1
00:00:03,000 --> 00:00:05,300
- Did you know that when you
look up in the dark night sky,

2
00:00:05,300 --> 00:00:07,366
you are, in a way,
looking back in time?

3
00:00:07,366 --> 00:00:08,666
It's really true.

4
00:00:08,666 --> 00:00:10,866
Much of the light you see
coming from the stars

5
00:00:10,866 --> 00:00:13,566
has been travelling across
space for thousands of years

6
00:00:13,566 --> 00:00:16,000
by the time it reaches us
here on Earth.

7
00:00:16,000 --> 00:00:19,233
Some of those stars that you can
see tonight in the night sky

8
00:00:19,233 --> 00:00:22,066
may have burned out
millions of years ago.

9
00:00:22,066 --> 00:00:24,466
If you have ever wondered
where stars come from,

10
00:00:24,466 --> 00:00:26,366
how they change,
and what happens to them

11
00:00:26,366 --> 00:00:27,866
when their life
comes to an end,

12
00:00:27,866 --> 00:00:30,000
hang with me for a few minutes
as this episode

13
00:00:30,000 --> 00:00:31,866
of "NASA Launchpad"
takes a closer look

14
00:00:31,866 --> 00:00:33,433
at the life cycle of stars,

15
00:00:33,433 --> 00:00:36,600
and bonus, we are going to talk
a little bit about how

16
00:00:36,600 --> 00:00:39,300
each of us is actually
made from dead stars.

17
00:00:39,300 --> 00:00:40,333
Yeah, really.

18
00:00:40,333 --> 00:00:42,466
[upbeat electronic music]

19
00:00:42,466 --> 00:00:43,733
- Lift off.

20
00:00:43,733 --> 00:00:49,733
[upbeat electronic music]

21
00:00:51,166 --> 00:00:53,666
- Most things in the universe
have a life cycle.

22
00:00:53,666 --> 00:00:56,633
Thankfully for some things,
like these guys,

23
00:00:56,633 --> 00:00:58,933
the life cycle
is incredibly short.

24
00:00:58,933 --> 00:01:01,000
But for other things,
like stars,

25
00:01:01,000 --> 00:01:03,833
the life cycle
can be billions of years long.

26
00:01:03,833 --> 00:01:06,566
The life cycles for stars begin
in giant stellar nurseries

27
00:01:06,566 --> 00:01:07,666
called nebula.

28
00:01:07,666 --> 00:01:09,666
If you look at one of these
star-forming nebula,

29
00:01:09,666 --> 00:01:13,300
you will see beautiful
giant clouds of dust and gas.

30
00:01:13,300 --> 00:01:15,433
How a star forms
is a little technical,

31
00:01:15,433 --> 00:01:17,866
so let's hear an explanation
from an expert.

32
00:01:17,866 --> 00:01:21,866
- A star is basically
a nuclear furnace.

33
00:01:21,866 --> 00:01:24,733
It's this collection of
mostly hydrogen gas,

34
00:01:24,733 --> 00:01:27,800
and at the center it's really,
really hot and dense,

35
00:01:27,800 --> 00:01:30,166
where you can actually get
nuclear fusion occurring,

36
00:01:30,166 --> 00:01:32,600
and that's how you get the heat
and the light from the star.

37
00:01:32,600 --> 00:01:35,233
In space you have this
collection of sort of

38
00:01:35,233 --> 00:01:37,166
diffused gas and dust particles.

39
00:01:37,166 --> 00:01:39,066
It's just sort of everywhere
in space.

40
00:01:39,066 --> 00:01:41,200
Occasionally it comes
together through gravity.

41
00:01:41,200 --> 00:01:43,200
It's attracted to itself
basically,

42
00:01:43,200 --> 00:01:45,966
and so you get these
giant molecular clouds

43
00:01:45,966 --> 00:01:47,366
that are called
these big nebula.

44
00:01:47,366 --> 00:01:50,133
As that stuff comes together
through its own gravity,

45
00:01:50,133 --> 00:01:53,666
you eventually get these places
where you have enough material

46
00:01:53,666 --> 00:01:55,466
where you can start
to form a star,

47
00:01:55,466 --> 00:01:58,466
where it all comes together
and the gravity pushes on it

48
00:01:58,466 --> 00:02:00,300
so hard that it heats up
in the center,

49
00:02:00,300 --> 00:02:03,666
and that heating up
is what will eventually lead to

50
00:02:03,666 --> 00:02:05,966
fusion and the birth of a star.

51
00:02:05,966 --> 00:02:07,900
Two of the most important
properties of a star

52
00:02:07,900 --> 00:02:10,400
are its color
and its brightness.

53
00:02:10,400 --> 00:02:13,600
And so if you take stars and
you sort of sort them by color,

54
00:02:13,600 --> 00:02:16,766
you get anything from
red to blue,

55
00:02:16,766 --> 00:02:18,933
where the red stars
will be the cooler stars

56
00:02:18,933 --> 00:02:20,666
and the blue stars
will be the hotter stars,

57
00:02:20,666 --> 00:02:22,266
so that's really
a measure of temperature.

58
00:02:22,266 --> 00:02:24,633
And then you can also sort them
by their brightness,

59
00:02:24,633 --> 00:02:26,300
and so you have
the very bright stars,

60
00:02:26,300 --> 00:02:28,200
which are usually
the more massive stars,

61
00:02:28,200 --> 00:02:30,766
and the dimmer stars,
which are usually less massive.

62
00:02:30,766 --> 00:02:32,466
And just by
these two parameters,

63
00:02:32,466 --> 00:02:34,466
you can actually tell a lot
from a star.

64
00:02:34,466 --> 00:02:36,600
You can tell how massive it is.

65
00:02:36,600 --> 00:02:39,266
You can tell how big it is,
its radius.

66
00:02:39,266 --> 00:02:41,200
You can tell how old it is.

67
00:02:41,200 --> 00:02:43,533
You can know what stage
of evolution it's in,

68
00:02:43,533 --> 00:02:46,733
and you can learn about
the environment of the star--

69
00:02:46,733 --> 00:02:47,933
that the star was born in.

70
00:02:47,933 --> 00:02:50,033
- As you know,
our sun is a star.

71
00:02:50,033 --> 00:02:52,300
It is actually
a fairly modest sized star.

72
00:02:52,300 --> 00:02:54,633
It is believed that our sun
is about halfway through

73
00:02:54,633 --> 00:02:56,866
its 10-billion-year life cycle.

74
00:02:56,866 --> 00:02:59,466
Yes, that makes our sun about
5 billion years old.

75
00:02:59,466 --> 00:03:00,533
But don't worry.

76
00:03:00,533 --> 00:03:03,566
We're all good for at least
another 5 billion more years.

77
00:03:03,566 --> 00:03:06,233
So how will our sun's life cycle
play out?

78
00:03:06,233 --> 00:03:09,066
- So our sun is a low mass star,

79
00:03:09,066 --> 00:03:12,100
and it's actually gonna go
through a really long evolution.

80
00:03:12,100 --> 00:03:14,566
It's going to be in the phase
that it's currently in,

81
00:03:14,566 --> 00:03:17,233
where it's just fusing hydrogen
into helium,

82
00:03:17,233 --> 00:03:18,833
for about 10 billion years.

83
00:03:18,833 --> 00:03:21,566
And then once it runs out
of fuel in its center,

84
00:03:21,566 --> 00:03:24,333
it's going to evolve into
a red giant star,

85
00:03:24,333 --> 00:03:25,966
red meaning
that it's gonna be cooler,

86
00:03:25,966 --> 00:03:29,366
and it's gonna be so large
that its outer radius

87
00:03:29,366 --> 00:03:31,266
is actually gonna reach
the Earth's orbit.

88
00:03:31,266 --> 00:03:32,666
It's gonna be a huge star.

89
00:03:32,666 --> 00:03:34,933
And then eventually
it'll blow off its outer layers

90
00:03:34,933 --> 00:03:37,266
and become a white dwarf star,

91
00:03:37,266 --> 00:03:39,733
and that will be the--
its final phase.

92
00:03:39,733 --> 00:03:42,300
- So at the end
of a massive star's life,

93
00:03:42,300 --> 00:03:45,166
we have what's called
a core collapse super nova.

94
00:03:45,166 --> 00:03:49,200
So the core region collapses
in on itself

95
00:03:49,200 --> 00:03:53,000
and the outer region infalls
and then rebounds,

96
00:03:53,000 --> 00:03:55,900
and you get left with
a neutron star or a black hole.

97
00:03:55,900 --> 00:03:58,933
- You have may have noticed that
no matter the size of the star,

98
00:03:58,933 --> 00:04:01,566
at the end of its life cycle,
most of its material

99
00:04:01,566 --> 00:04:04,833
is expelled back into clouds
of dust and gas in the galaxy.

100
00:04:04,833 --> 00:04:07,300
The life cycle of a star
can begin again.

101
00:04:07,300 --> 00:04:10,266
- Throughout a star's life,
it's throwing off material,

102
00:04:10,266 --> 00:04:12,200
and this material
has been enriched

103
00:04:12,200 --> 00:04:14,400
by nuclear fusion reaction,

104
00:04:14,400 --> 00:04:18,433
so originally
really only hydrogen

105
00:04:18,433 --> 00:04:21,900
and a little bit of helium
was produced in the big bang,

106
00:04:21,900 --> 00:04:24,766
and all of the elements
that we get after that

107
00:04:24,766 --> 00:04:27,366
have been produced
in either a star's life

108
00:04:27,366 --> 00:04:31,200
or in its explosion if
it's massive enough to explode.

109
00:04:31,200 --> 00:04:36,666
And that material gets mixed in
with the other gasses and dust

110
00:04:36,666 --> 00:04:38,566
in the interstellar medium,

111
00:04:38,566 --> 00:04:41,666
and produces the next generation
of stars.

112
00:04:41,666 --> 00:04:44,866
So every generation of stars
that you produce

113
00:04:44,866 --> 00:04:48,266
is more and more enriched
with material from the life

114
00:04:48,266 --> 00:04:49,400
and death of stars.

115
00:04:49,400 --> 00:04:51,366
- So what does all of this
mean for us?

116
00:04:51,366 --> 00:04:53,866
And what is our connection
to the cosmos?

117
00:04:53,866 --> 00:04:55,766
- All of that fusion
that's going on in the centers

118
00:04:55,766 --> 00:04:58,333
of stars is creating heavier
and heavier elements,

119
00:04:58,333 --> 00:05:01,600
and that's how you get basically
everything you see around you,

120
00:05:01,600 --> 00:05:04,533
from the carbon to the iron,
the oxygen, everything.

121
00:05:04,533 --> 00:05:07,566
You can't get any of those
elements without having a star

122
00:05:07,566 --> 00:05:08,866
forming it
in the first place.

123
00:05:08,866 --> 00:05:10,966
And so everything that your body
is made up,

124
00:05:10,966 --> 00:05:12,433
everything that you see
around you

125
00:05:12,433 --> 00:05:14,466
all came from the center
of a star.

126
00:05:14,466 --> 00:05:16,200
- Pretty amazing, isn't it?

127
00:05:16,200 --> 00:05:17,833
When you look at
that periodic table

128
00:05:17,833 --> 00:05:20,800
hanging in your science class,
it represents all of the natural

129
00:05:20,800 --> 00:05:22,433
and man-made elements.

130
00:05:22,433 --> 00:05:24,900
Most of those natural elements
were formed and fused

131
00:05:24,900 --> 00:05:26,866
inside of long-dead stars.

132
00:05:26,866 --> 00:05:28,166
Yeah, that's right.

133
00:05:28,166 --> 00:05:30,733
Everything around you,
including you and me,

134
00:05:30,733 --> 00:05:33,000
was formed from the remnants
of exploded stars

135
00:05:33,000 --> 00:05:34,833
and the birth of the universe.

136
00:05:34,833 --> 00:05:37,000
We may look and act
differently from each other,

137
00:05:37,000 --> 00:05:39,466
but we are all made up
of the same stuff.

138
00:05:39,466 --> 00:05:40,866
Want to find out more?

139
00:05:40,866 --> 00:05:43,033
You can learn more about stars
and their life cycles

140
00:05:43,033 --> 00:05:44,833
from these NASA websites.

141
00:05:44,833 --> 00:05:45,900
That's it for now.

142
00:05:45,900 --> 00:05:47,966
See you next time
on "NASA Launchpad."

143
00:05:47,966 --> 00:05:53,966
[upbeat electronic music]