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Origins of the Short-Lived Radionuclides and the Astrophysical Environment of the Solar System’s Formation Steve Desch Arizona State University Gordon.

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Presentation on theme: "Origins of the Short-Lived Radionuclides and the Astrophysical Environment of the Solar System’s Formation Steve Desch Arizona State University Gordon."— Presentation transcript:

1 Origins of the Short-Lived Radionuclides and the Astrophysical Environment of the Solar System’s Formation Steve Desch Arizona State University Gordon Research Conference Origins of Solar Systems July 24, 2011

2 41 Ca 36 Cl 26 Al 10 Be 60 Fe 53 Mn 107 Pd 182 Hf 129 I Isotopic analyses of meteorites reveal the one- time presence of many short-lived radionuclides: (Wadhwa et al. 2007) 9 Be / 11 B 10 B 11 B 10 B 10 Be 11 Be 9 Be = Be x t 1/2 = 0.10 Myr t 1/2 = 0.30 Myr t 1/2 = 0.71 Myr t 1/2 = 1.51 Myr t 1/2 = 2.6 Myr t 1/2 = 3.7 Myr t 1/2 = 6.5 Myr t 1/2 = 8.9 Myr t 1/2 = 15.7 Myr Srinivasan et al. (1994; 1996) 41 Ca/ 40 Ca ≈ 1.5 x Cl/ 35 Cl ≈ x Al/ 27 Al ≈ 5 x Be/ 9 Be ≈ Fe/ 56 Fe ≈ 3 x Mn/ 55 Mn ≈ 1 x Pd/ 108 Pd ≈ 5-40 x Hf/ 180 Hf ≈ 1 x I/ 127 I ≈ 1 x Lin et al.(2005), Jacobsen et al.(2011) Lee et al. (1976); MacPherson et al. (1995) McKeegan et al. (2000), etc. Tachibana & Huss (2003) Lugmair & Shukolyukov (1998) Chen & Wasserburg (1996); Carlson & Hauri (2001) Kleine et al. (2002, 2005); Yin et al. (2002) Swindle & Podosek (1998) y = y 0 + m x Multiple minerals within a single inclusion (like this CAI), with different Be/B ratios, are measured

3 41 Ca 36 Cl 26 Al 10 Be 60 Fe 53 Mn 107 Pd 182 Hf 129 I t 1/2 = 0.10 Myr t 1/2 = 0.30 Myr t 1/2 = 0.71 Myr t 1/2 = 1.51 Myr t 1/2 = 2.6 Myr t 1/2 = 3.7 Myr t 1/2 = 6.5 Myr t 1/2 = 8.9 Myr t 1/2 = 15.7 Myr These 3 nuclei have 3 different origins Isotopic analyses of meteorites reveal the one-time presence of many short-lived radionuclides (SLRs): (Wadhwa et al. 2007) 60 Fe: injection. Neutron-rich. Not produced significantly by spallation; requires stellar nucleosynthesis. Only remotely likely source is core collapse supernova(e). Levels consistent with nearby supernova in same star-forming region. 10 Be: inheritance. Present in a wide variety of samples, including CAIs and hibonite grains, first to form. Ubiquitous and uniform. Not produced by stellar nucleosynthesis. Levels consistent with 10 Be cosmic rays trapped in molecular cloud (Desch et al. 2004), although this is debated (but keep watching). 36 Cl: irradiation. Present only in late-stage alteration products. Very short half-life. Levels too high too have been injected by supernova or inherited from molecular cloud. 107 Pd, 182 Hf, 129 I, probably inherited from ISM enriched in these SLRs by long-term Galactic nucleosynthesis (Harper 1996; Jacobsen 2005).

4 Radionuclides inherited from the molecular cloud Irradiation at several AU: 36 Cl, 53 Mn? Galactic cosmic rays enrich ISM: 10 Be Ongoing galactic nucleosynthesis enriches ISM: 129 I, 182 Hf, 107 Pd ~ 1 local supernova injected radionuclides into molecular cloud or protoplanetary disk: 41 Ca, 26 Al, 60 Fe, 53 Mn?, 107 Pd Scenario #1: Desch et al. (2004); Ouellette et al. (2005, 2007, 2009, 2010); Hester et al. (2004); Hester & Desch (2005); Ellinger et al. (2009); Desch et al. (2010)

5 Radionuclides inherited from the molecular cloud Irradiation at < 0.1 AU, followed by outward transport (X-wind): 41 Ca, 36 Cl, 26 Al, 10 Be, 53 Mn Ongoing galactic nucleosynthesis enriches ISM: 129 I, 182 Hf, 107 Pd, 53 Mn? ~ dozens of local supernovae injected radionuclides into Sun’s molecular cloud ~15 Myr before solar system forms (SPACE model): 60 Fe, 53 Mn?, Scenario #2: Shu et al. (1996, 1997, 2001); Gounelle et al. (2001, 2006, 2009); Gounelle (2006); Gounelle & Meibom (2007, 2008).

6 The SLRs 41 Ca, 36 Cl, 10 Be, 26 Al and 53 Mn can be produced in their observed proportions, incorporated into CAIs near the Sun, then ejected to 2-3 AU, a la the X-wind model (Gounelle et al. 2001). There is no need to invoke supernova injection for these SLRs (Gounelle 2006).

7 The X-wind can’t make CAIs, and can’t produce those SLRs in the correct proportions. They require some other origin, especially 60 Fe (Desch, Morris, Connolly & Boss 2010)!

8 The X-wind model Shu et al. (1996, 2001) HH30: Krist et al. (2000) Desch et al. (2010) ApJ 725, 692, critiqued the X-wind model. They found several problems.

9 Problem 1: Bipolar outflows often cited as support for X-winds, but observations show outflows launched at AU, not 70% of outflow (Woitas et al. 2005). Problem 2 : Observations show X point well inside where solids evaporate (Eisner et al. 2005). Shu et al. (1996) estimated T 2 x M  yr -1, T > 1440 K. OOPS! Problem 3: Solids do not fall out of funnel flow: they are entrained with gas all the way to the star unless already > 4 mm in diameter. "Ad hoc" factor F=0.01 not at all justified. Problem 4: If particles do fall out of funnel flow, their velocity relative to reconnection ring will be ~ tens of km/s, enough to shatter particles in the disk. Problem 5: Particles in reconnection ring feel dense, ~ 10 7 K plasma. Thermal sputtering (neglected by Shu) prevents particle growth. CAI atoms remain gas, are swept into star. Sputtering rate in 10 7 K plasma: Jones et al. (1996) OOPS!

10 Problem 6: CAIs grow by recondensing rock vapor following big flares. Oxygen fugacity fO 2 > 10 5 x solar, inconsistent with CAI oxygen barometers like Ti +3 /Ti +4 ratios in fassaite & rhonite, and osbornite in CAIs (Beckett et al 1986; Krot et al. 2000; Meibom et al. 2007). Shu et al. (2001) "X-wind = eXtra oXidizing" Problem 8: Magnetocentrifugal outflows only launch material from > 2 scale heights from midplane (Wardle & Konigl 1993), but disk of CAIs & chondrules in reconnection ring < 1 / 25 times as thick. X-wind model doesn't explain lofting or calculate trajectories. Problem 7: Energetic ions cannot produce 10 Be, 26 Al & 41 Ca in right proportions. Ca does not sequester itself in "refractory core", so 41 Ca overproduced. 10 Be overproduced relative to 41 Ca and 26 Al by factors > 3, especially if 10 Be is trapped GCRs (Desch et al. 2004). And 60 Fe is underproduced by > 5 orders of magnitude (Leya et al. 2003; Gounelle 2006). Ca Al Fe Mg O O Si Ca,Al-bearing minerals in CAIs melt at lower T than Fe,Mg-silicates. They don't form these structures! (Simon et al. 2002) Bottom line: Protostellar jets don’t necessarily mean X winds, X winds don’t make CAIs, and X winds don’t produce SLRs in right proportions.

11 10 Be can only be produced by irradiation, not by supernovae. It may be a “smoking gun” for the X-wind model (Gounelle et al. 2001; Gounelle 2006).

12 10 Be has other sources, especially 10 Be Galactic cosmic rays trapped in our molecular cloud (Desch et al. 2004). The X-wind actually overproduces 10 Be (Desch et al. 2004, 2010).

13 Galactic Cosmic Rays (GCRs) = nuclei of ions accelerated to relativistic speeds: Mostly protons, ~10% alpha particles, heavier ions in roughly solar proportions. The fluxes and energy spectra of GCRs, including 10 Be nuclei, have been measured by satellites (Webber et al. 2002; see Desch et al and references therein). 10 Be/H ratio is known… and is 10 6 x solar! (Spallations of ambient H on GCR O.) GCR fluxes scale with supernova rate, therefore star formation rate, which was x2.2 higher 4.5 Gyr ago (see multiple references in Desch et al. 2004). GCRs follow magnetic field lines, which bend in regions of star formation. Schleuning et al. (1998)

14 Simulations by Desch & Mouschovias (2001) show how gas in a collapsing molecular cloud core drags in magnetic field lines. Magnetic field lines are concentrated in core, focusing GCRs inward. High-pitch angle GCRs are mirrored out of the cloud core. High-energy GCRs pass through the cloud core. Some cause spallations of local O to form 10 Be. Low-energy 10 Be GCRs are stopped by ionizations and trapped within the core. Desch, Connolly & Srinivasan (2004),ApJ 602, 528, calculated the rates of all these processes in a collapsing cloud core.

15 Desch and Mouschovias (2001) and Desch et al. (2004) calculate S(t) and B(t) for different B fields. 30 μG collapses in 10 Myr, 5 μG collapses in 2 Myr. Final 10 Be/ 9 Be ratio very insensitive to B field because it saturates in 10 Be half-life (1.5 Myr). 10 Be produced by spallation 10 Be GCRs trapped in core Total 10 Be / 9 Be ratio. Numerical error in Desch et al (2004) overestimated stop- ping rate by x3. Should have found 10 Be/ 9 Be ≈ 6 x Bottom line: GCRs provide molecular cloud with right amount of 10 Be. Additional sources overproduce 10 Be!

16 If 10 Be comes from 10 Be GCRs trapped in the Sun’s molecular cloud, 10 Be/ 9 Be should be uniform, but it’s not (Gounelle 2006).

17 Yeah! We measured 5.3 ± 1.0 x in hibonites (Liu et al. 2009, 2010), which is not consistent with 8.8 ± 0.6 x in Allende CAI (Chaussidon et al. 2006) !

18 Actually, 10 Be is uniform. Not all the data were analyzed correctly (Desch, Ogliore, Morris & Huss 2011, in prep) If 10 Be comes from 10 Be GCRs trapped in the Sun’s molecular cloud, 10 Be/ 9 Be should be uniform, but it’s not (Gounelle 2006). Yeah! We measured 5.3 ± 1.0 x in hibonites (Liu et al. 2009, 2010), which is not consistent with 8.8 ± 0.6 x in Allende CAI (Chaussidon et al. 2006) !

19 9 Be / 11 B 10 B 11 B 10 B 10 Be 11 Be 9 Be = Be x y = y 0 + m x Slope = 5.75 ± 1.90 x χ ν 2 = 0.85 Goodness of fit tells you whether the assumption of an isochron is valid! MacPherson et al. (2003) 9 Be/ 11 B

20 10 B 11 B 10 B 10 Be 11 Be 9 Be = Be x y = y 0 + m x Slope = 12.7 ± 0.78 x χ ν 2 = 29.8!! Isochrons are meaningless if you can’t fit a line to the data!! Chaussidon et al. (2006) The slope reported by Chaussidon et al. (2006), 8.8 ± 0.6 x 10 -4, is incorrect, based on a wrong equal fit of all data points. 9 Be/ 11 B

21 Chaussidon et al. (2006) Many points have 10 B/ 11 B > 0.25 Spallogenic B has 10 B/ 11 B ~ 0.40 Our interpretation: B isotopes in Allende reflect overall trend of incorporating live 10 Be, and variable contamination by spallogenic B Isochron cannot be fit to the data. Chondritic ratio 10 B/ 11 B = 0.248

22 Leoville, Vigarano, Efremovka CAIs Murchison hibonites Axtel l FUN CAI Allende CAIs There are 17 analyses of 16 different samples. They all cluster around an average value. Average value is close to 10 Be/ 9 Be ≈6 x Allende

23 Leoville, Vigarano, Efremovka CAIs Murchison hibonites Axtel l FUN CAI Allende CAIs Eliminating the two analyses with the worst fits to an isochron (Axtell 2771 FUN CAI, χ ν 2 = 4.4, and Allende , χ ν 2 = 29.8) leaves 15 analyses with average 10 Be/ 9 Be = 6.3 x All other analyses have χ ν 2 ≤ 2.2 and are consistent with average at 2 sigma level (except Allende , which is probably contaminated). Bottom line: No evidence for 10 Be heterogeneity! Allende

24 There was also 7 Be in the solar nebula, with t 1/2 = 53 days (Chaussidon et al. 2006)!

25 That’s a smoking gun for irradiation in the solar nebula (Chaussidon & Gounelle 2007)!

26 There was also 7 Be in the solar nebula, with t 1/2 = 53 days (Chaussidon et al. 2006)! That’s a smoking gun for irradiation in the solar nebula (Chaussidon & Gounelle 2007)! The evidence for 7 Be was driven by model assumptions and probably contamination by spallogenic Li; there is no evidence for 7 Be (Desch & Ouellette 2006).

27 The only evidence for live 7 Be comes from the same CAI Allende , analyzed by Chaussidon et al. (2006), which is probably contaminated. These data points are not the measured values; they have already been corrected for GCR spallation within Allende. A better correction yields lower slope. Best fit, done properly, is 7 Li/ 6 Li = ( /- 0.02) + ( / ) (9Be/6Li), χ ν 2 = 17!! Slope is driven entirely by points with 9Be/6Li < 30, with subchondritic Li ratios; eliminating these yields fit 7 Li/ 6 Li = ( /- 0.07) + ( / ) (9Be/6Li), χ ν 2 = Bottom line: We interpret all variability in 7 Li/ 6 Li due to contamination, not 7 Be. Chondritic ratio 7 Li/ 6 Li = Many points have 7 Li/ 6 Li < < 12 Spallogenic Li has 7 Li/ 6 Li ~ 2

28 It’s not possible to inject 36 Cl from a supernova along with 26 Al and 41 Ca, its levels are too high (Gounelle 2006; Jacobsen et al. 2011). 36 Cl must be formed in the solar nebula.

29 Yes, 36 Cl must be produced in the solar nebula, but not in an X-wind (Desch et al. 2010). It probably formed by irradiation of ices in the disk during the transition disk stage (Jacobsen et al. 2011; Desch et al. 2011, in prep).

30 Evidence for 36 Cl found only in late-stage aqueous alteration products like sodalite (Lin et al. 2005) and wadalite (Matzel et al. 2010; Jacobsen et al. 2011), at levels up to 36 Cl/ 35 Cl ~ 1.7 x Al-Mg age of wadalite is 2.6 Myr after CAIs. Injecting 36 Cl and 26 Al from same supernova requires 36 Cl/ 35 Cl ~ 7 x 10 -3, higher than any supernova models predict. Jacobsen et al. (2011; ApJ) hypothesize irradiation of ices at a few AU in late stage of disk in which gas had thinned, followed by accretion of ices by carbonaceous chondrite parent bodies; predicted that (additional) 10 Be should accompany 36 Cl. Desch et al. (2011; LPSC) also hypothesize irradiation of ices in transition disk stage, predict spallogenic Li and B, and maybe 53 Mn, should accompany 36 Cl. 36 Cl must be produced by irradiation, but X-wind region is too hot for 36 Cl or its targets (S, Cl, Ar, K) to condense. Irradiation must take place further out in disk. Courtesy Sasha Krot

31 Spitzer observations show 10-20% of observed disks are transitions disks like TW Hydrae and DM Tau (Williams & Cieza 2011). Disks probably spend 0.5 – 1 Myr in this stage, at ages 3-6 Myr. Column densities ~ 1 g cm -2, optically thin to energetic ions.

32 Desch, Krot, Alexander & Allu Peddinti (2011; LPSC) modeled isotope production in transition disk, including new reaction 38 Ar(p,ppn) 36 Cl. Very little mass is irradiated, but that which is sees no dilution. Preliminary Predictions: 36 Cl/ 35 Cl = 3 x Li/ 6 Li = Mn/ 55 Mn =2 x Be/ 9 Be ~ Bottom Line: Late irradiation in a transition disk may explain 36 Cl, as well as B and Li anomalies. Of these, Cl, Li, Mn mobilized; 10 Be will precipitate before reaching interior

33 Injection of 60 Fe, 26 Al and 41 Ca into our protoplanetary disk would have noticeably altered the oxygen isotopic composition of the disk (Gounelle and Meibom 2007).

34 If only supernova dust is injected, this is no problem at all (Ellinger et al. 2010). Injection of 60 Fe, 26 Al and 41 Ca into our protoplanetary disk would have noticeably altered the oxygen isotopic composition of the disk (Gounelle and Meibom 2007).

35 Ouellette et al. (2005, 2007, 2010) advanced the “aerogel” model in which ejecta are injected directly into the protoplanetary disk as dust grains. Ouellette et al. (2007) showed gas-phase ejecta are not injected (< 1% efficiency). Ouellette et al. (2010) showed that large supernova dust grains (diameters > 100 nm) are injected efficiently (up to 90%).

36 If only condensible dust is injected, oxygen isotopic shifts are small. Fraction of supernova ejecta that condenses into dust is hotly debated, as reviewed in Ouellette, Desch & Hester (2010) ApJ 711, 597. Observations of dust in high-z galaxies imply 0.1 – 1 M   of dust per supernova (Morgan & Edmunds 2003). Dust in SN1987A formed ~ 2 years after explosion; only M  directly seen in IR. But emission was from optically thick (at 30 μm) clumps (Wooden et al. 1993). Ouellette et al. (2010) argued most supernova observations miss dust because it is in clumps, and SN1987A could have held up to 1 M  of dust. Recent Herschel observations (Matsuura et al. 2011) have revealed M  of cold (T = 20 K) dust in SN 1987A, implying condensation efficiency ~ 30 – 60% Corundum (Al 2 O 3 ) grains only have M( 26 Al)/M( 16 O) = If all 26 Al is in corundum grains and only corundum grains are injected, isotopic shifts < per mil. Injection of dust alone leads to isotopic shifts << 1 permil, too small to be noticed.

37 Ouellette et al. (2010) presented a model for P-T conditions in clumpy ejecta. In these clump models, P reaches bar, 10 3 times higher than previously considered Fedkin et al. (2010) Many models (e.g., Kozasa et al. 2010) predict high condensation efficiencies, but still predict unobserved features, because they have ignored clumpiness.

38 P ≤ bar yields graphite condensing before SiC, FeSi, metal… Clumpy ejecta pressures P ≥ bar yields TiC, then SiC / FeSi / metal, then graphite. Same sequence observed by Croat et al. (2011 LPSC) in an Orgueil SN presolar grain!! Fedkin et al. (2010) Strong evidence that SN presolar grains condensed in clumps. Clumps enhance dust growth and hide dust emission… suggests supernova dust condenses more efficiently than thought.

39 Meteorites and planetary materials have 54 Cr anomalies due to incorporating different proportions of some 54 Cr carrier (Qin et al 2010; Trinquier et al 2007). This carrier just discovered: presolar “nanospinels” < 100 nm in size, with 54 Cr/ 52 Cr 3.6 x solar (Dauphas et al. 2011), some up to 50 x solar (Qin et al. 2011). Must have been formed in a supernova. Dauphas et al. (2011), Qin et al. (2011) argues for late injection of these presolar grains. Larsen et al. (2011) find correlation between 54 Cr anomalies and 26 Mg excesses… nanospinels may also be the carrier of 26 Al! Bottom line: Supernovae make abundant (~ 0.5 M  ) dust; at least half of condensible material condenses into dust. ~50% of 100nm dust can be injected into a protoplanetary disk (Ouellette et al. 2010). Relatively high percentage of 26 Al and 60 Fe, etc., can be injected as dust into disk. Injection of dust without gas will not significantly alter oxygen isotopic composition of solar nebula (Ellinger et al. 2010).

40 But SLRs in CAIs like 26 Al and 41 Ca must be formed in situ... it’s not possible to inject SLRs from a supernova, within the first < 1 Myr, at the required levels (Gounelle and Meibom 2008).

41 And we know 60 Fe requires a supernova origin. It is possible, with triggered star formation and clumpy supernova ejecta. Injection into disk has ~1% probability (Ouellette et al. 2010). Injection into molecular cloud also works and is likely ( Pan et al. 2011, in prep ).

42 HST/K.Luhman Thousands of protostars with disks lie < few x 0.1 pc from O stars in Orion Nebula… … but that star won’t explode for > 4 Myr. By the time it does, coevally formed disks won’t be young disks anymore! Simple geometric arguments show that disk must be 5 x (Ouellette et al. 2005; Looney et al. 2006).

43 NGC 6357: Healy et al. (2004) Some disks do lie < 1 pc from stars < 1 Myr from exploding, but they’re rare. Still, H II regions like NGC 6357 provide evidence for triggered star formation. O3If* star Pismis 24, already evolved off main sequence

44 Hester & Desch (2005) O stars’ UV drives ionization fronts and shocks into molecular cloud, triggering star formation.

45 Combined Spitzer / HST survey of 2-Myr-old region NGC 2467 (Snider et al. 2009) and other H II regions ( Snider PhD thesis, 2008 ) show protostars continue to form many Myr after O stars, and their locations are highly correlated with ionization fronts, indicating a triggered formation. Triggered star formation continues until most massive stars go supernova. NGC 2467: Snider et al. (2009) Easily 30-50% of low-mass stars in H II regions are triggered by massive stars. ~ 10% form just < 1 Myr before supernova.

46 Hester & Desch (2005) The problem is these disks are far from the O star. Ionization fronts advance ~ 0.5 – 1 km/s = 2 – 4 pc in 4 Myr. Stars that do form just before supernova are far away (>2 pc). Isotropic supernova ejecta too diluted to explain 26 Al/ 27 Al ratio (by a factor ~ 300). > 2 pc!

47 Cassiopeia A, 300-year-old supernova remnant (X ray = NASA Chandra, optical = NASA HST; infrared = JPL) But supernovae are NOT isotropic! 4 pc

48 At d ~ 2 pc from explosion center, HST resolves thousands of knots, each ~ M , each ~ 0.1 – 1” (~ cm), probably formed by R-T instabilities during explosion. HST: Fesen & Morse

49 N ~ 3000 bullets of mass ~ 3 x M  each, expanding homologously with radius R = d / 300 (consistent with numerical simulations and observed clumps in SN1987A and Cas A) have filling fraction N πR 2 / (4πd 2 ) ~ 0.8% Only 0.8% of disks receive ejecta, but those that do get 120 times what they’d get if ejecta were isotropic, equivalent to being 11x closer. Bottom line: Disks at 2 pc can form and within 1 Myr receive sufficient ejecta to explain 26 Al and 60 Fe abundances… but only % of disks in H II region conform to this scenario. (But multiple supernovae may ameliorate problem somewhat) And the fact remains… 60 Fe requires a supernova origin!

50 2-D Flash simulations by Pan, Scannapieco, Desch & Timmes (2011, in prep) These same bullets colliding with the surrounding molecular cloud penetrate about 0.5 pc before stopping and mixing with cloud gas in channel with area ~ 0.02 pc 2. Cloud area per bullet ~ 0.02 pc 2. All molecular cloud cores on verge of collapse will be mixed with one ~10 -4 M  bullet of supernova ejecta from some zone in the progenitor. Multiple (~ 10) supernovae in H II region may lead each star to be mixed with ~10 -3 M  of supernova ejecta from ~10 zones in different supernovae. Work in progress. This may be how supernovae delivered 60 Fe to solar system. Supernova bullet

51 60 Fe does require a supernova origin, but not a single nearby supernova. Contamination of the molecular cloud by dozens of supernovae over the previous 15 Myr (SPACE model) is sufficient (Gounelle et al. 2009).

52 The SPACE model overestimates the efficiency by which 60 Fe is mixed into molecular clouds (Desch et al. 2010). And it overpredicts the 53 Mn / 60 Fe ratio by orders of magnitude!

53 Gounelle et al. (2009), SPACE (Supernova Propagation and Cloud Enhancement) model …this gas must be swept up and compressed… …to form new molecular clouds… This low-density gas is heated when shocked and can’t cool and compress… SPACE relies on a thermal instability to cool (Koyama & Inutsuka 2002; Audit & Hennebelle 2010) that works at shock speeds < 100 km/s and T < 10 4 K, not the 2000 km/s shock speeds and 10 7 K gas here. …and 60 Fe mixed in with 100% efficiency To get 60 Fe/ 56 Fe ~ in forming system… Molecular cloud 1 has ~ 3000 M , Molecular cloud 2 has ~ 8000 M  Shocks from cloud 1 can’t cause contraction of a new molecular cloud 15 Myr later unless gas can cool. Low- density ISM

54 A problem recognized by Gounelle et al. (2009): supernovae produce too much 53 Mn along with 60 Fe. 60 Fe produced in innermost 6 M , 53 Mn in innermost 3 M . If all of the ejecta are mixed, 53 Mn / 60 Fe ~ 10 2 x higher than meteoritic ratio For a single supernova may not eject all its material: progenitors > 20 M  often experience “fallback” of innermost few M  (Umeda & Nomoto 2002, 2005; Nomoto et al. 2006; Tominaga et al. 2007), resolving the 53 Mn / 60 Fe problem (Takigawa et al. 2008). A disk or molecular cloud may receive a clump of supernova ejecta from one zone in the progenitor. SPACE model invokes 4-22 (average 12) supernovae and mixes all of their ejecta. They can’t all experience fallback. Bottom line: not clear how formation of new molecular clouds are triggered by massive stars; not clear how 60 Fe is mixed into new clouds; not clear how to avoid mixing in too much 53 Mn.

55 Short-lived radionuclides are important probes of the Solar System’s formation environment. Multiple SLR origins are needed. 36 Cl formed by irradiation in solar nebula. 60 Fe came from 1 or dozens “nearby” and “recent” supernova(e).

56 Conclusion: Scenario #1! 1. Sun’s molecular cloud already enriched with 107 Pd, 182 Hf, 129 I… as it collapses, 10 Be GCRs trapped in it. 2. Massive stars’ ionization fronts trigger formation of low-mass stars, including Sun. 3. Supernova injects 26 Al, 41 Ca, 53 Mn, 60 Fe into disk or cloud. 4. Irradiation in Sun’s transition disk, ~ 3 Myr later, creates 36 Cl, spallogenic Li & B, maybe some 53 Mn.


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