Nucleosynthesis and stellar lifecycles

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 Stellar lifecycles

What nucleosynthesis is, and where it occurs

Nucleosynthesis formation of elements Except for H, He (created in Big Bang), all other elements created by fusion processes in stars Relative abundance

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

Beta Stability Valley. Nucleons with right mix of neutrons (n) to protons (p) are stable. Those that lie outside of this mix are radioactive. n > p >

Beta Stability Valley. 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. n > p > too many n

Beta Stability Valley. Too many p: electron captured by nucleus, p converted to n. e.g., 41 Ca + electron -> 41 K Other stellar nucleosynthesis produced short-lived p-rich nucleons. n > p > too many p

Stellar lifecycles: from birth to death low mass star (< 5 M sun ) high mass star (> 5 M sun )

Stellar lifecycles: low mass stars 1 & 5. molecular cloud low mass star (< 5 M sun ) 3. Red Giant 2. Main Seq. 4. Planetary nebula 4. White dwarf Stellar nucleosynthesis Nucleosynthesis possible if white dwarf in binary system (during nova or supernova)

Stellar lifecycles: high mass stars 1 & 6. molecular cloud high mass star (>5 M sun ) 3. Red Giant/ Supergiant 2. Main Seq. (luminous) 4. Supernova 5. Black hole 5. Neutron star Stellar nucleosynthesis

Track stellar evolution on H-R diagram of T vs luminosity Luminosity: energy / time

Distribution of stars on H-R diagram. When corrected for intrinsic brightness, there are MANY more cool Main Sequence stars than hot.

On main sequence, luminosity depends on mass L ~ M 3.5

Molecular clouds: Where it begins & ends molecular cloud

Molecular clouds cold, dense areas in interstellar medium (ISM) Horsehead Nebula Mainly molecular H 2, also dust, T ~ 10s of K

Famous Eagle Nebula image. Cool dark clouds are close to hot stars that are causing them to evaporate.

Dust in ISM consists of: -- 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)

2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms H2H2 C3*C3*c-C 3 HC5*C5*C5HC5HC6HC6H AlFC2HC2Hl-C 3 HC4HC4Hl-H 2 C 4 CH 2 CHCN AlClC2OC2OC3NC3NC 4 SiC2H4*C2H4*CH 3 C 2 H C 2 **C2SC2SC3OC3Ol-C 3 H 2 CH 3 CNHC 5 N CHCH 2 C3SC3Sc-C 3 H 2 CH 3 NCCH 3 CHO CH + HCNC2H2*C2H2*CH 2 CNCH 3 OHCH 3 NH 2 CNHCONH 3 CH 4 *CH 3 SHc-C 2 H 4 O COHCO + HCCNHC 3 NHC 3 NH + H 2 CCHOH CO + HCS + HCNH + HC 2 NCHC 2 CHO CPHOC + HNCOHCOOHNH 2 CHO SiCH2OH2OHNCSH 2 CNHC5NC5N HClH2SH2SHOCO + H2C2OH2C2Ol-HC 4 H*l-HC 4 H* (?) KClHNCH 2 COH 2 NCNl-HC 4 N NHHNOH 2 CNHNC 3 NOMgCNH 2 CSSiH 4 * NSMgNCH3O+H3O+ H 2 COH + NaClN2H+N2H+ c-SiC 3 OHN2ON2OCH 3 * 2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms PNNaCN SOOCS SO + SO 2 SiNc-SiC 2 SiOCO 2 * SiSNH 2 CSH3+*H3+* SH*SiCN HDAlNC FeO?SiNC O 2 ? 8 atoms 9 atoms 10 atoms 11 atoms 12 atoms 13 atoms CH 3 C 3 NCH 3 C 4 HCH 3 C 5 N (?)HC 9 NC 6 H 6 *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 (CH 2 OH) 2 (?) C7HC7HCH 3 CH 2 OH H 2 NCH 2 COOH GlycineH 2 NCH 2 COOH Glycine ? H2C6H2C6 HC 7 NCH 3 CH 2 CHO CH 2 OHCHOC8HC8H l-HC 6 H*l-HC 6 H* (?) CH 2 CHCHOCH 2 CHCHO (?) 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. Molecules in ISM as of 12 / 2004 Note many C-compounds HF H 2 D +, HD 2 +

Photochemistry can occur in icy mantles to create complex hydrocarbons from simple molecules

Gravity in molecular clouds helps promote collapse of cloud …and sometimes is assisted by a trigger

Young stellar objects (YSOs) & protoplanetary disks (proplyds) YSOs

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

Herbig-Haro Objects-- YSOs with disks & bipolar outflows

Magnetic fields around YSOs can create polar jets and X winds

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

Main Sequence phase: Middle age Main sequence

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

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 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 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

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

Old age and death of low mass stars Planetary nebula White dwarf Red Giant

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

Red Giant (Horizontal branch) star: He fusion in core Red Giant (AGB) star: He burning in shell AGB star

Convective dredge-ups bring products of fusion to surface Red Giant includes: s-process nucleosynthesis

s-process nucleosynthesis: slow neutron addition beta decay keeps pace with n addition No. protons (Z)

An AGB can lose its outer layers— Ultimately a planetary nebula forms, leaving a white dwarf in the center Planetary nebula White dwarf

Note: planetary nebula have nothing to do with planets! Planetary nebulas

Nuclear fusion stops when the star becomes a white dwarf— It gradually cools down

Old age & death of high mass stars Supernova Black hole Super Giant Neutron star

High-mass stars: Progressive core fusion of elements heavier than C

Includes: s-process nucleosynthesis as Supergiant, r-process nucleosynthesis during core collapse

r-process nucleosynthesis: rapid neutron addition beta decay does not keep pace with n addition No. protons (Z)

End for high mass star comes as it tries to fuse core Fe into heavier elements– and finds this absorbs energy STAR COLLAPSES & EXPLODES AS SUPERNOVA

--Fe core turns into dense neutrons --Supernova forms because overlying star falls onto dense core & bounces off of it

Supernova remnants

Crab Nebula supernova remnant. A spinning neutron star (pulsar) occurs in the central region.

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

Type 1b & c supernovae had lost upper layers

Type 1a supernovae occur in binary systems when material from companion falls onto white dwarf

Nucleosynthesis & pre-solar grains

processmaincomment products H-burning 4 Hemain seq. He-burning 12 C, 16 ORed Giant C-O-Ne-Si 20 Ne, 28 Si, 32 Si,Supergiants burningup to 56 Fe s-processmany elementsRed Giants, Supergiants r-processmany heavysupernova elements Summary of nucleosynthesis processes

materialsuggested astrophysical site Ne-Eexploding nova S-XeRed Giant or Supergiant Xe-HLsupernovae Macromolecular Clow-T ISM SiCC-rich AGB stars, supernovae CorundumRed Giant & AGB stars Nanodiamondsupernovae Graphite, Si 3 N 4 supernovae Pre-solar material in meteorites Solar system formed out of diverse materials.