Dark Matter and Aliens in NGC 2403 - Deep Sky Videos

0:00 I thought I'd talk about NGC 2403.

0:03 Oh, at last.

0:05 What is it?

0:06 It's a galaxy.

0:07 It's actually a pretty bright galaxy.

0:08 It's a Here it's a picture that I took.

0:10 You took that?

0:11 Yeah.

0:11 This is one of mine.

0:12 That was from my back garden.

0:13 Nice.

0:16 And it's actually quite a big bright galaxy, right?

0:18 It's one of the brightest galaxies that Messier missed.

0:21 So, it could have been a Messier galaxy, but for some reason, you never saw it.

0:24 Why do you think he didn't see it?

0:26 The Messier catalog is not done in a very systematic way, right?

0:29 It's, you know, things that Messier happened

0:30 to spot while he was looking for comets.

0:32 It's things that he happened to have read that other people had seen.

0:35 So, it's not like he did a systematic

0:37 sweep of the sky trying to find every object.

0:39 So, it's just by chance that this is

0:41 probably one of the brightest ones that he missed.

0:44 All right.

0:44 It's it's the it's the fish that got away.

0:46 Yeah.

0:46 And it's a very nice little spiral galaxy, right?

0:48 It's a shame to have missed it cuz it's it's nice.

0:50 It looks a little bit like Messier 33.

0:52 It's that kind of spiral galaxy, but very pretty.

0:54 Probably the thing that this thing is most famous for that no one much knows is

0:58 it's where dark matter was first sort

1:00 of fairly definitively detected in a galaxy and it's

1:03 sort of a lost bit of the story right in that you know whenever people talk

1:06 about dark matter in galaxies everyone knows about

1:09 Vera Rubin and the work that she did

1:10 but it turns out that there were a lot of other people working in similar fields

1:14 and she was building on a lot of things

1:16 that have already been done um and in fact

1:18 the person who discovered dark matter in this galaxy

1:21 is a guy called Seth Shustak who

1:23 in the early 1970s wrote a thesis in which he looked at a couple of galaxies.

1:28 is you know so this is early 1970s so it's quite early for doing high

1:31 resolution radio astronomy but he was looking

1:33 at that 21 cm line from hydrogen using a radio array in California um and making

1:40 images quite high resolution images in the radio

1:42 part of the spectrum which essentially told him where the gas was in his galaxy

1:46 and also because you're measuring an emission

1:48 line you can measure the doppler shift whether

1:50 it's coming towards you or away from you from the shift in its frequencies so

1:53 he was able to measure the rotation speed of the galaxy and the rotation speed

1:57 because he had this high resolution data as a function of how far out you are.

2:02 And so he ended up producing one of the early versions of one of these plots

2:07 which is how fast the galaxy's rotating versus

2:10 how far out you are in the galaxy.

2:12 And it has that what became, you know,

2:14 a very well-known structure that it rises in the middle and then it stays flat.

2:18 And this is this evidence of dark matter.

2:20 The fact that you would expect as you

2:22 get further away the pull of gravity should be

2:24 getting smaller and smaller which means that to stay

2:26 in orbit you should be going slower and slower.

2:28 Just like you know in the planets in the solar

2:30 system as you go out in the solar system because all

2:32 the mass is concentrated in the middle as you get further

2:35 and further from that mass the planets go around slower and slower.

2:38 In this case things don't get slower and slower.

2:40 They stay at the same speed.

2:41 That tells you that there's more and more

2:43 mass as you go to larger and larger radi.

2:46 So, dark matter, I know we don't know what it is.

2:48 It's like a mystery thing, isn't it?

2:50 Does it live in galaxies?

2:51 Does it live between galaxies or what do we what do we know?

2:55 Everywhere.

2:55 It's everywhere.

2:56 So, in fact, the highest density of dark matter is in the middle of the galaxy,

3:00 but it's actually just in a more extended halo.

3:02 So, even after you've run out of stars and gas, there's still dark matter.

3:06 So, there's still mass increasing.

3:08 And because there's kind of more area at large radi,

3:11 more volume at large radi, there's actually a lot of mass out there.

3:14 Even though the density is that bit lower,

3:16 there's a whole load of space, so there's a whole load of mass out.

3:19 It's always struck me as a little

3:20 strange that people think it's mysterious, right?

3:22 But actually, I'm not sure it is in that there's no reason why

3:25 the universe had to be laid on for the benefit of astronomers, right?

3:28 There's no reason why everything has to glow in the dark.

3:30 And so, why shouldn't there be material out there which just doesn't

3:33 let its presence be known by emitting

3:35 electromatic radiation that astronomers can detect?

3:38 So, the only way we detect dark matter

3:39 at the moment is by its gravitational influence.

3:42 Yeah.

3:42 And there are a lot, you know,

3:43 so it could be that it's made up of massive particles and there's a lot of work

3:46 going on of people trying to detect

3:47 those massive particles because the dark matter is everywhere.

3:49 So it means it's passing through the earth at this minute.

3:52 So there are a lot of people who've set up detectors to try

3:54 and detect that dark matter and it interactions with material on Earth.

3:57 None have yet detected anything at all.

3:59 As someone who spent their career studying galaxies,

4:03 galaxy evolution, galaxy formation,

4:06 motion, how much of a thorn in your side is dark matter?

4:10 It's not.

4:10 I mean you know you take the universe

4:12 you're given right and so actually it's not it

4:14 it's just one of those things we have

4:15 to try to understand and in some level that's what

4:17 makes astronomy interesting that we don't understand everything

4:20 so actually you know the fact there are things

4:21 that we yet to get our heads around what's

4:23 really going on is what makes the subject interesting

4:26 in the first place this guy Seth Shostak's

4:28 thesis couple more things to say about it so let me read I just read a bit

4:32 from what what he actually said about the the detection

4:34 or how he how close he got to the detection

4:36 of dark matter so this is from the conclusions

4:38 of his thesis it says the flat rotation curve

4:40 of NGC 2403 seen in other late type spirals.

4:43 So it's already a known thing right even

4:45 then although he's the first person I think

4:46 to really talk about it implies a mass density dropping as slowly as 1/ r squ.

4:51 So that's this slow fall off of density

4:54 with radius in the dark matter around this galaxy.

4:56 Uncertain total masses result just because if you actually

4:59 keep adding up all that mass it actually diverges.

5:01 You end up with more and more mass as you go to larger and larger radi.

5:04 And for this reason is felt that only bounded masses limits

5:07 by the last point on the measured rotation curve should be quoted.

5:09 So he can't actually say what the mass of a galaxy is because it's still

5:12 increasing as you go to larger radi beyond

5:14 the last point he's been able to measure.

5:16 This is the bit where he gets as close

5:17 as possible to actually saying that there's dark matter there.

5:19 The flat curve also requires high mass

5:21 to light ratios in the outer galactic regions.

5:24 So the mass to light ratio is how much

5:25 mass there is for every given bit of light.

5:28 So a high mass to light ratio means there's a lot of mass and not much light.

5:31 And so he's saying there's loads of mass here but not many stars.

5:34 So we really don't know what's going on.

5:36 Um so that's kind of as close as he got.

5:38 He almost said there was dark matter there.

5:40 He just couched it in the sort of the the vocabulary of the day,

5:43 which was to say that you have a high mass to light ratio.

5:46 If I went back in time and asked him,

5:48 "What do you think's going on there?" What would he have told me?

5:51 I think he'd have said that he didn't know.

5:53 Even I mean, you know, that's what we say now, right?

5:55 So, it's not like things have changed that much.

5:57 It would have been a bit of a leap to say

5:59 there's some mysterious matter that we don't know what it is,

6:01 but he might well have said that.

6:04 Were you speculating?

6:05 Were you talking to your supervisor?

6:06 Did you have any wild theories or was it just like a complete mystery to you?

6:12 I think it was pretty much a mystery.

6:14 I mean, you I I knew that there had to be

6:16 some mass out there to account for this fast rotation,

6:20 but you know, you couldn't see it.

6:22 I mean, it wasn't luminous.

6:23 It wasn't stars, at least not luminous stars.

6:27 I mean, it could have been, and as I said,

6:29 I think at the time, it could have been footballs.

6:31 you know, the the galaxy could have been filled with footballs,

6:34 which don't make a whole lot of light,

6:36 but if you have enough of them, they might, you know,

6:38 provide enough mass to account for this this peculiar phenomenon.

6:43 I didn't know what it was.

6:44 And uh I think that that that actually is still the case.

6:48 We don't know what the dark matter really is,

6:50 but we do, you know, it's generally accepted that it's out there.

6:54 Is there any part of you that thinks there

6:56 was like a missed opportunity for you to be Mr.

6:58 dark matter for you to have been the first person

7:00 to kind of pin down this mysterious substance that's now so famous.

7:05 Well, yes, of course.

7:07 I mean, you know, when you later in later I mean,

7:10 it's like many things that uh you know,

7:13 were discovered in that era when you thought gosh,

7:16 you know, I could have written that paper, right?

7:19 I had the data, but you know that that's all the benefit of hindsight.

7:23 Seth Schuststak isn't famous for this.

7:25 Cesak is famous for being one of the world leaders in SETI,

7:29 the search for extraterrestrial intelligence and being

7:31 a director of the SETI institute and getting very involved in in searching

7:35 for intelligence elsewhere in the universe.

7:37 And I discovered if you look at the acknowledgements for his thesis,

7:40 so acknowledgements to the thesis is where you kind of thank

7:43 everybody and thank your mom and all that kind of stuff.

7:46 But he also mentioned at the end of his thesis

7:48 he gave a dedication and the dedication in his thesis

7:50 is this thesis is dedicated to NGC 2403 and all

7:54 its inhabitants to whom copies will be furnished at cost.

7:57 So even then he was thinking about extraterrestrial intelligence in NGC 2403.

8:03 I I think I was just being a wise guy.

8:06 I I don't think there was anything very deep in any of that.

8:08 I mean I I looked at the dedications of other thesis

8:12 and you know they they followed the pattern you would expect.

8:15 I mean, people would d, you know,

8:17 dedicate it to their wives or girlfriends or whatever or boyfriends.

8:22 I mean, that was common.

8:23 And I just decided to dedicated to NG2403.

8:27 That was the result of about one minute's worth of thought.

8:30 How much would it cost to send one

8:31 of these papers to that galaxy, do you reckon?

8:34 I think he's going to have a long while

8:35 to wait for them even for the request to arrive,

8:37 let alone to have to worry about the shipping cost to get it out there.

8:40 How likely do you think it is that there are inhabitants of NGC243?

8:44 as you referred to.

8:46 Yeah.

8:46 Well, I I would bet I would bet my next month's paycheck,

8:50 which uh given I'm semi-retired, is not terribly large,

8:54 but yeah, I I'm sure there are.

8:55 Look, the the number of stars in NGC 2403 is,

9:00 you know, it's on the order of maybe hundreds of billions.

9:04 And yeah, most of those stars are kind

9:06 of worthless for supporting life on a planet

9:08 around them because they're too bright

9:10 or they're too dim or something like that.

9:11 But nonetheless, 10% of them are probably okay.

9:14 So that's still a very large number of star systems.

9:18 And and unless you are convinced that the origin

9:21 of life is some sort of miracle, some sort of highly unlikely event,

9:27 then life will have arise risen uh you know on on many many planets,

9:33 you know, billions and billions as Carl

9:36 Sean would occasionally say in that galaxy.

9:40 And uh you know maybe most of that life is not terribly interesting.

9:44 It's all single-sellled life or insects or something like that.

9:48 But you know it's it's hard to believe that advanced life you know that has

9:53 the capability to invent science and do science

9:57 things like that is restricted only to this planet.

10:00 We have a lot of history that suggests every

10:02 time you think you're very special uh you're usually wrong.

10:06 Hi there.

10:06 Thanks for watching.

10:07 If you'd like to see us make more and better Deep Sky videos,

10:10 why not support us on Patreon?

10:11 Like the peoples whose name you see

10:13 on the screen at the moment, thank you to them.

10:16 And as Patreon supporters, they and you could go along and hear the answer

10:20 when I asked Professor Marfield who he dedicated his thesis to.

10:25 Did you put anything cute in your acknowledgements to your thesis?

10:28 Were you Were you a smart Alec?

10:29 You strike me as someone who would have done something like that.

10:31 The answer may or may not surprise you.

10:34 I'm guessing it won't surprise you, but Mike didn't want you to hear it.

10:37 Don't put that in the video.