STELLAR EVOLUTION

1
STELLAR EVOLUTION

• THE LIVES OF STARS

2
BIRTH OF A STAR

• From cold gas and dust to thermonuclear reactions

3
WHERE ARE THE NURSERIES WHERE STARS ARE BORN?

• LOOK FOR COLD, DARK CLOUDS OF GAS AND DUST.

4
A REGION OF NEW STAR FORMATION
5
CENTER OF ORION NEBULA-GAS AND DUST
A REGION THAT NORMALLY WOULD BE DARK IS
SCATTERING LIGHT FROM NEARBY STARS
6
HORSEHEAD NEBULAA SEA OF GAS AND DUST
7
EVAPORATING GASEOUS GLOBULE (EGG) AT TIP OF
NEBULAR COLUMN
8
A STELLAR NUSERY BEING TORN APART BY RADIATION
FROM A NEARBY NEW STAR
9
DARK GLOBULES OF GAS AND DUST SILHOUTTED BY A
BRIGHT EMISSION NEBULA
10
DARK CLOUDS OF COLD GAS AND DUST COLLAPSE BY
GRAVITY TO FORM LARGE SPHERICAL MASSES CALLED
PROTOSTARS.
WHAT STARTS THE COLLAPSE?
11
PERHAPS A SHOCK WAVE CREATED BY A MASSIVE STAR
EXPLOSION, OR SOMETHING ELSE, COMPACTS THE COLD
GAS AND DUST TO START THE GRAVITATIONAL
CONTRACTION.
12
A SPHERICAL SHOCK WAVE FROM AN EXPLODING STAR
13
A SHOCK WAVE CREATED BY A NEW STAR THAT CAN BEGIN
THE CREATION OF OTHER NEW STARS
14
JUST LIKE A FIGURE SKATER WHO PULLS HER ARMS IN,
THE PROTOSTAR SPINS FASTER AND FASTER AS IT
COLLAPSES TO FORM PROTO-PLANETARY DISKS AROUND
THE PROTOSTAR.
15
CLOSE-UP OF PROTO-PLANETARY DISKS
CLOSE-UP OF PROTO-PLANETARY DISKS
16
THE PROTOSTAR HAS TO SLOW ITS ROTATION BEFORE IT
CAN COLLAPSE FURTHER ON ITS ROAD TO BECOME A STAR.

• MAYBE MAGNETIC FIELD LINES WIND UP AT THE POLES
  TO PROVIDE THE BRAKE.

17
VIOLENT CHANGE FROM A PROTOSTAR TO A REAL STAR
18
WHAT STOPS THE COLLAPSE AND MAKES THE PROTOSTAR A
REAL STAR?
WHAT IS A REAL STAR?
BOTH ANSWERS THERMONUCLEAR REACTIONS! THE
REACTIONS PROVIDE THE PRESSURE TO OPPOSE GRAVITY
AND THE ENERGY FOR STARLIGHT.
19
THERMONUCLEAR REACTIONS

• THERMO HEAT, TEMPERATURE (THERMOMETER, THERMOS,
  THERMOSTAT)
• NUCLEAR THE CENTER OF AN ATOM
• REACTION TWO OR MORE THINGS COME TOGETHER TO
  CREATE SOMETHING NEW AND DIFFERENT

20
HYDROSTATIC EQUILIBRIUM

WHEN THE FORCE OF GRAVITY IS BALANCED BY
THE PRESSURE PRODUCED BY THE ENERGY GENERATED
BY THERMONUCLEAR REACTIONS, THE STAR
BECOMES STABLE.


21
LIFE CYCLES OF STARS
22
WHEN THE THERMONUCLEAR REACTIONS START AND
HYDROSTATIC EQUILIBRIUM IS ESTALISHED, A STAR
BEOMES STABLE.

• WE NOW CALL IT A MAIN SEQUENCE STAR. THE SUN IS
  A
• MAIN SEQUENCE
• STAR.

23
STRUCTURE OF A MAIN SEQUENCE STAR



24
MAIN SEQUENCE STAR STRUCTURE
25
HYDROGEN CORE FUSION

• THE MAIN SEQUENCE IS MARKED BY HYDROGEN FUSION
  REACTIONS IN THE CORE OF THE STAR.

HYDROGEN FUSION REACTIONS TAKE PLACE AT THE
LOWEST TEMPERATURE OF ALL THERMONUCLEAR
REACTIONS.
OTHER THERMONUCLEAR REACTIONS THAT CAN TAKE PLACE
LATER REQUIRE MUCH HIGHER TEMPERTURES.
26
HELIUM CORE BEGINS TO COLLAPSE
27
COLLAPSE OF BUILT-UP HELIUM CORE



28
WHEN THE CORE BECOMES HOT ENOUGH TO USE HELIUM AS
A THERMONUCLEAR FUEL, SO MUCH ENERGY IS PRODUCED
THAT THE OUTWARD PRESSURE MAKES THE OUTER PART OF
THE STAR EXPAND.

• IT BECOMES A

RED GIANT
29
STRUCTURE OF A RED GIANT
30
ACTUAL SCALE MODEL OF A RED GIANT STAR
1 MQ ONE SOLAR MASS
31
STRUCTURE OF A RED GIANT
32
THE SUN WILL EXPAND TO ABOUT 100 TIMES ITS
PRESENT SIZE. RADIUSRED GIANT 1 AU
33
AS THE GRAVITY AT THE SURFACE OF A SMALL STAR
DECREASES, GAS IS BLOWN OFF, REDUCING ITS MASS.
FOR THE SUN, THIS IS KNOWN AS THE SOLAR WIND.
34
(No Transcript)
35
IN GENERAL, STARS MAY LOSE A LOT OF MASS WHEN
THEY ARE RED GIANTS. THE LARGER SUN-LIKE STARS
END UP WITH A MASS CLOSER TO ONE SOLAR MASS.
36
AT THE END OF THE HELIUM SHELL NUCLEAR ACTIVITY,
MANY STARS HAVE A HICCUP AS A BURST OF ENERGY
IS PRODUCED. THAT EVENT CAN BLOW OFF 10 OF THE
STARS MASS AND PRODUCE A BEAUTIFUL PLANETARY
NEBULA.
37
THE RING NEBULAA PLANETARY NEBULA
38
THE CATS EYE PLANETARY NEBULA
39
THE HELIX NEBULA
40
IC 418 THE SPIROGRAPH NEBULA
41
ANOTHER PLANETARY NEBULA
42
A PLANETARY NEBULA IS ONE OF THE LAST STAGES IN
THE LIFE OF A STAR LIKE OUR SUN. THE STAR AT THE
CENTER OF THE SPIROGRAPH NEBULA WAS A RED GIANT A
FEW THOUSAND YEARS AGO WHEN IT EJECTED ITS OUTER
LAYERS TO FORM THE NEBULA.
?
43
WHAT REMAINS OF THE HOT CORE OF THE RED GIANT IS
AT THE CENTER OF THE NEBULA. ITS UV LIGHT CAUSES
THE NEBULA TO FLUORESCE JUST LIKE A FLUORESCENT
LIGHT BULB.
44
OUR OWN SUN IS TO UNDERGO A SIMILAR FATE,
FORTUNATELY NOT UNTIL 4.5 BILLION YEARS FROM NOW.
45
WHITE DWARFS, NEUTRON STARS, AND BLACK HOLES
THE DEATHS OF STARS
46
STAR MASSES AND EVOLUTIONARY OUTCOMES
RED DWARFSLESS THAN 40 THE MASS OF THE SUN (M
)CAN ONLY CONVERT H TO He. THEY NEVER BECOMES
A RED GIANT. CENTRAL T 4 MILLION DEGREES. 1 M
ONE SOLAR MASS
47
0.4 M TO 4 M
SUN-LIKE STARS CAN FUSE HELIUM (He) TO CARBON
(C) AND OXYGEN (O) WHEN CONTRACTION OF THE He
CORE HEATS THE CENTER TO T 120 MILLION
DEGREES.
48
THE FATE OF LOW MASS STARS
COLLAPSE UNTIL ELECTRON PRESSURE
(QUANTUM ELECTRON DEGENERACY) EQUALS THE FORCE
OF GRAVITY LEADING TO A
WHITE DWARF
49
The white dwarf Sirius B blazes in X-rays next to
its companion, the normal star Sirius A.
Sirius A, an A1 star, is the brightest star seen
in the sky in visual light. Its white dwarf
companion is barely visible here.
50
WHITE DWARFS
51
ABOVE 4 SOLAR MASSES THE FORCE OF GRAVITY CAN
SQUEEZE THE CORE TO RAISE THE TEMPERATURES TO
EXTREMES, UP TOT 2.7 BILLION DEGREES.



52
FUELS, PRODUCTS, TEMPERATURES
REACTIONS T (DEGREES C) H ? He
4 MILLION He ?
C,O 120 MILLION C ? Ne,
Na, Mg, O 600 MILLION Ne ? O, Mg
1.2 BILLION O ? Si, S, P
1.5 BILLION Si ? Ni to Fe
2.7 BILLION
OVER 8 SOLAR MASSES
53
REACTION SHELLS OF HIGH MASS STARS



54
FUSION SHELLS REGION IS A TINY FRACTION OF
THE STARS VOLUME
55
(No Transcript)
56
ENERGIES RELEASED WITH FUSION AND FISSION
57
REMEMBER HYDROSTATIC EQUILIBRIUM?



58
IF GRAVITY STARTS TO WIN, BECAUSE IRON CANT FUSE
TO PRODUCE ANY ENERGY, THE CORE STARTS TO
COLLAPSE.

FOR MEDIUM MASS STARS, THE NUCLEI ARE COMPRESSED
TOGETHER AND THE PROTONS ARE FORCED TO COMBINE
WITH ELECTRONS TO PRODUCE


59
NEUTRONS!
WHEN THE NEUTRONS ARE SQUEEZED TOGETHER BY
GRAVITY, THE STRONG NUCLEAR FORCES CREATE A
PRESSURE TO RESIST GRAVITY AND THE COLLAPSE OF
THE CORE STOPS. UNLIKE NORMAL MATTER, THERE IS
NO SPACE BETWEEN NUCLEI.
60
THE COLLAPSE OF THE IRON CORE LETS ALL OF THE
MASS ABOVE IT TO START TO FALL INWARD. WHEN THE
INFALLING MATERIAL HITS THE TOTALLY COMPRESSED
CORE OF NEUTRONS, IT IS ALSO COMPRESSED TO
EXTREME DENSITIES AND
61
HEATED TO EXTREME TEMPERATURES SO THAT
THERMONUCLEAR REACTIONS RUN WILD! A SUPERNOVA IS
PRODUCED. IN A FEW SECONDS, MORE ENERGY IS
RELEASED THAN MILLIONS OF SUNS COULD GENERATE IN
BILLIONS OF YEARS.
62
BEFORE AND AFTER PICTURE OF A SUPERNOVA
63
Pictographs of indigenous Americans of the
southwest depicting the supernova of 1054.
64
HULA-HOOPS! THE STRANGE REMNANT OF A 1987
SUPERNOVA SEEN SEVEN YEARS LATER. S.
65
THE CRAB NEBULA-REMNANT OF THE 1054 SUPERNOVA



66
THE SAME NEBULA SEEN WITH INFRARED
67
THE SAME NEBULA SEEN WITH X-RAYS
68
WHAT HAPPENED TO THE COLLAPSED IRON CORE THAT
BECAME A SOLID BALL OF NEUTRONS ABOUT THE SIZE OF
A SMALL CITY?
69
REMEMBER THE SPINNING FIGURE SKATER? WHAT WAS
LEFT OF THE IRON CORE--THAT SOLID BALL OF
NEUTRONS CALLED A NEUTRON STAR--IS RAPIDLY
SPINNING ALSO.
70
THE NEUTRON STAR IS LIKE A STRONG ROTATING MAGNET.
ELECTRONS TRAPPED BY THAT MAGNET

• WHIP AROUND THE STAR AND PRODUCE A BEAM OF RADIO
  SIGNALS.

THAT BEAM IS LIKE THE BEAM OF A LIGHTHOUSE.
71
IF THAT LIGHT HOUSE BEAM OF RADIO SIGNALS
SWEEPS IN THE DIRECTION OF EARTH, THE NEUTRON
STAR IS CALLED A PULSAR.
72
THE TILTED MAGNETIC FIELDS SWING TRAPPED
ELECTRONS TO PRODUCE A BEAM OF RADIO SIGNALS.
73
RADIO SIGNALS FROM A PULSAR.
74
THIS THE THE CRAB NEULA AGAIN. SCENE OF THE 1054
SUPERNOVA AND A PULSAR.

75
THE LOCATION OF THE PULSAR IN THE NEBULA
76
AS THE PULSAR LOSES ROTATIONAL ENERGY, IT SLOWS
DOWN.
THE PERIOD OF ROTATION INCREASES.
77
THE PERIOD OF THE PULSAR IS INCREASING.
WHAT ARE THOSE EVENTS INDICATED BY THE RED
ARROWS?
THEY ARE LITTLE SPEED-UPS.
78
THE SURFACE OF A NEUTRON STAR IS A HARD SOLID
LIKE THE MANTLE OF THE EARTH. BECAUSE IT IS
ROTATING SO FAST, ITS SHAPE IS DISTORTED FROM A
SPHERE, JUST LIKE THE EARTHS DIAMETER IS GREATER
AT THE EQUATOR THAN FROM POLE TO POLE.

• AS THE NEUTRON STAR SLOWS DOWN, THE SURFACE HAS A
  STARQUAKE AS ITS SHAPE BECOMES MORE SPHERICAL.
  LIKE THE FIGURE SKATER, THAT SHIFT IN MASS CAUSES
  THE STAR TO ROTATE A LITTLE FASTER.

79
IF THE IRON CORE OF A STAR IS EXTREMELY MASSIVE,
NOT EVEN THE NUCLEAR FORCES BETWEEN NEUTRONS CAN
STOP GRAVITY. IT WILL BECOME A.
80
BLACK HOLE
81
YOU COULD JUMP FAST ENOUGH OFF OF AN ASTROID TO
FLY INTO SPACE.
BUT YOU COULD NOT JUMP FAST ENOUGH TO ESCAPE
FROM THE MORE MASSIVE EARTH OR EVEN FROM THE
MOON. YOU CANT REACH THE ESCAPE VELOCITY.
82
LIKEWISE, LIGHT CAN ESCAPE FROM MOST OBJECTS, BUT
NOT A BLACK HOLE.

• THE ESCAPE VELOCITY OF A BLACK HOLE IS GREATER
  THAN THE SPEED OF LIGHT.

83
THERE IS A REGION IN SPACE NEAR A BLACK HOLE FROM
WHICH NOTHING CAN EVER ESCAPE.

• THE BOUNDARY OF THAT SPACE IS CALLED THE EVENT
  HORIZON.

THE BLACK HOLE IS AT THE CENTER OF THAT SPACE.
84
THE BLACK HOLE AT THE CENTER IS INFINITELY SMALL
AND, THEREFORE, HAS AN INFINITE DENSITY.
THAT CENTRAL POINT OF INFINITIES IS CALLED
A SINGULARITY.
85
IF YOU GET TOO CLOSE TO THE EVENT HORIZON OF A
SMALL
BLACK HOLE, THE DIFFERENCE IN GRAVITY BETWEEN
YOUR FEET AND YOUR HEAD WILL STRETCH YOU OUT LIKE
SPAGHETTI.
86
The Hubble telescope may have, for the first
time, provided direct evidence for the existence
of black holes by observing how matter disappears
when it falls beyond the "event horizon," the
boundary between a black hole and the outside
universe. Astronomers found their evidence by
watching the fading and disappearance of pulses
of ultraviolet light from clumps of hot gas
swirling around a massive, compact object called
Cygnus XR-1. This activity suggests that the hot
gas fell into a black hole.
87
AT THE CENTER OF GALAXIES THERE APPEAR TO BE
MASSIVE BLACK HOLESMILLIONS AND EVEN BILLIONS
TIMES MORE MASSIVE THAN OUR SUN.
88
The gravitational pull of a suspected
super-massive black hole forms a frisbee-like
disk of cool gas, at the core of an energetic
galaxy. Subsequent Hubble observations of yet
another active galaxy (M87) confirmed the reality
of monstrous black holes -- gravitational sink
holes'' that trap everything, even light.
November 1992
89
BLACK HOLES AT THE CENTER OF GALAXIES
90
A CASE OF CANNIBALISMA MASSIVE BLACK HOLE IN A
GIANT GALAXY IS FEEDING ON A SMALLER GALAXY.
91
BECAUSE LIGHT IS BENT IN THE STRONG GRAVITY NEAR
A BLACK HOLE, THE IMAGE OF SOMETHING LIKE A
GALAXY LOCATED DIRECTLY BEHIND THE BLACK HOLE CAN
BECOME DISTORTED. THIS IS CALLED A
GRAVITATIONAL LENS EFFECT.
92
A GRAVITATIONAL LENS EFFECT AN EINSTEIN CROSS.
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THE GEOMETRY BEHIND THE GRAVITATIONAL LENS EFFECT
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ARCS FORMED BY THE GRAVITATIONAL LENS EFFECT OF A
BLACK BODYS GRAVITY
95
MORE ARCS CAUSED BY A GRAVITATIONAL LENS
96
ANOTHER EXAMPLE
97
AND MORE EXAMPLES
98
HOW DO WE KNOW ABOUT THE LIVES OF STARS?

• WE LOOK AT A CLUSTER OF STARS. IN THAT CLUSTER
  ALL THE STARS ARE ABOUT THE SAME AGE.

IT IS A SNAPSHOT OF DIFFERENT TYPES OF STARS AT
THE SAME AGE.
99
WHAT IF WE WANT TO KNOW ABOUT HOW A CERTAIN TYPE
OF STAR CHANGES WITH AGE?

• WE LOOK AT MANY CLUSTERS, EACH WITH A DIFFERENT
  AGE.

THAT GIVES US MANY SNAPSHOTS OVER A RANGE OF
TIMES.
100
AN OPEN CLUSTER IN THE MAKING
101
BECAUSE ALL THE STARS IN A CLUSTER ARE FORMED
TOGETHER FROM THE SAME CLOUD OF COLD GAS AND
DUST, THEY ARE ALL AT THE SAME DISTANCE FROM US.

• SO WE CAN COMPARE THEIR LUMINOSITIES EASILY.

102
A YOUNG OPEN CLUSTER
103
A TYPICAL HERTZSPRUNG-RUSSELL DIAGRAM FOR A YOUNG
CLUSTER.

• THIS DIAGRAM SHOWS THE RELATIONSHIPS BETWEEN
  TEMPERATURE (SPECTRAL CLASS) AND ABSOLUTE
  MAGNITUDE (LUMINOSITY)

104
THE PLEIADESAN OPEN STAR CLUSTER
105
HERTZSPRUNG-RUSSELL (HR) DIAGRAM OF A YOUNG OPEN
CLUSTER
THE TURNOFF POINT INDICATES HOW OLD THE CLUSTER
IS. HOTTER STARS USE UP THEIR NUCLEAR
FUEL FASTER.
106
AN OLDER GLOBULAR CLUSTER IN THE CONSTELLATION OF
HERCULES
107
HR DIAGRAM OF A GLOBULAR CLUSTER ABOUT THE AGE OF
OUR SUN
NOTICE THAT THE TURNOFF HAS GONE
TO LOWER TEMPERATURES. NO HIGH TEMPERATURE STARS
ARE LEFT.
108
STARS ARE LEAVING THE MAIN SEQUENCE LINE IN A
GLOBULAR CLUSTER
109
HR DIAGRAMS OF SEVERAL STAR CLUSTER OF DIFFERENT
AGES
AS THE AGE OF THE CLUSTER INCREASES,
THE TEMPERATURE OF THE TURNOFF POINT DECREASES.
110
WHEN THE THERMONUCLEAR REACTIONS AT THE CENTER OF
A STAR CHANGE THEIR FUEL FROM HYDROGEN TO HELIUM,
WHICH INCREASES THE AMOUNT OF ENERGY PRODUCED,
THE STAR BEGINS TO
.
EXPAND

• 3 He ?1 C LOTS OF ENERGY

111
THE STAR EXPANDS SO MUCH, IT SURFACE AREA BECOMES
SO LARGE, IT DOESNT HAVE TO BE AS HOT TO RADIATE
OFF ALL THE ENERGY PRODUCED.

• THE SURFACE NOW GLOWS A COOLER RED

112
THE STAR LEAVES THE MAIN SEQUENCE LINE, BECOMES
REDDER AND BRIGHTER.

• IT IS ON IT WAY TO BECOME A
• RED GIANT.

113
EVOLUTIONARY PATHS OF TWO STARS FROM A NORMAL
MAIN SEQUENCE STAR TO A RED GIANT
THE POSITIONS OF SOME WELL-KNOWN STARS ARE
SHOWN ON THIS H-R DIAGRAM.
114
PATH OF A SUN-LIKE STAR AND A MASSIVE STAR ON THE
H-R DIAGRAM
115
SUMMARY OF PATHWAYS FROM THE MAIN SEQUENCE TO
DEATHS
116
THE MASS OF A STAR DETERMINES ITS FATE

• SMALL MASS ? WHITE DWARF
• MEDIUM MASS ? NEUTRON STAR
• LARGE MASS ? BLACK HOLE