WEBVTT
0
00:00:00.000 --> 00:00:02.400
Andrew Dunkley: Hi there. Thanks for joining us again. This
1
00:00:02.400 --> 00:00:05.040
is Space Nuts, a Q and A edition where we,
2
00:00:05.420 --> 00:00:07.760
uh, get questions, we look at them and go,
3
00:00:08.160 --> 00:00:10.640
no clue. No, I haven't got any idea what
4
00:00:10.640 --> 00:00:13.200
we're doing. So we're not doing that today.
5
00:00:13.440 --> 00:00:14.240
Professor Fred Watson: Actually, we will.
6
00:00:14.380 --> 00:00:17.280
Andrew Dunkley: Uh, we've got a question from Ron, uh, asking
7
00:00:17.280 --> 00:00:20.120
about, uh, astronomy in regard to
8
00:00:20.120 --> 00:00:22.680
a super fast moving planet. How would that
9
00:00:22.680 --> 00:00:24.760
work if you were living on it, is what he's
10
00:00:24.760 --> 00:00:27.640
saying. Uh, Jeff wants to know about photon
11
00:00:27.640 --> 00:00:30.440
pressure. Um, Brian is asking
12
00:00:30.440 --> 00:00:33.070
about, um, what a black hole
13
00:00:33.070 --> 00:00:35.350
covers up. Interesting.
14
00:00:35.830 --> 00:00:38.430
And when is a moon no longer a
15
00:00:38.430 --> 00:00:41.270
moon? Bob asks. We'll see if we can answer
16
00:00:41.270 --> 00:00:43.910
all of those questions on today's episode of
17
00:00:43.910 --> 00:00:44.870
space nuts.
18
00:00:45.110 --> 00:00:46.190
Professor Fred Watson: 15 seconds.
19
00:00:46.190 --> 00:00:48.514
Guidance is internal. 10,
20
00:00:48.666 --> 00:00:51.510
9. Ignition sequence start.
21
00:00:51.670 --> 00:00:52.391
Professor Fred Watson: Space nuts.
22
00:00:52.463 --> 00:00:53.820
Professor Fred Watson: 5, 4, 3, 2.
23
00:00:53.892 --> 00:00:56.679
1, 2, 3, 4, 5, 5, 4, 3,
24
00:00:56.751 --> 00:00:57.430
2, 1.
25
00:00:57.510 --> 00:00:58.710
Andrew Dunkley: Space nuts.
26
00:00:58.710 --> 00:01:00.550
Professor Fred Watson: Astronauts report it feels good.
27
00:01:01.150 --> 00:01:03.430
Andrew Dunkley: He's back for more. His name is Professor
28
00:01:03.430 --> 00:01:05.550
Fred Watson Watson, astronomer at large.
29
00:01:05.710 --> 00:01:06.590
Hello, Fred Watson.
30
00:01:06.990 --> 00:01:09.350
Professor Fred Watson: Hello, Andrew. Uh, it's good to be back for
31
00:01:09.350 --> 00:01:09.630
more.
32
00:01:09.870 --> 00:01:12.710
Andrew Dunkley: It is. I'm trying to figure out why your
33
00:01:12.710 --> 00:01:14.470
parents gave you the first name Professor.
34
00:01:14.470 --> 00:01:15.230
That seems a little.
35
00:01:17.550 --> 00:01:20.430
Professor Fred Watson: I thought so too. It could have been, sir.
36
00:01:22.350 --> 00:01:24.790
Andrew Dunkley: I was probably not as bad as those parents
37
00:01:24.790 --> 00:01:26.750
in. I think it was Sweden or somewhere who
38
00:01:26.750 --> 00:01:29.380
named their kid Megadeth. Well,
39
00:01:29.380 --> 00:01:32.340
yes, and the government tried
40
00:01:32.340 --> 00:01:34.500
to stop them and they went to court and they
41
00:01:34.500 --> 00:01:34.780
won.
42
00:01:35.100 --> 00:01:37.420
Professor Fred Watson: Yes, I believe I remember that.
43
00:01:37.500 --> 00:01:40.240
Andrew Dunkley: Yeah, Quite a while back now. But m.
44
00:01:40.780 --> 00:01:43.210
That's beside the point. Uh, we've got, uh,
45
00:01:43.210 --> 00:01:45.420
answers to questions or we've got questions
46
00:01:45.580 --> 00:01:47.420
we're hoping we can answer.
47
00:01:48.460 --> 00:01:50.700
When I say we, I'm talking about you.
48
00:01:53.740 --> 00:01:54.540
Professor Fred Watson: No pressure.
49
00:01:54.930 --> 00:01:57.130
Andrew Dunkley: No, none at all. Um, this first question is
50
00:01:57.130 --> 00:01:59.890
brilliant, though. Uh, hi there. From upstate
51
00:01:59.890 --> 00:02:02.530
New York. How hope all is well,
52
00:02:02.750 --> 00:02:05.570
uh, as you approach spring. It's not, Ron.
53
00:02:06.130 --> 00:02:09.090
Hay fever sucks. I,
54
00:02:09.170 --> 00:02:11.930
I played 36 holes of golf this week in a, in
55
00:02:11.930 --> 00:02:13.820
a major local tournament. And, um,
56
00:02:15.330 --> 00:02:17.490
I, I paid for it dearly.
57
00:02:18.470 --> 00:02:21.310
Um, and I still am. But,
58
00:02:21.310 --> 00:02:23.620
uh, yeah, it's a tough time of year for
59
00:02:23.620 --> 00:02:26.420
people who suffer hay fever here. I came
60
00:02:26.420 --> 00:02:29.420
second, by the way. Anyway, um, sorry,
61
00:02:29.420 --> 00:02:31.300
this is a bit wordy. He says with the
62
00:02:31.300 --> 00:02:34.200
information just released on the star S300,
63
00:02:34.200 --> 00:02:36.740
uh, one orbiting Sagittarius A being one of
64
00:02:36.740 --> 00:02:39.420
the fastest stars in the Milky Way. And he
65
00:02:39.420 --> 00:02:42.300
sent us a link about that. Moving at 8% the
66
00:02:42.300 --> 00:02:43.780
speed of light. That sounds like a lot.
67
00:02:43.780 --> 00:02:46.660
25,000 kilometres per second. I was
68
00:02:46.660 --> 00:02:49.220
wondering how this would affect an astronomer
69
00:02:49.220 --> 00:02:52.010
on a hypothetical planet, um,
70
00:02:52.380 --> 00:02:55.020
around that region, um, relative
71
00:02:55.020 --> 00:02:57.820
to an Outside observer, their clocks would
72
00:02:57.960 --> 00:02:59.980
uh, slow dramatically due to the high
73
00:02:59.980 --> 00:03:02.940
velocity and uh, the depth in
74
00:03:02.940 --> 00:03:05.820
the black hole's gravitational well at
75
00:03:05.880 --> 00:03:08.300
um, I can't say that word. Peri.
76
00:03:08.540 --> 00:03:09.380
Professor Fred Watson: Periapsis.
77
00:03:09.380 --> 00:03:12.300
Andrew Dunkley: Yes. Uh, then speed up as they
78
00:03:12.380 --> 00:03:15.260
reach apoapsis.
79
00:03:15.420 --> 00:03:18.300
Yes. Uh, would that not cause their
80
00:03:18.300 --> 00:03:20.500
measurements of time related events like
81
00:03:20.500 --> 00:03:23.360
orbital periods of nearby planets or
82
00:03:23.360 --> 00:03:26.360
stars to vary during their orbit
83
00:03:26.440 --> 00:03:29.200
of the black hole? If so, it's crazy to
84
00:03:29.200 --> 00:03:31.960
think how this would skew their science until
85
00:03:31.960 --> 00:03:34.440
they learned about relativity. Thanks very
86
00:03:34.440 --> 00:03:37.400
much for a great podcast. Always enlightening
87
00:03:37.400 --> 00:03:38.680
Ron. Thank you Ron.
88
00:03:38.680 --> 00:03:41.240
I love this question, it's really
89
00:03:41.240 --> 00:03:41.720
clever.
90
00:03:42.520 --> 00:03:44.710
Professor Fred Watson: Well it is. Um, and um,
91
00:03:45.670 --> 00:03:47.720
uh, Ron's exactly right.
92
00:03:49.160 --> 00:03:51.960
This thing is in
93
00:03:51.960 --> 00:03:54.440
a very very unusual place within
94
00:03:56.020 --> 00:03:58.980
orbiting Sagittarius, a star which is the 4
95
00:03:58.980 --> 00:04:01.300
million solar mass black hole at the centre
96
00:04:01.300 --> 00:04:04.220
of our galaxy. So um, exactly
97
00:04:04.220 --> 00:04:06.740
as he says, both the relativistic
98
00:04:06.740 --> 00:04:09.700
speed and um, by that I mean speed close to
99
00:04:09.700 --> 00:04:12.220
the speed of light. 8% is close to the speed
100
00:04:12.220 --> 00:04:14.540
of light compared with most of the speeds
101
00:04:14.540 --> 00:04:17.540
that we uh, encounter uh, in astronomy.
102
00:04:18.100 --> 00:04:20.940
Uh, um, it is uh,
103
00:04:20.990 --> 00:04:23.470
that that relativistic speed changes,
104
00:04:23.950 --> 00:04:26.510
gives you time dilation as does the
105
00:04:26.510 --> 00:04:29.150
gravitational well that um, this
106
00:04:29.150 --> 00:04:31.230
star orbits. I
107
00:04:32.190 --> 00:04:34.910
didn't um, Let me just have a look at
108
00:04:34.910 --> 00:04:37.630
that uh, link. I have looked at it before,
109
00:04:38.240 --> 00:04:41.070
um, but I can't remember how elliptical its
110
00:04:41.070 --> 00:04:43.630
orbit is. Um, it's
111
00:04:44.110 --> 00:04:46.950
basically very elongated and so
112
00:04:46.950 --> 00:04:49.690
at what is what Ron uh,
113
00:04:49.830 --> 00:04:52.020
correctly calls periapsis, um
114
00:04:53.830 --> 00:04:56.670
the apse closest to the galactic
115
00:04:56.670 --> 00:04:57.190
centre.
116
00:04:57.350 --> 00:05:00.350
Apsidies are uh, the points in an orbit
117
00:05:00.350 --> 00:05:02.150
which are either ah, the nearest or the
118
00:05:02.150 --> 00:05:04.790
furthest periapsis nearest apoapsis
119
00:05:04.790 --> 00:05:07.670
furthest away. Um, we talk about perigee and
120
00:05:07.670 --> 00:05:10.230
apogee for satellites around the Earth.
121
00:05:10.370 --> 00:05:13.030
Um, that's the way the
122
00:05:13.030 --> 00:05:15.990
terminology works. So um, you're
123
00:05:15.990 --> 00:05:18.390
going to have different phenomena uh
124
00:05:18.520 --> 00:05:20.160
depending on where you are because the
125
00:05:20.160 --> 00:05:22.840
velocity will vary as you
126
00:05:22.840 --> 00:05:25.280
go around this elongated orbit. That's
127
00:05:25.280 --> 00:05:28.120
Kepler's laws. They still hold at these
128
00:05:28.290 --> 00:05:30.280
uh, high gravitational intensities.
129
00:05:30.930 --> 00:05:33.720
Um, um, so the time
130
00:05:33.720 --> 00:05:36.360
dilation phenomena uh, and
131
00:05:36.440 --> 00:05:38.520
the sorts of things that you would experience
132
00:05:38.760 --> 00:05:41.280
are exactly ah as Ron said there'd be another
133
00:05:41.280 --> 00:05:43.800
phenomenon as well. Um, I mean
134
00:05:45.300 --> 00:05:47.810
being near a black hole is gonna be weird uh
135
00:05:47.810 --> 00:05:49.820
as to what your sky looks like because the
136
00:05:49.820 --> 00:05:52.500
black hole is relatively nearby, there's
137
00:05:52.580 --> 00:05:54.540
stuff swirling around it with the accretion
138
00:05:54.540 --> 00:05:56.660
disc. It's kind of hard to imagine yourself
139
00:05:56.660 --> 00:05:59.060
in that situation. But at
140
00:05:59.060 --> 00:06:01.980
relativistic speeds like that, uh, it
141
00:06:01.980 --> 00:06:04.980
also changes the position of
142
00:06:04.980 --> 00:06:06.580
objects in your sky.
143
00:06:07.170 --> 00:06:09.260
Um, so if you imagine something hurtling
144
00:06:09.260 --> 00:06:12.260
along at, uh, a significant
145
00:06:12.500 --> 00:06:15.500
fraction of the speed of light, uh, the stars
146
00:06:15.500 --> 00:06:17.680
that you see tend to
147
00:06:18.560 --> 00:06:21.040
the positions you'll see will, um, be.
148
00:06:21.680 --> 00:06:24.200
They're erroneous, but the stars will look as
149
00:06:24.200 --> 00:06:26.680
though they're nearer to the direction in
150
00:06:26.680 --> 00:06:29.000
which you're heading than they really are. So
151
00:06:29.000 --> 00:06:30.760
there's a tendency, especially as you
152
00:06:30.760 --> 00:06:32.640
approach getting near the speed of light,
153
00:06:32.960 --> 00:06:34.720
basically all the stars that you'd see will
154
00:06:34.720 --> 00:06:37.480
be bunched up, uh, fairly close together in
155
00:06:37.480 --> 00:06:40.080
front of you, um, because that's the way
156
00:06:40.080 --> 00:06:41.680
their light is changing itself.
157
00:06:42.160 --> 00:06:44.640
Andrew Dunkley: I reckon, uh, being on a planet in a
158
00:06:44.640 --> 00:06:47.160
situation like that, uh, orbiting a fast
159
00:06:47.160 --> 00:06:49.360
moving star, your astrophotography would be
160
00:06:49.360 --> 00:06:49.880
awesome.
161
00:06:51.320 --> 00:06:52.200
Professor Fred Watson: Yeah, it would.
162
00:06:52.520 --> 00:06:55.240
Except, well, probably not. I mean,
163
00:06:56.360 --> 00:06:58.040
the star trails would all be in the wrong
164
00:06:58.040 --> 00:07:00.920
place. Yeah, the stars, yeah, but no, great
165
00:07:00.920 --> 00:07:03.800
question. And Ron, you're on the money there
166
00:07:03.800 --> 00:07:04.120
too.
167
00:07:04.120 --> 00:07:06.960
Andrew Dunkley: Yeah. And um, by comparison, I suppose we can
168
00:07:06.960 --> 00:07:08.680
draw on a science fiction movie,
169
00:07:08.920 --> 00:07:11.400
Interstellar, where they visited
170
00:07:11.400 --> 00:07:14.150
Miller's planet, which was near Gargantua,
171
00:07:14.150 --> 00:07:17.100
uh, which is, um, a black
172
00:07:17.100 --> 00:07:19.780
hole in the film. And for every
173
00:07:19.940 --> 00:07:22.860
hour they were on the surface of
174
00:07:22.860 --> 00:07:25.330
the planet, seven years passed on Earth. So,
175
00:07:25.330 --> 00:07:27.220
uh, that's the sort of gravitational effect
176
00:07:27.220 --> 00:07:29.900
we're talking about. But, um, in terms
177
00:07:29.900 --> 00:07:32.260
of the speed of a planet,
178
00:07:32.890 --> 00:07:35.780
um, in accordance with the fast moving star,
179
00:07:36.580 --> 00:07:38.250
it's a different kettle of fish, isn't it?
180
00:07:38.250 --> 00:07:41.100
Um, you're observing everything out of sync,
181
00:07:41.100 --> 00:07:42.860
I suppose would be the best way to describe
182
00:07:42.860 --> 00:07:43.140
it.
183
00:07:43.140 --> 00:07:45.620
Professor Fred Watson: Yes, that's right, exactly.
184
00:07:45.620 --> 00:07:48.200
Andrew Dunkley: So quite interesting. Thanks for the
185
00:07:48.200 --> 00:07:50.400
question, Ron, and great to hear from you.
186
00:07:54.400 --> 00:07:56.000
Professor Fred Watson: Also space nuts.
187
00:07:56.210 --> 00:07:58.160
Andrew Dunkley: Uh, our next question, Fred Watson, comes
188
00:07:58.160 --> 00:08:00.240
from Jeff, uh, also in the United States.
189
00:08:00.240 --> 00:08:02.880
He's in Colorado. Uh, hello
190
00:08:02.880 --> 00:08:04.920
Andrew and Fred Watson. Thanks for the
191
00:08:04.920 --> 00:08:06.960
amazing shows. Oh, have we done one? Have we.
192
00:08:08.650 --> 00:08:11.360
Uh, the sun emits millions of billions of
193
00:08:11.440 --> 00:08:14.200
photons every second and it's pretty
194
00:08:14.200 --> 00:08:16.000
much average as a star.
195
00:08:17.110 --> 00:08:19.680
Uh, could the radiation pressure from all the
196
00:08:19.680 --> 00:08:22.440
universe's photons exert enough force to
197
00:08:22.440 --> 00:08:25.000
affect the expansion of the universe? Now
198
00:08:25.000 --> 00:08:26.680
there's an interesting theory, Fred Watson.
199
00:08:27.320 --> 00:08:30.200
Professor Fred Watson: Uh, there is, yes. Uh, it's
200
00:08:30.200 --> 00:08:33.160
um, so 10 to the 45. 10 to
201
00:08:33.160 --> 00:08:35.840
the power. 45 photons per second coming from
202
00:08:35.840 --> 00:08:38.640
the sun. Um, I like that number. It's quite a
203
00:08:38.640 --> 00:08:39.640
lot. It is
204
00:08:41.720 --> 00:08:43.810
so that, uh,
205
00:08:45.540 --> 00:08:48.010
that basically that, um,
206
00:08:48.340 --> 00:08:50.580
flux of photons, if I can put it that way,
207
00:08:51.060 --> 00:08:53.660
is for every star is an
208
00:08:53.660 --> 00:08:56.660
outward flux, um, for the universe
209
00:08:56.660 --> 00:08:59.220
as a whole, it's kind of going to cancel out.
210
00:08:59.860 --> 00:09:01.940
Um, but it is something
211
00:09:02.740 --> 00:09:05.540
that is taken into account,
212
00:09:06.440 --> 00:09:09.300
um, in the study of
213
00:09:09.300 --> 00:09:11.980
cosmology, the behaviour of the universe as a
214
00:09:11.980 --> 00:09:14.760
whole. And so in particular, you know,
215
00:09:14.760 --> 00:09:16.960
the potentially nice idea that this could
216
00:09:16.960 --> 00:09:19.600
account for dark energy, uh, which is the
217
00:09:19.600 --> 00:09:22.280
energy of the universe itself. That
218
00:09:22.360 --> 00:09:25.160
is, um, two quite different
219
00:09:25.240 --> 00:09:28.120
things. Uh, dark energy is
220
00:09:28.120 --> 00:09:30.760
independent of any kind of photon pressure.
221
00:09:31.300 --> 00:09:34.240
Uh, and so, um, it's basically the
222
00:09:34.240 --> 00:09:36.960
idea of all the photons floating around the
223
00:09:36.960 --> 00:09:39.800
universe. Uh, I think they are the most
224
00:09:39.800 --> 00:09:42.640
common subatomic particle in the universe, if
225
00:09:42.640 --> 00:09:45.400
I remember rightly. And neutrinos are the
226
00:09:45.400 --> 00:09:47.220
second. I think that was one we covered a
227
00:09:47.220 --> 00:09:48.020
couple of weeks ago.
228
00:09:48.180 --> 00:09:48.740
Andrew Dunkley: Yep.
229
00:09:49.320 --> 00:09:51.940
Professor Fred Watson: Uh, so, um, they're accounted for
230
00:09:52.020 --> 00:09:54.540
in our understanding of the expansion of the
231
00:09:54.540 --> 00:09:57.220
universe. And it doesn't explain dark energy.
232
00:09:57.300 --> 00:10:00.100
Dark energy is still an issue. Uh, it's,
233
00:10:00.310 --> 00:10:02.700
uh, something just connected with space
234
00:10:02.700 --> 00:10:04.860
itself. It will be there. Even if the
235
00:10:04.860 --> 00:10:07.260
universe was completely dark, you'd still
236
00:10:07.260 --> 00:10:10.220
have dark energy, we believe. And
237
00:10:10.220 --> 00:10:11.140
we don't know what it is.
238
00:10:12.030 --> 00:10:14.990
Andrew Dunkley: No, we don't. So probably
239
00:10:15.070 --> 00:10:17.310
not contributing to the expansion of the
240
00:10:17.310 --> 00:10:17.790
universe.
241
00:10:18.270 --> 00:10:19.630
Professor Fred Watson: Yes, that's correct.
242
00:10:20.270 --> 00:10:21.950
Andrew Dunkley: And we don't really know what is
243
00:10:22.110 --> 00:10:22.910
contributing.
244
00:10:23.230 --> 00:10:25.910
Professor Fred Watson: Well, the main contribution is the Big Bang
245
00:10:25.910 --> 00:10:26.910
itself. Yeah, uh,
246
00:10:28.670 --> 00:10:31.630
Andrew Dunkley: it's just a continuing explosion of some
247
00:10:31.630 --> 00:10:31.950
kind.
248
00:10:32.450 --> 00:10:35.230
Professor Fred Watson: Um, so the
249
00:10:35.230 --> 00:10:37.790
Big Bang was what gave the
250
00:10:37.790 --> 00:10:40.270
universe the impetus to start expanding.
251
00:10:40.960 --> 00:10:43.500
Uh, and, uh, for the first.
252
00:10:43.900 --> 00:10:46.700
Well, uh, it actually, the expansion
253
00:10:46.700 --> 00:10:49.220
rate was very, very rapid at the beginning of
254
00:10:49.220 --> 00:10:51.420
this period that we call inflation, which
255
00:10:51.420 --> 00:10:53.740
lasted for a gazillionth of a second.
256
00:10:54.400 --> 00:10:56.260
Uh, and then it sort of settled down to
257
00:10:56.260 --> 00:10:57.500
something a bit more reasonable.
258
00:10:58.080 --> 00:10:58.090
Professor Fred Watson: Uh,
259
00:11:00.300 --> 00:11:02.700
Professor Fred Watson: but about 5 billion years ago,
260
00:11:03.260 --> 00:11:05.580
that's when the expansion started
261
00:11:05.580 --> 00:11:08.540
accelerating. Uh, and that's where we
262
00:11:08.540 --> 00:11:11.080
think the effect of dark energy really
263
00:11:11.080 --> 00:11:13.840
kicked in. Because dark energy was,
264
00:11:14.360 --> 00:11:16.040
uh, strong enough to overcome the
265
00:11:16.040 --> 00:11:17.800
gravitational pull of everything in the
266
00:11:17.800 --> 00:11:19.160
universe, which is trying to slow the
267
00:11:19.160 --> 00:11:22.000
expansion down gravitationally. And that's
268
00:11:22.000 --> 00:11:23.880
what we used to think would happen. And you
269
00:11:23.880 --> 00:11:26.560
get the big crunch. Uh, but yeah, when
270
00:11:26.720 --> 00:11:29.160
dark energy was. Oh, when the accelerated
271
00:11:29.160 --> 00:11:30.520
expansion was discovered back in
272
00:11:30.520 --> 00:11:33.040
1998,
273
00:11:33.710 --> 00:11:36.360
uh, that's when we realised there was
274
00:11:36.360 --> 00:11:39.120
something, um, lacking in our understanding
275
00:11:39.120 --> 00:11:41.440
of the universe. Something that is there,
276
00:11:41.440 --> 00:11:43.720
this energy that seems to
277
00:11:44.280 --> 00:11:46.400
impel the universe to be continuously
278
00:11:46.400 --> 00:11:49.360
accelerating. Uh, um, accelerating
279
00:11:49.360 --> 00:11:51.160
faster than it was before. And that's what's
280
00:11:51.160 --> 00:11:53.480
happening now? M. Yeah, I think
281
00:11:54.280 --> 00:11:56.200
just accelerating. It's the acceleration of
282
00:11:56.200 --> 00:11:58.800
the universe. The acceleration itself may be
283
00:11:58.800 --> 00:12:01.600
slowing down, but it is
284
00:12:01.600 --> 00:12:02.600
still going, I'm getting myself.
285
00:12:02.600 --> 00:12:04.520
Andrew Dunkley: Yeah, it's very confusing. It expanded
286
00:12:04.680 --> 00:12:06.480
initially. When the Big Bang happened, it
287
00:12:06.480 --> 00:12:08.830
expanded. Uh, am I right in saying fast?
288
00:12:08.900 --> 00:12:11.220
Faster than the speed of light for a period
289
00:12:11.220 --> 00:12:11.700
of time.
290
00:12:12.580 --> 00:12:15.260
Professor Fred Watson: Yes. I mean, space, um, can do
291
00:12:15.260 --> 00:12:16.100
whatever it likes.
292
00:12:16.100 --> 00:12:17.660
It's not limited to the speed of light.
293
00:12:17.660 --> 00:12:20.420
Andrew Dunkley: Then it's down now, started
294
00:12:20.900 --> 00:12:23.500
accelerating again. But now we think that
295
00:12:23.500 --> 00:12:26.420
acceleration is slowing down
296
00:12:26.500 --> 00:12:27.220
possibly.
297
00:12:28.040 --> 00:12:30.140
Professor Fred Watson: Ah, that's still an observation that's yet to
298
00:12:30.140 --> 00:12:32.140
be confirmed. That the acceleration is
299
00:12:32.140 --> 00:12:34.700
decreasing, but it's still accelerating.
300
00:12:34.700 --> 00:12:36.780
That's the thing. It's not, you know, the
301
00:12:36.780 --> 00:12:38.580
expansion of the universe is not slowing
302
00:12:38.580 --> 00:12:41.080
down. Uh, still
303
00:12:41.080 --> 00:12:43.360
accelerating, but the acceleration might be
304
00:12:43.360 --> 00:12:45.200
slowing down. It's.
305
00:12:46.320 --> 00:12:48.320
Yeah, it's a double derivative for those.
306
00:12:48.720 --> 00:12:49.520
Andrew Dunkley: It is, isn't it?
307
00:12:49.680 --> 00:12:50.560
Professor Fred Watson: Yeah, exactly.
308
00:12:50.640 --> 00:12:52.800
Andrew Dunkley: Yeah. Uh, one of our live viewers,
309
00:12:53.540 --> 00:12:56.400
uh, has suggested that the universe could
310
00:12:56.400 --> 00:12:58.880
be a doughnut shape. He doesn't have anything
311
00:12:58.880 --> 00:13:01.760
to prove that he's. It's just a hunch. I,
312
00:13:02.260 --> 00:13:04.520
uh, we. We can prove certain things, can't
313
00:13:04.520 --> 00:13:04.800
we?
314
00:13:05.520 --> 00:13:07.640
Professor Fred Watson: Yeah, Um, I mean, it's.
315
00:13:09.000 --> 00:13:11.960
You can have a doughnut. You can have, uh,
316
00:13:11.960 --> 00:13:14.400
what you might call, uh, the geometry of a
317
00:13:14.400 --> 00:13:16.880
doughnut, uh, without the thing actually
318
00:13:16.880 --> 00:13:19.280
looking like a doughnut. If I put it that
319
00:13:19.280 --> 00:13:22.160
way. Yeah. Um, uh, this is all
320
00:13:22.160 --> 00:13:24.280
to do with, for example, the geometry that we
321
00:13:24.280 --> 00:13:27.160
all deal with in everyday life is Euclidean
322
00:13:27.160 --> 00:13:29.000
geometry. Where parallel lines don't meet.
323
00:13:29.000 --> 00:13:31.720
But there are other geometries, uh, which
324
00:13:31.800 --> 00:13:33.640
could affect the shape of the universe. And
325
00:13:33.880 --> 00:13:36.000
doughnuts, I think, do come into
326
00:13:36.000 --> 00:13:36.760
consideration.
327
00:13:36.840 --> 00:13:38.820
Andrew Dunkley: Well, there you go, Moose. Well done.
328
00:13:40.100 --> 00:13:41.220
See, people just.
329
00:13:41.300 --> 00:13:43.700
They just think and ideas
330
00:13:44.580 --> 00:13:46.820
come forward. And sometimes they're worth
331
00:13:46.820 --> 00:13:48.420
investigating, indeed.
332
00:13:49.250 --> 00:13:52.060
Um, thank you for the question. I think it
333
00:13:52.060 --> 00:13:53.900
was from Jeff in Colorado.
334
00:13:53.900 --> 00:13:54.379
Professor Fred Watson: It was.
335
00:13:54.379 --> 00:13:57.020
Andrew Dunkley: This is Space Nuts, a Q A edition with Andrew
336
00:13:57.020 --> 00:13:59.220
Dunkley and Professor Fred Watson Watson.
337
00:14:00.900 --> 00:14:03.180
Professor Fred Watson: Hey, that's one of the better sims, believe
338
00:14:03.180 --> 00:14:05.480
me. We've had a couple of cool cardiac arrest
339
00:14:05.480 --> 00:14:08.280
down here too. Pete. Up
340
00:14:08.280 --> 00:14:08.560
here.
341
00:14:08.640 --> 00:14:09.760
Professor Fred Watson: Space Nuts.
342
00:14:11.070 --> 00:14:13.000
Andrew Dunkley: Uh, our next question comes from the Gold
343
00:14:13.000 --> 00:14:15.920
Coast. Not the one in, uh, Africa, the one in
344
00:14:15.920 --> 00:14:18.840
Australia. Uh, from Brian. He says.
345
00:14:18.840 --> 00:14:21.440
Hi. Long time listener, first question. Thank
346
00:14:21.440 --> 00:14:22.960
you, Brian. Good to hear from you. Sorry.
347
00:14:22.960 --> 00:14:23.840
About black holes.
348
00:14:23.840 --> 00:14:23.870
Professor Fred Watson: Ah.
349
00:14:23.870 --> 00:14:26.800
Andrew Dunkley: Uh, uh, since we cannot see behind a black
350
00:14:26.800 --> 00:14:29.360
hole, does it cover up the cosmic microwave
351
00:14:29.360 --> 00:14:32.080
background radiation. Or does that light get
352
00:14:32.240 --> 00:14:34.240
lensed around the black hole?
353
00:14:35.650 --> 00:14:38.080
Professor Fred Watson: Um. Uh, yes,
354
00:14:38.640 --> 00:14:41.120
it does. Uh, to an
355
00:14:41.120 --> 00:14:41.680
extent.
356
00:14:42.510 --> 00:14:42.520
Professor Fred Watson: Um,
357
00:14:45.040 --> 00:14:47.440
Professor Fred Watson: there are funny effects
358
00:14:47.920 --> 00:14:50.840
that come into play on the
359
00:14:50.840 --> 00:14:53.040
background radiation. And
360
00:14:54.320 --> 00:14:56.240
basically this sent my thinking,
361
00:14:57.090 --> 00:14:59.640
uh, to something I really read about for a
362
00:14:59.640 --> 00:15:02.380
long time. And, um,
363
00:15:02.380 --> 00:15:05.180
I've now lost it. Yes, here it is. Something
364
00:15:05.180 --> 00:15:06.420
called the Sunyaev
365
00:15:07.540 --> 00:15:09.940
Zeldovich effect, which
366
00:15:10.260 --> 00:15:13.120
is the way, um,
367
00:15:13.460 --> 00:15:15.860
the spectrum of the cosmic
368
00:15:15.860 --> 00:15:18.620
microwave background is
369
00:15:18.620 --> 00:15:21.140
modified as the Light
370
00:15:21.140 --> 00:15:23.220
passes through galaxy clusters.
371
00:15:23.860 --> 00:15:25.980
It comes about through a phenomenon called
372
00:15:25.980 --> 00:15:28.970
inverse Compton scattering. Uh,
373
00:15:29.380 --> 00:15:31.800
so that the radiation of the background
374
00:15:33.800 --> 00:15:36.600
is uh, modified. If that light passes through
375
00:15:36.600 --> 00:15:39.480
a galaxy cluster. I
376
00:15:39.480 --> 00:15:42.160
can't remember which way it works, whether
377
00:15:42.160 --> 00:15:44.600
it's. I, uh, think it is
378
00:15:45.320 --> 00:15:47.560
a decrease in the intensity
379
00:15:48.600 --> 00:15:51.360
of the background. It might be an
380
00:15:51.360 --> 00:15:53.040
increase. I might have that. It's a long time
381
00:15:53.040 --> 00:15:55.400
since I've thought about this. But that's the
382
00:15:55.400 --> 00:15:58.350
sort of thing that. That is taken into
383
00:15:58.350 --> 00:16:00.630
account when people consider
384
00:16:01.750 --> 00:16:04.750
uh, um. Basically
385
00:16:04.750 --> 00:16:07.310
the cosmic microwave background as we see it
386
00:16:07.310 --> 00:16:10.310
from planet Earth. Uh, and
387
00:16:10.710 --> 00:16:13.510
so, um, phenomena like black holes.
388
00:16:14.270 --> 00:16:17.230
Uh, Brian's question is
389
00:16:17.230 --> 00:16:19.670
a good one because there would be a
390
00:16:19.670 --> 00:16:22.630
modification of the radiation, um, and
391
00:16:23.230 --> 00:16:25.870
lensing would be part of that. You've got a
392
00:16:25.870 --> 00:16:28.590
black hole that uh, intensely
393
00:16:28.990 --> 00:16:31.710
modifies the gravitational field around it
394
00:16:31.710 --> 00:16:34.630
that makes it act like a lens. So that's
395
00:16:34.630 --> 00:16:37.430
going to happen with not just uh, the light
396
00:16:37.430 --> 00:16:39.190
of any stars behind it, but the
397
00:16:39.190 --> 00:16:41.750
gravitational, uh, sorry, the background
398
00:16:41.750 --> 00:16:43.790
radiation itself, the microwave background.
399
00:16:44.180 --> 00:16:47.020
Um, it's an interesting, um,
400
00:16:47.020 --> 00:16:49.310
question actually. I'd like to follow up a
401
00:16:49.310 --> 00:16:51.270
little bit more on that one, Brian, and maybe
402
00:16:51.270 --> 00:16:53.910
we'll get back to you. Uh, again, just to the
403
00:16:53.910 --> 00:16:56.010
extent, you know, is that a way of
404
00:16:56.010 --> 00:16:58.330
determining how many black holes there are in
405
00:16:58.330 --> 00:17:00.890
space? Uh, because we don't really have.
406
00:17:00.970 --> 00:17:03.210
We've got a few estimates based on
407
00:17:03.840 --> 00:17:06.530
um, our uh, knowledge of stellar
408
00:17:06.530 --> 00:17:09.490
evolution. Uh, we've got a few estimates
409
00:17:09.490 --> 00:17:12.460
based on galaxies themselves. Um,
410
00:17:12.890 --> 00:17:14.890
I guess, um,
411
00:17:15.530 --> 00:17:17.810
thinking aloud a bit and maybe this is the
412
00:17:17.810 --> 00:17:20.570
answer to the question, uh,
413
00:17:20.740 --> 00:17:23.140
the black hole itself.
414
00:17:23.380 --> 00:17:25.730
Let's just think about the black holes that
415
00:17:25.730 --> 00:17:28.620
uh, are uh, in the centres of
416
00:17:28.620 --> 00:17:30.580
galaxies, the supermassive black holes.
417
00:17:31.380 --> 00:17:34.180
So that uh, you might have a supermassive
418
00:17:34.180 --> 00:17:36.780
black hole that's a few billion times the
419
00:17:36.780 --> 00:17:38.820
solar mass, but that's still
420
00:17:39.460 --> 00:17:41.980
probably small compared with the mass of the
421
00:17:41.980 --> 00:17:44.660
galaxy itself. So the lensing effect
422
00:17:45.220 --> 00:17:48.100
is going to be what you would see from the
423
00:17:48.100 --> 00:17:50.860
galaxy and the black hole at the middle.
424
00:17:51.150 --> 00:17:53.460
Uh, and I think that's probably the likely
425
00:17:53.460 --> 00:17:56.460
answer to the question. Um, so I might
426
00:17:56.460 --> 00:17:58.940
not need to follow up on that,
427
00:17:59.420 --> 00:18:01.550
having kind of worked it out. Uh,
428
00:18:02.380 --> 00:18:05.340
and that lensing effect of galaxies is indeed
429
00:18:05.500 --> 00:18:07.500
taken into account when we look at
430
00:18:08.540 --> 00:18:10.420
the cosmic um, microwave background
431
00:18:10.420 --> 00:18:12.460
radiation. So yes is the answer.
432
00:18:13.060 --> 00:18:14.980
Andrew Dunkley: Okay, Easy peasy.
433
00:18:15.670 --> 00:18:18.570
Uh, and uh, thank you for the question, um,
434
00:18:18.570 --> 00:18:21.260
Brian. And uh, yeah, hope all is well in that
435
00:18:21.260 --> 00:18:22.980
horrible, horrible part of the world
436
00:18:24.180 --> 00:18:27.100
known as the Gold Coast. It's well named
437
00:18:27.100 --> 00:18:29.140
because it's got beautiful beaches,
438
00:18:29.300 --> 00:18:32.220
beautiful, uh, climate. Don't um, know
439
00:18:32.220 --> 00:18:34.420
about the people. No, I'm kidding. Queensland
440
00:18:34.420 --> 00:18:37.380
is a lovely. Wow.
441
00:18:38.340 --> 00:18:41.020
Like I mentioned last episode, my best friend
442
00:18:41.020 --> 00:18:42.980
Dave, he's a Queenslander. So there you are.
443
00:18:43.620 --> 00:18:45.000
Professor Fred Watson: Don't worry, Brian. He doesn't like
444
00:18:45.000 --> 00:18:46.000
Yorkshiremen either.
445
00:18:47.910 --> 00:18:50.720
Andrew Dunkley: Uh, I like everybody, I do.
446
00:18:50.930 --> 00:18:53.320
Ah, our final question, Fred Watson, comes
447
00:18:53.320 --> 00:18:55.240
from Bob. I don't know where Bob's from, but
448
00:18:55.240 --> 00:18:58.160
hello, Bob, wherever you are. Uh, how small
449
00:18:58.240 --> 00:19:01.040
and misshapen can a moon be and
450
00:19:01.120 --> 00:19:03.440
still with a straight face
451
00:19:04.000 --> 00:19:05.200
be called a moon?
452
00:19:05.760 --> 00:19:07.880
That's an interesting question. Brings Mars
453
00:19:07.880 --> 00:19:09.960
into the equation here because its moons are,
454
00:19:09.960 --> 00:19:12.700
uh, certainly not what you would consider
455
00:19:12.780 --> 00:19:15.620
moon shaped. We think of our moon as a
456
00:19:15.620 --> 00:19:18.420
sphere, and that's generally how it goes. And
457
00:19:18.420 --> 00:19:20.140
a lot of the other ones in the solar system
458
00:19:20.140 --> 00:19:22.820
are spherical. Uh, Mars is an
459
00:19:22.820 --> 00:19:24.780
exception. Um, we think they're captured
460
00:19:24.780 --> 00:19:26.700
asteroids, don't we? But, uh, yeah, when is a
461
00:19:26.700 --> 00:19:28.780
moon not a moon? I think is the precid
462
00:19:28.780 --> 00:19:29.660
version of the question.
463
00:19:31.260 --> 00:19:34.060
Professor Fred Watson: Yeah. Um, so this
464
00:19:34.060 --> 00:19:36.940
could be my old mate Bob Argyle, uh,
465
00:19:36.940 --> 00:19:39.880
who's in Cambridge. Ah, but
466
00:19:39.880 --> 00:19:42.240
I don't know. So, Bob, if this is you, drop
467
00:19:42.240 --> 00:19:44.650
us a line. Um,
468
00:19:45.360 --> 00:19:48.320
yeah, there's a very good friend, uh, going
469
00:19:48.320 --> 00:19:50.000
back a long way. We used to work together at
470
00:19:50.000 --> 00:19:52.720
the Royal Greenwich Observatory. Bob
471
00:19:52.720 --> 00:19:55.240
originated, if it's the same Bob, in, uh,
472
00:19:55.440 --> 00:19:57.720
Newcastle on Tyne, up there in the north of
473
00:19:57.720 --> 00:20:00.000
England. And I used to live there too. So,
474
00:20:00.960 --> 00:20:03.680
yeah, still got some records that he sold me.
475
00:20:05.890 --> 00:20:07.820
Um, okay. We've done all that before because
476
00:20:07.820 --> 00:20:10.500
I think Bob's asked us questions before and,
477
00:20:10.510 --> 00:20:13.060
um, it probably isn't the same, Bob,
478
00:20:13.300 --> 00:20:15.600
but it's a great question. Um,
479
00:20:16.820 --> 00:20:19.220
how small and misshapen can a moon be and
480
00:20:19.220 --> 00:20:21.300
still with a straight face be called a moon?
481
00:20:21.630 --> 00:20:23.960
Um, pretty small, actually. Uh,
482
00:20:24.020 --> 00:20:26.860
certainly. Um, some of
483
00:20:26.860 --> 00:20:29.800
the moons of Saturn, uh,
484
00:20:30.580 --> 00:20:33.250
their diameters are measured, you know,
485
00:20:33.730 --> 00:20:36.050
in single figure kilometres.
486
00:20:36.780 --> 00:20:39.770
Um, uh, we're kind of getting
487
00:20:39.770 --> 00:20:41.570
on that way. You mentioned the moons of Mars,
488
00:20:41.890 --> 00:20:42.530
Andrew.
489
00:20:42.530 --> 00:20:43.010
Professor Fred Watson: Yes.
490
00:20:43.090 --> 00:20:45.370
Professor Fred Watson: Phobos, 23 kilometres across or
491
00:20:45.370 --> 00:20:47.810
thereabouts. Deimos, the smaller one. I think
492
00:20:47.810 --> 00:20:50.650
it's about 15 kilometres and as you said,
493
00:20:50.650 --> 00:20:53.130
probably captured asteroids. But the fact
494
00:20:53.130 --> 00:20:55.050
that it's in orbit around, that these are in
495
00:20:55.050 --> 00:20:57.850
orbit around Mars makes them moons. They are
496
00:20:57.850 --> 00:21:00.850
satellites of Mars. Uh, and I think they get
497
00:21:00.850 --> 00:21:02.930
smaller when you look at Saturn. Some of the
498
00:21:02.930 --> 00:21:05.630
moons sort of wed into the
499
00:21:05.710 --> 00:21:08.030
ring system. I think, as I said,
500
00:21:08.430 --> 00:21:11.110
the diameters measured in single kilometres,
501
00:21:11.110 --> 00:21:13.350
but we still call them moons. They add to the
502
00:21:13.350 --> 00:21:16.350
total of. I think it's 297 at the moment. The
503
00:21:16.350 --> 00:21:18.830
total number of moons known around Saturn.
504
00:21:19.320 --> 00:21:22.150
Uh, so, um, yeah. How small can a moon be
505
00:21:22.150 --> 00:21:24.070
and still with a straight face be called a
506
00:21:24.070 --> 00:21:26.750
moon? Pretty damn small. A few kilometres.
507
00:21:26.910 --> 00:21:28.430
Yeah, maybe even a few metres.
508
00:21:29.710 --> 00:21:32.260
If you're talking about, um, you know,
509
00:21:32.660 --> 00:21:34.780
debris around a planet, there might be
510
00:21:34.780 --> 00:21:36.700
objects that size in orbit around Earth.
511
00:21:36.700 --> 00:21:39.300
Although we do tend to know now about near
512
00:21:39.300 --> 00:21:41.900
Earth objects, whether they're um, asteroids
513
00:21:41.900 --> 00:21:44.660
or moons. We think that
514
00:21:45.540 --> 00:21:47.780
our um, big moon is the only natural
515
00:21:47.780 --> 00:21:50.180
satellite of Earth. We've discussed some of
516
00:21:50.180 --> 00:21:53.180
that stuff as well. We do, sorry. There are
517
00:21:53.180 --> 00:21:56.020
objects that accompany Earth, uh, temporarily
518
00:21:56.020 --> 00:21:56.860
in its orbit.
519
00:21:56.860 --> 00:21:59.341
Andrew Dunkley: Well, I was about to mention 1, uh, 2025
520
00:21:59.508 --> 00:22:01.860
PN7 which was discovered in
521
00:22:02.740 --> 00:22:05.480
Aug. 2025 by the Pan Starrs
522
00:22:05.480 --> 00:22:08.040
Observatory. It's referred to as a
523
00:22:08.040 --> 00:22:10.160
quasi moon. Uh, and
524
00:22:10.640 --> 00:22:12.960
it's like 19 metres across,
525
00:22:13.040 --> 00:22:14.080
62ft.
526
00:22:14.240 --> 00:22:15.120
Professor Fred Watson: Yeah, yeah.
527
00:22:15.120 --> 00:22:17.600
Andrew Dunkley: So it's, it's, you know, it's only
528
00:22:18.240 --> 00:22:19.440
about the size of a house.
529
00:22:20.480 --> 00:22:21.440
Professor Fred Watson: Yeah, that's right.
530
00:22:22.880 --> 00:22:24.800
Andrew Dunkley: So, um, but, but it won't stay.
531
00:22:26.160 --> 00:22:29.120
Professor Fred Watson: That's correct. Um, and it's only
532
00:22:29.600 --> 00:22:31.760
a quasi moon. It's actually in orbit around
533
00:22:31.760 --> 00:22:34.760
the sun. Uh, a number of objects like that,
534
00:22:34.760 --> 00:22:35.200
they'.
535
00:22:35.740 --> 00:22:37.260
Andrew Dunkley: It's caught up with us at the moment, isn't
536
00:22:37.260 --> 00:22:37.500
it?
537
00:22:37.500 --> 00:22:40.260
Professor Fred Watson: That's right. When you look at its orbit, you
538
00:22:40.260 --> 00:22:42.780
realise that uh, uh,
539
00:22:43.300 --> 00:22:45.060
uh, it's in orbit around the sun, but it
540
00:22:45.060 --> 00:22:47.260
always hangs around the Earth as well.
541
00:22:47.820 --> 00:22:50.500
But it's not in orbit around the Earth. Uh, I
542
00:22:50.500 --> 00:22:52.860
think that's what defines a quasi moon.
543
00:22:53.020 --> 00:22:55.420
Andrew Dunkley: Here's a question. Um, with
544
00:22:56.780 --> 00:22:59.580
Mars probably capturing its moons
545
00:23:00.380 --> 00:23:03.380
because of their odd potato shapes, is it
546
00:23:03.380 --> 00:23:05.820
possible sometime that Earth could capture,
547
00:23:05.840 --> 00:23:08.680
uh, an asteroid and claim a second moon?
548
00:23:09.180 --> 00:23:11.560
Professor Fred Watson: Uh, yes. Yeah, that's right, it is.
549
00:23:11.880 --> 00:23:12.280
Andrew Dunkley: Wow.
550
00:23:12.280 --> 00:23:14.040
Professor Fred Watson: And it may have happened in the past as well.
551
00:23:14.200 --> 00:23:16.680
Andrew Dunkley: Yeah. Okay. Very
552
00:23:16.680 --> 00:23:17.240
interesting.
553
00:23:17.320 --> 00:23:19.200
Professor Fred Watson: All right. The um, thing about the Earth
554
00:23:19.200 --> 00:23:22.200
compared with Mars, Andrew though, is that
555
00:23:22.360 --> 00:23:25.360
what might inhibit that capture on
556
00:23:25.360 --> 00:23:27.960
Earth is our uh, main moon because
557
00:23:28.200 --> 00:23:31.040
it's compared with our uh, planet,
558
00:23:31.040 --> 00:23:33.420
it's a massive object. Uh,
559
00:23:33.960 --> 00:23:36.200
it's 1-80th of the mass of Earth.
560
00:23:36.810 --> 00:23:39.580
Uh, the mass of Phobos and Deimos together
561
00:23:39.580 --> 00:23:42.060
is, you know, basically
562
00:23:42.060 --> 00:23:44.420
infinitesimal compared with the mass of Mars.
563
00:23:45.220 --> 00:23:48.060
So the moon itself, its gravity is
564
00:23:48.060 --> 00:23:50.340
going to be something that, um, any
565
00:23:50.580 --> 00:23:52.870
wandering asteroid will feel, uh,
566
00:23:53.220 --> 00:23:55.780
alongside the gravity of Earth and that might
567
00:23:55.780 --> 00:23:58.620
tend to kick it out relatively quickly from
568
00:23:58.620 --> 00:24:00.180
being in orbit around the Earth.
569
00:24:00.420 --> 00:24:01.780
Andrew Dunkley: Okay, very cool.
570
00:24:02.790 --> 00:24:04.980
Um, Gosh, we went through those fast.
571
00:24:06.100 --> 00:24:08.260
Professor Fred Watson: We did. Great questions too.
572
00:24:08.340 --> 00:24:11.050
Andrew Dunkley: They were indeed, yes. If, uh, you have
573
00:24:11.360 --> 00:24:13.680
questions for us, um, please send them in.
574
00:24:13.680 --> 00:24:15.520
We'd love to hear from you. You, uh, can jump
575
00:24:15.520 --> 00:24:17.680
on our website to get more information about
576
00:24:17.680 --> 00:24:19.880
how to do that. Well, I'll tell you. Click
577
00:24:19.880 --> 00:24:22.560
the AMA button at the top of the
578
00:24:22.560 --> 00:24:25.280
screen and you can send text and audio
579
00:24:25.280 --> 00:24:27.600
questions. Don't forget to tell us who you
580
00:24:27.600 --> 00:24:29.760
are and maybe where you're from. That'd be
581
00:24:29.760 --> 00:24:32.200
nice. We love to know where our audience is.
582
00:24:32.200 --> 00:24:33.840
We had someone from Yemen the other day,
583
00:24:33.840 --> 00:24:36.740
which was terrific. Uh, but, uh,
584
00:24:36.800 --> 00:24:39.640
nice to have an international flavour in our,
585
00:24:39.640 --> 00:24:41.800
in our shows. And thanks, uh, to our live
586
00:24:41.800 --> 00:24:44.790
viewers as well, who pop questions in once
587
00:24:44.790 --> 00:24:47.110
in a while, which is terrific. And thank you,
588
00:24:47.110 --> 00:24:48.830
Fred Watson. Uh, we'll catch you on the next
589
00:24:48.830 --> 00:24:50.270
episode of Space Nuts.
590
00:24:50.910 --> 00:24:53.030
Professor Fred Watson: Great pleasure, Andrew, and thanks again to
591
00:24:53.030 --> 00:24:54.870
all the listeners sending in those fabulous
592
00:24:54.870 --> 00:24:55.470
questions.
593
00:24:55.790 --> 00:24:58.470
Andrew Dunkley: Indeed. And thanks to Huw in the studio.
594
00:24:58.470 --> 00:25:00.510
Couldn't be with us today because he's a
595
00:25:00.590 --> 00:25:03.110
quasi Huw. And from me, Andrew
596
00:25:03.110 --> 00:25:05.630
Dunkley, thanks for your company. We'll see
597
00:25:05.630 --> 00:25:07.470
you on the next episode of Space Nuts.
598
00:25:07.470 --> 00:25:08.110
Professor Fred Watson: Bye. Bye.
599
00:25:08.770 --> 00:25:11.510
Andrew Dunkley: Uh, you've been listening to the Space Nuts
600
00:25:11.510 --> 00:25:14.500
podcast, available at
601
00:25:14.500 --> 00:25:16.420
Apple Podcasts, Spotify,
602
00:25:16.660 --> 00:25:19.420
iHeartRadio or your favourite podcast
603
00:25:19.420 --> 00:25:21.140
player. You can also stream on
604
00:25:21.140 --> 00:25:24.100
demand@bytes.com. this has been another
605
00:25:24.100 --> 00:25:26.180
quality podcast production from
606
00:25:26.180 --> 00:25:27.300
bytes.com.
0
00:00:00.000 --> 00:00:02.400
Andrew Dunkley: Hi there. Thanks for joining us again. This
1
00:00:02.400 --> 00:00:05.040
is Space Nuts, a Q and A edition where we,
2
00:00:05.420 --> 00:00:07.760
uh, get questions, we look at them and go,
3
00:00:08.160 --> 00:00:10.640
no clue. No, I haven't got any idea what
4
00:00:10.640 --> 00:00:13.200
we're doing. So we're not doing that today.
5
00:00:13.440 --> 00:00:14.240
Professor Fred Watson: Actually, we will.
6
00:00:14.380 --> 00:00:17.280
Andrew Dunkley: Uh, we've got a question from Ron, uh, asking
7
00:00:17.280 --> 00:00:20.120
about, uh, astronomy in regard to
8
00:00:20.120 --> 00:00:22.680
a super fast moving planet. How would that
9
00:00:22.680 --> 00:00:24.760
work if you were living on it, is what he's
10
00:00:24.760 --> 00:00:27.640
saying. Uh, Jeff wants to know about photon
11
00:00:27.640 --> 00:00:30.440
pressure. Um, Brian is asking
12
00:00:30.440 --> 00:00:33.070
about, um, what a black hole
13
00:00:33.070 --> 00:00:35.350
covers up. Interesting.
14
00:00:35.830 --> 00:00:38.430
And when is a moon no longer a
15
00:00:38.430 --> 00:00:41.270
moon? Bob asks. We'll see if we can answer
16
00:00:41.270 --> 00:00:43.910
all of those questions on today's episode of
17
00:00:43.910 --> 00:00:44.870
space nuts.
18
00:00:45.110 --> 00:00:46.190
Professor Fred Watson: 15 seconds.
19
00:00:46.190 --> 00:00:48.514
Guidance is internal. 10,
20
00:00:48.666 --> 00:00:51.510
9. Ignition sequence start.
21
00:00:51.670 --> 00:00:52.391
Professor Fred Watson: Space nuts.
22
00:00:52.463 --> 00:00:53.820
Professor Fred Watson: 5, 4, 3, 2.
23
00:00:53.892 --> 00:00:56.679
1, 2, 3, 4, 5, 5, 4, 3,
24
00:00:56.751 --> 00:00:57.430
2, 1.
25
00:00:57.510 --> 00:00:58.710
Andrew Dunkley: Space nuts.
26
00:00:58.710 --> 00:01:00.550
Professor Fred Watson: Astronauts report it feels good.
27
00:01:01.150 --> 00:01:03.430
Andrew Dunkley: He's back for more. His name is Professor
28
00:01:03.430 --> 00:01:05.550
Fred Watson Watson, astronomer at large.
29
00:01:05.710 --> 00:01:06.590
Hello, Fred Watson.
30
00:01:06.990 --> 00:01:09.350
Professor Fred Watson: Hello, Andrew. Uh, it's good to be back for
31
00:01:09.350 --> 00:01:09.630
more.
32
00:01:09.870 --> 00:01:12.710
Andrew Dunkley: It is. I'm trying to figure out why your
33
00:01:12.710 --> 00:01:14.470
parents gave you the first name Professor.
34
00:01:14.470 --> 00:01:15.230
That seems a little.
35
00:01:17.550 --> 00:01:20.430
Professor Fred Watson: I thought so too. It could have been, sir.
36
00:01:22.350 --> 00:01:24.790
Andrew Dunkley: I was probably not as bad as those parents
37
00:01:24.790 --> 00:01:26.750
in. I think it was Sweden or somewhere who
38
00:01:26.750 --> 00:01:29.380
named their kid Megadeth. Well,
39
00:01:29.380 --> 00:01:32.340
yes, and the government tried
40
00:01:32.340 --> 00:01:34.500
to stop them and they went to court and they
41
00:01:34.500 --> 00:01:34.780
won.
42
00:01:35.100 --> 00:01:37.420
Professor Fred Watson: Yes, I believe I remember that.
43
00:01:37.500 --> 00:01:40.240
Andrew Dunkley: Yeah, Quite a while back now. But m.
44
00:01:40.780 --> 00:01:43.210
That's beside the point. Uh, we've got, uh,
45
00:01:43.210 --> 00:01:45.420
answers to questions or we've got questions
46
00:01:45.580 --> 00:01:47.420
we're hoping we can answer.
47
00:01:48.460 --> 00:01:50.700
When I say we, I'm talking about you.
48
00:01:53.740 --> 00:01:54.540
Professor Fred Watson: No pressure.
49
00:01:54.930 --> 00:01:57.130
Andrew Dunkley: No, none at all. Um, this first question is
50
00:01:57.130 --> 00:01:59.890
brilliant, though. Uh, hi there. From upstate
51
00:01:59.890 --> 00:02:02.530
New York. How hope all is well,
52
00:02:02.750 --> 00:02:05.570
uh, as you approach spring. It's not, Ron.
53
00:02:06.130 --> 00:02:09.090
Hay fever sucks. I,
54
00:02:09.170 --> 00:02:11.930
I played 36 holes of golf this week in a, in
55
00:02:11.930 --> 00:02:13.820
a major local tournament. And, um,
56
00:02:15.330 --> 00:02:17.490
I, I paid for it dearly.
57
00:02:18.470 --> 00:02:21.310
Um, and I still am. But,
58
00:02:21.310 --> 00:02:23.620
uh, yeah, it's a tough time of year for
59
00:02:23.620 --> 00:02:26.420
people who suffer hay fever here. I came
60
00:02:26.420 --> 00:02:29.420
second, by the way. Anyway, um, sorry,
61
00:02:29.420 --> 00:02:31.300
this is a bit wordy. He says with the
62
00:02:31.300 --> 00:02:34.200
information just released on the star S300,
63
00:02:34.200 --> 00:02:36.740
uh, one orbiting Sagittarius A being one of
64
00:02:36.740 --> 00:02:39.420
the fastest stars in the Milky Way. And he
65
00:02:39.420 --> 00:02:42.300
sent us a link about that. Moving at 8% the
66
00:02:42.300 --> 00:02:43.780
speed of light. That sounds like a lot.
67
00:02:43.780 --> 00:02:46.660
25,000 kilometres per second. I was
68
00:02:46.660 --> 00:02:49.220
wondering how this would affect an astronomer
69
00:02:49.220 --> 00:02:52.010
on a hypothetical planet, um,
70
00:02:52.380 --> 00:02:55.020
around that region, um, relative
71
00:02:55.020 --> 00:02:57.820
to an Outside observer, their clocks would
72
00:02:57.960 --> 00:02:59.980
uh, slow dramatically due to the high
73
00:02:59.980 --> 00:03:02.940
velocity and uh, the depth in
74
00:03:02.940 --> 00:03:05.820
the black hole's gravitational well at
75
00:03:05.880 --> 00:03:08.300
um, I can't say that word. Peri.
76
00:03:08.540 --> 00:03:09.380
Professor Fred Watson: Periapsis.
77
00:03:09.380 --> 00:03:12.300
Andrew Dunkley: Yes. Uh, then speed up as they
78
00:03:12.380 --> 00:03:15.260
reach apoapsis.
79
00:03:15.420 --> 00:03:18.300
Yes. Uh, would that not cause their
80
00:03:18.300 --> 00:03:20.500
measurements of time related events like
81
00:03:20.500 --> 00:03:23.360
orbital periods of nearby planets or
82
00:03:23.360 --> 00:03:26.360
stars to vary during their orbit
83
00:03:26.440 --> 00:03:29.200
of the black hole? If so, it's crazy to
84
00:03:29.200 --> 00:03:31.960
think how this would skew their science until
85
00:03:31.960 --> 00:03:34.440
they learned about relativity. Thanks very
86
00:03:34.440 --> 00:03:37.400
much for a great podcast. Always enlightening
87
00:03:37.400 --> 00:03:38.680
Ron. Thank you Ron.
88
00:03:38.680 --> 00:03:41.240
I love this question, it's really
89
00:03:41.240 --> 00:03:41.720
clever.
90
00:03:42.520 --> 00:03:44.710
Professor Fred Watson: Well it is. Um, and um,
91
00:03:45.670 --> 00:03:47.720
uh, Ron's exactly right.
92
00:03:49.160 --> 00:03:51.960
This thing is in
93
00:03:51.960 --> 00:03:54.440
a very very unusual place within
94
00:03:56.020 --> 00:03:58.980
orbiting Sagittarius, a star which is the 4
95
00:03:58.980 --> 00:04:01.300
million solar mass black hole at the centre
96
00:04:01.300 --> 00:04:04.220
of our galaxy. So um, exactly
97
00:04:04.220 --> 00:04:06.740
as he says, both the relativistic
98
00:04:06.740 --> 00:04:09.700
speed and um, by that I mean speed close to
99
00:04:09.700 --> 00:04:12.220
the speed of light. 8% is close to the speed
100
00:04:12.220 --> 00:04:14.540
of light compared with most of the speeds
101
00:04:14.540 --> 00:04:17.540
that we uh, encounter uh, in astronomy.
102
00:04:18.100 --> 00:04:20.940
Uh, um, it is uh,
103
00:04:20.990 --> 00:04:23.470
that that relativistic speed changes,
104
00:04:23.950 --> 00:04:26.510
gives you time dilation as does the
105
00:04:26.510 --> 00:04:29.150
gravitational well that um, this
106
00:04:29.150 --> 00:04:31.230
star orbits. I
107
00:04:32.190 --> 00:04:34.910
didn't um, Let me just have a look at
108
00:04:34.910 --> 00:04:37.630
that uh, link. I have looked at it before,
109
00:04:38.240 --> 00:04:41.070
um, but I can't remember how elliptical its
110
00:04:41.070 --> 00:04:43.630
orbit is. Um, it's
111
00:04:44.110 --> 00:04:46.950
basically very elongated and so
112
00:04:46.950 --> 00:04:49.690
at what is what Ron uh,
113
00:04:49.830 --> 00:04:52.020
correctly calls periapsis, um
114
00:04:53.830 --> 00:04:56.670
the apse closest to the galactic
115
00:04:56.670 --> 00:04:57.190
centre.
116
00:04:57.350 --> 00:05:00.350
Apsidies are uh, the points in an orbit
117
00:05:00.350 --> 00:05:02.150
which are either ah, the nearest or the
118
00:05:02.150 --> 00:05:04.790
furthest periapsis nearest apoapsis
119
00:05:04.790 --> 00:05:07.670
furthest away. Um, we talk about perigee and
120
00:05:07.670 --> 00:05:10.230
apogee for satellites around the Earth.
121
00:05:10.370 --> 00:05:13.030
Um, that's the way the
122
00:05:13.030 --> 00:05:15.990
terminology works. So um, you're
123
00:05:15.990 --> 00:05:18.390
going to have different phenomena uh
124
00:05:18.520 --> 00:05:20.160
depending on where you are because the
125
00:05:20.160 --> 00:05:22.840
velocity will vary as you
126
00:05:22.840 --> 00:05:25.280
go around this elongated orbit. That's
127
00:05:25.280 --> 00:05:28.120
Kepler's laws. They still hold at these
128
00:05:28.290 --> 00:05:30.280
uh, high gravitational intensities.
129
00:05:30.930 --> 00:05:33.720
Um, um, so the time
130
00:05:33.720 --> 00:05:36.360
dilation phenomena uh, and
131
00:05:36.440 --> 00:05:38.520
the sorts of things that you would experience
132
00:05:38.760 --> 00:05:41.280
are exactly ah as Ron said there'd be another
133
00:05:41.280 --> 00:05:43.800
phenomenon as well. Um, I mean
134
00:05:45.300 --> 00:05:47.810
being near a black hole is gonna be weird uh
135
00:05:47.810 --> 00:05:49.820
as to what your sky looks like because the
136
00:05:49.820 --> 00:05:52.500
black hole is relatively nearby, there's
137
00:05:52.580 --> 00:05:54.540
stuff swirling around it with the accretion
138
00:05:54.540 --> 00:05:56.660
disc. It's kind of hard to imagine yourself
139
00:05:56.660 --> 00:05:59.060
in that situation. But at
140
00:05:59.060 --> 00:06:01.980
relativistic speeds like that, uh, it
141
00:06:01.980 --> 00:06:04.980
also changes the position of
142
00:06:04.980 --> 00:06:06.580
objects in your sky.
143
00:06:07.170 --> 00:06:09.260
Um, so if you imagine something hurtling
144
00:06:09.260 --> 00:06:12.260
along at, uh, a significant
145
00:06:12.500 --> 00:06:15.500
fraction of the speed of light, uh, the stars
146
00:06:15.500 --> 00:06:17.680
that you see tend to
147
00:06:18.560 --> 00:06:21.040
the positions you'll see will, um, be.
148
00:06:21.680 --> 00:06:24.200
They're erroneous, but the stars will look as
149
00:06:24.200 --> 00:06:26.680
though they're nearer to the direction in
150
00:06:26.680 --> 00:06:29.000
which you're heading than they really are. So
151
00:06:29.000 --> 00:06:30.760
there's a tendency, especially as you
152
00:06:30.760 --> 00:06:32.640
approach getting near the speed of light,
153
00:06:32.960 --> 00:06:34.720
basically all the stars that you'd see will
154
00:06:34.720 --> 00:06:37.480
be bunched up, uh, fairly close together in
155
00:06:37.480 --> 00:06:40.080
front of you, um, because that's the way
156
00:06:40.080 --> 00:06:41.680
their light is changing itself.
157
00:06:42.160 --> 00:06:44.640
Andrew Dunkley: I reckon, uh, being on a planet in a
158
00:06:44.640 --> 00:06:47.160
situation like that, uh, orbiting a fast
159
00:06:47.160 --> 00:06:49.360
moving star, your astrophotography would be
160
00:06:49.360 --> 00:06:49.880
awesome.
161
00:06:51.320 --> 00:06:52.200
Professor Fred Watson: Yeah, it would.
162
00:06:52.520 --> 00:06:55.240
Except, well, probably not. I mean,
163
00:06:56.360 --> 00:06:58.040
the star trails would all be in the wrong
164
00:06:58.040 --> 00:07:00.920
place. Yeah, the stars, yeah, but no, great
165
00:07:00.920 --> 00:07:03.800
question. And Ron, you're on the money there
166
00:07:03.800 --> 00:07:04.120
too.
167
00:07:04.120 --> 00:07:06.960
Andrew Dunkley: Yeah. And um, by comparison, I suppose we can
168
00:07:06.960 --> 00:07:08.680
draw on a science fiction movie,
169
00:07:08.920 --> 00:07:11.400
Interstellar, where they visited
170
00:07:11.400 --> 00:07:14.150
Miller's planet, which was near Gargantua,
171
00:07:14.150 --> 00:07:17.100
uh, which is, um, a black
172
00:07:17.100 --> 00:07:19.780
hole in the film. And for every
173
00:07:19.940 --> 00:07:22.860
hour they were on the surface of
174
00:07:22.860 --> 00:07:25.330
the planet, seven years passed on Earth. So,
175
00:07:25.330 --> 00:07:27.220
uh, that's the sort of gravitational effect
176
00:07:27.220 --> 00:07:29.900
we're talking about. But, um, in terms
177
00:07:29.900 --> 00:07:32.260
of the speed of a planet,
178
00:07:32.890 --> 00:07:35.780
um, in accordance with the fast moving star,
179
00:07:36.580 --> 00:07:38.250
it's a different kettle of fish, isn't it?
180
00:07:38.250 --> 00:07:41.100
Um, you're observing everything out of sync,
181
00:07:41.100 --> 00:07:42.860
I suppose would be the best way to describe
182
00:07:42.860 --> 00:07:43.140
it.
183
00:07:43.140 --> 00:07:45.620
Professor Fred Watson: Yes, that's right, exactly.
184
00:07:45.620 --> 00:07:48.200
Andrew Dunkley: So quite interesting. Thanks for the
185
00:07:48.200 --> 00:07:50.400
question, Ron, and great to hear from you.
186
00:07:54.400 --> 00:07:56.000
Professor Fred Watson: Also space nuts.
187
00:07:56.210 --> 00:07:58.160
Andrew Dunkley: Uh, our next question, Fred Watson, comes
188
00:07:58.160 --> 00:08:00.240
from Jeff, uh, also in the United States.
189
00:08:00.240 --> 00:08:02.880
He's in Colorado. Uh, hello
190
00:08:02.880 --> 00:08:04.920
Andrew and Fred Watson. Thanks for the
191
00:08:04.920 --> 00:08:06.960
amazing shows. Oh, have we done one? Have we.
192
00:08:08.650 --> 00:08:11.360
Uh, the sun emits millions of billions of
193
00:08:11.440 --> 00:08:14.200
photons every second and it's pretty
194
00:08:14.200 --> 00:08:16.000
much average as a star.
195
00:08:17.110 --> 00:08:19.680
Uh, could the radiation pressure from all the
196
00:08:19.680 --> 00:08:22.440
universe's photons exert enough force to
197
00:08:22.440 --> 00:08:25.000
affect the expansion of the universe? Now
198
00:08:25.000 --> 00:08:26.680
there's an interesting theory, Fred Watson.
199
00:08:27.320 --> 00:08:30.200
Professor Fred Watson: Uh, there is, yes. Uh, it's
200
00:08:30.200 --> 00:08:33.160
um, so 10 to the 45. 10 to
201
00:08:33.160 --> 00:08:35.840
the power. 45 photons per second coming from
202
00:08:35.840 --> 00:08:38.640
the sun. Um, I like that number. It's quite a
203
00:08:38.640 --> 00:08:39.640
lot. It is
204
00:08:41.720 --> 00:08:43.810
so that, uh,
205
00:08:45.540 --> 00:08:48.010
that basically that, um,
206
00:08:48.340 --> 00:08:50.580
flux of photons, if I can put it that way,
207
00:08:51.060 --> 00:08:53.660
is for every star is an
208
00:08:53.660 --> 00:08:56.660
outward flux, um, for the universe
209
00:08:56.660 --> 00:08:59.220
as a whole, it's kind of going to cancel out.
210
00:08:59.860 --> 00:09:01.940
Um, but it is something
211
00:09:02.740 --> 00:09:05.540
that is taken into account,
212
00:09:06.440 --> 00:09:09.300
um, in the study of
213
00:09:09.300 --> 00:09:11.980
cosmology, the behaviour of the universe as a
214
00:09:11.980 --> 00:09:14.760
whole. And so in particular, you know,
215
00:09:14.760 --> 00:09:16.960
the potentially nice idea that this could
216
00:09:16.960 --> 00:09:19.600
account for dark energy, uh, which is the
217
00:09:19.600 --> 00:09:22.280
energy of the universe itself. That
218
00:09:22.360 --> 00:09:25.160
is, um, two quite different
219
00:09:25.240 --> 00:09:28.120
things. Uh, dark energy is
220
00:09:28.120 --> 00:09:30.760
independent of any kind of photon pressure.
221
00:09:31.300 --> 00:09:34.240
Uh, and so, um, it's basically the
222
00:09:34.240 --> 00:09:36.960
idea of all the photons floating around the
223
00:09:36.960 --> 00:09:39.800
universe. Uh, I think they are the most
224
00:09:39.800 --> 00:09:42.640
common subatomic particle in the universe, if
225
00:09:42.640 --> 00:09:45.400
I remember rightly. And neutrinos are the
226
00:09:45.400 --> 00:09:47.220
second. I think that was one we covered a
227
00:09:47.220 --> 00:09:48.020
couple of weeks ago.
228
00:09:48.180 --> 00:09:48.740
Andrew Dunkley: Yep.
229
00:09:49.320 --> 00:09:51.940
Professor Fred Watson: Uh, so, um, they're accounted for
230
00:09:52.020 --> 00:09:54.540
in our understanding of the expansion of the
231
00:09:54.540 --> 00:09:57.220
universe. And it doesn't explain dark energy.
232
00:09:57.300 --> 00:10:00.100
Dark energy is still an issue. Uh, it's,
233
00:10:00.310 --> 00:10:02.700
uh, something just connected with space
234
00:10:02.700 --> 00:10:04.860
itself. It will be there. Even if the
235
00:10:04.860 --> 00:10:07.260
universe was completely dark, you'd still
236
00:10:07.260 --> 00:10:10.220
have dark energy, we believe. And
237
00:10:10.220 --> 00:10:11.140
we don't know what it is.
238
00:10:12.030 --> 00:10:14.990
Andrew Dunkley: No, we don't. So probably
239
00:10:15.070 --> 00:10:17.310
not contributing to the expansion of the
240
00:10:17.310 --> 00:10:17.790
universe.
241
00:10:18.270 --> 00:10:19.630
Professor Fred Watson: Yes, that's correct.
242
00:10:20.270 --> 00:10:21.950
Andrew Dunkley: And we don't really know what is
243
00:10:22.110 --> 00:10:22.910
contributing.
244
00:10:23.230 --> 00:10:25.910
Professor Fred Watson: Well, the main contribution is the Big Bang
245
00:10:25.910 --> 00:10:26.910
itself. Yeah, uh,
246
00:10:28.670 --> 00:10:31.630
Andrew Dunkley: it's just a continuing explosion of some
247
00:10:31.630 --> 00:10:31.950
kind.
248
00:10:32.450 --> 00:10:35.230
Professor Fred Watson: Um, so the
249
00:10:35.230 --> 00:10:37.790
Big Bang was what gave the
250
00:10:37.790 --> 00:10:40.270
universe the impetus to start expanding.
251
00:10:40.960 --> 00:10:43.500
Uh, and, uh, for the first.
252
00:10:43.900 --> 00:10:46.700
Well, uh, it actually, the expansion
253
00:10:46.700 --> 00:10:49.220
rate was very, very rapid at the beginning of
254
00:10:49.220 --> 00:10:51.420
this period that we call inflation, which
255
00:10:51.420 --> 00:10:53.740
lasted for a gazillionth of a second.
256
00:10:54.400 --> 00:10:56.260
Uh, and then it sort of settled down to
257
00:10:56.260 --> 00:10:57.500
something a bit more reasonable.
258
00:10:58.080 --> 00:10:58.090
Professor Fred Watson: Uh,
259
00:11:00.300 --> 00:11:02.700
Professor Fred Watson: but about 5 billion years ago,
260
00:11:03.260 --> 00:11:05.580
that's when the expansion started
261
00:11:05.580 --> 00:11:08.540
accelerating. Uh, and that's where we
262
00:11:08.540 --> 00:11:11.080
think the effect of dark energy really
263
00:11:11.080 --> 00:11:13.840
kicked in. Because dark energy was,
264
00:11:14.360 --> 00:11:16.040
uh, strong enough to overcome the
265
00:11:16.040 --> 00:11:17.800
gravitational pull of everything in the
266
00:11:17.800 --> 00:11:19.160
universe, which is trying to slow the
267
00:11:19.160 --> 00:11:22.000
expansion down gravitationally. And that's
268
00:11:22.000 --> 00:11:23.880
what we used to think would happen. And you
269
00:11:23.880 --> 00:11:26.560
get the big crunch. Uh, but yeah, when
270
00:11:26.720 --> 00:11:29.160
dark energy was. Oh, when the accelerated
271
00:11:29.160 --> 00:11:30.520
expansion was discovered back in
272
00:11:30.520 --> 00:11:33.040
1998,
273
00:11:33.710 --> 00:11:36.360
uh, that's when we realised there was
274
00:11:36.360 --> 00:11:39.120
something, um, lacking in our understanding
275
00:11:39.120 --> 00:11:41.440
of the universe. Something that is there,
276
00:11:41.440 --> 00:11:43.720
this energy that seems to
277
00:11:44.280 --> 00:11:46.400
impel the universe to be continuously
278
00:11:46.400 --> 00:11:49.360
accelerating. Uh, um, accelerating
279
00:11:49.360 --> 00:11:51.160
faster than it was before. And that's what's
280
00:11:51.160 --> 00:11:53.480
happening now? M. Yeah, I think
281
00:11:54.280 --> 00:11:56.200
just accelerating. It's the acceleration of
282
00:11:56.200 --> 00:11:58.800
the universe. The acceleration itself may be
283
00:11:58.800 --> 00:12:01.600
slowing down, but it is
284
00:12:01.600 --> 00:12:02.600
still going, I'm getting myself.
285
00:12:02.600 --> 00:12:04.520
Andrew Dunkley: Yeah, it's very confusing. It expanded
286
00:12:04.680 --> 00:12:06.480
initially. When the Big Bang happened, it
287
00:12:06.480 --> 00:12:08.830
expanded. Uh, am I right in saying fast?
288
00:12:08.900 --> 00:12:11.220
Faster than the speed of light for a period
289
00:12:11.220 --> 00:12:11.700
of time.
290
00:12:12.580 --> 00:12:15.260
Professor Fred Watson: Yes. I mean, space, um, can do
291
00:12:15.260 --> 00:12:16.100
whatever it likes.
292
00:12:16.100 --> 00:12:17.660
It's not limited to the speed of light.
293
00:12:17.660 --> 00:12:20.420
Andrew Dunkley: Then it's down now, started
294
00:12:20.900 --> 00:12:23.500
accelerating again. But now we think that
295
00:12:23.500 --> 00:12:26.420
acceleration is slowing down
296
00:12:26.500 --> 00:12:27.220
possibly.
297
00:12:28.040 --> 00:12:30.140
Professor Fred Watson: Ah, that's still an observation that's yet to
298
00:12:30.140 --> 00:12:32.140
be confirmed. That the acceleration is
299
00:12:32.140 --> 00:12:34.700
decreasing, but it's still accelerating.
300
00:12:34.700 --> 00:12:36.780
That's the thing. It's not, you know, the
301
00:12:36.780 --> 00:12:38.580
expansion of the universe is not slowing
302
00:12:38.580 --> 00:12:41.080
down. Uh, still
303
00:12:41.080 --> 00:12:43.360
accelerating, but the acceleration might be
304
00:12:43.360 --> 00:12:45.200
slowing down. It's.
305
00:12:46.320 --> 00:12:48.320
Yeah, it's a double derivative for those.
306
00:12:48.720 --> 00:12:49.520
Andrew Dunkley: It is, isn't it?
307
00:12:49.680 --> 00:12:50.560
Professor Fred Watson: Yeah, exactly.
308
00:12:50.640 --> 00:12:52.800
Andrew Dunkley: Yeah. Uh, one of our live viewers,
309
00:12:53.540 --> 00:12:56.400
uh, has suggested that the universe could
310
00:12:56.400 --> 00:12:58.880
be a doughnut shape. He doesn't have anything
311
00:12:58.880 --> 00:13:01.760
to prove that he's. It's just a hunch. I,
312
00:13:02.260 --> 00:13:04.520
uh, we. We can prove certain things, can't
313
00:13:04.520 --> 00:13:04.800
we?
314
00:13:05.520 --> 00:13:07.640
Professor Fred Watson: Yeah, Um, I mean, it's.
315
00:13:09.000 --> 00:13:11.960
You can have a doughnut. You can have, uh,
316
00:13:11.960 --> 00:13:14.400
what you might call, uh, the geometry of a
317
00:13:14.400 --> 00:13:16.880
doughnut, uh, without the thing actually
318
00:13:16.880 --> 00:13:19.280
looking like a doughnut. If I put it that
319
00:13:19.280 --> 00:13:22.160
way. Yeah. Um, uh, this is all
320
00:13:22.160 --> 00:13:24.280
to do with, for example, the geometry that we
321
00:13:24.280 --> 00:13:27.160
all deal with in everyday life is Euclidean
322
00:13:27.160 --> 00:13:29.000
geometry. Where parallel lines don't meet.
323
00:13:29.000 --> 00:13:31.720
But there are other geometries, uh, which
324
00:13:31.800 --> 00:13:33.640
could affect the shape of the universe. And
325
00:13:33.880 --> 00:13:36.000
doughnuts, I think, do come into
326
00:13:36.000 --> 00:13:36.760
consideration.
327
00:13:36.840 --> 00:13:38.820
Andrew Dunkley: Well, there you go, Moose. Well done.
328
00:13:40.100 --> 00:13:41.220
See, people just.
329
00:13:41.300 --> 00:13:43.700
They just think and ideas
330
00:13:44.580 --> 00:13:46.820
come forward. And sometimes they're worth
331
00:13:46.820 --> 00:13:48.420
investigating, indeed.
332
00:13:49.250 --> 00:13:52.060
Um, thank you for the question. I think it
333
00:13:52.060 --> 00:13:53.900
was from Jeff in Colorado.
334
00:13:53.900 --> 00:13:54.379
Professor Fred Watson: It was.
335
00:13:54.379 --> 00:13:57.020
Andrew Dunkley: This is Space Nuts, a Q A edition with Andrew
336
00:13:57.020 --> 00:13:59.220
Dunkley and Professor Fred Watson Watson.
337
00:14:00.900 --> 00:14:03.180
Professor Fred Watson: Hey, that's one of the better sims, believe
338
00:14:03.180 --> 00:14:05.480
me. We've had a couple of cool cardiac arrest
339
00:14:05.480 --> 00:14:08.280
down here too. Pete. Up
340
00:14:08.280 --> 00:14:08.560
here.
341
00:14:08.640 --> 00:14:09.760
Professor Fred Watson: Space Nuts.
342
00:14:11.070 --> 00:14:13.000
Andrew Dunkley: Uh, our next question comes from the Gold
343
00:14:13.000 --> 00:14:15.920
Coast. Not the one in, uh, Africa, the one in
344
00:14:15.920 --> 00:14:18.840
Australia. Uh, from Brian. He says.
345
00:14:18.840 --> 00:14:21.440
Hi. Long time listener, first question. Thank
346
00:14:21.440 --> 00:14:22.960
you, Brian. Good to hear from you. Sorry.
347
00:14:22.960 --> 00:14:23.840
About black holes.
348
00:14:23.840 --> 00:14:23.870
Professor Fred Watson: Ah.
349
00:14:23.870 --> 00:14:26.800
Andrew Dunkley: Uh, uh, since we cannot see behind a black
350
00:14:26.800 --> 00:14:29.360
hole, does it cover up the cosmic microwave
351
00:14:29.360 --> 00:14:32.080
background radiation. Or does that light get
352
00:14:32.240 --> 00:14:34.240
lensed around the black hole?
353
00:14:35.650 --> 00:14:38.080
Professor Fred Watson: Um. Uh, yes,
354
00:14:38.640 --> 00:14:41.120
it does. Uh, to an
355
00:14:41.120 --> 00:14:41.680
extent.
356
00:14:42.510 --> 00:14:42.520
Professor Fred Watson: Um,
357
00:14:45.040 --> 00:14:47.440
Professor Fred Watson: there are funny effects
358
00:14:47.920 --> 00:14:50.840
that come into play on the
359
00:14:50.840 --> 00:14:53.040
background radiation. And
360
00:14:54.320 --> 00:14:56.240
basically this sent my thinking,
361
00:14:57.090 --> 00:14:59.640
uh, to something I really read about for a
362
00:14:59.640 --> 00:15:02.380
long time. And, um,
363
00:15:02.380 --> 00:15:05.180
I've now lost it. Yes, here it is. Something
364
00:15:05.180 --> 00:15:06.420
called the Sunyaev
365
00:15:07.540 --> 00:15:09.940
Zeldovich effect, which
366
00:15:10.260 --> 00:15:13.120
is the way, um,
367
00:15:13.460 --> 00:15:15.860
the spectrum of the cosmic
368
00:15:15.860 --> 00:15:18.620
microwave background is
369
00:15:18.620 --> 00:15:21.140
modified as the Light
370
00:15:21.140 --> 00:15:23.220
passes through galaxy clusters.
371
00:15:23.860 --> 00:15:25.980
It comes about through a phenomenon called
372
00:15:25.980 --> 00:15:28.970
inverse Compton scattering. Uh,
373
00:15:29.380 --> 00:15:31.800
so that the radiation of the background
374
00:15:33.800 --> 00:15:36.600
is uh, modified. If that light passes through
375
00:15:36.600 --> 00:15:39.480
a galaxy cluster. I
376
00:15:39.480 --> 00:15:42.160
can't remember which way it works, whether
377
00:15:42.160 --> 00:15:44.600
it's. I, uh, think it is
378
00:15:45.320 --> 00:15:47.560
a decrease in the intensity
379
00:15:48.600 --> 00:15:51.360
of the background. It might be an
380
00:15:51.360 --> 00:15:53.040
increase. I might have that. It's a long time
381
00:15:53.040 --> 00:15:55.400
since I've thought about this. But that's the
382
00:15:55.400 --> 00:15:58.350
sort of thing that. That is taken into
383
00:15:58.350 --> 00:16:00.630
account when people consider
384
00:16:01.750 --> 00:16:04.750
uh, um. Basically
385
00:16:04.750 --> 00:16:07.310
the cosmic microwave background as we see it
386
00:16:07.310 --> 00:16:10.310
from planet Earth. Uh, and
387
00:16:10.710 --> 00:16:13.510
so, um, phenomena like black holes.
388
00:16:14.270 --> 00:16:17.230
Uh, Brian's question is
389
00:16:17.230 --> 00:16:19.670
a good one because there would be a
390
00:16:19.670 --> 00:16:22.630
modification of the radiation, um, and
391
00:16:23.230 --> 00:16:25.870
lensing would be part of that. You've got a
392
00:16:25.870 --> 00:16:28.590
black hole that uh, intensely
393
00:16:28.990 --> 00:16:31.710
modifies the gravitational field around it
394
00:16:31.710 --> 00:16:34.630
that makes it act like a lens. So that's
395
00:16:34.630 --> 00:16:37.430
going to happen with not just uh, the light
396
00:16:37.430 --> 00:16:39.190
of any stars behind it, but the
397
00:16:39.190 --> 00:16:41.750
gravitational, uh, sorry, the background
398
00:16:41.750 --> 00:16:43.790
radiation itself, the microwave background.
399
00:16:44.180 --> 00:16:47.020
Um, it's an interesting, um,
400
00:16:47.020 --> 00:16:49.310
question actually. I'd like to follow up a
401
00:16:49.310 --> 00:16:51.270
little bit more on that one, Brian, and maybe
402
00:16:51.270 --> 00:16:53.910
we'll get back to you. Uh, again, just to the
403
00:16:53.910 --> 00:16:56.010
extent, you know, is that a way of
404
00:16:56.010 --> 00:16:58.330
determining how many black holes there are in
405
00:16:58.330 --> 00:17:00.890
space? Uh, because we don't really have.
406
00:17:00.970 --> 00:17:03.210
We've got a few estimates based on
407
00:17:03.840 --> 00:17:06.530
um, our uh, knowledge of stellar
408
00:17:06.530 --> 00:17:09.490
evolution. Uh, we've got a few estimates
409
00:17:09.490 --> 00:17:12.460
based on galaxies themselves. Um,
410
00:17:12.890 --> 00:17:14.890
I guess, um,
411
00:17:15.530 --> 00:17:17.810
thinking aloud a bit and maybe this is the
412
00:17:17.810 --> 00:17:20.570
answer to the question, uh,
413
00:17:20.740 --> 00:17:23.140
the black hole itself.
414
00:17:23.380 --> 00:17:25.730
Let's just think about the black holes that
415
00:17:25.730 --> 00:17:28.620
uh, are uh, in the centres of
416
00:17:28.620 --> 00:17:30.580
galaxies, the supermassive black holes.
417
00:17:31.380 --> 00:17:34.180
So that uh, you might have a supermassive
418
00:17:34.180 --> 00:17:36.780
black hole that's a few billion times the
419
00:17:36.780 --> 00:17:38.820
solar mass, but that's still
420
00:17:39.460 --> 00:17:41.980
probably small compared with the mass of the
421
00:17:41.980 --> 00:17:44.660
galaxy itself. So the lensing effect
422
00:17:45.220 --> 00:17:48.100
is going to be what you would see from the
423
00:17:48.100 --> 00:17:50.860
galaxy and the black hole at the middle.
424
00:17:51.150 --> 00:17:53.460
Uh, and I think that's probably the likely
425
00:17:53.460 --> 00:17:56.460
answer to the question. Um, so I might
426
00:17:56.460 --> 00:17:58.940
not need to follow up on that,
427
00:17:59.420 --> 00:18:01.550
having kind of worked it out. Uh,
428
00:18:02.380 --> 00:18:05.340
and that lensing effect of galaxies is indeed
429
00:18:05.500 --> 00:18:07.500
taken into account when we look at
430
00:18:08.540 --> 00:18:10.420
the cosmic um, microwave background
431
00:18:10.420 --> 00:18:12.460
radiation. So yes is the answer.
432
00:18:13.060 --> 00:18:14.980
Andrew Dunkley: Okay, Easy peasy.
433
00:18:15.670 --> 00:18:18.570
Uh, and uh, thank you for the question, um,
434
00:18:18.570 --> 00:18:21.260
Brian. And uh, yeah, hope all is well in that
435
00:18:21.260 --> 00:18:22.980
horrible, horrible part of the world
436
00:18:24.180 --> 00:18:27.100
known as the Gold Coast. It's well named
437
00:18:27.100 --> 00:18:29.140
because it's got beautiful beaches,
438
00:18:29.300 --> 00:18:32.220
beautiful, uh, climate. Don't um, know
439
00:18:32.220 --> 00:18:34.420
about the people. No, I'm kidding. Queensland
440
00:18:34.420 --> 00:18:37.380
is a lovely. Wow.
441
00:18:38.340 --> 00:18:41.020
Like I mentioned last episode, my best friend
442
00:18:41.020 --> 00:18:42.980
Dave, he's a Queenslander. So there you are.
443
00:18:43.620 --> 00:18:45.000
Professor Fred Watson: Don't worry, Brian. He doesn't like
444
00:18:45.000 --> 00:18:46.000
Yorkshiremen either.
445
00:18:47.910 --> 00:18:50.720
Andrew Dunkley: Uh, I like everybody, I do.
446
00:18:50.930 --> 00:18:53.320
Ah, our final question, Fred Watson, comes
447
00:18:53.320 --> 00:18:55.240
from Bob. I don't know where Bob's from, but
448
00:18:55.240 --> 00:18:58.160
hello, Bob, wherever you are. Uh, how small
449
00:18:58.240 --> 00:19:01.040
and misshapen can a moon be and
450
00:19:01.120 --> 00:19:03.440
still with a straight face
451
00:19:04.000 --> 00:19:05.200
be called a moon?
452
00:19:05.760 --> 00:19:07.880
That's an interesting question. Brings Mars
453
00:19:07.880 --> 00:19:09.960
into the equation here because its moons are,
454
00:19:09.960 --> 00:19:12.700
uh, certainly not what you would consider
455
00:19:12.780 --> 00:19:15.620
moon shaped. We think of our moon as a
456
00:19:15.620 --> 00:19:18.420
sphere, and that's generally how it goes. And
457
00:19:18.420 --> 00:19:20.140
a lot of the other ones in the solar system
458
00:19:20.140 --> 00:19:22.820
are spherical. Uh, Mars is an
459
00:19:22.820 --> 00:19:24.780
exception. Um, we think they're captured
460
00:19:24.780 --> 00:19:26.700
asteroids, don't we? But, uh, yeah, when is a
461
00:19:26.700 --> 00:19:28.780
moon not a moon? I think is the precid
462
00:19:28.780 --> 00:19:29.660
version of the question.
463
00:19:31.260 --> 00:19:34.060
Professor Fred Watson: Yeah. Um, so this
464
00:19:34.060 --> 00:19:36.940
could be my old mate Bob Argyle, uh,
465
00:19:36.940 --> 00:19:39.880
who's in Cambridge. Ah, but
466
00:19:39.880 --> 00:19:42.240
I don't know. So, Bob, if this is you, drop
467
00:19:42.240 --> 00:19:44.650
us a line. Um,
468
00:19:45.360 --> 00:19:48.320
yeah, there's a very good friend, uh, going
469
00:19:48.320 --> 00:19:50.000
back a long way. We used to work together at
470
00:19:50.000 --> 00:19:52.720
the Royal Greenwich Observatory. Bob
471
00:19:52.720 --> 00:19:55.240
originated, if it's the same Bob, in, uh,
472
00:19:55.440 --> 00:19:57.720
Newcastle on Tyne, up there in the north of
473
00:19:57.720 --> 00:20:00.000
England. And I used to live there too. So,
474
00:20:00.960 --> 00:20:03.680
yeah, still got some records that he sold me.
475
00:20:05.890 --> 00:20:07.820
Um, okay. We've done all that before because
476
00:20:07.820 --> 00:20:10.500
I think Bob's asked us questions before and,
477
00:20:10.510 --> 00:20:13.060
um, it probably isn't the same, Bob,
478
00:20:13.300 --> 00:20:15.600
but it's a great question. Um,
479
00:20:16.820 --> 00:20:19.220
how small and misshapen can a moon be and
480
00:20:19.220 --> 00:20:21.300
still with a straight face be called a moon?
481
00:20:21.630 --> 00:20:23.960
Um, pretty small, actually. Uh,
482
00:20:24.020 --> 00:20:26.860
certainly. Um, some of
483
00:20:26.860 --> 00:20:29.800
the moons of Saturn, uh,
484
00:20:30.580 --> 00:20:33.250
their diameters are measured, you know,
485
00:20:33.730 --> 00:20:36.050
in single figure kilometres.
486
00:20:36.780 --> 00:20:39.770
Um, uh, we're kind of getting
487
00:20:39.770 --> 00:20:41.570
on that way. You mentioned the moons of Mars,
488
00:20:41.890 --> 00:20:42.530
Andrew.
489
00:20:42.530 --> 00:20:43.010
Professor Fred Watson: Yes.
490
00:20:43.090 --> 00:20:45.370
Professor Fred Watson: Phobos, 23 kilometres across or
491
00:20:45.370 --> 00:20:47.810
thereabouts. Deimos, the smaller one. I think
492
00:20:47.810 --> 00:20:50.650
it's about 15 kilometres and as you said,
493
00:20:50.650 --> 00:20:53.130
probably captured asteroids. But the fact
494
00:20:53.130 --> 00:20:55.050
that it's in orbit around, that these are in
495
00:20:55.050 --> 00:20:57.850
orbit around Mars makes them moons. They are
496
00:20:57.850 --> 00:21:00.850
satellites of Mars. Uh, and I think they get
497
00:21:00.850 --> 00:21:02.930
smaller when you look at Saturn. Some of the
498
00:21:02.930 --> 00:21:05.630
moons sort of wed into the
499
00:21:05.710 --> 00:21:08.030
ring system. I think, as I said,
500
00:21:08.430 --> 00:21:11.110
the diameters measured in single kilometres,
501
00:21:11.110 --> 00:21:13.350
but we still call them moons. They add to the
502
00:21:13.350 --> 00:21:16.350
total of. I think it's 297 at the moment. The
503
00:21:16.350 --> 00:21:18.830
total number of moons known around Saturn.
504
00:21:19.320 --> 00:21:22.150
Uh, so, um, yeah. How small can a moon be
505
00:21:22.150 --> 00:21:24.070
and still with a straight face be called a
506
00:21:24.070 --> 00:21:26.750
moon? Pretty damn small. A few kilometres.
507
00:21:26.910 --> 00:21:28.430
Yeah, maybe even a few metres.
508
00:21:29.710 --> 00:21:32.260
If you're talking about, um, you know,
509
00:21:32.660 --> 00:21:34.780
debris around a planet, there might be
510
00:21:34.780 --> 00:21:36.700
objects that size in orbit around Earth.
511
00:21:36.700 --> 00:21:39.300
Although we do tend to know now about near
512
00:21:39.300 --> 00:21:41.900
Earth objects, whether they're um, asteroids
513
00:21:41.900 --> 00:21:44.660
or moons. We think that
514
00:21:45.540 --> 00:21:47.780
our um, big moon is the only natural
515
00:21:47.780 --> 00:21:50.180
satellite of Earth. We've discussed some of
516
00:21:50.180 --> 00:21:53.180
that stuff as well. We do, sorry. There are
517
00:21:53.180 --> 00:21:56.020
objects that accompany Earth, uh, temporarily
518
00:21:56.020 --> 00:21:56.860
in its orbit.
519
00:21:56.860 --> 00:21:59.341
Andrew Dunkley: Well, I was about to mention 1, uh, 2025
520
00:21:59.508 --> 00:22:01.860
PN7 which was discovered in
521
00:22:02.740 --> 00:22:05.480
Aug. 2025 by the Pan Starrs
522
00:22:05.480 --> 00:22:08.040
Observatory. It's referred to as a
523
00:22:08.040 --> 00:22:10.160
quasi moon. Uh, and
524
00:22:10.640 --> 00:22:12.960
it's like 19 metres across,
525
00:22:13.040 --> 00:22:14.080
62ft.
526
00:22:14.240 --> 00:22:15.120
Professor Fred Watson: Yeah, yeah.
527
00:22:15.120 --> 00:22:17.600
Andrew Dunkley: So it's, it's, you know, it's only
528
00:22:18.240 --> 00:22:19.440
about the size of a house.
529
00:22:20.480 --> 00:22:21.440
Professor Fred Watson: Yeah, that's right.
530
00:22:22.880 --> 00:22:24.800
Andrew Dunkley: So, um, but, but it won't stay.
531
00:22:26.160 --> 00:22:29.120
Professor Fred Watson: That's correct. Um, and it's only
532
00:22:29.600 --> 00:22:31.760
a quasi moon. It's actually in orbit around
533
00:22:31.760 --> 00:22:34.760
the sun. Uh, a number of objects like that,
534
00:22:34.760 --> 00:22:35.200
they'.
535
00:22:35.740 --> 00:22:37.260
Andrew Dunkley: It's caught up with us at the moment, isn't
536
00:22:37.260 --> 00:22:37.500
it?
537
00:22:37.500 --> 00:22:40.260
Professor Fred Watson: That's right. When you look at its orbit, you
538
00:22:40.260 --> 00:22:42.780
realise that uh, uh,
539
00:22:43.300 --> 00:22:45.060
uh, it's in orbit around the sun, but it
540
00:22:45.060 --> 00:22:47.260
always hangs around the Earth as well.
541
00:22:47.820 --> 00:22:50.500
But it's not in orbit around the Earth. Uh, I
542
00:22:50.500 --> 00:22:52.860
think that's what defines a quasi moon.
543
00:22:53.020 --> 00:22:55.420
Andrew Dunkley: Here's a question. Um, with
544
00:22:56.780 --> 00:22:59.580
Mars probably capturing its moons
545
00:23:00.380 --> 00:23:03.380
because of their odd potato shapes, is it
546
00:23:03.380 --> 00:23:05.820
possible sometime that Earth could capture,
547
00:23:05.840 --> 00:23:08.680
uh, an asteroid and claim a second moon?
548
00:23:09.180 --> 00:23:11.560
Professor Fred Watson: Uh, yes. Yeah, that's right, it is.
549
00:23:11.880 --> 00:23:12.280
Andrew Dunkley: Wow.
550
00:23:12.280 --> 00:23:14.040
Professor Fred Watson: And it may have happened in the past as well.
551
00:23:14.200 --> 00:23:16.680
Andrew Dunkley: Yeah. Okay. Very
552
00:23:16.680 --> 00:23:17.240
interesting.
553
00:23:17.320 --> 00:23:19.200
Professor Fred Watson: All right. The um, thing about the Earth
554
00:23:19.200 --> 00:23:22.200
compared with Mars, Andrew though, is that
555
00:23:22.360 --> 00:23:25.360
what might inhibit that capture on
556
00:23:25.360 --> 00:23:27.960
Earth is our uh, main moon because
557
00:23:28.200 --> 00:23:31.040
it's compared with our uh, planet,
558
00:23:31.040 --> 00:23:33.420
it's a massive object. Uh,
559
00:23:33.960 --> 00:23:36.200
it's 1-80th of the mass of Earth.
560
00:23:36.810 --> 00:23:39.580
Uh, the mass of Phobos and Deimos together
561
00:23:39.580 --> 00:23:42.060
is, you know, basically
562
00:23:42.060 --> 00:23:44.420
infinitesimal compared with the mass of Mars.
563
00:23:45.220 --> 00:23:48.060
So the moon itself, its gravity is
564
00:23:48.060 --> 00:23:50.340
going to be something that, um, any
565
00:23:50.580 --> 00:23:52.870
wandering asteroid will feel, uh,
566
00:23:53.220 --> 00:23:55.780
alongside the gravity of Earth and that might
567
00:23:55.780 --> 00:23:58.620
tend to kick it out relatively quickly from
568
00:23:58.620 --> 00:24:00.180
being in orbit around the Earth.
569
00:24:00.420 --> 00:24:01.780
Andrew Dunkley: Okay, very cool.
570
00:24:02.790 --> 00:24:04.980
Um, Gosh, we went through those fast.
571
00:24:06.100 --> 00:24:08.260
Professor Fred Watson: We did. Great questions too.
572
00:24:08.340 --> 00:24:11.050
Andrew Dunkley: They were indeed, yes. If, uh, you have
573
00:24:11.360 --> 00:24:13.680
questions for us, um, please send them in.
574
00:24:13.680 --> 00:24:15.520
We'd love to hear from you. You, uh, can jump
575
00:24:15.520 --> 00:24:17.680
on our website to get more information about
576
00:24:17.680 --> 00:24:19.880
how to do that. Well, I'll tell you. Click
577
00:24:19.880 --> 00:24:22.560
the AMA button at the top of the
578
00:24:22.560 --> 00:24:25.280
screen and you can send text and audio
579
00:24:25.280 --> 00:24:27.600
questions. Don't forget to tell us who you
580
00:24:27.600 --> 00:24:29.760
are and maybe where you're from. That'd be
581
00:24:29.760 --> 00:24:32.200
nice. We love to know where our audience is.
582
00:24:32.200 --> 00:24:33.840
We had someone from Yemen the other day,
583
00:24:33.840 --> 00:24:36.740
which was terrific. Uh, but, uh,
584
00:24:36.800 --> 00:24:39.640
nice to have an international flavour in our,
585
00:24:39.640 --> 00:24:41.800
in our shows. And thanks, uh, to our live
586
00:24:41.800 --> 00:24:44.790
viewers as well, who pop questions in once
587
00:24:44.790 --> 00:24:47.110
in a while, which is terrific. And thank you,
588
00:24:47.110 --> 00:24:48.830
Fred Watson. Uh, we'll catch you on the next
589
00:24:48.830 --> 00:24:50.270
episode of Space Nuts.
590
00:24:50.910 --> 00:24:53.030
Professor Fred Watson: Great pleasure, Andrew, and thanks again to
591
00:24:53.030 --> 00:24:54.870
all the listeners sending in those fabulous
592
00:24:54.870 --> 00:24:55.470
questions.
593
00:24:55.790 --> 00:24:58.470
Andrew Dunkley: Indeed. And thanks to Huw in the studio.
594
00:24:58.470 --> 00:25:00.510
Couldn't be with us today because he's a
595
00:25:00.590 --> 00:25:03.110
quasi Huw. And from me, Andrew
596
00:25:03.110 --> 00:25:05.630
Dunkley, thanks for your company. We'll see
597
00:25:05.630 --> 00:25:07.470
you on the next episode of Space Nuts.
598
00:25:07.470 --> 00:25:08.110
Professor Fred Watson: Bye. Bye.
599
00:25:08.770 --> 00:25:11.510
Andrew Dunkley: Uh, you've been listening to the Space Nuts
600
00:25:11.510 --> 00:25:14.500
podcast, available at
601
00:25:14.500 --> 00:25:16.420
Apple Podcasts, Spotify,
602
00:25:16.660 --> 00:25:19.420
iHeartRadio or your favourite podcast
603
00:25:19.420 --> 00:25:21.140
player. You can also stream on
604
00:25:21.140 --> 00:25:24.100
demand@bytes.com. this has been another
605
00:25:24.100 --> 00:25:26.180
quality podcast production from
606
00:25:26.180 --> 00:25:27.300
bytes.com.
