Search for Supernova 60 Fe in the Earth s Microfossil Record

Transcription

1 Search for Supernova 60 Fe in the Earth s Microfossil Record A Cosmic Message in a Bottle Carpathian Summer School of Physics,

2 Where in Nature are Elements Beyond Fe-Peak Made? Iron-group abundance peak ~5 or 6 order drop in abundance from Fe-group Carpathian Summer School of Physics,

3 Something to think about... Sun s Luminosity: x erg/s Age of Sun: about 4 x 10 9 yr In its life so far, energy output of Sun has been ~1.3 x erg Order of magnitude luminous energy output of SN: erg over first 2 weeks post explosion How many Sun-like stars required to match SN energy output? This is approximately: /10 41 = 10 9 (one billion) Number of stars in a typical spiral galaxy? About one billion In short: a single exploding star in the course of 2 weeks outputs more energy than the total energy output, over 4 billion years, of one billion sun-like stars. Carpathian Summer School of Physics,

4 Supernova Cassaeopae Remnant Production of elements, such as: Carbon Oxygen Silicon Sulfur Titanium Iron 23 Lightyears Production of radioactive isotopes such as: 26 Al (half-life 717 kyr) 44 Ti (half-life 60 yr) 60 Fe (half-life 2.6 Myr) Carpathian Summer School of Physics,

5 Cosmic Sites of 60 Fe Production Stars with masses > 10 solar masses Conclusion of core He-burning He-burning shell T ~ 4 x 10 8 Temp. drives the reaction sequence: Followed by: Free neutrons drive an s-process in the shell 60 Fe production 12 C( 12 C,a) 20 Ne occurs in core Free a s undergo reaction sequence above 60 Fe production Convection carries 60 Fe to lower temperatures, so that some survives against further n-capture H Envelope C & O Carpathian Summer School of Physics,

6 Core Collapse Supernova M. Limongi et al., ApJ. 647:483, (2006) Shock wave from core bounce slams into carbon and He shells Shells are shock heated Heating drives the reaction to faster rate Shells are also expanding (explosively) Neutron capture process as before occurs, but much faster Neutron capture rates are comparable, or faster, than expansion rate of shell 60 Fe synthesized in these shells ejected into space (5000 km/s) Carpathian Summer School of Physics,

7 60 Fe Astrophysics Points Half-life = 2.62 Myr Gamma-rays observed with INTEGRAL satellite of European Space Agency Technische Universität München G. Rugel et al., PRL 103 (2009) Wang et al., Astron. & Astrophys. 469 (2007) 60 Fe data obtained from observing same region as 26 Al 26 Al also known to be produced in massive stars that become supernovae Finding 60 Fe in same places as 26 Al => observational confirmation 60 Fe comes from massive stars and SN Carpathian Summer School of Physics,

8 How to Find a Needle in the Haystack ACCELERATOR MASS SPECTROMETRY Carpathian Summer School of Physics,

9 AMS Facility: Schematic Technische Universität München Carpathian Summer School of Physics,

10 60 Ni Isobaric Contamination in AMS 60 Ni 61 Ni 62 Ni Carpathian Summer School of Physics,

11 The Trick for Background Suppression Magnet selects charge:mass ratio For same ion energy from Tandem: Kinetic E is same: If masses are same, cannot separate Magnet filled with few mbar N 2 gas Then, q depends on atomic number: Carpathian Summer School of Physics,

12 The Business End of the AMS Facility Technische Universität München Ion Chamber Beam Carpathian Summer School of Physics,

13 Final Particle Identification Carpathian Summer School of Physics,

14 Where can we look? TERRESTRIAL 60 FE RESERVOIRS Carpathian Summer School of Physics,

15 The FeMn Crust 60 Fe Results C. Fitoussi et al, PRL 101 (2008) K. Knie et al, PRL 93 (2004) t ~ 2.2 Myr ago Carpathian Summer School of Physics,

16 Results from Ferro-Manganese Crust Findings Terrestrial 60 Fe fluence determined as f 60 = 2.8 x 10 8 atom/cm 2 (after new 60 Fe t 1/2 correction) Fluence: Uptake used was 0.6%, but: Could, in fact, be as large as unity (arguments for this soon to be published) If unity, Knie et al. fluence reduced by ~165 times Distance estimate wrong by ~15 Motivated to find a different/new 60 Fe reservoir for cross checking and constraining uncertainties What is the new reservoir? Carpathian Summer School of Physics,

17 There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy. -- W. Shakespeare SUPERNOVA SIGNATURE OF BIOGENIC ORIGIN Carpathian Summer School of Physics,

18 The Hypothesis Technische Universität München Supernova 60 Fe flux arrives in upper atmosphere Atomic, molecular, fine grains Mixes into atmosphere enters Earth s Fe-cycle SN 60 Fe (and stable Fe) oxidized Forms nano-size oxide grains Nano-oxides reach ocean Rapidly dissolves and re-precipitates Forms poorly crystalline ferric hydroxides ( rust ) Settles into sediment Ocean Carpathian Summer School of Physics, Sediment

19 Magnetotactic Bacteria: The Essentials Form ~90 nm sized magnetic crystals of magnetite: Fe 3 O 4 Live in sediment just below the surface-water interface Process ferric hydroxide nano-grains into magnetosomes Bulk Fe phases from detrital sources not the primary Fe source magnetosomes effectively sequester 60 Fe Bacteria co-move with sediment-water interface as it grows Magnetosomes become magnetofossils Any 60 Fe is locked inside 150 Myr BP Carpathian Summer School of Physics,

20 HOW MUCH FOSSIL MASS IS IN THE DIRT? Carpathian Summer School of Physics,

21 Ocean Drill Core Samples Core 848, leg 138, equatorial Pacific Water depth: 3870 m Predominantly Calcium-carbonate (80%) and SiO 2 (20%) Column height obtained: Myr BP Location: reduces detrital Fe inputs from continental run-off Technische Universität München Core 848, leg 138, 3870 m Carpathian Summer School of Physics,

22 Extracting the Microfossil 60 Fe and Measuring It WHAT HAS BEEN HAPPENING? Carpathian Summer School of Physics,

23 Citrate Carbonate-Dithionite (CBD) Technische Universität München Carpathian Summer School of Physics,

24 Extraction of fine-grained magnetite (40-80nm) from marine sediment samples Using the CBD-extraction technique Fe(II) Fe(III) Sediment sample ~50 g mostly calcite containing ~40ppm magnetite of organic origin (Magnetosomes of bacterial fossils) Fe(III) Fe(II) 1 h extraction of iron in CBD solution: Reduction of Fe using Sodiumdithionite. Fe(II) is chelated in Sodiumcitrate. Remaining sediment is filtered out. Anion exchange column to separate Fe from other metals like Al, Ti, Ni, Fe(III) Fe(II) Organic residues from CBD method ~15 g 300 C Fe(II) Oxidize Fe with nitric acid and extract with 7.1 M HCl Destruction of citrate with heat Fe(II) Fe(III) Fe(III) Precipitate Fe as hydroxyde using ammonium > centrifuge ~ 40 ml HCl Washing with water After precipitating again with ammonium, more washing with water, sample is dried yielding ~ 5 mg Fe 2 O 3 Fe(III) Mix with silver to increase thermal conductivity and hammer into AMS sample holder Carpathian Summer School of Physics, 2014 Determine ratio 60 Fe/Fe at the GAMS setup at the MLL in Garching 26

25 First Results: April 2013 (Old Stuff) Carpathian Summer School of Physics,

26 Latest Results: Core Fe/Fe Fe events Age (Myr) 10 kyr wide bins! Carpathian Summer School of Physics,

27 Latest Results: Core Fe/Fe Fe events Age (Myr) Carpathian Summer School of Physics,

28 Magnetic Extraction (MagEx) Technische Universität München Carpathian Summer School of Physics,

29 TEM MagEx Results: Core 851 from Myr Carpathian Summer School of Physics,

30 Summary Technische Universität München Biogenic supernova signal looks plausible Upcoming AMS measurements on MagEx material should confirm it Fluence ( 60 Fe atoms/cm 2 ) is consistent with FeMn crust FeMn crust uptake factor is indeed probably unity If signal confirmed: Opens the possibility to sample northern/southern hemisphere (bacteria are ubiquitous, FeMn crusts are not): is the terrestrial deposition uniform? If non-uniform, SN-Earth distance estimates are invalid Other Geological Reservoirs and r-process Isotopes to look for? Yes..ask in question period.or with sufficient wine at tonight s banquet Carpathian Summer School of Physics,

31 The Challenge of Going Beyond Fe-Peak Technische Universität München Iron-group abundance peak ~5 order drop in abundance from Fe-group Carpathian Summer School of Physics,

32 It gets stranger.. FUTURE IDEAS Carpathian Summer School of Physics,

33 Is (any one of the possible) r-processes occurring in CCSN? AN IDEA COMES OFF THE BACK- BURNER OF MY MIND: 129 I Carpathian Summer School of Physics,

34 Where to Look for 129 I Geologically stable No earthquakes No rainfall No water transport No erosion Minimal biological activity Harsh conditions to minimize microbe activity A catchment for Iodine My BP My BP 10-6 My BP 36 Carpathian Summer School of Physics, 2014

35 129 I Facts Beta-decay half-life: 15.7 Myr Technische Universität München Produced by cosmic ray spallation on Xe On dust in the ISM On 130 Xe in upper atmosphere r-process nuclide 129 I detection with 60 Fe would show that SN are a site for the r- process In steady state equilibrium with atmosphere and oceans Biological exchange with micro-organisms in oceans and aquatic plants Not such a clean system 37 Carpathian Summer School of Physics, 2014

36 38 Carpathian Summer School of Physics, 2014 Technische Universität München

37 Atacama Desert Features Hyper-arid region: Driest place on Earth Decades pass with no rain Surface erosion in alluvial fans: < 10 cm/myr Region in general unchanged ~ 10 Myr Rich in Salts! Sulfates Nitrates Iodates (IO 3- ) 17,18 O isotope shifts in Nitrate salts indicate deposition is from atmos/stratosphere Iodates expected to follow the same deposition pathway 39 Carpathian Summer School of Physics, 2014

38 For More Information Carpathian Summer School of Physics,

39 Bacterial Magnetosomes Doped with 60 Fe: AMS Results Cuts e determined with sample of known 60 Fe/Fe Given: 60 Fe/Fe = 2.37 Carpathian Summer School of Physics,

40 Earth: A SN Yield Detector Technische Universität München B. D. Fields et al., ApJ. 621 (2005) Particle Flux of isotope i at radius D without decay: D Cross sectional area of Earth intercepting SN debris: This debris deposited on Earth uniformly, over an area of: Number of atoms i deposited in uniform layer on Earth s surface (now include decay) after a time T since SN occurred: Ratio of any 2 nuclides: Independent of unknown distance D Carpathian Summer School of Physics,

41 Conjectural Outlook (If we find 60 Fe in the fossils) Gallionella bacterial biofilms: Can concentrate lanthanides/actinides up to ~10 3 times higher than surrounding rock And up to 10 6 (!) times higher than surrounding water (C. Anderson et al., Geobiology 1 (2003) 169) Are any such biofilms known to occur in the georecord within the SN time window? Example: 236 U half-life 26 Myr Could a spike exist in an actinide biofilm somewhere, with right time stamp Could confirm the site of r-process as CC-SN Carpathian Summer School of Physics,

42 First Order Reversal Curves (FORC s) Technische Universität München Reversal field = r r Each curve has it s associated H r. With grid in (H r,h), one makes the mixed derivative. Carpathian Summer School of Physics,

43 ODP Drill Core 838 Hysterisis FORC Untreated Sample Untreated 1 st Treatment 1 st Treatment 3 rd Treatment Carpathian Summer School of Physics,

44 Comparison Between Lake Sample High resolution lake sample R. Egli et al., Geochem. Geophys. Geosys., 10 (2011) Carpathian Summer School of Physics,

45 Untreated SD Ridge Subtracted ~75-80% of fossils extracted After Treatment Carpathian Summer School of Physics,