Probing the Creation of the Heavy Elements in Neutron Star Mergers

Transcription

1 Probing the Creation of the Heavy Elements in Neutron Star Mergers Daniel Kasen UC Berkeley/LBNL r. fernandez, j. barnes, s. richers, f. foucart, d. desai, b. metzger, n. badnell, j. lippuner, l. roberts Foucart et al., 2016

2 origin of the elements BBN massive stars core collapse supernovae neutron capture nuclei (s- and r-process) core collapse supernovae or neutron star mergers? thermonuclear (Type Ia) supernovae solar system abundances lodders (1999) light r-process heavy r-process

3 Type Ia supernova light curves and spectra powered by ~0.6 Msun of 56 Ni

4 possible r-process sites need neutron rich ejecta: Ye = np/(nn + np) < 0.5 How often does these events occur (rate)? core-collapse supernovae (and what abundance pattern?) How much r-process do they make (yield)? neutron star merger n + e $ p + e neutrino driven wind from a proto-neutron star common event, low yield (if any) dynamical ejecta or post-merger disk winds rare event, high yield

5 Origin of the heavy (r-process) elements what are the astrophysical sites and physical conditions (neutron excess, entropy, expansion timescale, etc..) SkyNet reaction network jonaslippuner.com/research/skynet/ what are the nuclear properties of neutron rich isotopes (masses, reaction rates, beta decay, fission, etc..)

6 compact object mergers remnants of a tight massive star binary

7 GW emission of neutron star binary PSR B hulse-taylor pulsar separation: ~1 Rsun period: ~8 hours lifetime: ~300 million yrs estimated rate: 1 merger every years per galaxy (but very uncertain)

8 merger occurs at separation and orbital velocity orbital period so frequencies of f ~ 1/P ~ khz the power radiated at time of merger

9 aligo sensitivity from Francois Foucart

10 electromagnetic counterparts to compact object mergers gamma-ray burst relativistic jet non-thermal beamed Foucart et al., 2014 kilonova non-relativistic mass outflow thermal (radioactively powered) isotropic

11 Electromagnetic followup of LIGO sources e.g., Abbot et al (2016), Santos-Soares et al (2016), Cowperthwaite et al (2016)

12 end-to-end simulation of mergers binary evolution (~10 9 years) merger dynamics (miliseconds-secs) initial conditions (NS or BH, masses, spins, inclination) hydrodynamics, gravity, nuclear equation of state, neutrino physics, nuclear reactions, magnetic fields nucleosynthesis (seconds) kilonova transient (days/weeks) n n n reaction networks nuclear physics inputs radioactive heating (beta, alpha, fission) Boltzmann transport atomic opacities Z n n n

13 Neutron Star Mergers 4 Msun black hole Msun neutron star general relativistic merger simulation Francois Foucart (LBNL/UCB) foucart et al 2015

14 dynamical ejecta from mergers ~ Msun ejected on timescales of ~ milliseconds depends on mass ratio and nuclear equation of state neutron star + black hole cold, very neutron rich foucart neutron star + neutron star shocked, a bit less neutron rich bauswein+ 2013

15 Ye distribution: NS + BH merger (precessing) Foucart et al 2016

16 r-process abundances from neutron star merger ejecta dynamical ejecta with low Ye Barnes, Kasen,Wu, Martinez-Pinedo 2016

17 mass ejection from mergers both early time (dynamical) and late time (disk winds) contributions merger prompt ejecta (miliseconds) cold, very neutron rich (foucart+ 2015) post-merger winds (seconds) hot, less neutron rich (fernandez, kasen+ 2015)

18 BH post-merger ejection in disk winds viscous, neutrino, and nuclear driven outflows fernandez & metzger (2013, 2014), kasen, fernandez & metzger (2015)

19 neutrino irradiation of NS merger remnants neutrino energy density neutrino mean energy NS $ e + n $ p + e e + p $ n + e + richers, kasen, et al 2015

20 physical conditions in wind ejecta neutron richness depends on lifetime on remnant neutron star disk winds kasen, fernandez, and metzger 2015 c dynamical ejecta

21 different pathways for heavy element production in NS mergers prompt merger ejecta (cold, very neutron-rich) heavy r-process SkyNet reaction network jonaslippuner.com/research/skynet/ post-merger winds (hot, less neutron-rich) light r-process

22 3D multi-component structure of a BH-NS merger fernandez, quataert, schwab, kasen, and rosswog (2015)

23 calculated nuclear abundances fernandez et al. (2016 in prep) dyn +wind dyn only

24 kilonova: pure cloud of heavy radioactive r-process at t ~ 1 day r ~ cm ρ ~ g cm -3 T ~ 5000 K L ~ 10 7 Lsun isotopes ejected from merger at v ~ 0.1c Z Z+1 beta decay νν e- Υ e- n neutron decay p ν fission, alpha decay t = 1

25 Radioactive decay heating barnes, kasen, wu, martinez-pinedo (2016)

26 simulated kilonova light curves Type Ia SN M ~ 1.4 Msun Li and Paczynski (1998) Kulkarni (2005) Metzger et al. (2010) Roberts et al. (2011) Goriely et al (2012) Grossman et al (2013) barnes&kasen 2013 NS merger kilonova M ~ 10-2 Msun

27 kilonova opacity mean free path set by density of lines cross-section mean free path ~ (Δλ/λ) c t redshifting photon

28 atomic structure and radiative data limited data available for high Z species Autostructure cacluations kasen, badnell, and barnes (2013) ab-initio atomic structure calculations for select heavy species atomic structure modeling needed for level/line data

29 opacity and atomic complexity s-shell (g=2) g! N lev n!(g n)! N lines Nlev 2 p-shell (g=6) d-shell (g=10) f-shell (g=14)

30 optical photon opacities atomic level structures calculations (kasen+ 2013) HI s-shell SiII p-shell FeII d-shell NdII f-shell

31 optical opacity of heavy atoms T = 5000 K rho = g cm -3 kasen+ 2013

32 light curves of kilonova transients effect of high lanthanide opacity lanthanide free A< 130 opacities 1D models M = 10-2 Msun v = 0.1 c lanthanides A > 130 opacities kasen barnes & kasen 2013

33 kilonova color depends on composition optical infrared lanthanide-free A < 130 T ~ 5500 K lanthanides A > 130 T ~ 2500 K kasen barnes & kasen 2013 kasen+ day 2.5 don t trust the features!

34 GRB130603B relatively nearby short GRB (z = 0.356) HST optical HST infrared after before difference Tanvir+ 2013, Berger+ 2013

35 simulated heavy r-process kilonova light curves Hubble data point

36 simulated light curves of merger winds blue light probes weak r-process, red strong r-process tns = 0 ms MA<130 = 7.0x10-5 MA>130 = 1.5x10-3 tns = 30 ms MA<130 = 7.1x10-4 MA>130 = 2.4x10-3 tns = 100 ms MA<130 = 6.0x10-3 MA>130 = 4.0x10-6 infrared optical kasen+2015

37 multiple ejecta components t = 100 ms disk wind inside10-2 Msun dynamical ejecta infrared optical

38 astrophysical probes of nuclear physics in neutron star mergers cold dynamical ejecta or disk wind with BH low Ye low neutrino irradiation high hot dynamical ejecta or disk wind with NS high Ye strong r-process nuclear physics (N = 82 closed shell) weak r-process high opacity red kilonova atomic physics (lanthanide f-shell e - ) lower opacity blue kilonova

39 future/ongoing work improved dynamical and disk wind simulations (GRMHD w/ neutrinos) parameter studies of ejecta mass properties (dependence on EOS, initial conditions, spin and eccentricity) improve nucleosynthesis and radioactive heating rate calculations (nuclear data for neutron rich isotopes) improved light curves and spectra (better atomic data + opacities)

40 GRMHD simulations of post-merger disks HARM code: Tchekovskoy, Ferndandez,Quataert, Foucart, Kasen

41 future possibilities multi-messenger data on mergers? LIGO detections plus EM follow-up of kilonovae? gives a detailed picture of the environments and physics of compact object mergers answer to the origin of the r-process elements? 1) determine the rate, Rm, of mergers in the Galaxy? (from LIGO detections) 2) determine the average mass, Mm, of r-process nuclei produced in each event? (from fitting kilonova light curves) Mgalaxy = 5 x 10 3 Msun = Mm x Rm x tgal?