Meteoritic Constraints on Astrophysical Models of Star and Planet Formation Steve Desch, Arizona State University

Star Formation

Chondrites: Leftover crumbs from solar system formation Cross section of Carraweena (L3.9) CAIsMATRIX GRAINSCHONDRULES

CAIs: The first minerals formed in the solar system CAIs contain many minerals that are the first to condense out of a solar nebula gas (Grossman 1972) : melilite: Ca(Al,Mg)(Si,Al) 2 O 7, hibonite: Ca 2 (AlTi) 24 O 35, anorthite: CaAl 2 Si 2 O 8, pyroxene: (FeMg)SiO 3 McSween 1999

CAIs Fluffy Type A: Not as large as other CAIs (< 1 mm) Most abundant (about 1% of all CCs and OCs, 2% of Allende) aggregations of small, zoned spheroids with spinel at their cores and mantles of melilite (Wark & Lovering 1977) Group II Rare Earth Element patterns show ultrarefractory component depleted (Tanaka & Masuda 1973); that component apparently concentrated in nuggets like those recently found (Hiyagon et al 2003) Formed (condensed?) in hot environment: 1400 K < T < 1800 K Compact Type A: Same compositions as fluffy type A, but were melted

CAIs Types B and C: Larger (up to cm-size) Very abundant in CVs (6-10% of volume), nonexistent in others Clearly melted after formation Type B CAI cooling rates constrained from chemical zoning in melilite: K/hr (Stolper & Paque 1986; Jones et al 2000) At one time contained 26 Al, 41 Ca, 10 Be, etc.

CAIs FUN inclusions : “Fractionation and Unknown Nuclear effects” Very rare (only 6) Large mass-dependent fractionations in O, Mg, Si: apparently were severely heated and evaporated Are anomalous in certain neutron-rich nuclei: 48 Ca, 50 Ti Contain evidence they once contained 10 Be Contain no evidence they ever contained 26 Al, 41 Ca, etc.

Short-Lived Radionuclides CAIs contained live short-lived radionuclides: 41 Ca (t 1/2 = 0.1 Myr) (Srinivasan et al. 1994) 36 Cl (t 1/2 = 0.3 Myr) (Murty et al. 1997) 26 Al (t 1/2 = 0.7 Myr) (Lee et al. 1976) 60 Fe (t 1/2 = 1.5 Myr) (Tachibana & Huss 2003) 10 Be (t 1/2 = 1.5 Myr) (McKeegan et al. 2000) 53 Mn (t 1/2 = 3.7 Myr) (Birck & Allegre 1985) These half-lives are so short, the radionuclides must have been created shortly before, or during, solar system formation CAIs with evidence for 26 Al all have remarkably uniform ratio 26 Al/ 27 Al = 5 x : they all formed within ~10 5 years of each other

10 Be/ 9 Be Ratios Excess 10 B correlates with amount of Be: this 10 B is from the decay of 10 Be McKeegan et al. (2000) Natural 10 B/ 11 B level CAIs formed with 10 Be/ 9 Be = 9 x Slope gives initial 10 Be/ 9 Be ratio 10 Be decays to 10 B with t 1/2 =1.5 Myr

10 Be/ 9 Be Ratios 10 Be has been found in every CAI looked at, at levels consistent with 10 Be/ 9 Be = 9 x Be is present even if other radionuclides such as 26 Al, 41 Ca are not, in FUN inclusions and hibonites (Marhas et al. 2002; MacPherson et al. 2003) 10 Be has a different origin than 26 Al, 41 Ca, etc. (Marhas et al. 2002): Could it be Galactic Cosmic Rays? Table from Desch et al. (2004)

Collapse of Cloud Cores: Observations Stars form in parts of molecular clouds that have gravitationally collapsed, dragged in magnetic field lines Even the Orion Nebula must have gone through this stage (Schleuning 1998) 10 Be GCRs follow magnetic field lines, are trapped when column densities first exceed ~ g cm -2 (before first stars) Schleuning (1998) 1.3 pc Side view:

Collapse of Cloud Cores: Calculations Numerical simulations show how magnetic fields and gas densities vary with time in collapsing molecular cloud core (Desch & Mouschovias 2001) We calculate rates at which 10 Be GCRs are trapped, and 10 Be is produced by spallation First stars form << 1 Myr after t=0 Desch & Mouschovias (2001) 1.5 pc

10 Be in a Collapsing Cloud Core 10 Be/ 9 Be ratio = CAI ratio as first stars form! All of the 10 Be in CAIs is attributable to GCRs: 80% from 10 Be GCRs trapped in cloud core 20% produced by spallation reactions 10 Be/ 9 Be ratio does indeed peak when column densities exceed ~ g cm -2 CAI ratio Trapped 10 Be GCRsTotal 10 Be produced by GCR protons spalling CNO nuclei in gas 9.5 x 10 -4

Supernova Injection of Radionuclides We attribute 10 Be to trapped 10 Be Galactic cosmic rays A type II supernova is the most likely source of all the other radionuclides: 41 Ca, 36 Cl, 26 Al, 60 Fe produced in proportions seen in meteorites (Meyer & Clayton 2000; Meyer et al. 2003) We do not claim that a supernova triggered the collapse of the solar system’s cloud core We claim the solar nebula already existed and CAIs were forming when the supernova ejecta entered the solar system (Sahijpal & Goswami 1998): “Late injection” FUN inclusions are CAIs that formed before 26 Al, 41 Ca, 60 Fe, and anomalous 48 Ca and 50 Ti were injected by supernova

The Sun’s Star-Formation Environment 80% of Sunlike stars form near a star massive enough to supernova (Adams & Laughlin 2001) Before massive star goes supernova it ionizes, heats, and “photoevaporates” surrounding gas Evaporating gaseous globules: new solar systems Hester et al (1996) Ionization fronts probably triggered star formation in Eagle Nebula

The Sun’s Star-Formation Environment After EGG stage, solar system emerges into H II region as a “proplyd” Disk resides in H II region for ~10 5 yr until O star(s) supernova Disk intercepts supernova ejecta with radionuclides Proplyds in Orion will acquire 26 Al/ 27 Al ~ 5 x when  1 Ori C supernovas

Protoplanetary Disks HH30: Watson, Stapelfeldt, Krist & Burrows (2000)

outflow Mass accretes onto star through disk Protoplanetary disks are accretion disks Angular momentum is transported outward, mass moves inward Angular momentum transport probably due to magnetohydrodynamic turbulence (Desch 2004) PPDs:

As mass moves inward, gravitational energy is released, mostly at midplane Temperatures highest at midplane, lowest at surfaces Heat flux drives convection (Bell et al 1997) Gas rises, cools in convection cells, rocks condense PPDs:

Evidence for Condensation T = 1770 K T = 1370 K All vapor Metallic Fe condenses FeMg silicates Refractory minerals condense as rising gas cools Z T = 1270 K Simon et al (2002)

More Evidence for Condensation Meibom et al (1999, 2000) FeNi metal condenses as gas moves from T=1370 K to 1270 K Ni zoning reproduced if condensation takes a few weeks, as in a convection cell model (Meibom, Desch et al 2000)

Convection repeatedly moves material through hot midplane, evaporates most silicates Only most refractory minerals grow (CAIs) Convection and turbulence disperse CAIs widely (Cuzzi et al 2003a,b, 2004) This stage requires dM/dt > M sol /yr, ends after ~10 5 yr (Bell et al 2000) PPDs:

After few x 10 5 years, magnetohydrodynamic turbulence occurs only in surface layers Temperatures are everywhere much cooler, FeMg silicates form at midplane (chondrules) Accretion is unsteady with time, leads to shocks Shocks melt CAIs and chondrules, cool at rates ~ 50 K/hr (Desch & Connolly 2002) PPDs:

Conclusions CAI radionuclides constrain setting of solar system formation: 10 Be attributable to trapped 10 Be Galactic cosmic rays Other radionuclides ( 26 Al, 41 Ca, esp. 60 Fe) injected by supernova Injection occurred after first CAIs (FUN inclusions) formed Implicates formation in H II region like Orion or Eagle Nebula CAIs constrain disk temperatures, dynamics, timescales… CAI mineralogy implicates hot (> 1400 K) protoplanetary disk Condensates implicate convection Requires high mass accretion rates through disk > M sol /yr, attainable only for ~ 10 5 yr Convection, turbulence will then widely disperse CAIs