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 29NSCI 314LIFE IN THE COSMOS3 – STARS AND THEIR EVOLUTION (CONTINUED)ANDBASIC PROPERTIES OF LIFEDr. Karen KolehmainenDepartment of PhysicsCSUSBCOURSE WEBPAGE:http://physics.csusb.edu/~karenREVIEW OF STAR FORMATIONFORMED FROM A NEBULA (DENSER PART OF THE INTERSTELLAR MEDIUM)NEBULA CONTRACTS DUE TO GRAVITYSPINS FASTER AND FLATTENS INTO A DISK AS IT CONTRACTS GETS HOTTER, EVENTUALLY HOT ENOUGH FOR NUCLEAR FUSION (H TO He) TO BEGIN IN THE CENTERNOW IT IS A MAIN SEQUENCE STARPLANETS AND SMALLER OBJECTS FORM FROM MATERIAL LEFT OVER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 c 2ENERGY = 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, FUSION PROCEEDS SO MUCH MORE RAPIDLY (BECAUSE IT IS HOTTER) THAT THE HYDROGEN IN THE CENTER 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 MASSIVE 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 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. 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 SUPERNOVANEUTRON 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 PULSARSBLACK 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 LIGHTESCAPE VELOCITYSPEED NEEDED WHEN TAKING OFF FROM THE SURFACE OF A PLANET OR OTHER OBJECT IN ORDER 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 YOU'RE ESCAPING FROM, THE LARGER THE ESCAPE VELOCITY.THE SMALLER THE RADIUS OF THE OBJECT YOU'RE ESCAPING FROM, THE LARGER THE ESCAPE VELOCITY.THEREFORE, A MASSIVE BUT SMALL OBJECT (i.e., A DENSE OBJECT) HAS A LARGE ESCAPE VELOCITY.BLACK HOLEESCAPE VELOCITY EXCEEDS