Nucleosynthesis of heavy elements Almudena Arcones Helmholtz Young Investigator Group
The nuclear chart uranium masses measured at the ESR 82 silver gold r-proce path 126 stable nuclei 50 82 will be measured with CR at FAIR Z 20 28 50 nuclides with known masses 8 8 N 20 28
Solar system abundances Solar photosphere and meteorites: chemical signature of gas cloud where the Sun formed Contribution of all nucleosynthesis processes Big Bang: H, He Lodders 2003 iron peak burning in stellar interiors r-process neutron capture s-process s-process: slow neutron capture r-process: rapid neutron capture abundance = mass fraction / mass number
Z Big Bang: H, He 20 28 iron peak burning in stellar interiors stable nuclei 50 νp-process 50 r-process s-process neutron capture s-process masses measured at the ESR 82 82 p-process nuclides with known masses r-process silver uranium 126 will be measured with CR at FAIR gold r-proce path 8 8 N 20 28 Nuclear processes and solar abundances
The r-process: what do we know?
Solar system abundance solar r-process = total - s-process - p-process = residual abundances r-process peaks: 1 st peak: A 80 N=50 2 nd peak: A 130 N=82 3 rd peak: A 195 N=126 rare earth peak A 165? Sneden & Cowan 2003
r-process path uranium neutron capture faster than beta decay high neutron density seed nuclei + neutrons Yn/Yseed > 100 masses measured at the ESR 82 r-proce path Z 20 28 stable nuclei 50 50 82 nuclides with known masses r-process silver 126 will be measured with CR at FAIR gold 1 st peak: A 80 N=50 8 8 N 20 28 iron 2 nd peak: A 130 N=82 3 rd peak: A 195 N=126 rare earth peak A 165?
Oldest observed stars The very metal-deficient star HE 0107-5240 Silver Eu Gold Elemental abundances in: - ultra metal-poor stars and - solar system Robust r-process for 56<Z<83 Scatter for lighter heavy elements, Z~40 How many r-processes contribute to solar system and UMP stars abundances? Sneden, Cowan, Gallino 2008
Trends with metallicity core-collapse supernovae type Ia Fe and Mg produced in same site: core-collapse supernovae Significant scatter at low metallicities r-process production rare in the early Galaxy Mg and Fe production is not coupled to r-process production Sneden, Cowan, Gallino 2008
The r-process: what do we know? Solar system: residual r-process r-process peaks and path fast neutron capture Astrophysical environment: explosive and high neutron density UMP stars: robust process from 2 nd to 3 rd peak contribution from other process(es) below 2 nd peak Chemical evolution: r-process does not occur in every core-collapse supernovae What do we need to know better? Astrophysical site(s) Nuclear physics
Where does the r-process occur? Core-collapse supernovae Neutron star mergers Neutron stars Cas A (Chandra X-Ray observatory) Neutron-star merger simulation (S. Rosswog) neutrino-driven winds (Woosley et al. 1994,...) shocked surface layers (Ning, Qian, Meyer 2007) spiral arms neutrino-driven wind jets (Winteler et al. 2012) neutrino-induced in He shell (Banerjee, Haxton, Qian 2011) (Lattimer & Schramm 1974, Freiburghaus et al. 1999,..., Goriely et al. 2011)
Core-collapse supernova simulations Hot bubble Shock Proto-neutron star Long-time hydrodynamical simulations: - ejecta evolution from ~5ms after bounce to ~3s in 2D (Arcones & Janka 2011) and ~10s in 1D (Arcones et al. 2007) - explosion triggered by neutrinos - detailed study of nucleosynthesis-relevant conditions
Core-collapse supernova simulations slow ejecta shock reverse shock neutrino-driven wind Long-time hydrodynamical simulations: - ejecta evolution from ~5ms after bounce to ~3s in 2D (Arcones & Janka 2011) and ~10s in 1D (Arcones et al. 2007) - explosion triggered by neutrinos - detailed study of nucleosynthesis-relevant conditions
Arcones & Janka (2011)
Nucleosynthesis in core-collapse supernovae Explosive nucleosynthesis: O, Mg, Si, S, Ca, Ti, Fe shock wave heats falling matter shock neutrino-driven wind
nuclear matter nuclei Neutrino-driven winds R [km] 10 10 5 4 Neutrino Cooling and Neutrino Driven Wind (t ~ 10s) ν e,µ,τ,ν e,µ,τ neutrons and protons form α-particles α-particles recombine into seed nuclei 10 3 Ni Si 10 R ~ 10 ns 2 α r process? He O ν e,µ,τ,ν e,µ,τ R ν PNS 1.4 α,n n, p 9 α,n, Be, C, seed 12 3 M(r) [M ] NSE charged particle reactions / α-process r-process cur in a collapsing stellar iron core on the way to the weak r-process right) T visualize = 10 - the 8 physical GK conditions at the onset8 of- 2 GK νp-process on of the prompt shock, shock stagnation and revival utrino-driven wind of the newly formed neutron star, T < 3 GK In the upper parts of the figures the dynamical state
Neutrino-driven wind parameters r-process high neutron-to-seed ratio (Yn/Yseed~100) - Short expansion time scale: inhibit α-process and formation of seed nuclei - High entropy: photons dissociate seed nuclei into nucleons - Electron fraction: Ye<0.5 Otsuki et al. 2000 Ye=0.45 Conditions are not realized in recent simulations (Arcones et al. 2007, Fischer et al. 2010, Hüdepohl et al. 2010, Roberts et al. 2010, Arcones & Janka 2011) Swind = 50-120 kb/nuc τ = few ms Ye 0.4-0.6? Review: Arcones & Thielemann (2013) Additional ingredients: wind termination, extra energy source, rotation and magnetic fields, neutrino oscillations
1D simulations for nucleosynthesis studies Arcones et al 2007 Silver Shock Radius [cm] mass element no r-process Reverse shock Neutron star time [s]
Lighter heavy elements in neutrino-driven winds Elements from Sr to Ag produced in neutrino winds First comparison: nucleosynthesis based on simulations with observations (Arcones & Montes 2011) Weak r-process: charged-particle reactions + neutron capture (Hoffman et al. 1992,..., Wanajo et al. 2010, Farouqui et al. 2010) 30 40 50 60 70 80 90 proton number (Z) neutron rich LEPP: Lighter Element Primary Process observations Honda et al. 2006 (Travaglio et al. 2004, Montes et al. 2007)
Neutron or proton rich? Wind electron fraction still uncertain due to neutrino-matter interactions at high densities Fischer et al 2010 Woosley et al 1994 Arcones et al 2007 Hüdepohl et al 2010 Lea/Len = 1 Lea/Len = 1.1 Qian & Woosley 1996 neutron rich: (Δ=mn-mp) proton rich Elements from Sr to Ag produced also in proton-rich winds (Arcones & Montes 2011) vp-process (Fröhlich et al. 2006, Pruet et al. 2006, Wanajo et al. 2006,...) observations Honda et al. 2006 New studies: neutron rich (Martinez-Pinedo et al. 2012, Roberts & Reddy 2012)
Elemental abundances in metal stars Following Qian & Wasserburg 2007 three groups: Fe-like elements (A ~ 23 to 70): Na, Mg, Al, Si,..., Fe,..., Zn Sr-like elements (A ~ 88 to 110): Sr, Y, Zr,..., Ag Eu-like elements (A > 130): Ba,..., Eu,..., Au,..., Th,..., U α-elements heavy r-process elements CS 31082-001 HD 115444 HD 122563 Roederer 2012 lighter heavy elements Qian & Wasserburg 2007
Where is the r-process?
Supernova-jet-like explosion Ye 3D magneto-hydrodynamical simulations: rapid rotation and strong magnetic fields matter collimates: neutron-rich jets right r-process conditions Ye simulation: only ν emission Ye corrected for ν absorption Winteler, Käppeli, Perego et al. 2012
Neutron star mergers
Neutron star mergers Neutron-star merger simulation (S. Rosswog) Right conditions for a successful r-process (Lattimer & Schramm 1974, Freiburghaus et al. 1999,..., Goriely et al. 2011) Do they occur early enough to explain oldest star abundances (Argast et al. 2004)?
Neutron star mergers and GCE Do neutron star mergers occur early enough to explain UMP star abundances? Argast et al. 2004: galactic chemical evolution models r-process from: core-collapse supernovae neutron-star mergers GCE model observations Open questions: amount of mass ejected event rate
Neutron star mergers Neutron-star merger simulation (S. Rosswog) Right conditions for a successful r-process (Lattimer & Schramm 1974, Freiburghaus et al. 1999, Goriely et al. 2011) Do they occur early enough to explain oldest star abundances (Argast et al. 2004)? Korobkin, Rosswog, Arcones, Winteler (2012) Systematic nucleosynthesis study: 19 x (neutron star - neutron star) 2 x (neutron star - black hole) robust r-process: - extreme neutron-rich conditions - several fission cycles
T (GK) ρ (g cm -3 ) robust r-process Korobkin et al. 2012
Radioactive decay in neutron star mergers r-process heating affects merger dynamics: late X-ray emission in short GRBs (Metzger, Arcones, Quataert, Martinez-Pinedo 2010) Transient with kilo-nova luminosity (Metzger et al. 2010, Roberts et al. 2011, Goriely et al. 2011): direct observation of r-process, EM counter part to GW Multi messenger (e.g. Metzger & Berger 2012, Rosswog 2012, Bauswein et al. 2013)
r-process and extreme neutron-rich nuclei nuclear physics: masses, beta decays, neutron capture, fission barriers and yield distribution,... measured at GSI masses measured at the ESR 82 r-proces path stable nuclei 50 82 r-process 126 will be measured at will be measured with CR at FAIR Z 20 28 50 nuclides with known masses 8 8 N 20 28
Nuclear masses and r-process Trajectory from hydrodynamical simulations + entropy (S ~ T 3 /ρ) increased by a factor two (Arcones et al. 2007) Compare four different nuclear mass models: FRDM (Möller et al. 1995) ETFSI-Q (Pearson et al. 1996) HFB-17 (Goriely et al. 2009) Duflo&Zuker Can we link masses (neutron separation energies) to the final r-process abundances? Arcones & Martinez-Pinedo, 2011
Fission: barriers and yield distributions Korobkin, Rosswog, Arcones, Winteler (2012) Neutron star mergers: r-process with two simple fission descriptions 2nd peak (A~130): fission yield distribution 3rd peak (A~195): mass model, neutron captures
solar and UMP star abundances A=195, N=126 A=132, N=82 masses measured at the ESR 82 r-process path stable nuclei 50 126 82 will be measured with CR at FAIR 20 28 50 nuclides with known masses 8 8 20 28 chemical evolution fast neutron capture high neutron density explosive environment neutron rich hydrodynamical simulations high density EoS, neutrino transport nucleosynthesis calculations nuclear reaction network