The Local Bubble and the 60 Fe Anomaly in the Deep-Sea Ferromanganese Crust

Transcription

1 The Local Bubble and the 60 Fe Anomaly in the Deep-Sea Ferromanganese Crust Jenny Feige 1 D. Breitschwerdt 2 B. Fuchs 3 C. Dettbarn 3 1 University of Vienna 2 TU Berlin 3 ARI Heidelberg 3. March 2011

2 The 60 Fe Anomaly An increase corresponding to an age of 3 Myr of 60 Fe/Fe was found in the ferromanganese crust 237KD by Knie et al FeFe The 60 Fe/Fe ratio versus the age of the crust.

3 The Research Vessel Valdivia The crust was taken from the North equatorial Pacific. Courtesy of Google Maps (map) and D. Quadfasel (ship). J. Feige, D. Breitschwerdt, B. Fuchs, C. Dettbarn The LB and the 60 Fe Anomaly in the Ocean s Crust

4 A Hydrogenetic Ferromanganese Crust Ferromanganese crusts are found on sea-mountains and -plateaus, deep-sea volcanoes and the mid-ocean ridges Depth about m They obtain the composition of elements out of the ambient water 20 % Mn and 15 % Fe Low growth rate (< 10 mm/myr) A hydrogenetic ferromanganese crust. Courtesy of oceanexplorer.noaa.gov.

5 The hydrogenetic ferromanganese crust 237KD One of the biggest crusts ever recovered Depth: cm Dated by Segl et al Depth of this sample contains a time span of 0-60 Myr A piece of the ferromanganese crust 237KD, Courtesy of M. Poutivtsev. J. Feige, D. Breitschwerdt, B. Fuchs, C. Dettbarn The LB and the 60 Fe Anomaly in the Ocean s Crust

6 How to date a Crust Half-life of 10 Be: 1.51 Myr New half-life: 1.38 Myr (Korschinek et al. 2010) Assumption: constant 10 Be flux T d = t 1/2 ( 10 Be) ln(c 0/C d ) ln 2 T d... Age of the crust in depth d C 0... Concentration at the surface C d... Concentration in depth d Growthrate: 2.5 mm/myr New growthrate: 2.37 mm/myr

7 New 10 Be Dating of the Crust The peak shifts from Myr 60 FeFe The 60 Fe/Fe ratio versus the age of the crust based on the new 10 Be dating. Green dots: Confirmation of the peak by Fitoussi et al

8 The Local Bubble Cavity of thin hot gas Emits soft X-Rays Deficient of HI About 14 Myr old Caused by multiple Supernova Explosions Extension: 200 pc into the Galactic Plane 600 pc perpendicular to it Simulation of the Local ISM by D. Breitschwerdt and M. de Avillez, 2006.

9 Which Stars are to Blame? The LB was produced by SN explosions (Fuchs et al. 2006) 69 stars were found in the solar vicinity (radius 200 pc) that belong today to the subgroups UCL and LCC of the Scorpius OB2 association age of the moving group: Myr The paths of UCL and LCC over a time span of 30 Myr into the past, computed by Fuchs et al

10 The Trajectories of UCL and LCC The trajectories in the X-Z plane (Courtesy of C. Dettbarn). The trajectories in the X-Y plane (Courtesy of C. Dettbarn). Red: the closest trajectory closest point: 2.2 Myr ago, 65 pc Blue: the most distant trajectory

11 Determining the Explosion Times M τ N SN = 8.2 dn M 2.1 dm dm N The IMF of the UCL devided into intervals that each contain one star.

12 Determining the Explosion Times τ = τ 0 M α, τ 0 = yr, α = MM UCL LCC The explosion times of the stars of UCL (blue) and LCC (red) in correlation with their masses.

13 The 60 Fe Yields in Massive Stars 60 Fe is an unstable radionuclide with a half-life of 2.62 Myr (Rugel et al. 2009) It is only produced in massive stars (s- and r-process, SN explosion) The production depends on the masses of the stars Nucleosynthesis computations are sensitive to a variety of factors 60 Fe Yield10 4 M Woosley, Weaver 1995 Rauscher et al Limongi, Chieffi 2006 Woosley, Heger 2007 Fit Woosley, Heger 2007 Fit Limongi, Chieffi The 60 Fe yields as a function of stellar masses based on different computations.

14 A Supernova Exploding into a Low Density Region Model developed by Kahn in 1998 SNR expands not in a homogenous ambient medium, but into a medium that has already been shaped by a previous SN Ρ ρ = Ωr n, n = 9 2 The Radius of the expanding remnant is calculated with r s n+5 = (n + 5)(2n + 7) E SN t 2 6π Ω The density distribution of the interstellar medium shaped by a supernova explosion.

15 The Amount of 60 Fe arriving on Earth Fluence: number of atoms that reach the Earth per cm 2 F = U 4 M ej 4πAm p r 2 e t τ Particles are spread over a spherical shell with radius r r... Distance of the SN explosion to Earth M ej... Ejected 60 Fe mass A = Mass number m p... Proton masses U = 0.6 %... Uptake factor τ... Mean life Courtesy of TU Munich

16 Analytical Calculation vs. Measurements 60 FeFe UCL LCC Knie The computed data (UCL: blue, LCC: red) plotted over the 60 Fe measurements (black points) with an ISM density of n = 1 atom/cm 3.

17 Position of the closest SN in LCC LCC in the XY- and XZ-plane. Courtesy of C. Dettbarn.

18 EuroGENESIS Collaborative Research Programm ( ) Four Collaborative Research Projects (CPR s) CoDustMas: Cosmic Dust Grains as a Diagnostic for Massive Stars (Anton Wallner, Vienna) Measurement of trace element isotope ratios in presolar nanodiamonds isolated from meteorites (REE, U) Search for supernova-produced radionuclides in terrestrial deep-sea archives EXNUC: Physics of compact objects: explosive nucleosynthesis and evolution FirstStars: Nucleosynthetic fingerprints of the first stars MASCHE: Massive Stars as Agents of Chemical Evolution

19 EuroGENESIS Continue the search for supernova-produced radionuclides in terrestrial archives Main focus: Deep-Sea sediments Vienna Environmental Research Accelerator (VERA): 26 Al (t 1/2 = 0.7 Myr) 244 Pu (t 1/2 = 81 Myr) 247 Cm (t 1/2 = 15.6 Myr) TU Munich, Hebrew University, ANU (Canberra) & ANSTO (Sydney) and ETH Zürich: 60 Fe (t 1/2 = 2.6 Myr) 53 Mn (t 1/2 = 3.7 Myr) 182 Hf (t 1/2 = 8.9 Myr) Better understanding of nucleosynthesis in massive stars dust formation efficiency, transport mechanisms in supernova remnants deposition of radionuclides on earth

20 Conclusions In 2004 an 60 Fe anomaly was found in a deep-sea hydrogenetic ferromanganese crust by Knie et al. Signal corresponds to a time of 2-3 Myr ago 60 Fe is only produced in massive stars and ejected by SN explosions Number of SN were derived by fitting IMF to massive stars (Fuchs et al. 2006) belonging today to the Scorpius OB2 association Using the masses to calculate the explosion times. Computed the time the SNR takes to hit the Earth with the Model developed by Kahn (1998) With the 60 Fe yields we have been able to calculate the amount of this isotope that reaches the Earth The analytically computed data fits the measurements very well, especially the peak position As part of the EuroGENESIS research programm we will continue the search for supernova produced radionuclides in terrestrial archives.