Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34NSCI 314LIFE IN THE COSMOS3 – STARS AND THEIR EVOLUTIONANDBASIC PROPERTIES OF LIFEDr. Karen KolehmainenDepartment of PhysicsCSUSBCOURSE WEBPAGE:http://physics.csusb.edu/~karenTHE 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 FORMATIONCONSERVATION 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 FORMATIONOUTLINE 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 c2ENERGY = MASS x (SPEED OF LIGHT)²NUCLEAR 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 STARSMAIN 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)SpectralTypeNumber of Stars in MW Percent ofTotal100,0005001020.90.20.005OBAFGKM5 million10 million500 million1 billion10 billion100 billion1 trillion80,000360 million2.4 billion12 billion28 billion60 billion290 billion0.00002 %0.09 %0.6 %3 % 7 %15 %73 %Lifetime(Years)PROPERTIES OF MAIN SEQUENCE STARSAT 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 SUPERGIANTSLATE 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