NSCI 314

LIFE IN THE COSMOS

3 – STARS AND THEIR EVOLUTIONAND

BASIC PROPERTIES OF LIFE

Dr. Karen KolehmainenDepartment of Physics

CSUSB

COURSE WEBPAGE:http://physics.csusb.edu/~karen

THE INTERSTELLAR MEDIUM SPACE IS NOT TOTALLY EMPTY! ATOMS, MOLECULES, AND DUST

PARTICLES ARE PRESENT MOSTLY HYDROGEN, HELIUM IS THE NEXT

MOST ABUNDANT ELEMENT CONCENTRATED IN CLOUDS OR NEBULAE INTERSTELLAR MATTER IS VERY LOW

DENSITY, EVEN IN MOST NEBULAE STARS FORM FROM NEBULAE, AND

THEREFORE THEY CONTAIN THE SAME MIX OF ELEMENTS AS THE INTERSTELLAR MEDIUM OUT OF WHICH THEY FORMED (MOSTLY HYDROGEN)

- A SUFFICIENTLY DENSE NEBULA (TYPICALLY ABOUT 1 LIGHT YEAR IN DIAMETER) STARTS TO COLLAPSE DUE TO GRAVITY (THE MUTUAL GRAVITATIONAL FORCES BETWEEN ALL OF THE MOLECULES).

- AS THE CLOUD CONTRACTS, ITS ROTATION SPEEDS UP AND IT FLATTENS.

•THIS HAPPENS BECAUSE OF A LAW OF PHYSICS CALLED THE CONSERVATION OF ANGULAR MOMENTUM.

OUTLINE OF STAR FORMATION

CONSERVATION OF ANGULAR MOMENTUM

ANY SPINNING OBJECT HAS ANGULAR MOMENTUM. THE AMOUNT OF ANGULAR MOMENTUM DEPENDS ON

THE OBJECT'S MASS, HOW FAST IT'S SPINNING, AND HOW THE MASS IS DISTRIBUTED WITHIN THE OBJECT.

THE AMOUNT OF ANGULAR MOMENTUM IS CONSERVED, MEANING THAT IT CAN'T CHANGE (UNLESS SOME EXTERNAL AGENT ACTS ON IT IN A CERTAIN WAY).

WHEN MASS IS PULLED IN CLOSER TO THE AXIS OF ROTATION (THE LINE THE OBJECT SPINS AROUND), IT SPINS FASTER IN ORDER TO KEEP THE AMOUNT OF ANGULAR MOMENTUM FIXED.

EXAMPLE: AN ICE SKATER SPINS FASTER WHEN SHE PULLS HER ARMS IN.

- AS THE CLOUD CONTRACTS, GRAVITATIONAL POTENTIAL ENERGY IS LOST. SOME OF THE ENERGY CHANGES TO KINETIC ENERGY OF ROTATION AS THE CLOUD'S ROTATION SPEEDS UP. SOME OF IT CHANGES TO THERMAL ENERGY (HEAT).

- AS A RESULT, THE CENTRAL PART OF THE CLOUD GETS HOT ENOUGH:

•FOR MOLECULES TO BREAK APART INTO ATOMS•THEN FOR ATOMS TO IONIZE •THEN FOR HYDROGEN NUCLEI TO START TO FUSE TO FORM HELIUM NUCLEI.

- ONCE FUSION OF H TO He BEGINS, IT BECOMES A MAIN SEQUENCE STAR. SO FAR, THE ELAPSED TIME IS A FEW MILLION YEARS.

OUTLINE OF STAR FORMATION

OUTLINE OF STAR FORMATION- THE STAR STABILIZES (STOPS CONTRACTING).

THIS HAPPENS BECAUSE THE HIGH TEMPERATURE CAUSES A HIGH OUTWARD PRESSURE WHICH “BALANCES” THE INWARD PULL OF GRAVITY. (THE HIGH TEMPERATURE IS MAINTAINED BY THE ENERGY RELEASE FROM THE NUCLEAR REACTIONS). THE STAR REMAINS STABLE (NOT MUCH CHANGE IN SIZE, BRIGHTNESS, OR TEMPERATURE) FOR A LONG TIME.

- IN MANY CASES, PLANETS AND SMALLER BODIES FORM FROM SMALLER LUMPS IN THE CLOUD THAT WERE NOT PULLED INTO THE CENTER.

- SOMETIMES THE CLOUD BREAKS INTO SEVERAL LARGE FRAGMENTS AS IT CONTRACTS, EACH OF WHICH FORMS A SEPARATE STAR. THE RESULT IS A DOUBLE OR MULTIPLE STAR OR A SMALL CLUSTER OF STARS.

OUTLINE OF STAR FORMATION

HIGH TEMPERATURE IS NECESSARY FOR NUCLEAR FUSION. THE NUCLEI MUST BE MOVING FAST ENOUGH TO COLLIDE DESPITE THEIR ELECTRICAL REPULSION.

•IN THE CORE OF A MAIN SEQUENCE STAR, TEMPERATURE IS ABOUT 15 MILLION K (27 MILLION oF).

HYDROGEN NUCLEI (PROTONS) FUSE TO FORM HELIUM.

•FOUR 1H (PROTONS) FUSE TO ONE 4He + ENERGY.

•TWO OF THE PROTONS ARE CONVERTED TO NEUTRONS.

WHERE DOES THE ENERGY COME FROM?

•ONE 4He IS 0.7% LIGHTER THAN FOUR 1H COMBINED.

•THE LOST MASS IS CONVERTED TO ENERGY.

E = m c2

ENERGY = MASS x (SPEED OF LIGHT)²

NUCLEAR REACTIONS IN MAIN SEQUENCE STARS

THE SUN CONVERTS 4 BILLION kg OF MATTER INTO ENERGY EACH SECOND.

THE SUN HAS SUFFICIENT HYDROGEN TO DO THIS FOR 100 BILLION YEARS, BUT WILL STOP AFTER ABOUT 10 BILLION YEARS BECAUSE ONLY THE CORE UNDERGOES FUSION. (THE OUTER PARTS OF THE STAR AREN’T HOT ENOUGH FOR FUSION.)

WHEN HYDROGEN IN THE CORE RUNS OUT, THIS MARKS THE END OF THE MAIN SEQUENCE LIFETIME.

THE MORE MASSIVE THE STAR, THE SHORTER THE MAIN SEQUENCE LIFETIME.

•EVEN THOUGH THERE IS MORE HYDROGEN TO FUSE IN A MORE MASSIVE STAR, FUSION PROCEEDS SO MUCH MORE RAPIDLY (BECAUSE IT IS HOTTER) THAT THE HYDROGEN DOESN’T LAST AS LONG.

NUCLEAR REACTIONS IN MAIN SEQUENCE STARS

MAIN SEQUENCE STARSALL PROPERTIES OF A MAIN SEQUENCE STAR DEPEND ON

ITS MASS.

– MORE MASSIVE STARS ARE LARGER.

– MORE MASSIVE STARS ARE HOTTER.

– MORE MASSIVE STARS ARE BLUER.

– MORE MASSIVE STARS ARE BRIGHTER.

– MORE MASSIVE STARS HAVE SHORTER LIFETIMES. • EVEN THOUGH THEY HAVE MORE NUCLEAR FUEL, THEY USE IT

UP MORE QUICKLY BECAUSE OF THEIR HIGHER TEMPERATURES.

Brightness (Sun = 1)

SpectralType

Number of Stars in MW

Percent ofTotal

100,000

500

10

2

0.9

0.2

0.005

O

B

A

F

G

K

M

5 million

10 million

500 million

1 billion

10 billion

100 billion

1 trillion

80,000

360 million

2.4 billion

12 billion

28 billion

60 billion

290 billion

0.00002 %

0.09 %

0.6 %

3 %

7 %

15 %

73 %

Lifetime(Years)

PROPERTIES OF MAIN SEQUENCE STARS

AT THE END OF THE MAIN SEQUENCE LIFETIME… THE OUTER PART OF THE STAR EXPANDS (BY UP TO 200

TIMES), BRIGHTENS (BY UP TO 100 TIMES), AND COOLS TO 3,000 K. THE STAR BECOMES A RED GIANT. IN MASSIVE STARS, A SECOND STAGE OF EXPANSION AND COOLING PRODUCES A SUPERGIANT.

MEANWHILE, THE CORE CONTRACTS AND HEATS UP UNTIL HELIUM BEGINS TO FUSE TO FORM CARBON AND HEAVIER ELEMENTS.

THE STAR GOES THROUGH OCCASIONAL EPISODES OF INSTABILITY, WITH RAPID OSCILLATIONS IN SIZE, TEMPERATURE, AND BRIGHTNESS.

He FUSES INTO CARBON , NITROGEN AND OXYGEN + ENERGY. IN LOW MASS STARS, FUSION STOPS HERE BECAUSE IT NEVER GETS HOT ENOUGH TO FUSE C, N, AND O TO EVEN HEAVIER ELEMENTS.

IN HIGH MASS STARS, CARBON FUSES TO FORM HEAVIER ELEMENTS, WHICH AGAIN FUSE TO FORM EVEN HEAVIER ELEMENTS, EVENTUALLY RESULTING IN IRON. AT EACH STEP, ENERGY IS PRODUCED.

FUSION OF IRON TO EVEN HEAVIER ELEMENTS WOULD REQUIRE ENERGY AS AN INPUT INSTEAD OF RELEASING ENERGY. (THE NUCLEUS THAT WOULD RESULT FROM FUSION IS HEAVIER THAN THE NUCLEI THAT WOULD FUSE TO FORM IT.)

THIS ENERGY IS UNAVAILABLE, SO FUSION DOESN’T PROCEED BEYOND IRON, NO MATTER HOW MASSIVE THE STAR.

NUCLEAR REACTIONS IN RED GIANTS AND SUPERGIANTS

LATE STAGES OF STELLAR EVOLUTION FOR SOLAR-TYPE (LOW MASS) STARS

PLANETARY NEBULA: THE OUTER PART OF THE STAR IS EJECTED. THE EJECTED MATERIAL EXPANDS, COOLS, AND ENRICHES THE INTERSTELLAR MEDIUM WITH HEAVIER ELEMENTS (FUSION PRODUCTS). THE CORE OF STAR REMAINS IN THE CENTER OF THE NEBULA, AND BECOMES A …

WHITE DWARF: CORE OF THE ORIGINAL STAR LEFT AFTER OUTER PARTS ARE EJECTED. IT SHRINKS TO ABOUT EARTH-SIZE, AND IS VERY DENSE. (A TEASPOONFUL OF WHITE DWARF MATERIAL WOULD WEIGH ABOUT A TON.) THERE IS NO MORE FUSION, SO THE WHITE DWARF COOLS AND DIMS (VERY, VERY SLOWLY) UNTIL EVENTUALLY IT BECOMES A …

BLACK DWARF: NO MORE LIGHT EMITTED. STELLAR CORPSE IS A DENSE SOLID BALL OF CARBON, NITROGEN, AND OXYGEN. THIS TAKES SO LONG THAT THE UNIVERSE ISN'T OLD ENOUGH FOR BLACK DWARFS TO HAVE FORMED YET.

LATE STAGES OF STELLAR EVOLUTION FOR MASSIVE STARS SUPERNOVA (TYPE II)

– IRON CORE OF RED SUPERGIANT COLLAPSES UNTIL NUCLEI COLLIDE WITH EACH OTHER.

– NUCLEI BOUNCE APART VIOLENTLY, PUSHING MATERIAL OUTWARD AND CAUSING STAR TO EXPLODE.

– LOTS OF ENERGY IS RELEASED IN EXPLOSION, STAR BRIGHTENS ENORMOUSLY.

– ENERGY OF EXPLOSION CAUSES FUSION OF HEAVY ELEMENTS (EVEN HEAVIER THAN IRON).

– EJECTED MATERIAL FORMS A SUPERNOVA REMNANT, WHICH EXPANDS AND ADDS MATERIAL (ENRICHED IN HEAVY ELEMENTS) TO THE INTERSTELLAR MEDIUM.

NEUTRON STAR OR BLACK HOLE: CORE OF ORIGINAL STAR LEFT OVER AFTER THE SUPERNOVA EXPLOSION, EXTREMELY DENSE

“BEFORE AND AFTER” PICTURES OF A SUPERNOVA

NEUTRON STAR BALL OF NEUTRONS (LIKE ONE BIG NUCLEUS)

MASS BETWEEN ABOUT 1.4 AND 3 SOLAR MASSES

RADIUS ABOUT 10 km

VERY HIGH DENSITY – ONE TEASPOONFUL OF NEUTRON STAR MATERIAL WOULD WEIGH A BILLION TONS

MANY NEUTRON STARS EMIT PULSES OF RADIO WAVES AND OTHER ELECTROMAGNETIC RADIATION, AND ARE OBSERVED AS “PULSARS”

BLACK HOLE IF THE STELLAR CORE LEFT AFTER A

SUPERNOVA IS SUFFICIENTLY MASSIVE (MORE THAN ABOUT 3 SOLAR MASSES), IT COLLAPSES TO FORM A BLACK HOLE

EVEN HIGHER DENSITY THAN A NEUTRON STAR

ESCAPE VELOCITY EXCEEDS THE SPEED OF LIGHT

ESCAPE VELOCITY SPEED NEEDED WHEN TAKING OFF FROM THE

SURFACE OF A PLANET OR OTHER OBJECT TO ESCAPE THE OBJECT’S GRAVITY

– TECHNICALLY, TO ESCAPE TO AN INFINITE DISTANCE AWAY, SLOWING TO ZERO SPEED IN THE PROCESS

EARTH'S ESCAPE VELOCITY IS 11 km/s

THE MORE MASSIVE THE OBJECT, THE LARGER THE ESCAPE VELOCITY.

THE SMALLER THE RADIUS OF THE OBJECT, THE LARGER THE ESCAPE VELOCITY.

THEREFORE, A MASSIVE BUT SMALL OBJECT WILL HAVE A LARGE ESCAPE VELOCITY.

BLACK HOLE ESCAPE VELOCITY EXCEEDS THE SPEED OF LIGHT. THEREFORE NOTHING CAN ESCAPE, NOT EVEN LIGHT. AN “EVENT HORIZON” SEALS OFF THE INTERIOR FROM THE REST

OF THE UNIVERSE. THE EVENT HORIZON HAS A RADIUS OF SEVERAL km FOR A

STELLAR MASS BLACK HOLE. MATTER INSIDE EVENT HORIZON PROBABLY CONTRACTS TO A

“SINGULARITY” – INFINITE DENSITY! CAN SOMETIMES BE DETECTED VIA GRAVITATIONAL EFFECTS

ON OTHER OBJECTS (FOR EXAMPLE, IN A DOUBLE STAR SYSTEM) AND/OR VIA X-RAYS EMITTED BY MATTER FALLING IN.

IN ADDITION TO STELLAR-MASS BLACK HOLES FORMED AT END OF LIVES OF MASSIVE STARS, LARGER BLACK HOLES EXIST IN THE CENTER OF MOST GALAXIES (INCLUDING THE MILKY WAY).

A CLOSED SYSTEM AND ITS ENVIRONMENT

CLOSED SYSTEM

MATTER ENERGY

MATTER ENERGY

AN OPEN SYSTEM AND ITS ENVIRONMENT

OPEN SYSTEM

MATTER ENERGY

WASTE ENERGYWASTE MATTER

ENTROPY AND ORDER ENTROPY: A MEASURE OF THE DISORDER IN A SYSTEM

– LOW ENTROPY = HIGHLY ORDERED

– HIGH ENTROPY = VERY DISORDERED OR MESSY SECOND LAW OF THERMODYNAMICS:

– IN ANY CLOSED SYSTEM (MEANING THAT NOTHING ENTERS OR LEAVES), NO PROCESS CAN OCCUR IN WHICH THE SYSTEM'S ENTROPY DECREASES. IN OTHER WORDS, A CLOSED SYSTEM CAN'T BECOME MORE ORDERED (LESS MESSY) AS TIME GOES ON.

– THEREFORE, THE AMOUNT OF DISORDER IN A CLOSED SYSTEM EITHER INCREASES WITH TIME OR IT DOESN’T CHANGE WITH TIME. USUALLY, THE ENTROPY INCREASES WITH TIME, IN OTHER WORDS, A CLOSED SYSTEM GETS MESSIER AS TIME GOES ON.

ENTROPY AND ORDER

SECOND LAW OF THERMODYNAMICS: IN ANY CLOSED SYSTEM, NO PROCESS CAN OCCUR IN WHICH THE ENTROPY DECREASES WITH TIME, IN OTHER WORDS, A CLOSED SYSTEM CANNOT BECOME MORE ORDERED WITH TIME.

WHAT ABOUT THE ENTROPY OF AN OPEN SYSTEM?

AN OPEN SYSTEM INTERACTS WITH ITS ENVIRONMENT. IF WE INCLUDE THE ENVIRONMENT AS PART OF THE SYSTEM (INSTEAD OF SOMETHING OUTSIDE OF THE SYSTEM), WE NOW HAVE A CLOSED SYSTEM, AND ITS TOTAL ENTROPY CAN'T DECREASE WITH TIME. HOWEVER, THE ENTROPY OF THE ORIGINAL OPEN SYSTEM CAN DECREASE, AS LONG AS THE ENTROPY OF ITS ENVIRONMENT INCREASES BY AN EVEN LARGER AMOUNT.

LIFE: ENTROPY DECREASES WITHIN AN ORGANISM AS RAW MATERIALS ARE REARRANGED IN HIGHLY ORDERED WAYS. HOWEVER, THE ORGANISM IS AN OPEN SYSTEM, AND THE ENTROPY OF ITS ENVIRONMENT INCREASES.

LIFE AND ITS ENVIRONMENT

ORGANISMENTROPY DECREASES

MATTER ENERGY

WASTE MATTER WASTE ENERGY

ENVIRONMENTENTROPY INCREASES

WHAT IS LIFE? HARD TO DEFINE, BUT LET'S LIST SOME

OF ITS PROPERTIES. NECESSARY PROPERTIES:

– USES ENERGY– INTERACTS WITH ITS ENVIRONMENT– MAINTAINS A LOW ENTROPY (HIGH DEGREE

OR ORDER OR COMPLEXITY) INTERNALLY LIKELY (BUT MAYBE NOT NECESSARY)

PROPERTIES:– GROWS AND DEVELOPS– REPRODUCES– MUTATES AND EVOLVES

REQUIREMENTS FOR LIFE MATTER:

PRODUCED IN BIG BANG (H & He) AND STARS (HEAVIER ELEMENTS)

ARE CERTAIN ELEMENTS NEEDED? STABLE ENERGY SOURCE:

LOW MASS MAIN SEQUENCE STARS (OR SOMETHING ELSE?)

PROTECTED ENVIRONMENT:PLANETARY OR LUNAR SURFACES

PLANETARY OR LUNAR INTERIORS

THICK PLANETARY OR LUNAR ATMOSPHERES CHEMICAL SOLVENT (LIQUID): WATER (OR SOMETHING ELSE?)

APPROPRIATE TEMPERATURE RANGE: NEEDED TO KEEP THE SOLVENT LIQUID (APPROXIMATELY 0 TO

100o C IF WATER IS THE LIQUID SOLVENT)

IF IT’S TOO HOT, COMPLEX STRUCTURES ARE BROKEN APART

IF IT’S TOO COLD, INTERACTIONS ARE TOO SLOW

Sun Earth Earth’s Crust

Hydrogen

Helium

Oxygen

Carbon

Neon

Nitrogen

Magnesium

Silicon

Iron

Sulfur

Argon

Aluminum

Calcium

Sodium

Nickel

Chromium

Phosphorus

90.99%

8.87

0.078

0.033

0.011

0.010

0.004

0.003

0.003

0.002

0.0003

0.0003

0.0002

0.0002

0.0002

0.00003

0.00003

Oxygen

Iron

Silicon

Magnesium

Sulfur

Nickel

Aluminum

Calcium

Sodium

Chromium

Phosphorus

50%

17

14

14

1.6

1.1

1.1

0.74

0.66

0.13

0.08

Oxygen

Silicon

Aluminum

Iron

Calcium

Sodium

Potassium

Magnesium

Titanium

Hydrogen

Phosphorus

Manganese

Fluorine

Strontium

Sulfur

47%

28

8.1

5.0

3.6

2.8

2.6

2.1

0.44

0.14

0.10

0.10

0.063

0.038

0.026

Earth’s Atmosphere Bacteria Human Beings

Nitrogen

Oxygen

Argon

Carbon**

Neon

Helium

78%

21

0.93

0.03

0.0018

0.00052

Hydrogen

Oxygen

Carbon

Nitrogen

Phosphorus

Sulfur

63%

29

6.4

1.4

0.12

0.06

Hydrogen

Oxygen

Carbon

Nitrogen

Calcium

Phosphorus

Sulfur

61%

26

10.5

2.4

0.23

0.13

0.13

BOTTOM LINE:

THE ELEMENTS THAT MAKE UP TERRESTRIAL LIVING ORGANISMS ARE VERY COMMON IN STARS AND IN THE INTERSTELLAR MATERIAL FROM WHICH STARS AND PLANETS ARE FORMED.

IN LIVING THINGS, THE ATOMS OF THESE ELEMENTS ARE ORGANIZED IN ORGANIC MOLECULES, MANY OF WHICH ARE LARGE AND COMPLEX.

ORGANIC MOLECULESMOLECULE: A COMBINATION OF TWO OR MORE ATOMSEXAMPLES: H2O CO2 CH4 NH3 H2 N2 O2 C2H5O2N

ORGANIC MOLECULE: A MOLECULE COMPOSED OF CARBON AND HYDROGEN ATOMS (AND OFTEN OTHER ELEMENTS ALSO)

EXAMPLES: CH4 C2H5O2N

MONOMER: A SIMPLE ORGANIC MOLECULE SUCH AS AN AMINO ACID, SIMPLE SUGAR, FATTY ACID, OR GENETIC BASE

POLYMER: A LARGE ORGANIC MOLECULE COMPOSED OF A CHAIN OF REPEATING MONOMERS

EXAMPLES OF POLYMERSCARBOHYDRATES: STARCHES, CELLULOSE, SUCROSE.

MONOMERS: SIMPLE SUGARS, GLUCOSE

LIPIDS: FATS, CHOLESTEROL, HORMONES, CELLULAR MEMBRANES.

MONOMERS: FATTY ACIDS

NUCLEIC ACIDS: DEOXYRIBONUCLEIC ACID (DNA) & RIBONUCLEIC ACID (RNA).

MONOMERS: GENETIC BASES

PROTEINS: STRUCTURAL PROTEINS FOR BONE, ORGANS, TISSUE, AND MEMBRANES; ENZYMES, CHEMICAL SENSORS AND TRANSPORTERS.

MONOMERS: AMINO ACIDS

NEXT TIME: LET’S EXAMINE NUCLEIC ACIDS AND PROTEINS IN MORE DETAIL.