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0:46

Hello.

0:53

Hello. Oh, hi, Jay.

0:56

Fantastic to be here. Yeah,

0:58

well, it's good to have you here. You see more stars

1:00

than we do in large parts

1:03

of the country. Welcome

1:05

to Science in Action from the BBC World

1:08

Service, coming to you this week from a garden

1:10

in South Wales, where

1:13

I'm about to see for myself a super

1:15

new star, a supernova. Actually,

1:18

the blazing show of death of an old

1:20

star 20 million

1:22

light years away in the pinwheel

1:24

galaxy. It's got astronomers around

1:26

the world excited and amateurs like

1:29

Dr Jane Clark.

1:30

You'll show me where to look in a moment, won't you? But

1:33

I should say we're also peering

1:35

in this programme into the future of the billions

1:38

of people whose well-being will be

1:40

under threat if we don't get a grip on global

1:42

warming. But first, that supernova

1:45

SN 2023 IXF,

1:48

it's been called. And

1:51

Jane, you're going to show me where to look at it.

1:53

Fantastic sky. What's

1:55

the tremendously red

1:58

star up there? It is. eye-catching

2:01

star. So Leo is

2:03

about there. If you

2:05

come down that blue one which you can just see over

2:08

the observatory roof there, that's

2:10

Spica which is the brightest star in

2:12

Virgo and between that

2:15

one there that's Denebola that

2:17

star and there is the Virgo cluster

2:19

of galaxies. Each of those

2:21

are dwarf galaxies but some of them make

2:24

ours look tiny. Where

2:27

it is, can you

2:28

see the plough up there? I

2:31

see the plough. Yeah right now

2:33

the end two stars there. Yeah.

2:36

Okay imagine. At the end of the handle. At

2:39

the end of the handle yeah. Imagine

2:41

a sort of equilateral triangle.

2:44

Yeah. That way. Yeah. And

2:46

it's sort of roughly there. This

2:51

is absolutely fantastic so I've come out

2:53

to darkest whales.

2:55

Well not quite dark enough whales but it's still

2:57

very dark. And

2:59

we're looking up at the sky. Thousands

3:02

of stars up there but

3:04

there's

3:05

one in particular. Yeah let's

3:07

have a look in the observatory. Gosh

3:15

and here we are in the observatory.

3:18

I mean this is quite a setup you've got here in your

3:20

back garden. It is. So

3:22

you've got a pretty impressive

3:25

telescope there but then a whole bunch

3:27

of cameras and electronics all. Right

3:29

that one's the camera that's taking the picture you

3:32

can see there. Now after five

3:34

minutes of this you can see the galaxy

3:36

quite nicely. I can see it's gorgeous.

3:40

It's gorgeous. I mean it's such a black background.

3:43

Dotted with a few stars

3:44

but then you know this

3:46

fantastic sort of fried

3:49

egg swirl in the middle and that bright

3:51

dot. That's

3:54

it. I mean it really does stand out. If

3:56

you know this galaxy that's when you

3:59

can say it.

3:59

That wasn't there last week. Exactly.

4:03

And that's what somebody in Japan did. And

4:05

that was Friday

4:07

night, Japanese time I think. And

4:09

I took my first picture of it on Saturday

4:12

night here.

4:14

That first image showing the supernova

4:16

by Koichi Itagaki was, as Jane

4:19

said, last Friday. But M101

4:21

is a popular galaxy with amateurs and one

4:23

of them, Bronco Oostomea, had photographed

4:26

the emerging explosion unknowingly

4:29

several hours earlier.

4:30

Actually 20 hours before the announcement

4:32

was made by Itagaki, so

4:35

he made the announcement on the 19th at 17

4:37

something UTC. I

4:42

started imaging on the 18th actually

4:44

at 21, 24 UTC.

4:47

And the point is you went back

4:49

and looked at that image. Well, what

4:51

I normally do is I just take a bunch of pictures.

4:54

Like I said, I'm not a visual astronomer, so I

4:56

just let my rig do the work and I go to bed. Then

4:59

I get up next morning and obviously I want to see

5:01

what's going on. So I use my software

5:03

to stack the pictures and

5:05

I put them on Astro Bin. The

5:08

website sort of flicker for us

5:10

to photograph. And I

5:12

didn't notice. I haven't looked that good.

5:15

So I didn't know there was a supernova

5:17

because it was pretty faint by the time

5:19

as well. So right now it's more

5:21

bright in the core of M101.

5:24

But back then it was like 300

5:26

times more faint, so it's barely

5:29

recognizable. Up until Itagaki

5:32

made the announcement and then scientists

5:34

were looking on Astro Bin. And he picked up my data

5:36

and he says, well, are you aware that

5:38

there may be a supernova on your picture, which

5:41

just went off. I was like, no. So

5:44

then I started digging into some pictures

5:46

I already had because I was there in January

5:48

or February or something. Then it's

5:50

like, okay, the old picture, the new picture.

5:53

And I was surprised.

5:54

Yes, there's actually something new there. So

5:56

I was aware by then that it was

5:59

a supernova. And as far as

6:01

I know, yours is one of the

6:03

first images after the

6:06

supernova went off. Yeah,

6:08

there's a Chinese guy called Mao, and

6:11

he was one hour before me, and I

6:14

basically got the second picture,

6:16

or at least maybe there are others. But

6:19

it's important in the sense that by

6:22

the time the real astronomers were taking their

6:24

images, it had already brightened

6:26

quite a lot. So the question is, when did it

6:29

actually start to explode? And that's

6:31

sort of what you and this character,

6:34

Mao, were able to catch. Yeah,

6:36

basically, it's just a trend line which goes

6:38

down and down. A lot of images are reviewed,

6:41

and then it's like, okay, there's nothing there, there's nothing

6:43

there, there's nothing there. And then all of a sudden, one

6:45

picture

6:46

shows up, the Mao picture, which

6:49

actually had the supernova. An

6:51

hour later, my picture came along. And

6:53

a lot of others, then, because MO101

6:56

is quite a popular target.

6:58

Jane, how's it going? Those spirals

7:01

in M101 are just signing out. Is

7:04

there even an effort in the corner? Oh, sorry, I'm

7:06

in the way. It moves the dome around slightly.

7:09

Just, I think

7:09

this is supposed to do it kind of

7:11

fine. We're

7:16

okay now.

7:18

So you just do

7:20

that every once in a while. There

7:22

are so many things. I mean, presumably when you're

7:25

looking up through this telescope,

7:28

you're seeing comets that come through

7:30

the solar system. You're seeing, I

7:32

don't know, all kinds of things that go on. Is

7:34

this on your bucket list

7:37

to have a good supernova like this? Oh,

7:39

yeah. This is my

7:41

one, two, three, fourth supernova

7:44

in there. So my bucket is pretty

7:46

full of them. And how

7:48

does it rank? This one.

7:52

I should think.

7:54

It ranks pretty high with the professionals

7:56

too. Oh my gosh. Oh my

7:58

gosh. Yeah. non-stop

8:01

ever since I found out about this on

8:04

Friday. This is Dan Militsavlievic,

8:07

an astronomer at Purdue University,

8:10

always on his toes. The thing is

8:12

the universe never sleeps, right?

8:14

And that means we often lose sleep

8:17

too, having to react to

8:19

these things. When I first learned

8:21

about it Friday night, I

8:23

was about to sit down for the night

8:25

with my wife to watch a movie and

8:27

I got this email and it would have been

8:30

very easy and potentially

8:32

appropriate in

8:33

the eyes of many people to

8:35

have just disregarded it and continue

8:38

on. But because it was

8:40

so nearby, because this is

8:42

a galaxy that has been heavily monitored,

8:45

I just had to move on this information

8:48

as quickly as possible. And

8:50

thankfully the payoff has been huge.

8:53

So by sending

8:54

an email to Win Observatory,

8:58

we were able to get on that target the first

9:01

night and get among the

9:03

the highest resolution data

9:05

of this supernova, the first night

9:08

that we could possibly do so. The

9:10

instrument on the Arizona telescope is

9:12

one of the best for breaking light from

9:14

stars into their component colors

9:17

spectroscopy and was designed for

9:19

the quest for exoplanets in our

9:21

galaxy. But it's perfect also

9:24

for seeing the details of a new supernova.

9:27

And Dan had

9:28

an arrangement to override their schedule

9:31

should one erupt. All he had to do

9:33

was log in and give the coordinates

9:35

and details.

9:37

But of course it's a comedy of errors

9:39

and everything goes wrong. So I send

9:41

the email and they say please

9:44

can you log on the website and do

9:46

all what you would normally do. Well I'm not

9:48

at my computer at work and of course

9:50

I don't have the password because there's a million

9:53

different passwords. And when I try

9:55

to update the password that that

9:57

function isn't working. Right?

9:59

The team over there was very helpful

10:02

and through a series of emails

10:04

back and forth, I was describing in

10:06

piecemeal all the information they needed so

10:09

that they could do that process for me. You

10:11

can't just sort of shout at them, it's M101,

10:13

it's one of the most famous galaxies

10:16

to all astronomers. Right,

10:18

yes and no. I could do that,

10:20

but they are good scientists, which

10:22

means they don't want to make mistakes and

10:25

they wanted to

10:25

hear from me as many details

10:28

as possible before acting on it. They

10:30

don't want to make a mistake here.

10:33

There were no mistakes with the Hubble

10:35

Space Telescope either. PhD student

10:38

Erez Zimmerman and his supervisor Avashay

10:40

Galiam of the Weizmann Institute have

10:43

a similar arrangement with NASA to prioritise

10:46

its venerable orbiting platform when

10:48

the right kind of supernova erupts. Preliminary

10:52

ground checks confirmed the one in M101

10:55

fit the bill and for Erez just

10:57

starting his scientific career,

10:59

this was quite a moment. Yeah,

11:02

it's definitely very exciting. So

11:05

Avashay was checking his emails around

11:07

midnight on Saturday and

11:10

there was a report on the transient name server

11:13

that there is a supernova in M101. So

11:17

within three hours, we already sent the form

11:19

to NASA to trigger HSD. We

11:22

then had to essentially go over the

11:24

observation details and yeah,

11:26

it stayed up the entire night that night. I

11:28

mean, I understand that you had a standing

11:31

sort of arrangement with the Hubble Telescope

11:33

that if this kind of supernova

11:35

should happen and it was close enough that

11:38

you could make some details, this is how it

11:40

would work. Yes,

11:42

we have an approved

11:43

proposal to observe a

11:45

supernova which shows what

11:48

we call flash features which is essentially ionised

11:51

elements that we see in very early supernovae

11:54

surrounded by circumstellar material. This

11:56

has been a big part of my thesis to observe

11:59

these lines.

13:56

crashes

14:00

into the material that was shed previously by

14:03

the progenitor star in its aging phases.

14:06

Untangling all those changing details is

14:08

made possible by using the light spectrum

14:11

in its full glory.

14:12

The story is still in full, it only happened

14:14

a few days ago, right? But

14:16

there's already clear indications

14:19

that this star,

14:21

before it exploded, was shedding

14:24

a lot of material.

14:25

So think of like if you're, you know, you

14:27

got a bad stomach ache, you're like, oh, you're

14:29

really grumpy, and in this case the star is

14:32

grumpy and it's emitting copious

14:34

amount of gas leading up

14:36

to the terminal explosion.

14:39

And we're on it early

14:41

enough that we can watch as the light

14:44

of the explosion, as it first

14:46

emerges from the star, interact

14:49

with the surrounding gas. So this

14:51

tells us very important things about

14:54

what we understand poorly about

14:56

what the star is doing leading up to

14:58

the final explosion.

15:00

So this is a bit like when a firework goes off,

15:03

it doesn't, you don't only see the light from the sparks

15:05

of it, but you can actually see the reflected

15:08

light off of smoke around it. Yes.

15:11

You're doing the same kind of thing. That is a beautiful analogy, that

15:13

exact, that's exactly correct. And

15:15

in this case, the analogy

15:18

breaks down because the explosion

15:20

of the supernova overwhelms

15:23

the surrounding, let's say, gas. The

15:26

supernova is overrunning it, and

15:28

you know, it's moving at tens of thousands

15:30

of kilometers per second. So that happens

15:33

very, very, very, very fast. That's

15:36

why in a matter of days from the first

15:38

night that we observed on

15:40

Friday to today, we're already

15:43

seeing those original features,

15:45

those spectral fingerprints being wiped

15:47

out by the supernova running over

15:49

it.

15:59

Which is why Berkeley astronomer

16:02

Raphael Amalgati also commandeered

16:04

an orbiting telescope called New

16:06

Star Made for just this kind of

16:09

radiation

16:09

So these x-rays can penetrate

16:12

very thick and dense material so

16:14

this is type of radiation that can go

16:17

through matter that other type of

16:19

radiation can be stopped by and in

16:21

particular here is exciting because

16:24

what we what we think is going on is that

16:27

the star before dying has

16:29

expelled a lot of matter and has

16:32

polluted the very local environment

16:34

and now the light from the stellar

16:37

explosion is shining through that amount

16:39

of

16:39

mass So the only

16:41

radiation that can escape

16:44

through that type of environment are the hard

16:47

x-rays and by studying them we can learn

16:49

about this sheet of

16:51

material that is in between

16:53

So this is like a medical

16:56

x-ray except instead of having an external

16:58

source. It's being lit from inside

17:01

That's very true. Yes is exactly what

17:03

it is and presumably then the environment

17:06

inside this explosion is extremely

17:08

hot. Give me a sense of the sort of I'd

17:10

know the temperatures the densities

17:13

What's going on inside? This

17:16

explosion at the moment.

17:17

Yeah, so the temperature of

17:19

the radiation of this hard x-rays

17:22

is going to be 10 to 100 million

17:25

degrees easily and

17:29

The and the densities are also

17:32

very high Because we

17:34

do not see all the x-rays but

17:36

just this very hard x-rays

17:38

In other words, this is a really thick wall

17:40

of material that you're looking through extremely

17:43

thick and I want to know

17:45

What happened in the last centuries

17:48

of life of this star? Precisely

17:51

I want to know why the star has ejected

17:55

all of that amount of mass and

17:57

when it did so and that's

17:59

because

17:59

The theories of stellar evolution

18:02

that we have right now, they are not predictive

18:04

when it comes to explaining

18:07

when and if a star should do that.

18:10

So we are trying to fill up a gap in our

18:12

understanding of the very last moments

18:15

of evolution of massive stars.

18:17

Yes, there are several mysteries about these

18:19

supernovae form massive stars. One

18:21

thing is that we have a general idea

18:24

about

18:24

how the explosion works, but we really

18:26

don't understand the details. So

18:29

it's one thing to say, well, if you take a massive star,

18:31

eventually it's going to explode. That's something

18:33

that everybody agrees on. But then in

18:35

order to prove a theory like you said, okay,

18:37

the core collapses in the middle, then it rebounds,

18:39

there's a neutron star, and then there are shock waves,

18:42

and then the explosion happens, you really have

18:44

to be able to recapture all of

18:46

these physics in a computer simulation. You

18:49

take a simulation of a star, you put in all the physics,

18:51

you let it roll, and then you expect to

18:53

see an explosion and all the material going to infinity

18:56

and creating a lot of energy. This

18:58

has been very, very difficult to actually do

19:00

on a computer. So it's really hard to test

19:03

the theory. One of the problems

19:05

is that it's not clear with which star you

19:08

have to start. Stars are very different from each other.

19:10

So if I start my computer model with a 10

19:13

solar mass star with some composition and

19:15

you calculate a different model with 20 solar

19:18

masses in another composition, we might

19:20

not get the same thing. So which is the correct

19:22

model to calculate? Now one

19:24

of the basic parameters is say, what is the initial

19:26

condition? What star did explode? So

19:29

here we are able to say many

19:31

things about exploding stars. We could

19:33

say, I hope,

19:35

what was the composition? I think we

19:37

can limit what was the radius of the star.

19:40

And we may be able to say something deep

19:42

about what we call metallicity,

19:45

which is how much of the material

19:47

of the star was light elements, like hydrogen and

19:49

helium, and how much was heavier elements.

19:51

This is very important for understanding the evolution of

19:54

the star. So all of these physical characteristics,

19:56

once we are able to measure them, they would

19:59

create very powerful.

19:59

inputs to really understand

20:02

the physics of the explosion which is not well

20:04

understood. And that would be general,

20:07

not true only for this supernova but for all

20:09

of them. My patience in Jane's

20:11

backyard telescope dome was paying

20:13

off. That's the nucleus of the galaxy.

20:16

And there's the supernova

20:19

now. What you can just

20:20

barely see just there is

20:22

a bright nebula in

20:24

this galaxy. And last

20:26

night the supernova was about the same

20:28

brightness as that. Now it's brighter. And

20:31

look you see it's brighter than the whole galaxy. So

20:34

that one star outshines a hundred

20:36

billion stars. Can you believe it? Something

20:40

to keep astronomers worldwide busy for

20:42

a long time. Is this going to push aside all

20:45

the other work that you actually had lined up? Is

20:47

it that important?

20:49

Essentially yes. We

20:52

do have a very unique dataset now from

20:54

the Hubble Space Telescope. So there's

20:56

quite a lot of work still to be done

20:58

that is very exciting. I think

21:00

my summer is going to be very much

21:03

on this supernova for sure. We

21:06

never seem to get far from global warming

21:08

and the dangers it presents if

21:10

temperatures rise more than 1.5 degrees

21:13

above pre-industrial. The current

21:16

exceptional heatwave in India is a

21:18

taste of where we're heading.

21:20

And this week we saw a new take highlighting

21:23

the number of people who could be afflicted

21:25

in the future up to a fifth of

21:27

the world's population if we don't

21:30

take serious action. It's based

21:32

on a new concept called the climate niche.

21:35

Effectively climatologist Tim Lenten

21:38

told me the range of temperatures over which

21:40

humans have historically fared

21:42

well. There's a clear distribution

21:46

of human population density with temperature

21:48

and with rainfall and those things have barely

21:50

changed for hundreds if not thousands

21:53

of years which gives a strong clue that

21:55

it represents some constraints

21:58

on where we like to live and where we like to live

22:00

and where we flourish and where we don't flourish. So

22:03

we find that the highest population

22:05

densities are centred

22:07

on about 12 or 13 degrees centigrade

22:10

on the annual average. There's a secondary

22:12

peak of population density centred on

22:14

about 25 to 27 degrees centigrade. Now

22:18

we can also bring in that rainfall

22:20

or precipitation information. So we

22:22

put all that information together and

22:25

it gives us a clear notion

22:27

that like any other species we

22:29

have a preferred niche and then we

22:32

can ask the question as we go into a changing

22:35

climate in the future where

22:37

are people projected to be in

22:39

terms of climate and population density

22:41

in the future and we find enormous

22:44

mismatches including unsurprisingly

22:46

people getting pushed out into hot climates

22:49

that are essentially unprecedented

22:51

in the past and then there's the fact

22:54

that clearly this niche isn't

22:56

just about pure physiological

22:58

constraints on humans.

22:59

It's ecological. It's the fact that

23:02

you know our crops and our livestock also

23:05

follow a very very similar distribution of

23:07

density of crops and livestock with respect

23:09

to temperature and rainfall and we depend

23:11

on those obviously. What your paper seems

23:14

to show is that we're now at the

23:16

point where every small increment

23:18

of temperature change in terms of

23:21

global temperatures is going to have a pretty

23:23

big impact on the number of people who are affected.

23:26

Yes one of the striking things

23:28

is that above the present level

23:30

of global warming the number of

23:32

people who are going to get exposed

23:35

to this really unprecedented high temperatures

23:38

suddenly starts to kick up quite strikingly.

23:41

So right now or at about

23:43

one degree sea of global warming it

23:46

was around say 60 million people

23:48

exposed but once we go above

23:50

about 1.2 degrees centigrade of global

23:52

warming which arguably we're doing about now

23:54

with the coming El Nino

23:57

then we expect every 0.1 degree centigrade

24:00

of warming leads

24:02

to an additional 140 million people

24:05

being pushed out of the hot end of the niche into

24:08

extreme high temperatures. And that's because

24:10

you've got very large populations in these

24:12

sensitive regions. That's right,

24:14

particularly on the Indian subcontinent.

24:17

You've got high, lots of high population density

24:20

and flourishing, but it

24:22

is quite close to the point where

24:25

population density drops off really sharply

24:27

on the hot end. So you could be doing

24:29

great at 27 degrees on

24:32

the average, and then you'll find there's hardly

24:34

anywhere and anybody thriving

24:36

when you can push it just a few degrees

24:38

up to 29. It really

24:40

is conceptually possibly

24:43

living on the climate edge. We see

24:46

in the world that

24:47

current legally binding climate policies

24:50

such as they are are taking us towards, which

24:52

is about 2.7 degrees C warmer

24:55

later at the end of this century. We

24:57

see in that world, if it's populated by

24:59

the expected nine or nine and a half billion

25:02

people, that just over two

25:04

billion of those people will be

25:06

in unprecedented hot average

25:08

temperatures. The good news

25:10

is if we could act

25:12

more urgently to limit global warming

25:14

in the future towards 1.5 degrees

25:17

centigrade,

25:17

that could slash those

25:19

numbers globally by a factor of five.

25:22

In some of the most affected countries, the

25:24

proportional reduction is even greater. So

25:26

for India, the numbers would be reduced

25:29

by more than a factor of six, and in Nigeria

25:31

more than a factor of seven. I mean it's very

25:34

motivating. We talk so much about 1.5

25:37

degrees and when we're going to reach

25:39

that threshold. I

25:41

don't know what the current expectations

25:44

are. There's been a little bit of confusion in the

25:46

last week or so. As climate

25:48

scientists, climate is always defined as

25:50

the long-term average of the weather, usually

25:53

over 30 years, sometimes over 20. So

25:56

we're not quite as close to an average of 1.5

25:58

degrees C as might have been.

25:59

recently reported, but clearly we're all

26:02

worried that it's not far away and

26:04

it's hard to see how we're going to avoid it now.

26:06

This is not just about the level at which

26:09

human physiology gives up, but

26:11

it's also about the agricultural

26:13

system, the ability to feed ourselves. That's

26:16

right, and it's also tied up with

26:18

water availability as well. Some

26:21

people might want to imagine a future

26:23

where somehow the food

26:25

is being produced, or the water

26:27

is somewhere else in the world and is being somehow brought

26:29

to

26:29

us or piped to us. But there are

26:32

limits to that and we still live in a world where a lot,

26:35

for most people, food is sourced pretty

26:37

locally or regionally. When I

26:39

saw the maps and the numbers

26:42

in your paper I thought,

26:44

gosh, that's really

26:46

quite worrying. When you saw it presented

26:49

this way, did you have that kind of reaction?

26:51

Oh yes, I find it extremely

26:55

sobering, let's put it that way, and it's why

26:57

I also work very hard on trying

27:00

to convey that we can accelerate

27:02

action to reduce greenhouse gas

27:05

emissions. I wouldn't want any listener

27:07

in this richer, cooler

27:10

part of the world to think that this won't

27:13

have repercussions for all of us. One

27:16

of the clear adaptation options anyway

27:19

is if you're struggling to cope where

27:21

you are is to look to go somewhere else.

27:24

And I think it'll be a test of our

27:26

future humanity really, how

27:29

we respond to this kind of escalating

27:32

climate risk and the harm it's causing

27:34

to others. That was

27:36

Tim Lenton of the University of Exeter

27:38

with some grim projections about the future

27:40

of global warming if we don't

27:42

start acting faster. I'm

27:45

going to raise my spirits by raising

27:47

my eyes again up to the plow, make

27:49

that triangle with the last two stars

27:51

in the handle. That's where the Galaxy

27:54

Messier 101 is hosted, that new

27:56

star we've been talking about, which will be

27:59

brightening more for the future.

27:59

several days yet, but you'll

28:02

still need a telescope to see it, I'm afraid, and

28:05

not be too far south on the globe. I'm

28:07

Ronan Pease, with me is my producer Ella Hubber,

28:10

and my host, Dr. Jane Clark of the Cardiff

28:12

Astronomical Society. Thanks

28:15

so much for letting us see this. You

28:17

are more than welcome. Thank you so. And

28:20

we will doubtless be talking about

28:22

Supernova SN2023IXF

28:26

in future editions of Science in Action from the BBC.

28:29

But for now,

28:29

happy viewing.