WEBVTT FILE

1
00:00:00.000 --> 00:00:07.280
"Hubble inside the Image / RS Puppis"

2
00:00:07.280 --> 00:00:12.280
This is an image of a star, a very special 
star, which is called a Cepheid variable.

3
00:00:12.280 --> 00:00:15.760
And the particular star we're 
looking at is called RS Pupis.  

4
00:00:15.760 --> 00:00:18.720
It's in a southern hemisphere constellation.

5
00:00:18.720 --> 00:00:20.160
It's not a naked eye star,

6
00:00:20.160 --> 00:00:21.320
but it almost is.

7
00:00:21.320 --> 00:00:25.160
And so it's bright enough that you can 
see it through even small telescopes.

8
00:00:25.160 --> 00:00:30.040
And it's been observed by amateur and professional 
astronomers for a very long time. We have,  

9
00:00:30.040 --> 00:00:34.040
you know, over a hundred years worth of 
data on the variability of this star.

10
00:00:34.040 --> 00:00:37.960
The star gets five times brighter 
at peak than from its trough.

11
00:00:37.960 --> 00:00:41.800
So RS Pup goes 40 or more days between peaks

12
00:00:41.800 --> 00:00:44.200
That happens on a 41 day time scale

13
00:00:44.200 --> 00:00:47.920
brightness from its dimmest to its 
brightest is about five times brighter.

14
00:00:47.920 --> 00:00:50.160
So that's a huge change.

15
00:00:50.160 --> 00:00:56.040
It's about 6500 light years from Earth. And 
that's a really important number for us to know.

16
00:00:56.040 --> 00:00:58.080
The distance, the precise distance

17
00:00:58.080 --> 00:00:59.920
It turns out it's a really important

18
00:00:59.920 --> 00:01:03.080
benchmark in how we understand 
the scale of the universe

19
00:01:03.080 --> 00:01:06.720
Cepheid variables have a very special relationship  

20
00:01:06.720 --> 00:01:11.200
between the period of variability, how 
fast it goes from one peak to the next,

21
00:01:11.200 --> 00:01:15.400
and their absolute brightness. So how 
much energy is coming out of that star?

22
00:01:15.400 --> 00:01:17.760
And if we know something's relative brightness

23
00:01:17.760 --> 00:01:19.720
and we can measure its absolute brightness from  

24
00:01:19.720 --> 00:01:23.080
something like the period luminosity 
relationship of the Cepheid variable,  

25
00:01:23.080 --> 00:01:28.200
then we can tell you what distance it must 
be at to look as bright as it looks to us.

26
00:01:28.200 --> 00:01:30.000
So this is a Cepheid variable.

27
00:01:30.000 --> 00:01:32.640
They're very important in our 
history of understanding our  

28
00:01:32.640 --> 00:01:34.880
scale of the universe and how it evolves.

29
00:01:34.880 --> 00:01:36.720
And this particular Cepheid variable

30
00:01:36.720 --> 00:01:40.280
is in our galaxy. So it's nearby enough 
that we can study it really well.

31
00:01:40.280 --> 00:01:42.760
this one is so special because it's near the tip

32
00:01:42.760 --> 00:01:48.120
of that period luminosity relation. So it really 
allows us to calibrate the entire relation

33
00:01:48.120 --> 00:01:48.840
and

34
00:01:48.840 --> 00:01:54.280
the fact that it's embedded in this 
beautiful cloud of dust. It looks amazing.

35
00:01:54.280 --> 00:01:58.280
a stunning Hubble image with 
all the filamentary detail.

36
00:01:58.280 --> 00:02:01.960
But there's also science embedded in this light,

37
00:02:01.960 --> 00:02:06.240
and that science allows us to get an 
extremely accurate distance to this  

38
00:02:06.240 --> 00:02:10.240
Cepheid variable within about 
10% accuracy or even better.

39
00:02:10.240 --> 00:02:13.920
But this is a star that's about ten 
times more massive than the sun.

40
00:02:13.920 --> 00:02:15.120
More massive stars

41
00:02:15.120 --> 00:02:16.960
they live fast and they die young.

42
00:02:16.960 --> 00:02:20.280
and when that happens, the star 
starts to go through these changes.

43
00:02:20.280 --> 00:02:22.520
And so that's what is actually driving the period  

44
00:02:22.520 --> 00:02:26.720
luminosity relation is that the star 
is actually unstable during this time

45
00:02:26.720 --> 00:02:28.160
and
when it's got a lot of

46
00:02:28.160 --> 00:02:30.000
coming from the core, that core has to

47
00:02:30.000 --> 00:02:32.800
do something. When it expands, 
the radius gets much bigger,  

48
00:02:32.800 --> 00:02:37.360
the star gets brighter to a certain point where 
it cools down and that starts to contract again.

49
00:02:37.360 --> 00:02:40.560
Now, it doesn't have as much energy. 
It starts to fall back into gravity,

50
00:02:40.560 --> 00:02:43.080
where it gets close enough that 
it heats up again. That's actually  

51
00:02:43.080 --> 00:02:45.920
what's driving these period Luminosity relations.

52
00:02:45.920 --> 00:02:49.280
So even though the star is younger than our sun

53
00:02:49.280 --> 00:02:55.360
because it's ten times brighter, 
it's actually more evolved

54
00:02:55.360 --> 00:02:58.200
when you first look at it, it 
almost looks like the material  

55
00:02:58.200 --> 00:03:02.880
itself is spewing away from the star. 
But that's actually not what's happening.

56
00:03:02.880 --> 00:03:03.880
What's happening is that

57
00:03:03.880 --> 00:03:08.360
the light takes to get to the 
further out dust and gas is longer.

58
00:03:08.360 --> 00:03:12.720
So basically looking at almost like 
a snapshot through that gas and dust,

59
00:03:12.720 --> 00:03:14.120
reacting to the light.

60
00:03:14.120 --> 00:03:20.040
And that light echo allows us to make this 
extremely precise distance measurement.

61
00:03:20.040 --> 00:03:22.560
Now, due to improvements in our

62
00:03:22.560 --> 00:03:24.880
measurements of Cepheid variables like RS PUP

63
00:03:24.880 --> 00:03:27.680
we have now really narrowed down that window.

64
00:03:27.680 --> 00:03:29.320
What is the age of the universe?

65
00:03:29.320 --> 00:03:32.800
We now know it's 13 plus billion years old

66
00:03:32.800 --> 00:03:36.360
and we've seen that it's 
not just expanding linearly,  

67
00:03:36.360 --> 00:03:39.320
but it's actually an accelerating universe.

68
00:03:39.320 --> 00:03:43.360
it's all intimately tied to our 
understanding of Cepheid variables,  

69
00:03:43.360 --> 00:03:50.940
and this one is the best studied.

70
00:03:50.940 --> 00:03:58.929
"Follow us on social media @NASAHubble"