Stages of Star Formation 1 Giant Molecular Cloud fragments into solar mass size clumps or cores which have spatial sizes of order 0 01 2 First Dynamical Collapse 3 Second Dynamical Collapse parsecs or 2000 AU time scale of 2x106 years core collapses in free fall in 30 000 years cooled by infrared radiation emitted by dust grains keeping temperature and pressure low Collapse stops when core becomes optically thick to IR trapping heat and raising pressure radius now equals 100 AU 105 years R 100 AU inner core is now optically thick to IR dissociation of molecular hydrogen H2 and the ionization of hydrogen absorbs energy reducing the internal pressure and causing a second very rapid collapse outer region has formed a debris disk accretion continues onto protostellar core ends with R 100 R core temperature 500 000 K too low for nuclear reactions Object is now a protostar with L 103 L surface temperature 4000 K protostar is in quasi hydrostatic equilibrium must continue to shrink slowly since the only energy source is gravitational contraction 4 Hayashi Phase a Interior is cool opacity is high heat is efficiently transported by convection and temperature is roughly constant thus L decreases as R2 decreases under gravitational contraction takes 106 years b H opacity the surface temperature is controlled by the concentration denoted as H of negative hydrogen ions H which act as a thermostat it takes a photon of 0 75 eV to remove the extra electron from the negative hydrogen ion the higher H the higher the opacity If the surface temperature TS increases the H decreases the opacity decreases heat escapes more easily and TS then decreases If TS decreases H increases the opacity increases the escape of heat becomes harder and TS increases c d e Thus the concentration of H thermostats the temperature to be about constant during the Hayashi 5 Protostar 6 Hayashi phase ends when core becomes radiative core temperature and surface temperature increase phase hence L R2 and the luminosity decreases as the protostar contracts under gravity radius 10 R L 10 L and core T 106 K deuterium primordial burns to Helium 3 but little energy produced 107 years nuclear reactions start when core temperature reaches 107 K 107 years helium balances the energy lost by radiation with an internal energy source star no longer needs to contract stable central temperature is 1 5x107 K star lands on the ZAMS 3x107 years called the ZAMS since the chemical composition of the star has not been changed by nuclear reactions starts when the energy produced by nuclear burning of hydrogen into 7 Zero Age Main Sequence ZAMS Properties of the Solar System 1 Planetary orbits isolated in radius nearly in the same plane are nearly circular revolve in same sense as Sun s rotation spin in same sense except Venus and Uranus 2 Terrestrial planets low in volatiles high Si Fe Ni slow rotators 3 Jovian planets high in volatiles large rocky cores fast rotators 4 Asteroids very old primitive material silicon iron nickel and carbonaceous few basaltic asteroids 5 Kuiper belt ice and rocks 6 Comets most primitive bodies ice and dust fragments O RT cloud orbits are isotropic extend to limit of Interior Structure Fe Ni core extends to near surface Surface Atmosphere No atmosphere Sun s gravity Properties of the planets 1 Crust 2 Mantle 3 Outer core 4 Inner core 1 Crust 2 Mantle 3 Outer core 4 Inner core Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune 1 Crust 2 Mantle 3 Outer core 4 Inner core 1 Visible clouds 2 Gaseous hydrogen 3 Liquid hydrogen 4 Metallic hydrogen 5 Core of rock metals and hydrogen compounds 1 Visible clouds 2 Gaseous hydrogen 3 Liquid hydrogen 4 Metallic hydrogen 5 Core of rock metals and hydrogen compounds 1 Visible clouds 2 Gaseous hydrogen 3 Water methane and ammonia 4 Core of rock and metals 1 Visible clouds 2 Gaseous hydrogen 3 Water methane and ammonia 4 Core of rock and metals Properties of the moons Rock Rock Rock water Rock No surface No surface No surface Composition Minerals metals rock Minerals metals rock Minerals metals rock water Minerals metals rock Mostly H He H compounds rock H and He H compounds rock H and He 1 Carbon dioxide 2 Nitrogen compound 1 Nitrogen 2 Oxygen 3 Argon 4 Carbon dioxide 5 Water 3 Carbon dioxide 4 Nitrogen compound 5 Argon 1 Hydrogen compound 2 Helium 3 Methane 4 Ammonia 5 Water 1 Hydrogen compound 2 Helium 3 Methane 4 Ammonia 1 Hydrogen compound 2 Helium 3 Methane 1 Hydrogen compound 2 Helium 3 Methane No surface Mostly H He Formation of the Solar System SOLAR SYSTEM FORMATION CONTRACTION CONDENSATION ACCRETION CLEARING SOLAR SYSTEM FORMATION LARGE INTERSTELLAR CLOUD CORE CONTRACTS HEATS SPINS FASTER FLATTENS INTO DISK H AND He REMAIN GASEOUS AS T MINERALS CONDENSE INTO SOLID SEEDS PLANETESIMALS COLLIDE AND STICK TOGETHER TERRESTRIAL PLANETS ROCKS JOVIAN PLANETS ROCK CORES SWEEP UP GAS LEFTOVERS ARE ASTEROIDS AND COMETS NEBULAR EVOLUTION DELIVERY OF WATER TO TERRESTRIAL PLANETS Condensation model CONDENSATION MODEL CONDENSATION FROM ATOMIC GAS TO SOLIDS Si Fe Mg Al COMBINED WITH O ROCKY MINERALS OXIDES VOLATILES REMAIN GASEOUS 273 SNOW LINE INNER NEBULA HEATED BY PROTOSUN T 103 K DUST BROKEN INTO ATOMS T 2000 K ONLY METALIC GRAINS FORM VOLATILES DO NOT CONDENSE Evolution of a solar mass star VOLATILES GASEOUS H2O NH3 CH4 ICE MIXED WITH DUST AS CONDENSATION NUCLEI GAS AND DUST RADIATE AWAY HEAT OF COMPRESSION SHIELDED BY INNER NEBULA VOLATILES ICE Properties of white dwarfs A white dwarf also called a degenerate dwarf is a stellar remnant composed mostly ofelectron degenerate matter They are very dense a white dwarf s mass is comparable to that of the Sun and its volume is comparable to that of the Earth White dwarfs are thought to be the final evolutionary state of all stars whose mass is not high enough to become a neutron star over 97 of the stars in our galaxy 5 1 After thehydrogen fusing lifetime of a main sequence star of low or medium mass ends it will expand to a red giant which fuses helium to carbon and oxygen in its core by the triple alpha process If a red giant has insufficient mass to generate the core temperatures required to fuse carbon around 1 billion K an inert mass of carbon and oxygen will build up at its center After shedding its outer layers to form a planetary nebula it will leave behind this core which forms the remnant white dwarf 6 Usually therefore white dwarfs are composed of carbon and oxygen If the mass of the progenitor is above 8 solar