Nucleosynthesis and stellar lifecycles A. Ruzicka
Stellar lifecycles A. Ruzicka Outline: 1. What nucleosynthesis is, and where it occurs 2. Molecular clouds 3. YSO & protoplanetary disk phase 4. Main Sequence phase 5. Old age & death of low mass stars 6. Old age & death of high mass stars 7. Nucleosynthesis & pre-solar grains
What nucleosynthesis is, and where it occurs A. Ruzicka
Relative abundance A. Ruzicka Nucleosynthesis formation of elements Except for H, He (created in Big Bang), all other elements created by fusion processes in stars
A. Ruzicka Stellar Nucleosynthesis Some H destroyed; all elements with Z > 2 produced Various processes, depend on (1) star mass (determines T) (2) age (determines starting composition) Z = no. protons, determines element
p > A. Ruzicka Beta Stability Valley. Nucleons with right mix of neutrons (n) to protons (p) are stable. n > Those that lie outside of this mix are radioactive.
p > A. Ruzicka Beta Stability Valley. n > too many n Too many n: beta particle (electron) emitted, n converted to p. (Beta Decay) e.g. 26 Al -> 26 Mg + beta e.g. 53 Mn -> 53 Cr + beta Some stellar nucleosynthesis resulted in n-rich nucleons that are short-lived nuclides.
p > A. Ruzicka too many p Beta Stability Valley. Too many p: electron captured by nucleus, p converted to n. n > e.g., 41 Ca + electron -> 41 K Other stellar nucleosynthesis produced short-lived p-rich nucleons.
Stellar lifecycles: from birth to death A. Ruzicka low mass star (< 5 M sun ) high mass star (> 5 M sun )
Stellar lifecycles: low mass stars A. Ruzicka 3. Red Giant 2. Main Seq. Stellar nucleosynthesis low mass star (< 5 M sun ) 4. Planetary nebula 1 & 5. molecular cloud 4. White dwarf Nucleosynthesis possible if white dwarf in binary system (during nova or supernova)
Stellar lifecycles: high mass stars A. Ruzicka Stellar nucleosynthesis 2. Main Seq. (luminous) 3. Red Giant/ Supergiant 1 & 6. molecular cloud high mass star (>5 M sun ) 5. Neutron star 4. Supernova 5. Black hole
A. Ruzicka Track stellar evolution on H-R diagram of T vs luminosity Luminosity: energy / time
A. Ruzicka Distribution of stars on H-R diagram. When corrected for intrinsic brightness, there are MANY more cool Main Sequence stars than hot.
A. Ruzicka On main sequence, luminosity depends on mass L ~ M 3.5
A. Ruzicka Molecular clouds: Where it begins & ends molecular cloud
A. Ruzicka Molecular clouds cold, dense areas in interstellar medium (ISM) Horsehead Nebula Mainly molecular H 2, also dust, T ~ 10s of K
A. Ruzicka Famous Eagle Nebula image. Cool dark clouds are close to hot stars that are causing them to evaporate.
Dust in ISM consists of: A. Ruzicka -- ices, organic molecules, silicates, metal, graphite, etc. -- some of these preserved as pre-solar grains & organic components in meteorites
A larger Interplanetary Dust Particle (IDP) A. Ruzicka
A. Ruzicka 2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms 2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms H 2 C 3 * c-c 3 H C 5 * C 5 H C 6 H AlF C 2 H l-c 3 H C 4 H l-h 2 C 4 CH 2 CHCN PN SO NaCN OCS AlCl C 2 O C 3 N C 4 Si C 2 H 4 * CH 3 C 2 H C 2 ** C 2 S C 3 O l-c 3 H 2 CH 3 CN HC 5 N CH CH 2 C 3 S c-c 3 H 2 CH 3 NC CH 3 CHO CH + HCN C 2 H 2 * CH 2 CN CH 3 OH CH 3 NH 2 CN HCO NH 3 CH 4 * CH 3 SH c-c 2 H 4 O CO HCO + HCCN HC 3 N HC 3 NH + H 2 CCHOH CO + HCS + HCNH + HC 2 NC HC 2 CHO CP HOC + HNCO HCOOH NH 2 CHO SiC H 2 O HNCS H 2 CNH C 5 N HCl H 2 S HOCO + H 2 C 2 O l-hc 4 H* (?) KCl HNC H 2 CO H 2 NCN l-hc 4 N SO + SO 2 SiN c-sic 2 SiO CO 2 * SiS NH 2 CS H 3+ * SH* HD 8 atoms HF H 2 D +, HD 2 + FeO? O 2? SiCN AlNC SiNC 9 atoms 10 atoms Molecules in ISM as of 12 / 2004 Note many C-compounds 11 atoms 12 atoms 13 atoms NH HNO H 2 CN HNC 3 NO MgCN H 2 CS SiH 4 * NS MgNC H 3 O + H 2 COH + NaCl N 2 H + c-sic 3 OH N 2 O CH 3 * All molecules have been detected (also) by rotational spectroscopy in the radiofrequency to far-infrared regions unless indicated otherwise. * indicates molecules that have been detected by their rotation-vibration spectrum, ** those detected by electronic spectroscopy only. CH 3 C 3 N CH 3 C 4 H CH 3 C 5 N (?) HC 9 N C 6 H 6 * (?) HC 11 N HCOOCH 3 CH 3 CH 2 CN (CH 3 ) 2 CO CH 3 COOH (CH 3 ) 2 O (CH 2 OH) 2 (?) C 7 H CH 3 CH 2 OH H 2 NCH 2 COOH Glycine? H 2 C 6 HC 7 N CH 3 CH 2 CHO CH 2 OHCHO l-hc 6 H* (?) CH 2 CHCHO (?) C 8 H http://www.ph1.uni-koeln.de/vorhersagen/molecules/main_molecules.html
Photochemistry can occur in icy mantles to create complex hydrocarbons from simple molecules A. Ruzicka
A. Ruzicka Gravity in molecular clouds helps promote collapse of cloud and sometimes is assisted by a trigger
A. Ruzicka Young stellar objects (YSOs) & protoplanetary disks (proplyds) YSOs
A. Ruzicka YSOs & Proplyds: Molecular cloud fragments that have collapsed no fusion yet < Protoplanetary disk around glowing YSO in Orion Solar nebula: the Protoplanetary disk out of which our solar system formed
A. Ruzicka Herbig-Haro Objects-- YSOs with disks & bipolar outflows
Magnetic fields around YSOs can create polar jets and X winds A. Ruzicka
A. Ruzicka Collapse of molecular cloud fragments occurs rapidly ~10 5 to 10 7 yrs, depending on mass Protostellar disk phase lasts ~10 6 yrs
Single collapsing molecular cloud produces many fragments, each of which can produce a star A. Ruzicka
A. Ruzicka Main Sequence phase: Middle age Main sequence
A. Ruzicka Star turns on when nuclear fusion occurs main sequence star either proton-proton chain or CNO cycle nucleosynthesis P-P chain net: 4 H to 1 He
A. Ruzicka CNO cycle more efficient method, but requires higher internal temperature, so only for stars with mass higher than 1.1 solar masses 12 C + p -> 13 N 13 N -> 13 C 13 C + p -> 14 N 14 N + p -> 15 O 15 O -> 15 N 15 N + p -> 12 C + 4 He CNO cycle net reaction : 4 H to 1 He
Star stays on main sequence in stable condition so long as H remains in the core A. Ruzicka A more massive star must produce more energy to support its own weight reason there is a correlation of mass and luminosity on main sequence
But eventually the H runs out A. Ruzicka Lifetime on main sequence = fuel / rate of consumption ~ M / L ~ M / M 3.5 lifetime ~ 1/M 2.5 So a 4 solar mass star will have a main sequence lifetime 1/32 as long as our sun
A. Ruzicka So, what happens when the core runs out of hydrogen? Star begins to collapse, heats up Core contains He, continues to collapse But H fuses to He in shell greatly inflating star RED GIANT (low mass) or SUPERGIANT (high mass)
What happens next depends on stellar mass A. Ruzicka
A. Ruzicka Old age and death of low mass stars Red Giant Planetary nebula White dwarf
A. Ruzicka There are different types of Red Giant Stars 1) RGB (Red Giant Branch) 2) Horizontal branch 3) AGB (Asymptotic Giant Branch) These differ in position on H-R diagram and in interior structure
Red Giant (RGB) star: H burning in shell A. Ruzicka
A. Ruzicka Red Giant (Horizontal branch) star: He fusion in core Red Giant (AGB) star: He burning in shell AGB star
A. Ruzicka Convective dredge-ups bring products of fusion to surface Red Giant includes: s-process nucleosynthesis
No. protons (Z) A. Ruzicka s-process nucleosynthesis: slow neutron addition beta decay keeps pace with n addition
A. Ruzicka An AGB can lose its outer layers Ultimately a planetary nebula forms, leaving a white dwarf in the center Planetary nebula White dwarf
A. Ruzicka Planetary nebulas Note: planetary nebula have nothing to do with planets!
A. Ruzicka Nuclear fusion stops when the star becomes a white dwarf It gradually cools down
A. Ruzicka Old age & death of high mass stars Super Giant Neutron star Black hole Supernova
A. Ruzicka High-mass stars: Progressive core fusion of elements heavier than C
Includes: s-process nucleosynthesis as Supergiant, r-process nucleosynthesis during core collapse A. Ruzicka
A. Ruzicka No. protons (Z) r-process nucleosynthesis: rapid neutron addition beta decay does not keep pace with n addition
End for high mass star comes as it tries to fuse core Fe into heavier elements and finds this absorbs energy A. Ruzicka STAR COLLAPSES & EXPLODES AS SUPERNOVA
--Fe core turns into dense neutrons --Supernova forms because overlying star falls onto dense core & bounces off of it A. Ruzicka
Supernova remnants A. Ruzicka
A. Ruzicka Crab Nebula supernova remnant. A spinning neutron star (pulsar) occurs in the central region.
A. Ruzicka There are different types of Supernovae 1) Type 2 (kept upper H-rich portion) 2) Type 1b (lost H, but kept He-rich portions) 3) Type 1c (lost both H & He portions) 4) Type 1a (explosion on white dwarf in binary system)
Type 2 supernovae had intact upper layers A. Ruzicka
Type 1b & c supernovae had lost upper layers A. Ruzicka
Type 1a supernovae occur in binary systems when material from companion falls onto white dwarf A. Ruzicka
Nucleosynthesis & pre-solar grains A. Ruzicka
Summary of nucleosynthesis processes A. Ruzicka process main comment products H-burning 4 He main seq. He-burning 12 C, 16 O Red Giant C-O-Ne-Si 20 Ne, 28 Si, 32 Si, Supergiants burning up to 56 Fe s-process many elements Red Giants, Supergiants r-process many heavy supernova elements
Pre-solar material in meteorites A. Ruzicka material suggested astrophysical site Ne-E S-Xe Xe-HL Macromolecular C SiC Corundum Nanodiamond Graphite, Si 3 N 4 exploding nova Red Giant or Supergiant supernovae low-t ISM C-rich AGB stars, supernovae Red Giant & AGB stars supernovae supernovae Solar system formed out of diverse materials.