Latest / Space Nuts: Astronomy Insights & Cosmic Discoveries / Cosmic Queries: Understanding Black Holes, Galactic Centres, and Mars Days

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Cosmic Queries: Understanding Black Holes, Galactic Centres, and Mars Days · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: Hello again and thank you for joining us on
• 0:02
  another episode of Space Nuts. This is a Q
• 0:04
  and A edition where we take audience
• 0:06
  questions. We put them on paper and then we
• 0:09
  put them on a roll that goes on a little
• 0:11
  thing in a bathroom. Or we could
• 0:14
  answer them. We can do that. Uh, coming up
• 0:16
  today we have questions, uh, uh,
• 0:19
  from John about Martian days. The length
• 0:22
  of a Martian day. It's close, but is it
• 0:25
  close enough to Earth standard? We'll discuss
• 0:28
  that. Uh, the growth of a black
• 0:31
  hole has been, uh, brought up again.
• 0:34
  Uh, we've got a, um, a question, uh,
• 0:36
  from an 11 year old named Thomas. Hi, Thomas.
• 0:39
  He wants to talk about the galactic centre.
• 0:42
  And Paul is asking our, uh, about
• 0:44
  our galactic location. So we'll deal with
• 0:47
  all of that today on this episode of Space
• 0:50
  Nuts.
• 0:51
  Professor Fred Watson: 15 seconds. Guidance is internal.
• 0:54
  10, 9. Ignition
• 0:56
  sequence start.
• 0:58
  Professor Fred Watson: Space Nuts.
• 0:59
  Professor Fred Watson: 5, 4, 3. 2. 1. 2, 3, 4,
• 1:02
  5, 5, 4, 3. Space
• 1:04
  Nuts astronauts report it feels good.
• 1:08
  Andrew Dunkley: Joining us again to sort all that out is
• 1:11
  Professor Fred Watson Watson, astronomer at
• 1:13
  large. Hello, Fred Watson.
• 1:14
  Professor Fred Watson: Hello, Andrew. Good to see you again.
• 1:16
  Andrew Dunkley: Uh, good to see you too.
• 1:18
  Professor Fred Watson: Yes. Despite the hole in my head.
• 1:20
  Andrew Dunkley: Yeah, yeah. It doesn't look any better than
• 1:23
  last time.
• 1:24
  Professor Fred Watson: It doesn't, does it?
• 1:26
  Andrew Dunkley: No, I mean, you know, it's only been
• 1:28
  minutes. You'd think it would have improved
• 1:30
  by now.
• 1:32
  Professor Fred Watson: That's what happens when you walk into a,
• 1:34
  when you walk into a closed screen door.
• 1:36
  Andrew Dunkley: Yeah.
• 1:37
  Professor Fred Watson: In the dark it hurts.
• 1:40
  Andrew Dunkley: Now that's why they have stuff, um, on,
• 1:43
  on glass sliding doors, you know,
• 1:46
  uh, that, that's a standard safety standard
• 1:48
  required these days so that, you know, the
• 1:50
  door is there.
• 1:51
  Professor Fred Watson: Yeah.
• 1:52
  Andrew Dunkley: But when it's nighttime and it's a screen
• 1:54
  door. Not, not many excuses left there,
• 1:56
  Fred Watson.
• 1:57
  Professor Fred Watson: Really only stupidity, I think is the,
• 2:00
  is the last one. But that's, that's
• 2:02
  my excuse many, many times.
• 2:05
  Andrew Dunkley: Yeah, well, we've all done it.
• 2:09
  Shall we try and answer these questions?
• 2:11
  Professor Fred Watson: We should.
• 2:12
  Andrew Dunkley: Okay, let's go to question one. This one
• 2:14
  comes from John.
• 2:16
  Uh, we know that the Martian Day is 39
• 2:19
  minutes longer than an Earth Day. That's
• 2:22
  about four and a half hours a week. Uh, when
• 2:25
  and if Mars is populated with humans,
• 2:28
  how would we work with the longer
• 2:31
  day, week? Would human
• 2:33
  biology tend to keep to the 24 hour
• 2:36
  day or would we adapt to a longer day,
• 2:38
  Night. Cycle. Cycle. Thanks. Love the show
• 2:41
  and have been a listener since you started.
• 2:43
  Wow, you've got a lot of spare time, John.
• 2:47
  Thank you so much, uh, for sending your
• 2:49
  question in and hope all is well. Uh,
• 2:52
  I love this question because
• 2:55
  you've got a planet that is close enough for
• 2:58
  us to get to in the not too distant future.
• 3:00
  Probably not a
• 3:03
  permanent settlement, but a rotating
• 3:04
  settlement of some kind will be the initial
• 3:07
  stages of humans being on Mars.
• 3:11
  And yet you've got an extra 39
• 3:14
  minutes a day to deal with what
• 3:17
  is going to be the impact.
• 3:20
  Professor Fred Watson: Um, I think we've already, we have
• 3:23
  um, a lot of data on this
• 3:25
  Andrew Dunkley: because the, we've already talked about this
• 3:28
  once before in the deep dark past. Quite a
• 3:30
  lot came up again.
• 3:31
  Professor Fred Watson: Yeah, yeah, because of the, the um,
• 3:34
  rover, um, drivers, they,
• 3:38
  the people who are uh, in command of,
• 3:41
  if I can put it that way, because they don't
• 3:42
  actually drive them directly but in command
• 3:45
  of the rovers on Mars and the two active
• 3:48
  NASA ones at the moment are Curiosity. Uh,
• 3:50
  and perseverance. Uh, they
• 3:53
  Adapt to uh,
• 3:56
  24 hours, 39 minutes day,
• 3:59
  and do it quite successfully
• 4:02
  as far as I've been able to work out.
• 4:06
  Andrew Dunkley: Well I hope so, yeah.
• 4:09
  Professor Fred Watson: Otherwise there might be a pile up on Mars.
• 4:11
  Um, and in fact the reason why I said they
• 4:14
  don't actually drive them is because the
• 4:16
  rovers themselves have got to be to some
• 4:19
  extent autonomous because of the delay
• 4:22
  in signal time to get between Mars and
• 4:26
  the Earth. You can't have video coming back
• 4:28
  from your rover and a steering wheel so that
• 4:30
  you respond to that because you'd have a sort
• 4:32
  of 20 or 30 minute delay probably before
• 4:36
  uh, before um, you turn, before
• 4:38
  the wheels turned on the rover.
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  Andrew Dunkley: I would imagine that the manual
• 4:44
  driving of a rover from Earth
• 4:47
  on Mars would be damn near impossible because
• 4:51
  even your images would be out of sync with.
• 4:53
  Professor Fred Watson: Everything's out of sync. That's right.
• 4:54
  Andrew Dunkley: So you say, oh, there's a rock coming up.
• 4:56
  That was 40 minutes ago, I'll turn
• 4:59
  left now.
• 5:01
  Martin Berman Gorvine: Oops.
• 5:03
  Andrew Dunkley: Yeah.
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  Professor Fred Watson: Ah, um,
• 5:06
  so the rovers drive themselves basically,
• 5:09
  uh, with a lot of assistance, um,
• 5:12
  and monitoring from Earth, uh, in order
• 5:15
  to see what's coming up and see what
• 5:19
  the onboard computers are doing in terms of
• 5:21
  what route they're taking through the rocks
• 5:23
  and debris on Mars. Ah, uh,
• 5:27
  um, but those people, as I understand
• 5:29
  it, do go on to uh, this 24
• 5:32
  hours and 39 minutes day length.
• 5:35
  Uh, I think it's nearing enough to our 24
• 5:37
  hours that I think they adapt quite quickly.
• 5:39
  From my recollection of our previous
• 5:41
  conversation about this Andrew.
• 5:44
  Andrew Dunkley: Yeah, if I remember rightly, we were talking
• 5:47
  about the fact that if you're going to stay
• 5:49
  on Mars long term you would
• 5:51
  have to adapt.
• 5:54
  Um, you wouldn't adapt naturally
• 5:58
  at all you'd have to take catnaps
• 6:01
  or something like that to catch up. Um,
• 6:05
  or something to that effect.
• 6:08
  Professor Fred Watson: Well, yes. So your circadian rhythms
• 6:11
  would, they'd be under stress, they'd change
• 6:15
  and I suppose you'd have a permanent feeling
• 6:18
  of jet lag. Probably what it feels like.
• 6:20
  Andrew Dunkley: It would be tough. I read an article, uh,
• 6:23
  last weekend which I found fascinating
• 6:26
  and it was, um, detailing how
• 6:29
  the eight hour night cycle
• 6:32
  that humans have, like going to bed for eight
• 6:34
  hours, is a myth.
• 6:36
  Professor Fred Watson: Yes.
• 6:37
  Andrew Dunkley: And that, um, it was actually
• 6:40
  something invented by a mattress company back
• 6:42
  in 1938. Have you heard this?
• 6:45
  Professor Fred Watson: No. Yes, I do know that
• 6:48
  we used to sleep twice in the night.
• 6:50
  Andrew Dunkley: That's right. So you go to bed at like 9 o'
• 6:53
  clock and you'd sleep for four hours
• 6:56
  and then you'd get up for two hours and you'd
• 6:58
  do stuff like, stuff we can't talk about on
• 7:00
  this podcast, but other stuff like,
• 7:03
  um, they cited a couple of,
• 7:07
  um, famous people, um, whose names have
• 7:10
  dropped straight out of my head. Um,
• 7:13
  William Shakespeare apparently wrote
• 7:16
  a lot of his famous works between
• 7:18
  1 and 3 in the morning when he got up and
• 7:21
  then he'd go back to bed for four hours. And,
• 7:24
  uh, Beethoven did the same thing with some of
• 7:26
  his symphonies. He wrote some of the
• 7:29
  best works that he ever created
• 7:32
  at 3 o' clock in the morning, um,
• 7:35
  during his wake time between his two sleeps.
• 7:38
  So the eight hour sleep
• 7:41
  that we have at night was an invention
• 7:44
  apparently, to sell mattresses. That's
• 7:47
  what I'm told. Look, I haven't confirmed or
• 7:49
  denied that, but it seems
• 7:52
  possible, I suppose.
• 7:54
  Professor Fred Watson: Well, yes, I think we have,
• 7:58
  uh, I think, um, there's been evidence
• 8:00
  from the earliest times,
• 8:04
  uh, the times when people truly were ancient
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  peoples back thousands of years ago,
• 8:09
  uh, that that's how they lived their lives.
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  Exactly as you've said. And maybe the last
• 8:13
  vestiges of that were keeping
• 8:16
  going in Shakespeare's time and then in
• 8:17
  Beethoven's time. Um, there
• 8:20
  weren't that many clocks around then. There
• 8:22
  were some, but not that many. It wasn't like
• 8:24
  you had a smart watch by your bedside or
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  anything like that. So, uh, it would be a
• 8:30
  natural rhythm that they would use, uh,
• 8:34
  to sleep and wake up.
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  Andrew Dunkley: Yes. Modernization certainly
• 8:38
  messed us up, hasn't it?
• 8:40
  Professor Fred Watson: Yeah, yeah, that's right. I think in that
• 8:41
  case it has.
• 8:42
  Andrew Dunkley: And I think, uh, on Mars, um,
• 8:45
  it will be a pretty difficult thing,
• 8:47
  Professor Fred Watson: I imagine it may be.
• 8:50
  So maybe I can just sidestep here slightly,
• 8:53
  Andrew, um, because I would very much like to
• 8:56
  know uh, what
• 8:58
  answer one of our listeners would give to
• 9:01
  that, and that's Dr. Heidi DeBlock who's
• 9:03
  I think based in Houston, if I remember
• 9:06
  rightly, who is basically a space medic.
• 9:09
  Uh, and um, uh, it will be very interesting
• 9:12
  to hear her take on how humans will adapt
• 9:15
  to that. And if I may, she was in touch with
• 9:18
  us recently to comment on one of our earlier
• 9:20
  questions. Would it be all right if I. Yeah.
• 9:23
  Andrew Dunkley: And that was when we were talking about how
• 9:26
  people deal with um, gravity when they
• 9:28
  get back on Earth after being out in space
• 9:30
  for a while, correct?
• 9:32
  Professor Fred Watson: Yes, that's right. Uh, she
• 9:35
  says, um, I just finished the July
• 9:38
  5th space nuts and wanted to help answer the
• 9:40
  question about how the astronauts feel when
• 9:42
  they land back on Earth. Of course I haven't
• 9:44
  experienced it in person, but have worked
• 9:47
  with plenty of astronauts at landing. In
• 9:49
  particular, all of our, uh, physiology
• 9:51
  changes in space as we are designed for
• 9:54
  1G. Some astronauts are pretty good when
• 9:57
  they land, especially those who are on the
• 9:58
  shuttle and in space. For short time.
• 10:01
  Sorry, for a short time. Some had significant
• 10:04
  problems. They stemmed from the orthostatic
• 10:07
  hypotension as a result from the
• 10:10
  cardiovascular changes, some of the changes
• 10:13
  in the inner ear with balance and knowing
• 10:15
  where you physically are, some mild
• 10:17
  weaknesses, et cetera. These changes are more
• 10:20
  exaggerated with long duration flight in the
• 10:23
  International Space Station. The vision
• 10:25
  problems are called SANS S A N S
• 10:28
  which is an acronym for Spaceflight
• 10:30
  Associated Neuro Ocular
• 10:33
  Syndrome. Our lab is studying that
• 10:36
  as well. That's a whole other fascinating
• 10:38
  issue. I could tell you some
• 10:41
  fun storeys about astronauts and how weird
• 10:43
  some of them feel when they get back. Maybe
• 10:46
  we need to get Heidi on the show. Maybe we
• 10:48
  do. Yeah, no, that's um,
• 10:51
  uh, she has another interesting comment
• 10:53
  actually about the, about the uh,
• 10:56
  Voyager Golden Record. But we might talk
• 10:58
  about that another time. Fair enough.
• 11:00
  Andrew Dunkley: Yeah. All right. Thank you, Heidi. That was
• 11:02
  fascinating.
• 11:02
  Professor Fred Watson: Yeah.
• 11:03
  Andrew Dunkley: Um, what an amazing job working with all
• 11:06
  those incredible people trying to
• 11:09
  figure out how to deal with the zero G
• 11:11
  problem. But uh, on Mars the gravity will
• 11:13
  also be an issue. So, um, there's
• 11:16
  a heck of a lot that needs to be sorted out
• 11:19
  before we um, put people down
• 11:22
  there. Because it's such a long trip to
• 11:25
  get there. It's not like you can go, uh, ah,
• 11:26
  no, this is no good and come straight back.
• 11:28
  Professor Fred Watson: It's not going to be that simple. That's
• 11:30
  right. Once you're on your way. On your way.
• 11:32
  And the only way back is to keep going.
• 11:34
  Andrew Dunkley: Yeah, exactly. Thanks for the question, John.
• 11:37
  Uh, well asked. And yeah, it's not
• 11:40
  going to be a snack, that's for sure. Let's,
• 11:43
  uh, move on to our, uh, next question from
• 11:45
  Dan.
• 11:47
  Martin Berman Gorvine: Hello gentlemen. Dan from the Gold coast
• 11:49
  here. Uh, now I know you've been
• 11:52
  asked a million questions about black holes,
• 11:55
  uh, but I do have a quick two parter and I'm
• 11:57
  hoping that's something you've never had to
• 11:59
  answer before. Really quickly, from the
• 12:02
  point when a black hole is born,
• 12:05
  birth, created, whatever you want to call it,
• 12:07
  uh, how quickly is that growing to become a,
• 12:10
  let's say, supermassive black hole or just
• 12:12
  something a lot bigger? Um,
• 12:14
  or is that not how black holes work and I'm
• 12:17
  not understanding it properly? Two,
• 12:21
  Hypothetically, uh, if there's no matter or
• 12:23
  energy or anything surrounding
• 12:26
  the black hole to take in and let's say
• 12:29
  eat, uh, is the black hole still going to
• 12:32
  grow? Is there more to the black hole growing
• 12:34
  than I understand?
• 12:37
  Um, yeah. Hopefully that made sense and
• 12:39
  hopefully it's worth answering. Love the
• 12:41
  show. Love you guys. Work. Cheers,
• 12:44
  bye.
• 12:45
  Andrew Dunkley: Thank you, Dan. Uh, nice to hear from you.
• 12:48
  Uh, yeah, a couple of questions in that one.
• 12:51
  Um, we never talk about black holes, but we
• 12:53
  will today. Ah, speed of growth.
• 12:56
  Um, that's an interesting one. Um,
• 12:59
  given that we're starting to think that there
• 13:02
  were some absolutely
• 13:04
  enormous, um, black holes in the
• 13:07
  early universe. Um,
• 13:10
  and, and they're looking
• 13:13
  for more and more evidence to see what was
• 13:14
  going on early on. Um, but we've got some
• 13:17
  gargantuan ones still around. Uh,
• 13:20
  so how fast did they get that big? And
• 13:22
  I, um, I'm starting to think, Fred Watson,
• 13:25
  it wouldn't be a stock standard approach.
• 13:28
  Professor Fred Watson: Maybe not, maybe not. Uh, but I mean,
• 13:31
  Dan's asking, uh, one of the
• 13:33
  fundamental questions of astrophysics at the
• 13:35
  moment. This is a very hot topic. Uh, and
• 13:38
  what set the cat among the pigeons and made
• 13:40
  it a hot topic is the James Webb Space
• 13:42
  Telescope. Because, um, until
• 13:45
  that came along, the idea was
• 13:48
  that as basically as Daniel suggests,
• 13:51
  black holes were formed in
• 13:54
  the early universe by exploding stars that,
• 13:56
  um, collapsed at the end of their lives
• 13:59
  to form a black hole. The core would collapse
• 14:02
  to a black hole and that then
• 14:05
  over billions of years that black hole would
• 14:07
  grow. And eventually in our own epoch
• 14:10
  today, 13.8 billion years after the
• 14:13
  Big Bang, uh, you have supermassive black
• 14:16
  holes at the centre of every galaxy. That
• 14:19
  was the old wisdom. But the James Webb
• 14:21
  telescope has turned that completely on its
• 14:23
  head because we have serious
• 14:25
  evidence of supermassive black holes
• 14:29
  within the first 500 million years
• 14:32
  of the universe's existence. And that's
• 14:34
  too quick for, or too
• 14:37
  short a time for this, um, you
• 14:40
  know, this slow accretion of
• 14:43
  stuff, uh, as being the, um,
• 14:46
  the growth mechanism for black holes. Uh,
• 14:49
  it's too short a time for that to be the
• 14:51
  case. Uh, so
• 14:53
  either our ideas of how fast they gobble
• 14:56
  up matter is wrong. And they
• 14:59
  gobble up matter a lot faster than we
• 15:01
  thought. And we actually covered a storey on
• 15:03
  this, I think, about four or five episodes
• 15:06
  ago, because there are some scientists who
• 15:09
  came to conclusion that one of the things
• 15:11
  that we thought limited how fast a
• 15:14
  black hole can gobble stuff up, uh, was
• 15:17
  actually invalid under certain circumstances.
• 15:20
  So that's that one avenue of
• 15:23
  research that's come from the James Webb
• 15:25
  Telescope showing us that, ah, we've got
• 15:27
  these supermassive black holes in the early
• 15:29
  universe. But the other one is the idea of
• 15:31
  the little pink dots or the little red dots
• 15:34
  as they're called. And these are thought to
• 15:37
  be, uh, basically just
• 15:39
  clouds of gas, hydrogen gas,
• 15:42
  which are directly feeding a black hole
• 15:45
  that may have been formed in the Big Bang. In
• 15:48
  other words, you didn't have to have star
• 15:50
  formation and then stars blowing up to
• 15:53
  create black holes in order to kick this
• 15:55
  process off. The Big Bang itself might have
• 15:58
  kicked off the process of black hole
• 15:59
  formation by producing these things that we
• 16:02
  call primordial black holes. Um, and
• 16:05
  they may have turned out to be able
• 16:08
  to grow very quickly, um, by
• 16:10
  immersing themselves simply in big
• 16:13
  clouds of hydrogen and gobbling it all up.
• 16:16
  Andrew Dunkley: Yeah, of course, um,
• 16:19
  when they run out of stuff, they can't grow.
• 16:22
  Is that right?
• 16:23
  Professor Fred Watson: That's right. So that's part two of, uh,
• 16:25
  Dan's question. Uh, what happens when
• 16:28
  there's nothing there for them to eat and
• 16:29
  they become what we call quiescent black
• 16:31
  holes? They don't do anything. They're
• 16:34
  there, uh, and they're still, uh,
• 16:37
  things that, um, if a cloud of hydrogen
• 16:39
  strayed by, they might seize it
• 16:42
  by their own gravity and pull it in. But,
• 16:45
  um, they're not going to go out,
• 16:49
  um, roaming through the universe looking for
• 16:51
  stuff to accrete. In other words, looking for
• 16:53
  a snack.
• 16:54
  Professor Fred Watson: Yeah.
• 16:54
  Andrew Dunkley: Ah, I used to work with a guy whose nickname
• 16:57
  was quiescent black hole. He was there, but
• 16:58
  he didn't do anything.
• 17:03
  Professor Fred Watson: Yes, I think I know who you mean.
• 17:08
  Yeah. Anyway, quiescent black holes, uh, are,
• 17:10
  uh, basically what, uh, Dan has
• 17:13
  described. But the first part of his question
• 17:14
  is absolutely asking the same questions
• 17:17
  that today's astrophysicists are. Uh, it's
• 17:20
  one whose answer we don't know. But the
• 17:22
  consensus will emerge over the next. Probably
• 17:24
  not very long because we're getting so much
• 17:26
  data from the James Webb telescope that I
• 17:29
  think it'll be quite soon before this whole
• 17:31
  issue is resolved, I would think. Sorry,
• 17:34
  I was just going to say when, when there is
• 17:36
  hard evidence of a primordial black hole
• 17:38
  being discovered, one that was created in the
• 17:41
  Big Bang, then that'll be Nobel
• 17:43
  Prize winning science when we get to that
• 17:45
  stage. But it won't be us.
• 17:48
  Andrew Dunkley: Indeed, I was going to suggest that black um,
• 17:50
  holes are probably like humans. Consumption
• 17:53
  will decide how big they get.
• 17:55
  Professor Fred Watson: Maybe that's right, yeah, yeah, we'll have
• 17:58
  Andrew Dunkley: to wait and see. All right Dan. Hopefully uh,
• 18:02
  we covered that for you adequately. Thanks
• 18:04
  for sending in the question. This is Space
• 18:06
  Nuts with Andrew Dunkley and Professor
• 18:08
  Fred Watson Watson.
• 18:12
  Professor Fred Watson: Three, two, one.
• 18:15
  Andrew Dunkley: Space Nuts.
• 18:17
  Our next question, Fred Watson, comes from
• 18:19
  Thomas Reid. Thomas is 11 years old.
• 18:22
  He says something has been troubling me. In
• 18:24
  books I've read they say that the centres of
• 18:27
  galaxies are very big black holes and I
• 18:30
  have a few questions about them but uh, I'm
• 18:32
  only an 11 year old kid so the questions
• 18:34
  might sound silly but here they are. Now
• 18:36
  we've got five questions Fred Watson, so we
• 18:38
  can be brief on on them. Unless you wanted to
• 18:41
  sit here for another couple of hours. Um, if
• 18:43
  Jonty was here we would be a couple of hours.
• 18:46
  Um, can the galactic centre swallow all the
• 18:49
  stars and planets in the galaxy? How big are
• 18:52
  the galactic centres or do we not know,
• 18:55
  uh, if they can swallow up all the stars and
• 18:57
  planets. Is there a limit? If there is a
• 19:00
  limit, what is it? And if there is a
• 19:02
  limit happens when the limit is reached.
• 19:05
  Thank you for taking the time to read this
• 19:07
  and I would love it if you could reply. Well
• 19:09
  we are going to reply right now Thomas. Um,
• 19:13
  yeah, it's great that somebody, uh, so
• 19:16
  young is taking a keen interest in something
• 19:19
  so mysterious as a black hole. Uh,
• 19:22
  we want to start at the top. Can the galactic
• 19:24
  centre swallow all the stars and planets in
• 19:26
  the galaxy?
• 19:27
  Professor Fred Watson: Well so the answer is no. Um, so the
• 19:30
  galaxies are very big. Ours is about 100,000
• 19:33
  light years across. Uh, black holes
• 19:35
  have ah, a kind of sphere of
• 19:38
  influence um, which gravitationally
• 19:41
  stretches to the edge of the galaxy. But by
• 19:43
  the time you get there the gravity of the
• 19:45
  black hole is very, very weak indeed. And
• 19:48
  so it's only in the central region of a
• 19:51
  galaxy where you could get material
• 19:54
  being swallowed up uh, to create this
• 19:57
  activity that we talk about when we Talk
• 19:58
  about active black holes, uh, where
• 20:01
  there's, uh, an accretion disc, a disc of
• 20:03
  material swirling around it. And these jets,
• 20:07
  uh, point basically at right angles to the
• 20:09
  accretion disc, jets of material travelling
• 20:10
  at nearly the speed of light. Quite
• 20:12
  extraordinary. So, um, that's all
• 20:15
  great and black holes, like a factory or a
• 20:17
  furnace doing that, but its stretch is not
• 20:20
  very far. Uh, it's measured
• 20:23
  in light years, but not in hundreds of
• 20:25
  thousands of light years, which would have to
• 20:27
  be to grab everything in the galaxy. So the
• 20:29
  answer is no. The, uh, galactic centre, uh,
• 20:32
  black hole cannot swallow all the stars and
• 20:34
  planets in the galaxy.
• 20:36
  Andrew Dunkley: Uh, so Thomas can sleep well tonight. Um, how
• 20:39
  big are the galactic centres? Do we know how
• 20:42
  big?
• 20:42
  Professor Fred Watson: M. We do. Yes, we do, because
• 20:47
  we can measure the speed
• 20:50
  of rotation of stuff
• 20:52
  swirling around a black hole, if it's an
• 20:55
  active one. And that directly tells you
• 20:58
  the mass of the black hole. Um, because
• 21:01
  the bigger the black hole, the faster the
• 21:03
  stuff is going. And so, um, in terms
• 21:06
  of if, the if by
• 21:09
  big, Thomas means what's their mass?
• 21:12
  Uh, we can measure them quite accurately
• 21:15
  now because we can measure their mass. We can
• 21:18
  also work out their event horizon
• 21:20
  diameter or radius. The event horizon
• 21:23
  is that sort of imaginary sphere around a
• 21:26
  black hole beyond which light cannot
• 21:29
  escape. And so it would appear as a dark
• 21:32
  sphere. So the event horizon is the
• 21:34
  point of no return for anything going into a
• 21:37
  black hole. And it's also the point of no
• 21:40
  escape for light waves. Uh,
• 21:42
  so we can, knowing the mass of a black hole,
• 21:45
  we can calculate how big that event
• 21:48
  horizon would be. And some of the
• 21:50
  supermassive ones, ah, are really very big.
• 21:52
  They're measured in light years, tens of
• 21:55
  light years, perhaps for the supermassive
• 21:56
  black holes.
• 21:57
  Andrew Dunkley: Yeah. It's a level of enormity
• 22:00
  that you just struggle to get your head
• 22:01
  around.
• 22:02
  Professor Fred Watson: Yeah, yeah, I suppose.
• 22:03
  Andrew Dunkley: In terms of the rest of Thomas's questions,
• 22:05
  you've basically answered it with the answer
• 22:07
  to first question, because he's asking if
• 22:10
  they can swallow up all the stars and
• 22:11
  planets. Is there a limit? If there is a
• 22:13
  limit, what is it? Uh, and if there is a
• 22:16
  limit, what happens when the limit is
• 22:18
  reached? Well, the limit is probably
• 22:21
  the local area of the centre of the galaxy
• 22:24
  and what's available to eat.
• 22:26
  Professor Fred Watson: Yes, that's right. So the limiting factor,
• 22:29
  uh, is, um,
• 22:32
  basically what you might call the grasp of
• 22:34
  the black hole, how far it can reach to
• 22:37
  pull something in. And that is
• 22:40
  dependent on how fast the objects are moving.
• 22:43
  So you can have some stars and there are
• 22:45
  some. We've observed them, uh, with infrared
• 22:47
  radiation that are comfortably in
• 22:50
  orbit, uh, around
• 22:53
  the black hole at the centre of our own
• 22:55
  galaxy, which are not being pulled in,
• 22:57
  they're orbiting. And that's because their
• 22:59
  speed is enough to keep them out of the grasp
• 23:02
  of the black hole. Um, their distances from
• 23:05
  the black hole are measured in not two
• 23:08
  dissimilar units from the solar system. Sort
• 23:11
  of half a light day or something like that,
• 23:13
  you know, light day, that's
• 23:16
  the sort of measures that we're talking
• 23:18
  about. Um, which probably
• 23:21
  denies what I just said a few minutes ago
• 23:23
  about, um, some black hole event horizons
• 23:26
  being tens of light years. I don't think they
• 23:28
  are. I think they're smaller than that.
• 23:30
  Joe: Okay.
• 23:30
  Andrew Dunkley: I thought of a way to explain it to Thomas.
• 23:33
  So, uh, Thomas, you've won a competition
• 23:35
  kitchen and you can go to
• 23:37
  McDonald's and eat everything you want.
• 23:40
  Absolutely. Just keep eating until, you know,
• 23:43
  the cows come home. However, you aren't
• 23:46
  allowed to move from wherever you're standing
• 23:48
  and you can only eat what's within reach.
• 23:52
  Once you run out of food, you stop
• 23:54
  growing. And you're the black hole, by the
• 23:57
  way. How's that for an analogy?
• 23:59
  Professor Fred Watson: It's a nice one. I like it. Yes. Yeah,
• 24:01
  because your reach is the sort of
• 24:03
  gravitational force that you can exert. It's
• 24:06
  a good way of putting it.
• 24:07
  Professor Fred Watson: It.
• 24:07
  Andrew Dunkley: Andrew, well done.
• 24:08
  Professor Fred Watson: You should be on the I try
• 24:09
  Andrew Dunkley: to think on 11 year old level, but I'm
• 24:11
  thinking Thomas was probably much brighter at
• 24:13
  11 than I was struggle
• 24:15
  Professor Fred Watson: to get to 11. So do I.
• 24:17
  Andrew Dunkley: Yes, thanks Thomas. That was really terrific.
• 24:20
  Thanks for sending it in and uh, keep on
• 24:22
  listening.
• 24:26
  Professor Fred Watson: Tranquilly Base here. The eagle has landed.
• 24:29
  Professor Fred Watson: Space nets.
• 24:31
  Andrew Dunkley: Final question, Fred Watson, comes from Paul.
• 24:35
  Joe: Hello, Space Nights. Paul here from
• 24:36
  Sunnybris, Vegas, where it's currently
• 24:38
  bucketing down in what is being described
• 24:41
  as a rare rain occurrence.
• 24:45
  Anyway, I
• 24:48
  am currently looking through a very old book
• 24:51
  of mine. Guess it's old compared to
• 24:54
  these students I teach. It was published back
• 24:56
  in 1978. I think I got it in 1980 from
• 25:00
  uh, an uncle of mine, Uncle Jim. Thank you
• 25:02
  very much. It's called Stars and Planets and
• 25:04
  it's probably what got me into
• 25:07
  the whole field of astronomy in the first
• 25:10
  place. At least my interest in astronomy.
• 25:12
  Obviously
• 25:15
  Andrew Dunkley: very, uh, very grateful.
• 25:17
  Joe: I'm on the page where it's talking about
• 25:20
  how the American astronomer Carlo
• 25:22
  Shapley used
• 25:25
  the 1.5 metre reflector on
• 25:28
  top of Matt Wilson in California
• 25:31
  to work out that our sun is
• 25:34
  not at the centre of our galaxy. As was
• 25:36
  previously thought, but is about two thirds
• 25:39
  of the way to the edge. Could you
• 25:42
  please give us some idea how
• 25:45
  he actually managed to do that?
• 25:48
  Was it something about the
• 25:50
  density of stars? I mean, how many
• 25:53
  stars in the field of view?
• 25:56
  Andrew Dunkley: Uh, when you point it one way
• 25:57
  Joe: compared to the other other. How did you do
• 25:59
  it? I'm really curious and I know I could
• 26:01
  Google it, but I'd rather hear it from you
• 26:04
  guys. So thanks in advance. Love
• 26:07
  the show and dare I
• 26:10
  say, keep up the good work. Cheers.
• 26:13
  Professor Fred Watson: Cheers.
• 26:13
  Andrew Dunkley: Paul, thanks for sending that in. Uh,
• 26:16
  sending the question in and uh, we don't know
• 26:18
  the answer, so. But
• 26:21
  we're going to Google it. No, um, uh,
• 26:24
  1978, stars and planets. Uh,
• 26:27
  I tried to look it up. There are umpteen
• 26:29
  books named Stars and Planets.
• 26:31
  Professor Fred Watson: Yeah.
• 26:32
  Andrew Dunkley: So I haven't been able to, you know,
• 26:34
  distinguish one from the other as yet. So,
• 26:36
  um. Uh, yeah, you'll have to do some
• 26:39
  fishing to find the book that, uh, Paul was
• 26:41
  talking about.
• 26:42
  But he wanted to know about
• 26:45
  the man who decided or
• 26:47
  discovered that the sun was not the centre of
• 26:50
  everything. Uh, which was a common
• 26:53
  belief back in the day.
• 26:55
  Professor Fred Watson: It was, um, it was actually 1919 when that
• 26:58
  discovery was made.
• 27:00
  Andrew Dunkley: Was it that recent?
• 27:01
  Professor Fred Watson: Yeah. Wow. Uh, it's one of my favourite
• 27:04
  astronomical discoveries, which is why I
• 27:06
  didn't need to go to Google to look it up.
• 27:08
  Um, so it goes back to the time
• 27:11
  of William Herschel, uh, who was
• 27:14
  a German turned British
• 27:17
  astronomer, worked late in
• 27:20
  the 18th century and early in the 19th
• 27:23
  century, discovered the planet Uranus in
• 27:25
  1780. But what he was doing when
• 27:27
  he discovered Uranus was actually mapping the
• 27:30
  Milky Way. He was observing, um,
• 27:33
  the Milky Way in a very systematic way with a
• 27:36
  relatively small telescope. So sort of
• 27:39
  counting stars in the
• 27:42
  field of view of his telescope and then
• 27:44
  moving the telescope a bit further along the
• 27:46
  Milky Way, counting stars again, how many he
• 27:48
  could see in the field of view and doing that
• 27:51
  and doing it. He couldn't do it all the way
• 27:53
  around the Milky Way. Cause there's parts of
• 27:54
  it that he could never see because they're in
• 27:56
  the southern hemisphere. But he'd got round
• 27:58
  most of it. And what he discovered was that
• 28:02
  the star counts are pretty even all the way
• 28:05
  around. And so that led
• 28:08
  him to build the hypothesis that
• 28:11
  the stars are in a sort of flattened disc,
• 28:13
  which is correct. Uh, but that we're very
• 28:16
  near the middle, which is not correct.
• 28:18
  And the reason why he got that
• 28:21
  erroneous answer was that, uh, when you look
• 28:23
  through, I think it was a 7 inch telescope,
• 28:26
  if I remember right, a telescope of that
• 28:28
  size at, uh, the Milky Way, the stars that
• 28:31
  you see are all relatively
• 28:34
  nearby. They're perhaps 1000
• 28:36
  light years away or something like that,
• 28:38
  maybe a bit more, maybe a couple of thousand
• 28:41
  light years away in the plane of the Milky
• 28:43
  Way. And, uh, that's partly because the Milky
• 28:45
  Way is very dusty. Uh, there's a lot of dust
• 28:48
  everywhere. It's probably better described as
• 28:50
  smoke, but we call it dust in the world of
• 28:53
  astronomy. And so that dust limits how far
• 28:55
  you can see. And so when you look at the
• 28:58
  Milky Way, it does look generally relatively
• 29:01
  even. There's one bit in the constellation of
• 29:03
  Sagittarius where it's brighter and that's
• 29:06
  because you are looking towards, as we now
• 29:07
  know, the galactic centre. But, um, Herschel,
• 29:11
  um, he couldn't see that very well from the
• 29:13
  Northern hemisphere anyway. But he did sort
• 29:15
  of discount that. Uh, he said, by and large,
• 29:18
  it's the same count all the way around, so we
• 29:21
  must be in the middle, uh, roll
• 29:24
  on the years. And in 1919, Harlow
• 29:27
  Shapley, a very gifted American astronomer,
• 29:29
  although he did get one thing, one big thing
• 29:31
  wrong, uh, but what he did was
• 29:35
  he was interested in objects that we call
• 29:37
  globular clusters. And so these are, uh, in
• 29:39
  fact they were named by William Herschel. He
• 29:41
  gave them that name. Uh, clusters of stars
• 29:43
  that appear like a globe. Uh, and
• 29:47
  Harlow Shapley was, uh,
• 29:51
  he was interested in globular clusters. He
• 29:53
  noticed there were a lot of them in our, uh,
• 29:56
  skies. Uh, they tended
• 29:59
  to be different sizes. Uh,
• 30:02
  and he didn't know whether that was because
• 30:04
  they were all the same size and some were
• 30:06
  nearer than others or whether they were
• 30:08
  intrinsically different sizes. But what he
• 30:10
  did notice was that there's a concentration
• 30:13
  of them in the southern
• 30:15
  hemisphere sky. Uh, he was
• 30:18
  observing from California, so he could see,
• 30:20
  see a fair swath of the southern hemisphere
• 30:22
  sky. But he noticed that they were
• 30:25
  concentrated in that direction and that made
• 30:28
  him wonder if that
• 30:31
  was where the centre of the galaxy lay,
• 30:33
  rather than us being near the centre. Uh,
• 30:36
  but then his other step was that he
• 30:38
  recognised that within these globular
• 30:41
  clusters was something called, they
• 30:44
  called them cluster variables, stars that
• 30:47
  varied in a certain way with a
• 30:49
  periodicity of about a day. Uh, today
• 30:52
  we call them RR liry variables. And I
• 30:55
  actually started my astronomical research
• 30:56
  back in the 70s studying these things,
• 30:59
  uh, RR variables. Uh, and
• 31:03
  they are good because they've
• 31:06
  got basically a known distance.
• 31:09
  Uh, if you can see an RR
• 31:12
  variable and identify it as one, you know how
• 31:15
  intrinsically bright it is, uh, and then from
• 31:18
  that you can work out how far away it is.
• 31:21
  And so he found these variable stars in the
• 31:24
  globular clusters and recognised that he
• 31:27
  could draw a chart with the globular
• 31:29
  clusters all at their correct distance on it,
• 31:32
  make a kind of three dimensional map of the
• 31:35
  sky and sure enough, um, they
• 31:37
  concentrated around the galactic
• 31:40
  centre around a point. Uh, he actually got
• 31:42
  the answer wrong because his magnitude, his
• 31:45
  brightness that he had for the, uh, cluster
• 31:47
  variables was incorrect. And I can't remember
• 31:50
  what answer he got, but in my modern PARLANCE
• 31:54
  it's about 25,000 light years.
• 31:57
  The globular clusters themselves cluster
• 32:00
  around a point about 25,000 light years
• 32:03
  away, which is deeply hidden by the dust
• 32:05
  clouds in Sagittarius. So he
• 32:08
  figured out that that's where the centre of
• 32:10
  the galaxy was. A brilliant piece of
• 32:12
  detective work. We know he was right. Uh,
• 32:15
  what he was wrong about was, uh, he had a big
• 32:18
  discussion, I think in 1923,
• 32:21
  just before Hubble recogn that
• 32:24
  galaxies were big things a long way away. Uh,
• 32:27
  Shapley was arguing that galaxies lie within
• 32:29
  our own Milky Way, that they're small objects
• 32:32
  in our own Milky Way. And he was, um,
• 32:35
  arguing. It was a public debate actually,
• 32:37
  between Shapley and a guy called Heber
• 32:39
  Curtis. Uh, Curtis had the answer right. He
• 32:42
  said they're big and a long way off. Uh,
• 32:44
  Shapley said, no, they're small and nearby.
• 32:47
  And it was very soon after that that Hubble
• 32:49
  produced that they're big and a long way. Uh,
• 32:51
  uh, proved that they're big and a long way
• 32:53
  off. So Shapley was wrong in that, but he was
• 32:55
  right about galactic centre.
• 32:57
  Andrew Dunkley: Fantastic. Gee whiz. Um, great
• 33:00
  question, Paul. And, um, yeah, uh,
• 33:03
  if people are looking for that, uh, book
• 33:06
  Stars and Planets, uh, it is out there. Uh,
• 33:08
  look, I've found a couple that were actually
• 33:11
  published around that time that Paul
• 33:13
  mentioned, but not, um, sure if they're the
• 33:15
  ones. I can't remember the author now, um,
• 33:18
  that he said, but I don't think
• 33:19
  Professor Fred Watson: anyway, mentioned an author.
• 33:21
  Andrew Dunkley: I thought he did, but, uh, he might have
• 33:22
  mentioned it.
• 33:23
  Joe: Uncle.
• 33:24
  Professor Fred Watson: It was his uncle he mentioned.
• 33:25
  Andrew Dunkley: Uncle.
• 33:25
  Professor Fred Watson: Uncle Jim.
• 33:27
  Andrew Dunkley: Right. But, um,
• 33:30
  um, so, yeah, thanks, Paul. Thanks for the
• 33:32
  question. And, um, yeah, it's a fascinating,
• 33:35
  um, history in astronomy as we discover these
• 33:38
  things. I think one of my favourite
• 33:40
  moments, I suppose, in astronomical history
• 33:43
  was when they discovered that our sun was a
• 33:46
  star.
• 33:48
  Professor Fred Watson: M. That was a long time ago. Yeah,
• 33:51
  yeah.
• 33:51
  Andrew Dunkley: But for a while there we didn't think of It.
• 33:54
  Professor Fred Watson: I thought it was something else. That's
• 33:55
  right. Something a bit special. Yeah.
• 33:58
  Andrew Dunkley: Um, and I saw that on a BBC documentary
• 34:01
  many years ago and I sat there and went,
• 34:04
  wow. I never thought about that because I've
• 34:06
  always known it to be a star, but for
• 34:09
  generations they didn't.
• 34:12
  Quite intriguing. And why would you. It
• 34:15
  doesn't look like a star.
• 34:17
  Professor Fred Watson: That's right. Uh, uh, it's
• 34:20
  clearly quite different from a star. Uh,
• 34:23
  Andrew Dunkley: incredible.
• 34:24
  Thanks, Paul. Thanks for sending that in. And
• 34:26
  if you have a question for. Thanks to all our
• 34:29
  sender innerers, I've always wanted to say
• 34:31
  that, uh, for their questions. And if you
• 34:33
  would like to send a question, go to our
• 34:34
  website, spacenutspodcast.com or
• 34:37
  spacenuts IO and there's a little
• 34:40
  AMA M tab at the top, which stands for Ask
• 34:43
  me anything. Not me personally, it's the
• 34:45
  rookie royal me. And, um,
• 34:48
  just put your, uh, question in there. It can
• 34:50
  be text or audio. Don't forget to tell us who
• 34:53
  you are and where you're from and have a look
• 34:54
  around. While you're there, don't forget to
• 34:56
  leave a review at your favourite podcasting
• 34:59
  platform. We're all done. Thanks,
• 35:01
  Fred Watson.
• 35:02
  Professor Fred Watson: A great pleasure, Andrew. Um, we, uh,
• 35:04
  continue to get great questions from great
• 35:07
  listeners and long may it continue. Thank
• 35:09
  you.
• 35:09
  Andrew Dunkley: Yes, indeed, we continue to solve and evolve.
• 35:13
  Um, maybe not.
• 35:15
  Professor Fred Watson: I'm not evolving.
• 35:18
  Andrew Dunkley: Once you reach a certain age, evolving
• 35:21
  just is not part of the programme. That's
• 35:23
  right.
• 35:23
  Professor Fred Watson: Yeah.
• 35:24
  Andrew Dunkley: Ask my mum on the Internet. Uh, thanks,
• 35:26
  Fred Watson. We'll see you soon.
• 35:28
  Professor Fred Watson: Sounds great. Thanks, Andrea.
• 35:29
  Andrew Dunkley: Professor Fred Watson Watson, astronomer at
• 35:31
  large. And thanks to Huw in the studio. He's
• 35:33
  just turned up. Um, we started 39
• 35:35
  minutes ago and, um, Huw set his
• 35:38
  clock to a Martian day, so that's why he's
• 35:41
  39 minutes late.
• 35:42
  Professor Fred Watson: Boom, boom.
• 35:43
  Andrew Dunkley: And from me, Andrew Dunkley, thanks for your
• 35:45
  company. We'll see you on the next episode of
• 35:47
  Space Nuts.
• 35:48
  Professor Fred Watson: Bye. Bye.
• 35:49
  Joe: You've been listening to the Space Nuts
• 35:52
  Andrew Dunkley: podcast, available at
• 35:55
  Apple Podcasts, Spotify,
• 35:57
  iHeartRadio or your favourite podcast
• 35:59
  player. You can also stream on
• 36:01
  demand@bytes.com. this has been another
• 36:04
  quality podcast production from
• 36:06
  bytes.com.