh, gravitational waves. There've been
• 16:07
  several of those. We've had a couple of
• 16:09
  neutron stars merging as well. And that
• 16:12
  actually comes with celestial fireworks that
• 16:14
  you can observe with other types of
• 16:17
  telescope like neutrino telescopes, visible
• 16:19
  light telescopes, radio Telescopes, X ray
• 16:22
  telescopes, all of the above. Um, and
• 16:25
  that was a big story actually late last year
• 16:27
  if I remember rightly. But, um, until
• 16:30
  now we haven't had a confirmed,
• 16:33
  um, observation of a neutron star
• 16:36
  being absorbed by a black hole. And we still
• 16:38
  don't have. It's still a bit speculative,
• 16:41
  but from the masses that are inferred by the
• 16:44
  signal. And remember what you get is this
• 16:45
  weird gravitational chirp, uh,
• 16:48
  it's uh, the frequency of a sound wave
• 16:51
  going as the two things come
• 16:54
  together. Um, and it's that. That gives you
• 16:56
  all the details of what it is that that are
• 16:58
  colliding. The suspicion is it's two
• 17:01
  objects, one of which is three solar
• 17:04
  masses and the other is five
• 17:07
  solar masses. I think I'm right in saying
• 17:10
  that I should uh, check those numbers. But
• 17:12
  anyway, uh, that is the current
• 17:16
  expectation, uh, of what is colliding. So
• 17:19
  something three solar masses would have to
• 17:21
  be a neutron star because it's two
• 17:24
  lightweight uh, to be a black hole.
• 17:27
  And so, uh, that is what's making this
• 17:30
  interesting. What's
• 17:32
  perhaps, um, a bit surprising,
• 17:35
  uh, is that
• 17:38
  you might expect there to be once again
• 17:41
  radiation, uh, coming from this, not just
• 17:43
  gravitational radiation, but uh, noise
• 17:46
  in the X ray spectrum or uh,
• 17:49
  neutrinos, uh, particles, things of that
• 17:51
  sort, but it hasn't been
• 17:54
  observed. And um,
• 17:57
  one of the Australian astronomers, uh,
• 18:00
  uh, I've forgotten her first name. That's
• 18:02
  embarrassing, isn't it? Susan. Susan Scott.
• 18:04
  Uh, she's at um, anu Australian
• 18:07
  National University. Uh, she says that
• 18:10
  uh, if she said. Well
• 18:13
  what she says is we've looked for light
• 18:15
  signatures of the event, but no one has found
• 18:16
  any up to this point. That indicates that if
• 18:19
  it is a black hole and a neutron star, then
• 18:22
  very likely the neutron star has been
• 18:24
  swallowed whole by, by the black hole. Uh,
• 18:27
  uh, he said, and she says this could happen
• 18:29
  if the objects were of different masses.
• 18:32
  So it's. The smaller object gets sucked in
• 18:35
  more quickly and, and is swallowed whole. So
• 18:37
  you know, it's not strung out into, into this
• 18:41
  um, mess of material that does emit
• 18:44
  um, uh, signals in the
• 18:46
  electromagnetic uh, wave bands. Uh,
• 18:49
  if it gets sucked in hole, maybe you don't
• 18:52
  get any signal at all except for the
• 18:53
  gravitational wave signal.
• 18:55
  Andrew Dunkley: It's extraordinary how sudd
• 18:58
  impact be. I mean, you know, neutron
• 19:01
  stars, we've talked about them and they're
• 19:03
  pretty volatile individuals and
• 19:06
  quite dense, um,
• 19:08
  quite dense.
• 19:09
  Professor Fred Watson: It's just a slight understatement there.
• 19:12
  Yes, indeed.
• 19:13
  Andrew Dunkley: Um, so I imagine
• 19:16
  it'd be quite a cataclysmic collision.
• 19:19
  Professor Fred Watson: Yeah, that's right. Um, in fact, so
• 19:22
  when you've got two black holes, um, what you
• 19:25
  get at the end of it is a more massive black
• 19:27
  hole. Uh, and, um, you're
• 19:30
  talking there though about, you
• 19:32
  know, infinitely small, infinitesimally small
• 19:35
  points merging, uh, their event horizon.
• 19:38
  There are two event horizons merge as well,
• 19:41
  and you get something called the ring down
• 19:42
  where the event horizon itself vibrates.
• 19:45
  Um, I think with a neutron star you wouldn't
• 19:48
  have the event horizon, but it will be
• 19:51
  possible for the neutron star just basically
• 19:53
  to disappear. Over the black holes event
• 19:55
  horizon, you don't see anything. But, uh,
• 19:57
  neutron stars themselves, as you and I have
• 19:59
  talked about many times, are active in the
• 20:01
  sense that they've got highly intense
• 20:02
  magnetic fields on their surfaces and they
• 20:05
  beam this radiation out, which we see as
• 20:08
  pulsars. So they're not particularly
• 20:11
  quiet things. I mean, this thing could be a
• 20:13
  pulsar whose lighthouse beam of
• 20:16
  radiation is missing the Earth, if I can put
• 20:19
  it that way. Because the only reason we see
• 20:21
  pulsars is when you've got a neutron star
• 20:23
  whose, uh, beams of radiation from their
• 20:26
  poles actually sweeps across the Earth. And
• 20:28
  that of course, is a particular, uh,
• 20:30
  circumstance. Maybe this one wasn't like
• 20:33
  that and it's just got chewed up, uh, and
• 20:37
  we haven't seen its demise other than in
• 20:40
  the gravitational waves.
• 20:41
  I think there'll be more about this story,
• 20:43
  Andrew, and, um, I hope you and I can bring
• 20:45
  it to our, uh, Space Nuts
• 20:48
  listeners or listeners, our fraternity.
• 20:52
  Andrew Dunkley: Yes, uh, well, um,
• 20:55
  the more we can gather in terms of data,
• 20:58
  uh, on gravitational waves, the more we
• 21:01
  will learn and who knows what
• 21:04
  sort of problems it could solve down the
• 21:05
  track, so.
• 21:06
  Professor Fred Watson: Exactly. It's always my comment that you
• 21:09
  never know what you're setting in store for
• 21:12
  the future from all this knowledge.
• 21:13
  Andrew Dunkley: Exactly.
• 21:14
  Professor Fred Watson: Yeah.
• 21:14
  Andrew Dunkley: I, uh, mean, you just, just gather the
• 21:16
  knowledge. One day it might just go, you, ah,
• 21:18
  know, a penny will drop with someone else,
• 21:20
  maybe a generation down the track, who knows?
• 21:23
  It's all useful. And even if it's not, it's
• 21:25
  good to be able to gather it and they
• 21:28
  use it. Some, some.
• 21:29
  Professor Fred Watson: That's right. It's um, you know, all these
• 21:32
  things are constantly testing Einstein's
• 21:34
  theory of relativity. And that's
• 21:38
  very, um, important because we know there's
• 21:39
  something wrong with it, but we haven't found
• 21:41
  anything wrong with it yet. Even though it's
• 21:43
  been tested within an inch of its life, it's
• 21:45
  still holds up.
• 21:46
  Andrew Dunkley: Yeah, fascinating.
• 21:48
  All right, you're listening to the Space Nuts
• 21:51
  podcast With Andrew Dunkley and Fred Watson.
• 21:56
  Professor Fred Watson: Okay, we checked all four systems and being
• 21:58
  with a girl, Space Nuts.
• 22:00
  Andrew Dunkley: Now Fred, I do want to shout out once again
• 22:02
  to our patrons, um, that number
• 22:05
  39 now thank uh, you so
• 22:08
  much for supporting the Space Nuts podcast.
• 22:10
  We so appreciate it. And if you're interested
• 22:13
  in becoming a patron, you can, can do
• 22:14
  so@patreon.com spacenuts
• 22:17
  that's patreon.com
• 22:20
  spacenuts and um, thank you to
• 22:23
  everybody who has joined the Space Nuts
• 22:25
  podcast group. They number in their hundreds.
• 22:28
  Now Fred, we've only had the page going for
• 22:31
  a bit over a week and uh, already we've
• 22:33
  tracked the century and
• 22:36
  have over 100 people that are all Space Nuts
• 22:39
  fans who are all now talking to each other
• 22:41
  and uh, answering each other's questions and,
• 22:43
  and uh, having a fair bit of fun. So I'm
• 22:46
  so pleased we were able to put um, those
• 22:49
  people together and who uh, knows friends,
• 22:51
  friendships may be forged. Uh, that's
• 22:54
  great. Or collaborations that might solve
• 22:56
  some of the mysteries of the universe. Who
• 22:58
  knows, uh, that would be a lovely legacy I
• 23:01
  think. Uh, let's um, and of course if
• 23:03
  you would like to be a member uh, of the
• 23:06
  Space Nuts podcast group, um, just find it,
• 23:09
  it, it's on Facebook, uh, Space Nuts podcast
• 23:11
  group in your search engine and um, yes, just
• 23:14
  ask to join and we will click the approve
• 23:17
  button. Everybody seems to be like minded and
• 23:19
  enjoying themselves. So uh, that's what it's
• 23:21
  all about.
• 23:23
  Now Fred, some questions if you
• 23:26
  will. Um, hello again fellow nutters.
• 23:29
  I have a question I'm hoping you can help me.
• 23:31
  Um, understanding an old
• 23:33
  chestnut black holes. If a black hole is
• 23:36
  an infinite dense point, why does it have a
• 23:39
  diameter? I don't why astronomers refer
• 23:42
  to black holes by their size in terms of
• 23:44
  diameter. When it's meant to be a point of
• 23:46
  infinite density, are they
• 23:48
  mistakenly referring to the event horizon?
• 23:51
  Mario from Melbourne. Hello Mario. Thanks for
• 23:54
  the question.
• 23:55
  Professor Fred Watson: And the answer is yes, thank you Mario.
• 23:57
  Andrew Dunkley: Thanks for the question.
• 23:59
  Professor Fred Watson: Um, Mario then goes on to uh, you
• 24:02
  know, everything he says is absolutely right,
• 24:05
  that um, uh, if you've got a, a
• 24:07
  point of infinite density, it's got zero
• 24:10
  dimensions, so you can't refer to its
• 24:12
  diameter. Uh, what you can refer to is
• 24:15
  its mass because the mass is uh,
• 24:19
  variable. Uh, but the fact that
• 24:21
  it has no volume means that when you, you
• 24:24
  know, when you look at the mass per unit
• 24:26
  volume, you've got something of infinite
• 24:27
  density, which is how density is defined.
• 24:30
  So Mario is absolutely right. Uh, what
• 24:33
  does vary though? With the maps is the event
• 24:36
  horizon, the diameter of the event horizon,
• 24:38
  which you and I have spoken before. Um,
• 24:41
  uh, uh, it's a
• 24:44
  quantity that I suppose is
• 24:47
  important because if we are observing,
• 24:50
  um, a black hole, as we did with the Event
• 24:52
  Horizon telescope, then that's what you see.
• 24:55
  Uh, so a big one is going to be easier to
• 24:56
  observe than a smaller one. And that's why a
• 24:58
  supermassive black hole, uh, in the center of
• 25:00
  a galaxy called M M87 was chosen for the
• 25:03
  first target for that Event Horizon
• 25:05
  Telescope. But no, Mario, you're quite right.
• 25:07
  Um, it is that, uh, astronomers, when,
• 25:10
  if they talk about the diameter of a black
• 25:12
  hole, and that probably includes me as well,
• 25:14
  uh, are actually really referring to the
• 25:16
  event horizon because that's the parameter.
• 25:19
  And I love the way Mario signs off by saying
• 25:22
  thanks in advance to Dave and Fred. Uh,
• 25:25
  although he does say, AKA Andrew.
• 25:27
  Andrew Dunkley: Yes, that one's going to stick for a while,
• 25:30
  sorry to say. Thank you, Mario.
• 25:35
  Moving on. Uh, hi, Andrew and Fred. It's
• 25:37
  Andrew from Newcastle with another question,
• 25:39
  if I may. Just watched a doco on the quest
• 25:42
  to capture the first photograph of a black
• 25:44
  hole, uh, rather accurately, the shadow of a
• 25:47
  black hole, as Fred so eloquently explained.
• 25:49
  And I didn't understand one thing.
• 25:52
  Amongst others, of course, with the multiple
• 25:54
  observatories around the world and the use of
• 25:56
  atomic clocks to synchronize the data
• 25:58
  acquisition, why were they, uh, on
• 26:01
  tenterhooks, uh, regarding the weather
• 26:04
  at all the sites, with, uh, bad weather at
• 26:06
  just one, putting the whole venture in peril.
• 26:09
  I understand from the show and other sources
• 26:11
  that they were collecting radio wavelength
• 26:13
  data. And I thought that this was unaffected
• 26:16
  by the weather and atmospheric conditions. I
• 26:18
  thought that, uh, was the intrinsic beauty of
• 26:21
  radio astronomy. Day and night, rain and
• 26:23
  shine. Hope you can enlighten me.
• 26:26
  Wait for it. But over the radio. Dear,
• 26:29
  oh, dear. Uh, Andrew Broadhurst. Thank you,
• 26:31
  Andrew.
• 26:32
  Professor Fred Watson: That's a great question. Andrew.
• 26:33
  Andrew Dunkley: Leave the jokes to me, man.
• 26:37
  Professor Fred Watson: Yeah, well, I always leave them to you. So.
• 26:41
  Andrew Dunkley: Um, some to live. They're good.
• 26:43
  Professor Fred Watson: Oh, gosh. When was the last. Oh, never mind.
• 26:48
  Uh, Andrew's on the money. There is, you
• 26:49
  know, I thought radio waves were unaffected
• 26:52
  by the weather. And the answer is that radio
• 26:54
  waves come in different flavors. Uh, and
• 26:56
  so, uh, what you might call low frequency
• 26:59
  radio waves, um, which are still
• 27:01
  relatively, you know, they're way outside the
• 27:04
  medium wave band of radio and things of that
• 27:06
  sort. But low frequency in radio astronomy,
• 27:09
  um, I guess goes up to a couple of gigahertz
• 27:12
  or something like that. Um, those
• 27:15
  are largely unaffected by weather. That's
• 27:17
  absolutely right. So that's why it can be
• 27:19
  pouring down at Parkes, the radio dish there.
• 27:22
  And the astronomers are still happily
• 27:24
  observing through that. But the Event Horizon
• 27:26
  Telescope used higher frequencies. Uh, in
• 27:29
  fact, one of the telescopes that was
• 27:32
  incorporated into it was alma. The Atacama
• 27:34
  Large Millimeter Array, which has featured
• 27:37
  very, uh, very widely on space knots. That is
• 27:40
  a high frequency, uh, radio
• 27:43
  array. In fact, they have
• 27:46
  receivers that go up to, uh, more than
• 27:48
  900 gigahertz. So that's like, you know,
• 27:51
  nearly a thousand times higher frequencies
• 27:53
  than what we've just been talking about. And
• 27:56
  those sorts of frequencies, uh, the weather
• 27:59
  plays a very important role. Because water
• 28:01
  vapor actually dramatically
• 28:04
  absorbs the microwave signals.
• 28:07
  Andrew Dunkley: And that's what experience that watching
• 28:09
  satellite television. If there is a storm
• 28:11
  and it rains heavily, the wavelengths of the
• 28:14
  raindrops can absorb the signals from the
• 28:17
  satellite and you get nothing.
• 28:19
  Professor Fred Watson: Uh, that's interesting. I've never tried to
• 28:21
  watch satellite television. So that's, that's
• 28:24
  good thing to know.
• 28:25
  Andrew Dunkley: Um, it's one of the pitfalls.
• 28:27
  Professor Fred Watson: Yes, yes. In fact, I seldom watch television
• 28:30
  at all. So that's probably why. Um,
• 28:33
  but the bottom line is, um, you know, it's
• 28:35
  why facilities like ALMA and some
• 28:38
  of the other radio telescopes that were used,
• 28:41
  uh, to become the Event
• 28:44
  Horizon Telescopes, why they're all at high
• 28:46
  altitudes. Alma is at almost
• 28:48
  5,000 meters above sea level. Level,
• 28:51
  um, that's, you know, 15, 16,000ft.
• 28:54
  And at that height, there is very little
• 28:57
  water vapor in the atmosphere. Uh, but you
• 28:59
  can still get weather. And that's why they
• 29:01
  were indeed on tenterhooks about the weather.
• 29:03
  Because they don't want any of these, uh, if
• 29:06
  you lose one of those arrays, and
• 29:09
  I think there were eight of them that came
• 29:10
  together all around one hemisphere of the
• 29:12
  Earth, uh, to make up the Event
• 29:15
  Horizon Telescope. If you lose one of them,
• 29:17
  them, you lose a significant amount of your
• 29:20
  ability to reconstruct the image that they're
• 29:22
  seeing. Uh, and so that was why they were
• 29:24
  worried that the weather on just one of them
• 29:26
  might be, uh, moist, uh, or damper
• 29:29
  than they can cope with. And that would have
• 29:31
  screwed up the whole thing. But as it
• 29:33
  happened, it wasn't. It didn't happen. And it
• 29:35
  was great.
• 29:36
  Andrew Dunkley: They got global good weather.
• 29:38
  Professor Fred Watson: They did global good weather at these high
• 29:40
  altitude sites. That's right. The job.
• 29:41
  Andrew Dunkley: All right, there you are, Andrew. Uh, thank
• 29:44
  you for your question. And we've got one
• 29:46
  more. We'll squeeze in from John Sputh. I
• 29:49
  hope I pronounced that correctly. John,
• 29:51
  thanks for your question.
• 29:52
  Professor Fred Watson: Hi.
• 29:52
  Andrew Dunkley: I have a question that's been bugging me for
• 29:54
  some time and I need an expert to help me
• 29:56
  out. I think we should stop there. Fred.
• 30:00
  Professor Fred Watson: There's nobody here, is there? Who's that?
• 30:01
  Hang on. I'll go and see if I can find
• 30:03
  somebody.
• 30:04
  Andrew Dunkley: The cat could probably answer this one.
• 30:07
  Now, imagine, um, a spaceship traveling close
• 30:09
  to the speed of light. Disregarding that we
• 30:12
  don't have that sort of propulsion just yet.
• 30:14
  Would the increase in its
• 30:16
  relativistic mass at some point turn
• 30:19
  the spaceship into a black hole? And if so,
• 30:22
  would that spell the end of the ship and its
• 30:25
  crew? Or would they be able to slow down to
• 30:27
  reverse the process? What a great question.
• 30:30
  Professor Fred Watson: It is a fantastic question. Do you want to
• 30:32
  have a go at it?
• 30:33
  Andrew Dunkley: Uh, the answer is no.
• 30:36
  Professor Fred Watson: It is. You got right. Yeah, you're right on
• 30:38
  the money. They see. See, there is an expert.
• 30:40
  It's called Andrew Dunkley or Dave 50.
• 30:42
  Andrew Dunkley: 50 chance.
• 30:45
  Professor Fred Watson: Um, it's a great question. And it,
• 30:48
  it. The answer is a little bit, um,
• 30:51
  prosaic, I think. And that is that
• 30:54
  in the, in the rest frame of the
• 30:56
  spacecraft, you know. So if you're on the
• 30:59
  spacecraft and you're going at almost the
• 31:01
  speed of light, your mass doesn't change.
• 31:04
  It's only in the rest frame of
• 31:07
  a stationary observer. And by that I mean
• 31:10
  somebody watching you go past, somebody
• 31:12
  watches you hurl past. And your mass gets
• 31:15
  very much higher to the
• 31:17
  observer. But to the,
• 31:20
  the inhabitants of the spacecraft or the
• 31:23
  spacecraft itself, your mass doesn't change.
• 31:25
  Andrew Dunkley: It's.
• 31:25
  Professor Fred Watson: You're still normal. It is still normal.
• 31:28
  Yeah. And the same story is true with time
• 31:31
  dilation. You know that when you go
• 31:33
  nearer the speed of light, your clocks tick
• 31:36
  slower. Uh, that's a. Seen by a stationary
• 31:39
  observer. Uh, and so it's the same sort of
• 31:42
  thing. If you're on the spacecraft, your
• 31:43
  clock is ticking at the same rate as it ever
• 31:45
  was. But to a stationary observer, your
• 31:47
  clocks tick slower.
• 31:48
  Andrew Dunkley: And this has been proven with atomic clocks,
• 31:51
  hasn't it?
• 31:51
  Professor Fred Watson: It has. And indeed with mass as well. You can
• 31:54
  do this, you can see this sort of phenomenon
• 31:56
  with, um, uh. With uh,
• 31:58
  cosmic rays which travel very close to the
• 32:01
  speed of light. You can see their mass
• 32:02
  change. So, um, that's
• 32:05
  from the point of view of somebody who's, you
• 32:07
  know, not moving at the same speed. If you're
• 32:10
  moving at the same speed, you don't see any
• 32:11
  change at all.
• 32:13
  Andrew Dunkley: That's pretty boring. The more we Discuss
• 32:16
  black holes and the number of questions we
• 32:18
  get about them. People are really quite
• 32:22
  captivated by the strangeness of
• 32:25
  them. I suppose they throw up all these
• 32:27
  things that seem so alien to what we consider
• 32:30
  normal. Uh, and that's because we've only
• 32:32
  experienced um, what's happening on our
• 32:35
  planet at any given time. So to try
• 32:38
  and comprehend um, enough gravity to
• 32:41
  warp time to slow things down
• 32:44
  to the observer and increase mass. Just,
• 32:47
  it's really whack.
• 32:50
  Professor Fred Watson: Sad on the brain. That's true. But uh,
• 32:53
  look, John's question there is a great
• 32:56
  question because it's not intuitively
• 32:58
  obvious what is happening uh,
• 33:01
  in a situation like something traveling close
• 33:04
  to the speed of light. And it, and so he's
• 33:06
  right to ask would that mass actually turn it
• 33:09
  into a black hole? Uh, but the answer is no
• 33:11
  because of the reasons that I've outlined.
• 33:13
  But it's great, great thinking.
• 33:14
  Andrew Dunkley: It is indeed. Thank you John. Thanks for the
• 33:16
  question. Do appreciate it. Keep your
• 33:18
  questions coming in. We're trying to um, run
• 33:20
  them down but they, it's, it's, it's an ever
• 33:23
  growing mass really.
• 33:25
  Professor Fred Watson: It's. All right, look, as you said earlier
• 33:27
  Andrew, um, all the space nutters are going
• 33:30
  to get together and sort them out for
• 33:31
  themselves and we'll be, that'll be
• 33:33
  encouraged.
• 33:34
  Andrew Dunkley: Actually if uh, people want to ask questions
• 33:36
  of the group uh, and discuss it,
• 33:39
  they. Yeah, by all means. Um, that, that's
• 33:42
  part of the reason we set up the Space Nuts
• 33:44
  podcast group. So um, it's a good opportunity
• 33:46
  to not only meet like minded people who enjoy
• 33:49
  these, these topics, but also to maybe come
• 33:52
  up with your own ideas on, on what might,
• 33:54
  might be and you know, I'll keep an eye on it
• 33:55
  and if something pops in there that we think
• 33:57
  is worthy of further discussion, we will
• 34:00
  certainly investigate that. Thanks
• 34:03
  to everyone who um, who sent in their
• 34:05
  questions, uh, and uh, contributed and joined
• 34:08
  the Space Nuts podcast group and Patreon and
• 34:10
  everything else. We really appreciate it. Uh,
• 34:13
  but most of all we appreciate you Fred. Thank
• 34:15
  you so much.
• 34:16
  Professor Fred Watson: It's a pleasure, thank you for having me as
• 34:18
  always.
• 34:19
  Andrew Dunkley: And we will catch you next week. Professor
• 34:22
  Fred Watson, uh, astronomer at large and from
• 34:24
  me Andrew Dunkley. Thank you again and we'll
• 34:27
  catch you next time on another edition of
• 34:29
  SpaceNuts. Uh, you'll be
• 34:32
  listening to the Space Nuts podcast
• 34:36
  available at Apple Podcasts, Spotify,
• 34:39
  iHeartRadio or your favorite podcast
• 34:41
  player. You can also stream on
• 34:43
  demand@bytes.com.
• 34:45
  Professor Fred Watson: This has been another quality podcast
• 34:47
  production from bytes.com.