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Meteorite Myths, Daylight Fireballs & the Secrets of Ultra-Faint Galaxies · Space Nuts: Astronomy Insights & Cosmic Discoveries

• 0:00
  Andrew Dunkley: Hi there. Thanks for joining us on Space Nuts
• 0:02
  where we talk astronomy and space science. My
• 0:04
  name is Andrew Dunkley and hope, uh, you're.
• 0:07
  Well, coming up in this episode we are going
• 0:10
  to, uh, look at, oh, there's a whole bunch of
• 0:12
  stuff. We might not fit it all in. We'll do
• 0:14
  our very best. Uh, a meteorite versus a
• 0:17
  windscreen. Did it happen the way people
• 0:19
  think? We'll tell you. And over the
• 0:21
  weekend, uh, there was a fireball seen over,
• 0:25
  uh, southeastern states, uh, Victoria, New
• 0:27
  South Wales. The act. We'll talk about that.
• 0:31
  Uh, there's been a bit of chatter on social
• 0:32
  media, including the Space nuts podcast group
• 0:35
  about 3i Atlas. So we'll have
• 0:38
  an update on that. And time permitting, we
• 0:41
  will be looking at a huge black hole and a
• 0:44
  tiny galaxy. I mean tiny as in
• 0:46
  maybe only hundreds or thousands of stars. It
• 0:49
  sounds unusual, doesn't it? And life
• 0:52
  after an asteroid impact. That's all coming
• 0:55
  up on this episode of Space Nuts.
• 0:58
  15 seconds. Guidance is internal.
• 1:00
  10, 9, ignition
• 1:03
  sequence time.
• 1:04
  Jonti Horner: Uh, Space Nuts. 5, 4, 3, 2.
• 1:07
  Andrew Dunkley: 1, 2, 3, 4, 5, 5, 4, 3,
• 1:09
  2, 1. Space Nuts astronauts report
• 1:12
  it feels good.
• 1:14
  And with Fred still away, we are, uh,
• 1:17
  thrilled to welcome again Jonti Horner,
• 1:19
  professor of astrophysics at the University
• 1:21
  of Southern Queensland. Hello, Jonny.
• 1:24
  Jonti Horner: Good morning. How are you going?
• 1:25
  Andrew Dunkley: I am well. Good to see you. Nice backdrop
• 1:28
  too, by the way. What do you got there?
• 1:29
  Jonti Horner: Um, so another of the picks I've been playing
• 1:31
  around with with the telescope I bought about
• 1:33
  12 months ago. This is supplied ease I can
• 1:35
  slap out of shot.
• 1:36
  Andrew Dunkley: Um, very nice.
• 1:38
  Jonti Horner: My chair immediately interferes. The chair
• 1:40
  caption. Human being.
• 1:41
  Andrew Dunkley: But that was the, that was the Chair Nebula.
• 1:44
  Jonti Horner: Absolutely. But yes, I get the angle of the
• 1:47
  chair just right. The AI doesn't recognize it
• 1:49
  as a human being and we get to see it. Yeah,
• 1:51
  pretty good. But I'm going to have to have
• 1:53
  another go at that site. It doesn't quite
• 1:55
  feel right. It looks a little uncanny valley
• 1:56
  to me. So I may have to take some more photos
• 1:58
  later in the ah, year if the wonderful
• 2:00
  thunderstorms we're getting at the minute
• 2:02
  kind of stop because we've had some
• 2:03
  interesting weather appear again over the
• 2:05
  last few days. Um, there was a possible
• 2:08
  tornado within 30km of my house, which is
• 2:10
  cool. And some places got 10 centimeter
• 2:13
  diameter hail and lots of damage and
• 2:16
  yeah, tasty stuff going on and we might get a
• 2:18
  little bit more today and tomorrow. So it's
• 2:20
  another of those events which is spectacular
• 2:22
  and fun to watch. But you also sympathise
• 2:24
  with those who are directly in the thyroid
• 2:25
  line.
• 2:26
  Andrew Dunkley: Yeah, I saw those, uh, tornado
• 2:28
  forecasts pop up. And, uh,
• 2:31
  the bureau does not often go that far,
• 2:34
  uh, with their forecasting, but they were
• 2:36
  pretty confident. So, yeah, we get a few of
• 2:39
  those down our way too.
• 2:40
  Jonti Horner: It is an interesting one. I mean, growing up
• 2:42
  in the uk, I grew up in the country or one of
• 2:44
  the few countries that has the most tornadoes
• 2:46
  per year, which shocks everybody. But they're
• 2:49
  really, really itty bitty diddy ones that are
• 2:51
  associated with frontal systems. And I think
• 2:53
  a lot of Americans say, oh, no, they're not
• 2:55
  tornadoes, they're just gusnados or something
• 2:57
  like that. But in terms of the really
• 2:59
  damaging thunderstorms around the world,
• 3:02
  you've got the Great Plains in the US and
• 3:04
  then you've got the kind of area around
• 3:05
  Bangladesh, I think. But after that kind of
• 3:08
  Southeast Queensland, northeast New South
• 3:09
  Wales is the New South Wales is the third
• 3:12
  best place in the world for these kind of
• 3:14
  storms. And we get fewer tornadoes than
• 3:17
  the Great Plains because we get less wind
• 3:18
  shear at high altitudes. But we get
• 3:21
  equivalent amounts of mega hail and guerrilla
• 3:24
  hail is what they're calling it nowadays when
• 3:25
  you're bigger than giant hail. So we do get
• 3:28
  some really tasty and interesting stuff. And
• 3:29
  I did have one day not long after we built
• 3:32
  this house and moved in where the garage was
• 3:34
  still full of boxes, um, which is always a
• 3:37
  good thing. And this thunderstorm came in and
• 3:38
  suddenly there's the roaring of a freight
• 3:40
  train kind of noise, which was so weird, and
• 3:42
  hailstones, hailstones as my fist started
• 3:45
  coming down and I had to run out with
• 3:47
  blankets and a doona, uh, to cover the
• 3:50
  windscreen of my car to prevent it getting
• 3:51
  damaged. And unfortunately it didn't. Well,
• 3:53
  fortunately it didn't get much worse than
• 3:54
  that. But it was an interesting experience
• 3:56
  for someone who grew up in the uk, where the
• 3:57
  worst weather gets a bit of drizzle and a lot
• 3:59
  of wind.
• 4:00
  Andrew Dunkley: Yeah, yeah, it can get pretty volatile, uh,
• 4:02
  in Australia, and especially in the eastern
• 4:04
  parts.
• 4:06
  Uh, speaking of volatile, our first story
• 4:08
  is about, um,
• 4:12
  what people thought was a meteorite hitting
• 4:14
  the windscreen of a car. And when you see the
• 4:17
  photo, it's. It's one heck of a crack. It's,
• 4:19
  um, it's come in hard, whatever it was. Uh,
• 4:22
  what is the story here?
• 4:24
  Jonti Horner: It's a slightly weird one. Um, there's a
• 4:27
  guy driving along. Um, he's a vet down
• 4:30
  in South Australia, goes by the name of
• 4:32
  Melville Smith. It's his name, Andrew M.
• 4:35
  Melville Smith. Driving along in his
• 4:37
  Tesla. And the Tesla part is important to the
• 4:39
  story. Apparently about 40km out from
• 4:42
  a place called Port Garmin, when suddenly
• 4:45
  there's a really loud smash on his
• 4:46
  windscreen. Um, him and his partner in the
• 4:49
  front seats get showered with glass from this
• 4:52
  shattered windscreen and there's an impact
• 4:54
  crater on the windscreen. Um, and
• 4:57
  obviously the car just kept on driving
• 4:59
  because it's a Tesla and they don't seem to
• 5:01
  notice when they hit things, they just carry
• 5:03
  on. Um, all is good
• 5:07
  now. He thought it was weird, so he reached
• 5:09
  out to the museum in South Australia with
• 5:12
  the idea that this could have been a
• 5:14
  meteorite hitting a car. And that would be
• 5:17
  very unusual. Now we've had occasions in the
• 5:19
  past, um, most famously the Peekskill
• 5:22
  meteorite, and I think it was 1994, where
• 5:23
  meteorites have hit parked cars and done a
• 5:26
  lot of damage. And I think in the case of the
• 5:28
  Peekskill meteorite, it was a fairly hefty
• 5:31
  iron ore, stony iron meteorite that basically
• 5:33
  wrote off the rear end of the car. And the
• 5:36
  person who owned the car was very upset until
• 5:37
  a museum bought the car for a six figure sum,
• 5:39
  which kind of the blow. This, um,
• 5:42
  case, part of the reason that they thought it
• 5:45
  was a meteorite was that there was melting of
• 5:47
  the windscreen as well as just shattering of
• 5:50
  the windscreen. And this, the people at South
• 5:53
  Australia Museum basically came out with a
• 5:55
  fairly neutral statement and said, we're
• 5:56
  going to investigate this. It sounds really
• 5:58
  weird. The melting sounds odd. We're not sure
• 6:00
  what's going on. To me as an
• 6:03
  astronomer though, it speaks to one of the
• 6:04
  kind of really big Hollywood movie driven
• 6:07
  myths, I think, about meteorites.
• 6:10
  There's this idea that if a meteorite falls
• 6:12
  through the atmosphere and you pick it up
• 6:13
  immediately, it'll burn your hands, it'll be
• 6:15
  super, super hot. And that just really
• 6:18
  isn't the case now. I mean, it would be the
• 6:20
  case if something like the dinosaur killing
• 6:23
  asteroid hit the Earth. Uh, that'd get really
• 6:25
  hot, but you wouldn't be picking it up
• 6:26
  because you'd be vaporized and dead. Right.
• 6:29
  Um, for the smaller things that hit the, uh,
• 6:31
  Earth but can make it to the ground intact,
• 6:35
  they typically are slowed down by the
• 6:37
  atmosphere such that by the time they're 10
• 6:39
  or 20 kilometers above the ground, they've
• 6:41
  slowed down to below the speed of sound. And
• 6:44
  so that's why when you see the fireball for
• 6:45
  these things, that fireball terminates still
• 6:48
  quite high in the atmosphere. And while it
• 6:50
  might look like it was just over the next
• 6:51
  hill from you. The thing was still 20 or 30
• 6:54
  kilometers up. That's because the air
• 6:56
  resistance has been enough to slow them down.
• 6:58
  And at that point, they're falling at just a
• 7:00
  couple of hundred kilometers per hour at
• 7:02
  terminal velocity. Now, that's still pretty
• 7:04
  fast. And I mean, I wouldn't want to fall at
• 7:06
  200km an hour into the ground. No, but it
• 7:09
  means that from a height of 20 or 30 km, it
• 7:11
  takes a few minutes to reach the ground.
• 7:14
  What that means is that there's time for the
• 7:16
  rock to equilibrate to get
• 7:20
  the temperature equalized across this entire
• 7:22
  object. Now, the object's been held in space
• 7:24
  in cold storage for millions of years. Years.
• 7:27
  So the interior of the rock is bitterly,
• 7:29
  bitterly, bitterly cold. And, um, they've got
• 7:32
  rocky asteroids, rocky meteorites have a
• 7:35
  fairly high thermal inertia. They're not very
• 7:38
  conductive. And so what
• 7:40
  happens is that the thin outer layer gets
• 7:42
  super hot when it's coming through the
• 7:44
  atmosphere and it's luminous and that's
• 7:46
  getting ablated away. But very little
• 7:48
  of that heat actually is conducted to the
• 7:51
  interior. Once this thing slows down,
• 7:54
  it just keeps falling. And you've got a huge
• 7:56
  amount of cold material and a very, very tiny
• 7:58
  thin layer of hot material. So by the time it
• 8:01
  reaches the ground, meteorites are typically
• 8:03
  cold to the touch. And you're more likely to
• 8:05
  see frost forming on them or water vapor
• 8:08
  condensing on them. It's a bit like maybe
• 8:10
  deep fried ice cream. You deep fry the ice
• 8:12
  cream, you get a hot layer on the outside,
• 8:14
  but the ice cream in the middle stays cold.
• 8:16
  Same kind of idea. The one caveat to that
• 8:19
  is if you get an iron meteorite, a metal
• 8:21
  meteorite, that'll have a much higher thermal
• 8:23
  conductivity. So that can be quite warm when
• 8:25
  it reaches the ground. But rather than being
• 8:28
  super hot like the atmosphere, it's probably
• 8:30
  going to be nearer to room temperature.
• 8:32
  That's fine. What was pointed out to me,
• 8:35
  um, famous astronomer called Rob McNaught got
• 8:38
  in touch with me after he heard me on the
• 8:39
  radio talking about this one. Because I got
• 8:41
  called out, I got cold about this while I was
• 8:43
  driving back from the airport, having picked
• 8:45
  up colleague talked about it and Rob got
• 8:48
  in touch and pointed out that space junk,
• 8:51
  because it comes in at a much shallower
• 8:53
  angle, it actually ablates in the atmosphere
• 8:56
  for much, much, much longer. And it's usually
• 8:58
  much more conductive material. So you put
• 9:00
  those two things together and if a bit of
• 9:03
  space junk were to reach the Ground,
• 9:06
  there is a good chance that would be hot to
• 9:08
  the touch at the time you get to it. So one
• 9:11
  of the. Another thing that you could possibly
• 9:12
  use to differentiate, uh, between whether
• 9:14
  this is a meteorite or a bit of SpaceX
• 9:16
  material. All of that put together
• 9:19
  means that the melting of the windscreen and
• 9:21
  this rock being hot to me, actually kind of
• 9:24
  rules out it being a meteorite.
• 9:26
  Andrew Dunkley: Yeah.
• 9:26
  Jonti Horner: What adds to my argument that it's almost
• 9:29
  certainly not a meteorite is it was a
• 9:30
  nighttime event, the skies were clear in the
• 9:32
  area, nobody saw a fireball. There are no
• 9:34
  reports of a bright fireball, added to
• 9:37
  which are also no reports of sonic events
• 9:40
  or tremors, you know, things that would show
• 9:42
  up in the seismograph. So I think we can
• 9:44
  fairly definitively rule out a meteorite as
• 9:47
  the source of this impact on this car.
• 9:50
  Um, there is the amusing option that it could
• 9:52
  have been a SpaceX on Tesla impact, which
• 9:54
  would have been very entertaining. You know,
• 9:56
  it could have been a bit of space debris
• 9:58
  falling through the atmosphere and almost be
• 10:00
  friendly fire. But again, that would have
• 10:02
  created a very bright fireball that people
• 10:04
  would have seen. So I think we can rule that
• 10:05
  out as well. And the thing that to me
• 10:08
  tells the story here and will point me in a
• 10:11
  direction of investigation is in his
• 10:12
  interview, um, Dr. Melville Smith
• 10:15
  says a truck went past. Five or ten seconds
• 10:18
  later, there was an enormous explosion. Now,
• 10:20
  I've been hit by bits of gravel falling off
• 10:22
  trucks before and had my windscreen damaged.
• 10:24
  Yep. Quite possible that this was a rock that
• 10:26
  fell off that truck that went past, or that
• 10:29
  the truck kicked up a bit of rock from the
• 10:31
  surface of the road that bounced along the
• 10:32
  road and hit the windscreen. I still
• 10:35
  find it hard to see how that would have
• 10:38
  generated heat from the thing that hit the
• 10:40
  windscreen that will cause a bit of melting.
• 10:42
  Even though it's been really hot there, the
• 10:44
  road surface could have been hot. You still
• 10:46
  don't expect the surface of the road to be
• 10:48
  hot enough to melt glass. But the
• 10:51
  kinetic energy of an impact, if you've got a
• 10:53
  more massive impactor coming in a bit more
• 10:55
  slowly, you still can put a lot of energy in.
• 10:57
  And it may well just be that what they're
• 10:59
  mistaking for melting is actually this
• 11:02
  deformation, this crater in the windscreen,
• 11:04
  with all of the material in the windscreen
• 11:06
  that is designed to stop your windscreen
• 11:08
  shattering. And that's done a really good
• 11:10
  job. I know when I've had cracks in my
• 11:11
  windscreen, I'm always surprised how you get
• 11:13
  a break but it doesn't shatter, doesn't
• 11:15
  create a whole windscreen. Modern windscreens
• 11:18
  are designed to be like this multi layer
• 11:20
  thing that stops them doing that. And I'm
• 11:22
  wondering if what they think looked as signs
• 11:25
  of melting was actually the structure of the
• 11:27
  wind windscreen behaving as it's expected to,
• 11:29
  with a bigger impact. And um, because this is
• 11:32
  substantial, I mean it's bigger than some of
• 11:33
  the pictures of hail damage I saw over the
• 11:35
  weekend, for example. And it's bigger than
• 11:37
  the usual chip you see kicked up off the
• 11:39
  road. It's at a size that people might not
• 11:42
  expect it to look like that. So my take on
• 11:44
  this one is very confident it's not a rock
• 11:47
  from space, but it might have been a rock
• 11:48
  from truck.
• 11:49
  Andrew Dunkley: Yes, well, the timing sounds about right. And
• 11:52
  um, yeah, good picture of you on the ABC
• 11:55
  story on the website too, by the way.
• 11:57
  Jonti Horner: Yeah, back when I was younger and slimmer.
• 11:59
  Andrew Dunkley: Yeah, they generally use those photos for us.
• 12:01
  It's very nice. But yeah, it
• 12:04
  reminds me once when um, we, we had a brand
• 12:07
  new car and we decided to take it for a run
• 12:09
  and we were approaching roadworks and we were
• 12:12
  teaching our son to drive at the time. So
• 12:14
  he's hammering along at the minimum,
• 12:17
  you know, maximum, minimum speed of a, ah, a
• 12:20
  learner. And I told him to hit the brakes
• 12:23
  because I didn't want to hit that road work
• 12:25
  when a truck approached and that's exactly
• 12:27
  what happened. We got showered in gravel.
• 12:30
  That brand new car had so much,
• 12:33
  you know, chipping on the front. We were
• 12:35
  very, very upset.
• 12:37
  Jonti Horner: To say it's shocking. I mean, one of the good
• 12:39
  things is, and it's not often that you can
• 12:41
  readily praise insurance companies, but I got
• 12:44
  a big chip on my windscreen at the turn of
• 12:47
  the year last year and um, got in touch with
• 12:50
  my insurance company and they soldered a
• 12:52
  windscreen replacement free of charge without
• 12:55
  it impacting my excess or anything like that.
• 12:57
  Now, well, I guess it's not free of charge
• 12:58
  because I'm paying the insurance premiums.
• 13:00
  But you know, it didn't impact my insurance
• 13:02
  rates, it didn't cause an excess. And I'm
• 13:05
  guessing that's because if you don't fix
• 13:06
  that, uh, it can become a much bigger problem
• 13:08
  and cause them a much bigger accident. So
• 13:10
  from their point of view, it's a very
• 13:11
  valuable investment. But it does mean that
• 13:14
  when we get these kind of events, we can get
• 13:16
  our windscreens fixed fairly easily and
• 13:18
  probably means that the trucks that are
• 13:20
  driving around shedding their loads get off A
• 13:21
  little bit scot free compared to having
• 13:23
  people chasing them down to pay for repairs.
• 13:25
  Andrew Dunkley: Yes, yes indeed. Okay,
• 13:28
  so probably not a meteorite, but probably
• 13:31
  a rock. Um.
• 13:35
  Jonti Horner: Roger, you're allowed to clear also.
• 13:37
  Andrew Dunkley: Space nuts to another event that uh,
• 13:40
  happened over uh, Victoria, New South Wales
• 13:43
  and the act, which, which are next door
• 13:46
  to each other, a fireball, um,
• 13:49
  as recently as yesterday as we
• 13:51
  speak.
• 13:52
  Jonti Horner: Yes. So this is very much breaking news. So
• 13:55
  I'm aware this doesn't air immediately. So
• 13:57
  this was a fireball that was seen on Sunday
• 13:59
  2nd November, which as we're recording at
• 14:02
  the minute, this was actually about 18 hours
• 14:04
  ago from now, roughly. And so that means
• 14:07
  information's still coming in. It was at uh,
• 14:10
  just about 20 to 5 in the evening,
• 14:13
  which means it was broad daylight. So this is
• 14:16
  a daylight fireball. And to me that's always
• 14:18
  a really exciting flag that this could be a
• 14:21
  bigger event because to be bright enough to
• 14:23
  be seen in broad daylight, and particularly
• 14:25
  to be bright enough to be seen widely in
• 14:27
  broad daylight by the general public means
• 14:29
  that this was a fairly substantial thing
• 14:31
  coming into the atmosphere. There are
• 14:33
  observations of this in New South Wales, in
• 14:35
  the act, the Australian Capital Territory
• 14:38
  and down into Victoria. Um, it's also
• 14:41
  a sonic boom and rumbles have been heard
• 14:43
  across Victoria recorded on seismograph
• 14:46
  in Nurbuchen in eastern Victoria.
• 14:50
  So it kind of sounds really promising from
• 14:52
  the point of view of something that is big
• 14:54
  enough to potentially drop a meteorite.
• 14:56
  There's a lot of good footage popping up on
• 14:58
  Facebook groups like the Australian Meteor
• 15:00
  Reports Facebook group. And the
• 15:03
  one thing that gives me a little bit of
• 15:05
  caution about something making it to the
• 15:06
  ground here is on some of those videos I've
• 15:09
  seen, this single looks like it was a very
• 15:11
  fast moving object. Now
• 15:13
  typically really fast moving things
• 15:16
  coming into the atmosphere have a lower
• 15:18
  likelihood of leaving anything to make it to
• 15:20
  the ground. Couple of reasons for that.
• 15:22
  Firstly, they tend to detonate higher up in
• 15:25
  the atmosphere and ah, more things get
• 15:27
  destroyed. But the other thing which I think
• 15:29
  is more to the point is things that come in
• 15:31
  really, really fast are typically moving on
• 15:34
  more comet like orbits and asteroid like
• 15:36
  orbits and therefore are more likely to be
• 15:39
  cometary material than asteroidal material,
• 15:41
  which means they're likely to be more
• 15:43
  friable, more fragile, more dust and
• 15:45
  ice rather than rock and metal. And that
• 15:48
  means that uh, when you see something coming
• 15:50
  in at really high speed, like some of these
• 15:51
  videos seem to show, that possibly
• 15:54
  means that there is a lower chance of
• 15:56
  something surviving to the surface. Doesn't
• 15:59
  mean that there won't be a meteorite found
• 16:02
  from this. Particularly because this, like I
• 16:04
  said, was bright enough to see in broad
• 16:06
  daylight and bright enough to be quite widely
• 16:08
  observed. The fact that the explosion, the
• 16:11
  terminal detonation, the air burst happened
• 16:13
  low enough for people to hear the sonic booms
• 16:15
  and for it to pick up on seismographs, all of
• 16:17
  these things are kind of things that we'd
• 16:19
  look for to say this is a promising event.
• 16:22
  The one thing that's giving me some caution
• 16:23
  is a very high speed. So this is very much a
• 16:26
  developing story. It might be that by the
• 16:28
  time people listen to this episode, they can
• 16:31
  go online and have a look and there'll be
• 16:32
  more information available. I'm honestly
• 16:35
  quite surprised that there's not been more
• 16:36
  media interest in this this morning. Usually
• 16:38
  when there's a bright event like this,
• 16:40
  journalists are ringing up and saying, what
• 16:42
  do you think? And what's happened? Yeah, so
• 16:44
  it may be a little bit of a slow burn, but
• 16:46
  it'll be interesting to see what develops on
• 16:48
  this in the next week or two. Maybe that
• 16:50
  nothing had always found, but it could be yet
• 16:52
  another rock dropping to the surface of
• 16:53
  Australia to give us something to study.
• 16:55
  Andrew Dunkley: Yeah, indeed. Yeah, yeah. Um, I've never
• 16:58
  seen one myself, but we've, we've had a few
• 17:00
  over the years, um, crossing the. The
• 17:03
  sky in Dubbo. One particular daytime
• 17:06
  one that someone filmed many, many years ago.
• 17:09
  And, uh, yeah, quite spectacular.
• 17:12
  Okay, uh, this is Space Nuts with
• 17:14
  Andrew Dunkley and John de Horner.
• 17:21
  Jonti Horner: Space Nuts.
• 17:22
  Andrew Dunkley: Uh, now this next story takes, um,
• 17:26
  us back to 3I Atlas, the, um,
• 17:29
  exo comet, I
• 17:31
  suppose, um, that's currently moving through
• 17:34
  our solar system. Uh, the reason it's
• 17:37
  sort of gained more traction is because
• 17:39
  things have changed and it's
• 17:42
  doing weird things. And of course, that's
• 17:44
  brought out the popular press and a few of
• 17:46
  those other comments that we're not going to
• 17:48
  talk about, but, um, bit of chatter on
• 17:50
  Facebook through the Space Nuts podcast
• 17:52
  group. Uh, what's happening with 3i
• 17:55
  Atlas?
• 17:57
  Jonti Horner: Well, the latest update is that it got a lot
• 18:00
  of coverage last week. Not really because
• 18:02
  anything special was happening, but because
• 18:04
  last week was the point at which Comet Atlas
• 18:06
  went through perihelion. Yeah, so that was
• 18:08
  the time it was closest to the sun.
• 18:09
  Perihelion was on about 30 October,
• 18:12
  so people are obviously interested. Um, I see
• 18:15
  the astronomer who Shall Not Be Named and
• 18:17
  they'll call him Voldemort for now, has come
• 18:19
  out with new stories saying that this Thing
• 18:21
  is changing direction and the aliens are
• 18:23
  definitely invading and rocket engines have
• 18:25
  kicked off. And, um, all this stuff,
• 18:28
  um, and it clearly isn't, you know, we are
• 18:30
  safe, we're not going to be invaded by
• 18:31
  aliens. You don't have to worry and protect
• 18:33
  yourself and buy some wine, Cokes or whatever
• 18:35
  you need to do. Um, does open up the question
• 18:38
  at what point this guy lost his credibility
• 18:40
  with the scientific community. The best part
• 18:42
  of a decade ago. But I wonder at what point
• 18:45
  the Boy who Cried Wolf syndrome will kick in
• 18:47
  to such an extent to overwhelm the Harvard
• 18:49
  affiliation and that the stories this
• 18:52
  guy puts out will stop getting oxygen. That's
• 18:54
  going to be an interesting study in the,
• 18:57
  um, I guess the scientific literacy of
• 18:59
  journalists at the lowest common denominator
• 19:01
  publications. That might be the way I put it,
• 19:04
  but it is definitely not aliens. But what is
• 19:05
  happening with Comet 3i Atlas is it's giving
• 19:08
  us this unprecedented window into the
• 19:11
  behavior of a comet that formed around
• 19:12
  another star. It's also a comet that's coming
• 19:15
  in and traveling through the solar system at
• 19:17
  a higher speed than typical comets do. And
• 19:19
  that's of course, how we know it's from
• 19:20
  another star. What that means, though, is
• 19:23
  that, uh, the typical process by which
• 19:26
  comets do their thing will happen
• 19:29
  in a slightly different way for this object,
• 19:30
  naturally, because it's coming through
• 19:32
  quicker. So things happen at an accelerated
• 19:34
  rate. And that might be what's happening.
• 19:37
  That ties into a paper that's just been
• 19:39
  published that you can read on the archive,
• 19:41
  the preprint server that we as astronomers
• 19:43
  use to spread the word of our work and
• 19:46
  circumvent the exorbitant prices that
• 19:48
  journals charge for you to read. Then we put
• 19:50
  all our papers on Arxiv as well and say,
• 19:52
  don't pay the journal, read it for free here,
• 19:54
  because we're nice like that. Um, this paper
• 19:57
  has been looking at the light curve of this
• 20:00
  comet, so how it's brightening over time.
• 20:02
  And what it's found is that, ah3i Atlas has
• 20:05
  been brightening faster than typical OC cloud
• 20:08
  comets do at this distance from the sun.
• 20:11
  So when you've got a comet coming in from the
• 20:13
  sun, it brightens in
• 20:16
  a slightly predictable rate. And the reason I
• 20:18
  say slightly predictable rate is, uh, there's
• 20:21
  a famous quote from a comet astronomer called
• 20:23
  David Levy that says comets are like cats.
• 20:26
  They have tails and they do whatever the hell
• 20:28
  they want. And there's a truth in that. So
• 20:30
  what we tend to do is when we first find a
• 20:33
  comet, we can work out Fairly quickly, what
• 20:36
  orbit it's moving on around the sun to some
• 20:39
  degree, how far away it is from the sun and
• 20:41
  how quickly it's moving. And, um, by knowing
• 20:43
  how far away it is and how bright it is, when
• 20:45
  we find it, we can work out
• 20:48
  an absolute magnitude for it, which is a
• 20:50
  quantity that characterizes whether it's a
• 20:52
  big, bright comet or a small, faint comet.
• 20:55
  And we can use that and, um, the orbit it's
• 20:57
  going around the sun to make a first
• 20:59
  prediction of how the comet will brighten or
• 21:00
  fade. Then, as we observe it over a little
• 21:03
  bit of time, we can characterize how its
• 21:06
  activity is changing and work out not only
• 21:08
  whether it's a big comet or a small comet,
• 21:10
  but whether it's an active comet or whether
• 21:12
  it's a very quiescent comet. So whether it's
• 21:15
  brightening rapidly or brightening slowly
• 21:18
  for a comet of that size. And over time, this
• 21:20
  allows people to predict the brightness of
• 21:22
  the comet going forward. And assuming the
• 21:25
  comet doesn't do anything unusual, like
• 21:27
  fragmenting or having an outburst or
• 21:29
  something like this, we can get a fairly good
• 21:32
  handle several months ahead of time, of how
• 21:35
  bright the comet's going to be with a certain
• 21:37
  degree of uncertainty. And so we've got a
• 21:39
  fairly good feeling for how a comet coming in
• 21:42
  from the Oort Cloud that is about the size of
• 21:44
  Comet ATLAS should brighten.
• 21:47
  Now, some comets brighten a bit quicker
• 21:48
  because they're more active. Some brighten a
• 21:50
  bit slower. What's happened with Comet ATLAS
• 21:53
  is it started to brighten significantly
• 21:55
  quicker than we'd expect a typical Oort cloud
• 21:58
  comet to brighten at the same distance from
• 22:00
  the Sun. And that's what this paper's all
• 22:02
  about. Basically, the comet's brightening
• 22:04
  unusually quickly. Now, there's a
• 22:06
  variety of possible explanations for that,
• 22:08
  and we won't know which answer is true until
• 22:11
  we do more study. The most common reason
• 22:13
  for a comet to brighten unusually quickly
• 22:16
  is often linked to the comet's head becoming
• 22:18
  a bit more diffuse because it's a comet
• 22:20
  fragmentation event. So the comet's
• 22:23
  falling apart. You release a lot of
• 22:25
  dust as the comet falls apart, but you also
• 22:27
  increase the surface area exposed to
• 22:29
  sunlight, which means you increase the
• 22:31
  activity. And the analogy here will be the
• 22:33
  difference. If you've ever had the
• 22:34
  effervescent tablets you put in water and you
• 22:36
  let them dissolve. If you get two of them and
• 22:39
  you put one in a glass of water fully intact,
• 22:41
  and you crumble the other one up and drop in
• 22:43
  the crumbled one, the crumbled one reacts
• 22:45
  much quicker, and it foams up really quickly.
• 22:48
  The solid one takes a while to go.
• 22:51
  That could be the case. We'll only know if we
• 22:53
  observe for a little bit of time. And that
• 22:54
  wouldn't necessarily be that unsurprising.
• 22:56
  There is a suspicion that this comet, 3i
• 22:58
  atlas never actually got close enough to its
• 23:01
  parent star to be active as a comet. So it
• 23:03
  will be more equivalent to what we call the
• 23:05
  new Oort cloud comets coming through for the
• 23:07
  very first time, rather than one that's had
• 23:09
  multiple perihelion passages. And, um, we do
• 23:12
  know that new comets have a tendency to
• 23:14
  fragment more often than older comets that
• 23:16
  have been more baked in, essentially. So
• 23:18
  that's one possible explanation.
• 23:19
  But I think another one that's really
• 23:21
  interesting and would probably fit quite well
• 23:23
  is that our models of cometary
• 23:26
  activity have built within them. Though, uh,
• 23:29
  we don't normally think about it, the time at
• 23:31
  which activity driven by different ices
• 23:34
  kicks in. So as the comet gets closer to the
• 23:36
  sun and it gets hotter, different ices on
• 23:39
  the surface will reach the temperature where
• 23:41
  they can no longer be ices, and they turn
• 23:43
  from ice to gas in a process called
• 23:45
  sublimation. And that's what drives the
• 23:46
  activity of the comet. And as a comet heats
• 23:49
  up, different ices turn on, effectively.
• 23:52
  Now, when you're far from the sun, water ice
• 23:55
  is really cold and stays as water ice. But
• 23:57
  other volatile materials like carbon monoxide
• 24:00
  and carbon dioxide are, uh, what drive the
• 24:02
  activity of a comet when it's further from
• 24:04
  the Sun. Now, as it comes in closer, it
• 24:07
  heats up and water turns on. And certainly
• 24:09
  within a few astronomical units of the sun.
• 24:11
  Water is usually the dominant driving factor
• 24:13
  of comet reactivity. With Comet
• 24:16
  atlas, this brightening is happening
• 24:19
  interior to the distance where most comets
• 24:21
  would have turned on their water emission.
• 24:23
  But Comet ATLAS is coming in quicker, and
• 24:26
  so therefore, it is heating up
• 24:29
  due to the radiation from the Sun. But as
• 24:31
  it's coming in quicker, maybe it was closer
• 24:34
  to the sun by the time that the heat from the
• 24:36
  sun got to be enough to penetrate the surface
• 24:39
  material and start kicking on the water
• 24:41
  activity. But then that heating is happening
• 24:43
  really quickly because the distance to the
• 24:45
  sun is dropping quite fast. And so therefore,
• 24:48
  you've had this spike in temperature and
• 24:49
  therefore a spike in activity as the water
• 24:52
  activity is turned on, not so much as a
• 24:55
  trickle, but as a flood. And that ties in
• 24:57
  actually quite nicely to some of the recent
• 24:59
  stories in the last few weeks about the water
• 25:01
  vapor, uh, and the water being emitted from
• 25:03
  the comet I saw some article about the comet
• 25:06
  emitting a jet of water like a firehose. So
• 25:09
  this is one of those narratives that seems to
• 25:11
  fit together really, really well. And it
• 25:13
  could just be that the high speed of the
• 25:14
  comet means that it got closer in before the
• 25:16
  water turned on. And now it's catching up for
• 25:19
  lost time. What this means for the future is
• 25:22
  that, in all honesty, we are
• 25:24
  less confident in predicting the future
• 25:26
  brightness of the comet than we normally
• 25:28
  would be. Because it's all this cometary
• 25:30
  activity going on. It's effectively having a
• 25:32
  bit of an outburst. When we were talking
• 25:35
  about it months ago, we always said it would
• 25:36
  never get brighter than about magnitude 11,
• 25:38
  magnitude 12. There's a chance it might get a
• 25:41
  little bit brighter than that now. But it's
• 25:42
  really hard to model. We don't know whether
• 25:45
  the comet will brighten further than
• 25:46
  expected, brighten really rapidly, go back to
• 25:49
  behaving as normal. It might fade away
• 25:52
  because suddenly it's had this outburst. It's
• 25:54
  clogged itself up. It might even go out
• 25:56
  relatively quickly like a bit of a snuff
• 25:58
  torch if it has fully fragmented and
• 26:00
  disintegrated. And we saw that with the great
• 26:03
  comet earlier this year, Comet Atlas, which
• 26:06
  was really bright and spectacular. And then
• 26:07
  became the headless comet because its head
• 26:09
  just totally disintegrated. And all you were
• 26:12
  left was this tail gradually drifting through
• 26:14
  space with no comet to call its own. Yeah, so
• 26:17
  we just, honestly, we just don't, um, know
• 26:19
  There's a lot more to learn. And, yeah, this
• 26:22
  is getting a lot of hyperbolic stories
• 26:25
  about it and people arguing that it's
• 26:27
  actually the mass driver engine that's turned
• 26:29
  on as it will reroute itself to the Earth.
• 26:31
  Courtesy Harvard astronomer of doom.
• 26:34
  But in reality, this is why these objects are
• 26:36
  so exciting, because they give us a window
• 26:38
  into comets with different compositions that
• 26:40
  formed around different stars. And also how
• 26:42
  comets behave at higher speed. You know,
• 26:45
  this is why it's cool.
• 26:46
  Andrew Dunkley: Yeah. Uh, I must say I'm surprised that this
• 26:49
  one's receiving so much attention. But I
• 26:52
  shouldn't be surprised because it is a little
• 26:54
  bit different to most.
• 26:56
  And, um, being an ex. Extra, um,
• 27:00
  solar comet, um,
• 27:03
  it just, Just makes it that much more
• 27:05
  interesting. So, yeah, um, lots to learn,
• 27:07
  really. Uh, so, yeah, this one, uh, will no
• 27:10
  doubt, uh, be getting some attention for some
• 27:13
  time to come. Um, would be a pity if
• 27:16
  it kind of, you know,
• 27:19
  lost itself in our solar
• 27:21
  system. But, um, that's just the way it goes
• 27:24
  sometimes.
• 27:26
  Jonti Horner: Absolutely.
• 27:26
  Andrew Dunkley: Well, there it is.
• 27:28
  Jonti Horner: Yeah.
• 27:29
  I was going to say, while we're on the topic
• 27:31
  of comets, I should just flag up to everyone,
• 27:32
  particularly the Northern Hemisphere people,
• 27:34
  but also us in the Southern Hemisphere, a
• 27:37
  tiny little bit. Comet Lemon, which is
• 27:39
  getting a lot of media coverage, is at its
• 27:41
  brightest pretty much bang at the minute.
• 27:44
  It's about magnitude 4.3, which means
• 27:46
  technically it's visible to the naked eye.
• 27:47
  But in reality, because comets are diffuse
• 27:50
  objects, it'll be a very hard spot unless
• 27:52
  you're somewhere incredibly dark. But it is
• 27:54
  very photogenic comet. It is most visible to
• 27:57
  people in the Northern Hemisphere. For those
• 27:59
  of us in Australia, it's basically lost in
• 28:02
  the glare of twilight, even though it's at a
• 28:04
  declination where it could be visible if it
• 28:06
  was in a dark sky. It's too near the sun in
• 28:08
  the sky. But these few days around now,
• 28:10
  the next week or so, it's the best chance
• 28:12
  we'll get to see it from Australia while it's
• 28:15
  bright. And, um, that'll be very low in the
• 28:17
  west after sunset, um, as the sky
• 28:20
  gets darker. Have a look on
• 28:22
  planetarium programs like Stellarium to find
• 28:24
  the location. But my memory is that, uh, the
• 28:27
  planet Mercury is going to be visible low to
• 28:29
  the west after sunset. And if you can find
• 28:30
  Mercury and you go to the right of Mercury,
• 28:33
  it's about the same height as Mercury on the
• 28:35
  7th or 8th of November. So worth
• 28:38
  looking at. It is not the best comet of the
• 28:41
  year. We already have that back in January,
• 28:42
  despite what some of the articles said. But
• 28:44
  if you do want to see a comet that's
• 28:46
  borderline bright enough to see the naked
• 28:47
  eye, that's your one. It should be quite good
• 28:49
  in binoculars and certainly for people doing
• 28:52
  astrophotography. Have a look online. Some of
• 28:54
  the photos of this thing are really
• 28:55
  spectacular. There's people who've done, um,
• 28:57
  yeah, pretty clever things imaging it with
• 28:59
  lovely foreground views like lakes or rocks
• 29:02
  or castles or whatever. So there's lovely
• 29:04
  images of this comet out there if you want to
• 29:07
  feast your eyes on what people who are
• 29:08
  talented photographers can do.
• 29:10
  Andrew Dunkley: Yes, very good. Uh, that's Three Eye, Three
• 29:13
  Eye Atlas. Uh, now, um,
• 29:16
  oh, and you can, you can read, uh, about
• 29:18
  that, uh, on, um, the archive website,
• 29:21
  as Jonti mentioned.
• 29:25
  Jonti Horner: Okay.
• 29:25
  Andrew Dunkley: We checked all four systems and being with a
• 29:27
  girl, space nats, uh, let's move on to
• 29:30
  this really interesting story. An enormous
• 29:33
  black hole has been found. But what's really
• 29:36
  interesting is the galaxy that it's in is
• 29:39
  tiny. And when I, when I read into the
• 29:42
  details of this Story. We're talking about a
• 29:45
  galaxy with very few stars,
• 29:48
  surprisingly few stars.
• 29:50
  Jonti Horner: And, um, this fascinated me reading it now. I
• 29:52
  always say, particularly when we're doing the
• 29:54
  questions, and we get lots of cosmology type
• 29:56
  questions. I'm not a cosmologist, I'm not a
• 29:58
  galactic type astronomer. Uh, my expertise
• 30:01
  and my focus is very much on the things
• 30:03
  closer to home. So I tend to try and pick
• 30:05
  stories where I can talk from a position of
• 30:07
  some authority rather than no authority, if
• 30:09
  that makes sense. But this story was so cool,
• 30:12
  I thought we had to include it, even if, um,
• 30:14
  it might be a little bit of the blind leading
• 30:16
  the blind in a way. But this is one of the
• 30:17
  Milky Way's satellite galaxies. And our
• 30:19
  galaxy has many, many satellites, from the
• 30:22
  incredibly large and bright, large and Small
• 30:24
  Magellanic Clouds, which we can see here in
• 30:27
  the Southern Hemisphere, really high in the
• 30:28
  sky at the minute, really spectacular, down
• 30:31
  to really, really tiny satellite galaxies
• 30:33
  that almost push our understanding of what it
• 30:36
  means to be a galaxy. And this galaxy
• 30:39
  is one such galaxy. It's what's described as
• 30:41
  an ultra faint dwarf galaxy. And there are
• 30:44
  likely an enormous number of these in space
• 30:47
  that we just don't find. I guess the analogy
• 30:49
  I'd use here is that if you go out and look
• 30:51
  at the stars in the night sky, the stars that
• 30:53
  you're seeing are very much the superstars of
• 30:55
  our galaxy. They're stars that are much more
• 30:57
  massive than the sun that we're seeing from
• 30:59
  great distances. The most common stars in
• 31:02
  the galaxy are the dim little red dwarfs like
• 31:05
  Proxima Centauri. And Proxima is fairly
• 31:07
  massive and fairly luminous for a red dwarf.
• 31:10
  It is the closest star to the solar system,
• 31:12
  and it's too fancy with the naked eye by a
• 31:14
  factor of 100 times. So there's lots and lots
• 31:17
  of very small, faint things that until we
• 31:19
  have telescopes, we couldn't find at all.
• 31:21
  There are always more small things than big
• 31:23
  things. So it seems likely that there are,
• 31:26
  uh, many, many, many faint,
• 31:28
  ultra faint dwarf galaxies that have simply
• 31:31
  not been discovered even in our local area,
• 31:33
  never mind at the far parts of the cosmos.
• 31:36
  When we talk about galaxies that are many
• 31:38
  hundreds of millions of light years away,
• 31:40
  we're only seeing the superstars. We're not
• 31:41
  seeing the little baby ones like this. The
• 31:44
  galaxy in the story here is called Segue one.
• 31:47
  And I must admit that I don't think I'd ever
• 31:50
  heard of this, or I'd only ever heard of it
• 31:51
  in passing before this story came out. It is
• 31:54
  really tiny and very Anonymous. It's about
• 31:57
  75,000 light years from the Earth.
• 32:00
  Like I say, it's one of our satellite
• 32:01
  galaxies. And, uh, our, uh, best
• 32:03
  observations. There's a photograph in the
• 32:05
  Space.com article which is fabulous. It says,
• 32:07
  you know, here's this dwarf galaxy with only
• 32:09
  a handful of stars, and I'm not sure where
• 32:11
  the galaxy is because there's so little in
• 32:13
  the photograph. That's what it's like. And so
• 32:15
  you're talking here of just a few hundred or
• 32:17
  a few thousand stars held together.
• 32:21
  Now, that's been a puzzle for galaxy
• 32:23
  astronomers for a long time, because so few
• 32:25
  stars have so little mass that the
• 32:28
  galaxy shouldn't hold itself together. The
• 32:30
  galaxy should have dispersed over time. And
• 32:33
  for a long time, the best explanation people
• 32:35
  have had for this is that these are kind of
• 32:37
  dark matter galaxies, that they've got a
• 32:40
  massive dark matter agglomerated as a big
• 32:42
  dark matter halo, giving you enough mass
• 32:45
  there that we can't see to provide enough
• 32:47
  gravity to hold this very small number of
• 32:49
  stars together to keep them kind of whizzing
• 32:51
  around one another. And that kind of makes
• 32:54
  sense. We know that a lot of galaxies have
• 32:57
  big amounts of dark matter. In fact, all
• 32:58
  galaxies do. So you could almost have dark
• 33:01
  matter galaxies where you've got a clump of
• 33:02
  dark matter with very few stars. That kind of
• 33:04
  made sense. But the new story
• 33:08
  comes from improved observations of this
• 33:10
  galaxy, coupled with some computational
• 33:12
  numerical orbital modeling. And what they've
• 33:14
  found is that the stars near the middle of
• 33:16
  Segue one are, uh, going round the middle
• 33:19
  really, really quickly. Now, that allows us
• 33:21
  to take a measurement of the mass that is
• 33:24
  closer to the middle of the galaxy than those
• 33:26
  stars are. So anything feels
• 33:29
  gravity from the things closer to the middle
• 33:31
  than they do fundamentally. So what this
• 33:34
  means is by observing those stars that are in
• 33:36
  the middle of this galaxy, seeing them move,
• 33:38
  we can weigh the very innermost parts of that
• 33:41
  galaxy. And, um, what that tells us is that
• 33:44
  there is about 450,000 times
• 33:46
  more mass in the middle of that galaxy than
• 33:48
  the mass of our sun that we cannot see.
• 33:51
  Andrew Dunkley: Yeah.
• 33:51
  Jonti Horner: Which makes this a black hole, and it makes
• 33:54
  this a supermassive black hole, albeit a
• 33:57
  relatively low mass supermassive black hole
• 33:59
  compared to the one in the middle of Milky
• 34:01
  Way. Now, that in itself is not hugely
• 34:04
  unexpected. Pretty much all big galaxies have
• 34:06
  supermassive black holes, but we've not
• 34:08
  really seen them in teeny, tiny little
• 34:10
  galaxies like this before. Even
• 34:13
  more so, we've not really seen cases where
• 34:16
  there are galaxies whose black hole is, is
• 34:18
  more than 10 times the mass of all of the
• 34:20
  stars we can see in that galaxy. Feels like a
• 34:23
  really kind of weird imbalance. The black
• 34:25
  hole is more massive than the galaxy around
• 34:27
  it seems to suggest there would have been
• 34:29
  enough material for. But it's
• 34:32
  really weird from a few reasons, but really
• 34:34
  cool in the same way in that it's suggesting
• 34:36
  that this galaxy is not held together by dark
• 34:38
  matter, it's held together by this
• 34:40
  supermassive black hole at the middle. That
• 34:43
  maybe gives us an insight into how other
• 34:45
  ultra faint dwarf galaxies behave. This is
• 34:48
  probably not alone suggesting that there
• 34:50
  could be a lot more of these supermassive
• 34:52
  black holes out there in the cosmos than we
• 34:54
  thought. It also possibly is a bit of a
• 34:56
  hint that segue one was once a more massive
• 34:59
  galaxy. You know, if you think about the
• 35:01
  idea of the mass of this supermassive black
• 35:03
  hole and think, well, what kind of galaxy
• 35:05
  would normally expect to have a mass massive
• 35:08
  black hole like that in its center? How many
• 35:10
  stars should it have had? Maybe Segue one was
• 35:13
  like that in the past, but because it's so
• 35:15
  close to the Milky Way, it has been
• 35:18
  continually stripped and denuded of its stars
• 35:20
  from the outside inwards by our galaxy,
• 35:23
  essentially playing Pac man and gobbling it
• 35:25
  up going nom nom, nom, essentially, which is
• 35:27
  how galaxies grow. Galaxies grow through
• 35:29
  cannibalizing their neighbors. And we see
• 35:31
  that to an extent even with our largest
• 35:33
  satellite galaxies which have been disrupted
• 35:35
  and devoured a bit by the Milky Way and will
• 35:37
  eventually be gone. So there's a lot in this,
• 35:39
  it is a really fascinating story, albeit one,
• 35:42
  like I say, where I'm much further from being
• 35:44
  an expert than a lot of the other stuff that
• 35:46
  we talk about. Um, but you can find more
• 35:48
  about it online. And it is just a really cool
• 35:50
  little story, you know, it may well totally
• 35:53
  revolutionize our understanding of how the
• 35:54
  smallest galaxies work.
• 35:56
  Andrew Dunkley: Yes, indeed. Um, I, I, you kind of took the
• 35:59
  question out of my mouth, but I wasn't
• 36:01
  thinking of a neighboring galaxy stripping
• 36:03
  the, the stars away from segue. I was
• 36:06
  thinking the black hole might be devouring
• 36:08
  the stars within galaxy, but.
• 36:11
  Jonti Horner: Uh, you'd probably get a bit of that as well
• 36:13
  because the thing with the black hole is
• 36:16
  that uh, its gravitational pull is exactly
• 36:18
  the same as, ah, a group of objects of the
• 36:20
  same mass would have. Um, so it doesn't
• 36:23
  really pull things in any harder than the
• 36:24
  material that was there beforehand. But if
• 36:27
  you've got a neighboring galaxy like the
• 36:28
  Milky Way stirring up and um, numbing
• 36:31
  on this galaxy. It will also stir up the
• 36:33
  orbits of the stars in that galaxy, making
• 36:36
  some of them sufficiently elongated that they
• 36:38
  could fall onto that central black hole. So
• 36:40
  it's likely that the process of the Milky Way
• 36:42
  eating this galaxy has also led to the black
• 36:45
  hole in the middle of it getting a bit of a
• 36:47
  feed as well. A bit like the, um, white dwarf
• 36:50
  we were talking about last week, getting fed
• 36:52
  asteroids by the planets going around it.
• 36:54
  Same kind of idea.
• 36:55
  Andrew Dunkley: Yeah. It sounds like these stars, uh, in
• 36:57
  segue, are like a school of fish being
• 36:59
  attacked from all sides by predators, and
• 37:02
  eventually they'll just all be gone. Uh,
• 37:05
  yeah, you can read all about that@space.com
• 37:07
  or, or you can look at the paper that was
• 37:10
  published in astrophysical journal letters.
• 37:15
  3, 2, 1.
• 37:18
  Space nuts.
• 37:20
  I think we've got time for one more quick
• 37:22
  yarn, Jonti. And this is a story
• 37:25
  that I find fascinating, uh, and certainly
• 37:28
  relates to, um, the history of Earth in many
• 37:31
  ways. Uh, life after an
• 37:33
  asteroid impact. Now, a big
• 37:36
  asteroid conking the Earth, uh, can
• 37:39
  have cataclysmic effects, as
• 37:41
  we've seen in our history. And the,
• 37:44
  um, geology certainly backs that up.
• 37:47
  But, um, you know, fast forward a few
• 37:50
  gazillion years or whatever the number is,
• 37:53
  uh, and life does return. Um,
• 37:57
  they've been looking into this effect,
• 37:59
  haven't they?
• 38:00
  Jonti Horner: Now, this is some lovely research that's come
• 38:02
  out of Finland, where there's a beautiful
• 38:05
  impact crater. And I will apologize for
• 38:07
  anybody listening who speaks a beautiful
• 38:08
  Finnish language. Um, but there's a beautiful
• 38:11
  impact crater, uh, in Finland called Lake
• 38:13
  Lapijavi, which is an impact
• 38:16
  basin about 23 kilometers across that was
• 38:19
  formed 78 million years ago. It's a
• 38:22
  fairly hefty impact. It's the kind of thing
• 38:24
  that would be a bit of a drama if you lived
• 38:26
  in that part of the world, but not large
• 38:28
  enough to cause a global mass extinction
• 38:30
  event. So this is nothing like the one that
• 38:32
  killed the dinosaurs 65, 66 million
• 38:35
  years ago. This is a bit smaller, a bit more
• 38:37
  run of the mill. Now, there's a vague rough
• 38:40
  rule of thumb for impacts that if an impact
• 38:43
  happens, the size of the crater is about 19
• 38:45
  times the diameter of the impactor. So that
• 38:48
  tells me that the rock that hit to create
• 38:50
  this crater was probably a bit more than a
• 38:53
  kilometer across. So it's fairly substantial.
• 38:56
  That's the kind of impact that statisticians
• 38:59
  would argue would kill about a quarter of the
• 39:00
  world's human population. So not an
• 39:03
  extinction event, but a very bad day.
• 39:06
  The Team that have looked into this were
• 39:09
  really interested in how quickly
• 39:11
  life can reestablish itself in the
• 39:14
  rocks left behind from an impact. Because you
• 39:16
  have an impact happen, it superheats
• 39:19
  and sterilize the rocks. This would have
• 39:21
  sterilized the rocks in the impact site by
• 39:23
  heating them to more than 2,000 degrees C.
• 39:25
  That's 3,600 Fahrenheit for the American.
• 39:29
  Enough to kind of really sterilize the place
• 39:31
  it hit. It would have also, though, caused
• 39:34
  huge temperature gradients. It would have
• 39:36
  shattered the rocks, and it would have driven
• 39:38
  some interesting chemistry. So that means
• 39:40
  that, uh, once the clouds clear and there's
• 39:43
  time for things to settle down, you have a
• 39:45
  site here that is similar to the kind of
• 39:48
  conditions at, uh, locations where people
• 39:50
  think the first life on Earth may have got
• 39:52
  started. So there's some interesting
• 39:55
  what happened after. So to study that,
• 39:58
  this team have gone to the, um,
• 40:01
  store of drill cores that they can get to in
• 40:03
  Finland, where there are, uh, results,
• 40:06
  resources left behind from drilling
• 40:08
  expeditions that dug into this crater lake
• 40:11
  back in the 1980s, 1990s. Now this is a
• 40:14
  really good example, incidentally, of how
• 40:16
  legacy materials continue to have
• 40:19
  worth. And we've talked about that with the
• 40:21
  rocks from the Apollo missions, where they
• 40:22
  put a lot of them and preserve them for
• 40:24
  future use, because our technology improves
• 40:27
  all the time. So we can go back and look at
• 40:29
  things that were collected in the past and
• 40:30
  get new insights. So the team
• 40:33
  went back to these rocks that, uh, were dug
• 40:35
  up back in the 80s and 90s from drill
• 40:38
  cores that dug down all the way into this
• 40:41
  crater lake, into the floor of it. And they
• 40:43
  got 33 different drill core samples from
• 40:45
  different locations, looked at them
• 40:48
  essentially with a microscope and a pair of
• 40:49
  tweezers, and, um, plucked out a number of
• 40:52
  crystals of calcite and. And
• 40:55
  what was the other rock? There were a couple
• 40:56
  of things, calcite and pyrite, these rocks.
• 40:59
  And they use these for chemical analyses. And
• 41:01
  what they were interested in doing was
• 41:03
  getting a chronology of what happened in the
• 41:06
  years after this crater was formed.
• 41:09
  Now, similar work has been done before for
• 41:11
  the Rhys Crater in Germany and the Horton
• 41:13
  Crater in Canada, which suggested for those
• 41:16
  craters, the material under and around the
• 41:19
  crater cooled fairly quickly in geological
• 41:21
  times. For those craters, it cooled to about
• 41:24
  50 degrees C within a quarter of a million
• 41:26
  years. For the Reese Crater and for the
• 41:28
  Horton Crater in Canada for about 50,000
• 41:30
  years. So that cooled down fairly quickly.
• 41:33
  But this Finnish team, looking at these
• 41:35
  crystals from, um, this beautiful Lake
• 41:38
  Lapiavi, found that it took about 4 million
• 41:41
  years for the rocks to cool to 50 degrees C,
• 41:44
  which to me is astonishingly long time.
• 41:47
  That's very slow cool. And they're saying, we
• 41:49
  don't really understand why it took so long,
• 41:51
  but it's probably to do with the kind of
• 41:52
  rocks that were around and the kind of
• 41:54
  insulating properties. But what they did
• 41:57
  then was that they looked at the chemistry of
• 41:59
  these samples. They used mass spectrometry
• 42:01
  to look at basically the different isotopes
• 42:04
  of oxygen, carbon and sulfur in the rock.
• 42:07
  And they were doing that because microbes
• 42:09
  tend to process oxygen, carbon and sulfur and
• 42:12
  preferentially use one isotope over the
• 42:14
  other. So they can put this very distinctive
• 42:16
  chemical signature in to what's left behind.
• 42:19
  So the team were very much looking for, in
• 42:22
  addition to this cooling data, uh, the point
• 42:25
  at which you started to get the fingerprints
• 42:27
  of microbial life once again. And what they
• 42:29
  found was that, uh, 4 million year point when
• 42:31
  it cooled to about 50 degrees C. That was
• 42:34
  when you started to get life there again. And
• 42:36
  you started to get life that was turning
• 42:38
  sulfates into sulfides. I think that was
• 42:41
  the chemical terminology there.
• 42:44
  So there were processing materials and
• 42:47
  life had recolonized effectively, yes,
• 42:50
  sulfate into sulfide. That was after 4
• 42:53
  million years. 10 million years after that,
• 42:55
  the temperature dropped to about 30 degrees
• 42:57
  C. And you got the kind of microbes that make
• 42:59
  methane recolonize there. So you've now got
• 43:02
  this really nice chronological timeline of
• 43:04
  the recolonization of this site. And, um,
• 43:07
  they talk about this being a surprisingly
• 43:09
  quick time. To me, this is surprisingly slow
• 43:12
  given how much life we've got around on the
• 43:14
  Earth. So obviously they are more expert than
• 43:17
  I am, and I'm happy to take their
• 43:20
  word that this is a very quick
• 43:21
  recolonisation. But to me, it's interesting
• 43:24
  that it took it so long to cool down and for
• 43:26
  life to get going again afterwards. That's
• 43:29
  maybe telling us something about the kind of
• 43:30
  rocks the impact happened in. I don't know
• 43:33
  whether it could also be telling us something
• 43:34
  about the underlying geology of the area at
• 43:36
  the time. I'm just not expert enough. But
• 43:39
  it's a really fascinating study and it's a
• 43:42
  really good example of how the science of
• 43:45
  astrobiology, which is the science of the
• 43:47
  search for life elsewhere and the science of
• 43:49
  the question of how we learn in the universe
• 43:51
  and of how did life get started on Earth, all
• 43:53
  those really thorny questions. That's not a
• 43:56
  science that can be answered by just one
• 43:57
  discipline within astronomy. It's a really
• 44:00
  multidisciplinary area where you need people
• 44:02
  from an incredibly wide and diverse
• 44:06
  variety of areas in the sciences to come
• 44:08
  together because no one area has the
• 44:10
  knowledge and the skill set and the
• 44:11
  methodology and the samples to provide an
• 44:14
  answer on their own. It's why conference
• 44:17
  on this kind of topic are so, uh, fascinating
• 44:19
  to me because you go to talks from biology
• 44:21
  and chemistry and geophysics rather than just
• 44:24
  a lot of talks from astronomers on astronomy
• 44:26
  things. And um, this is the kind of study no
• 44:29
  one I work with directly would have been able
• 44:30
  to do. But these people have been able to
• 44:33
  drill down, do this awesome work and get some
• 44:35
  really fascinating results. So I'm looking
• 44:38
  forward to hearing more about this. And to be
• 44:40
  honest, this would almost set the scene for
• 44:41
  groups elsewhere in the world to start
• 44:43
  drilling down into other creators to see if
• 44:45
  we can get a feel for. Is this unusual? Is
• 44:47
  this common? And, um, the other two unusual,
• 44:50
  essentially, what's going on?
• 44:52
  Andrew Dunkley: Yeah, yeah. And uh, as you said, it's just
• 44:54
  great that historical studies,
• 44:57
  uh, being dredged back up and
• 45:00
  reused with modern, um,
• 45:03
  techniques and technology to, to uh, find out
• 45:06
  more. I think that's amazing. And uh,
• 45:08
  keeping rocks for future reference,
• 45:11
  um, when we can do things even
• 45:14
  better, um, may reveal more answers.
• 45:17
  So, ah, that's. That. That in itself is a
• 45:19
  terrific part of that particular story.
• 45:22
  Uh, and I was just wondering about the Tim
• 45:25
  Horton, the uh, Horton crater. It couldn't
• 45:28
  be named after Tim Horton the famous ice
• 45:30
  hockey player, could it?
• 45:32
  Jonti Horner: Ice hockey player. Are there not some famous
• 45:34
  pancakes? Uh, Tim Hortons.
• 45:37
  Andrew Dunkley: Yeah.
• 45:37
  Jonti Horner: Well, that's. Yeah.
• 45:38
  Andrew Dunkley: I mean you can't go to Canada and not go to
• 45:40
  Tim Hortons.
• 45:41
  Jonti Horner: Um, I think the spelling may be different.
• 45:43
  This is Horton. H, A, U, G, H. Right.
• 45:46
  So probably a distant relative.
• 45:48
  Andrew Dunkley: You never know. Uh, okay, that brings us to
• 45:51
  the end. Johnny, thank you so much.
• 45:53
  Jonti Horner: Matt, it's an absolute pleasure. Thank you.
• 45:55
  Andrew Dunkley: Good, uh, to see you. Jonti Horner, professor
• 45:57
  of Astrophysics at the University of Southern
• 45:59
  Queensland, joining us. Don't forget to visit
• 46:02
  us online, uh, at our website and check
• 46:05
  everything out. You can, uh, send us
• 46:06
  questions via the uh, website as well and
• 46:09
  check out the shop and maybe, uh, sign up to
• 46:11
  become a supporter. Whatever floats your
• 46:14
  boat. Uh, it's@Space
• 46:16
  Nutspodcast.com uh, and
• 46:19
  thanks to Huw in the studio who couldn't be
• 46:21
  with us today. I don't know if you know this
• 46:22
  about Huw, but he's a bit old. He doesn't use
• 46:25
  satnav, but he heard about this great new
• 46:27
  book and he's gone to a bookshop to try and
• 46:29
  get it today. Uh, it's, um. It's the
• 46:32
  Three Eye Atlas book.
• 46:35
  Um, I'm not going to tell him. And from me,
• 46:38
  Andrew Dunkley, thanks for your company.
• 46:39
  We'll see you on the next episode of Space
• 46:41
  Nuts. Bye. Bye. You'll be
• 46:43
  listening to the Space Nuts.
• 46:45
  Jonti Horner: Podcast, available at
• 46:48
  Apple Podcasts, Spotify,
• 46:50
  iHeartRadio or your favorite podcast player.
• 46:53
  You can also stream on demand@bytes.com M.
• 46:57
  Andrew Dunkley: This has been another quality podcast
• 46:59
  production from bytes.com.