Neutron star post-merger simulations: origin of kilonovae and the heavy elements

Transcription

1 4-color Process 100% Cyan 72% Magenta logo can also be rendered in black, grey (60% black), Pantone 280, or Pantone 286; on a darker color background, the logo can be rendered in Pantone 290, 291, or 284, depending on which color works best with the overall design of your product, the media in which it will be reproduced, and its intended use. Neutron star post-merger simulations: origin of kilonovae and the heavy elements White or Pantone 290 (Columbia Blue) Background: Pantone 286 Daniel M. Siegel Center for Theoretical Physics & Columbia Astrophysics Columbia University For photographs, use the logo in white against a darker area, positioning it either at top left/right or Laboratory bottom left/right. Einstein Fellows Symposium, Harvard-Smithsonian Center for Astrophysics, Oct 12-13,

2 1/10 NS post-merger accretion disks: formation Movie: long-term evolution of post-merger accretion disk, MBH=3Msun (spin: 0.8), Mdisk=0.02Msun Movie: BNS merger and formation of post-merger accretion disk Radice+ 2016

3 NS post-merger accretion disks: numerical setup First self-consistent simulations modeling r-process nucleosynthesis from disk outflows from first principles: GRMHD: magnetic instabilities (MRI) mediating turbulence (transport of angular momentum) in the disk weak interactions in GRMHD approximate neutrino transport (leakage scheme) realistic EOS (Helmholtz EOS) valid at low temperatures and densities, capturing nuclear binding energy release from alpha-particle formation full r-process network calculations on disk outflows using 104 tracer particles (SkyNet; Lippuner & Roberts 2015) Previous Newtonian alpha-disk simulations: Fig.: disk properties; contours: optical depth for electron neutrinos Fernandez & Metzger 2013 Metzger & Fernandez 2014 Fernandez Fernandez Just /10

4 MHD turbulence Fig.: disk properties; contours: optical depth for electron neutrinos Fig.: magnetic fields in the disk; contours: rest-mass density magnetic properties very similar to Ciolfi /10

5 MHD turbulence average radially for space-time diagram Fig.: disk properties; contours: optical depth for electron neutrinos Fig.: magnetic fields in the disk; contours: rest-mass density magnetic properties very similar to Ciolfi /10

6 Accretion disk dynamo: butterfly diagram magnetic energy is generated in the mid-plane migrates to higher latitudes dissipates into heat off the mid-plane hot corona hot corona launches thermal outflows (neutron-rich wind) NS post-merger accretion disk are cooled from the mid-plane by neutrinos (rather than from the EM photosphere)! 4/10

7 Self-regulation neutrinos Neutrino-cooled accretion disks self-regulate themselves to mild degeneracy (low Ye matter): Beloborodov 2003, Chen & Beloborodov 2007, Metzger viscous heating via magnetic turbulence neutrino cooling charged-current processes: e + p! n + e e+ + n! p + e pair annihilation: e + e+! e + e e + e+! µ, + µ, plasmon decay:! e + e! µ, + µ, Fig.: disk properties; contours: rest-mass density 5/10

8 Self-regulation neutrinos Neutrino-cooled accretion disks self-regulate themselves to mild degeneracy (low Ye matter): Beloborodov 2003, Chen & Beloborodov 2007, Metzger viscous heating via magnetic turbulence neutrino cooling balance with feedback mechanism: higher degeneracy µe /kt fewer e-, e+ (lower Ye) less neutrino emission, i.e., cooling higher temperatures lower degeneracy µe /kt Fig.: disk properties; contours: rest-mass density direct evidence of self-regulation 5/10

9 6/10 The origin of the elements r-process s-process How are the heavy elements formed?

10 The origin of heavy nuclei: r-process nucleosynthesis Movie: r-process nucleosynthesis from NS merger remnant disks 7/10

11 8/10 r-process nucleosynthesis 1st peak 2nd peak 3rd peak 2nd peak rare-earth peak 3rd peak rare-earth peak neutrino absorption robust 2nd and 3rd peak r-process! including neutrino absorption: additional good fit to 1st & 2nd peak elements production of all r-process elements!

12 /mnras.oxfordjournals.org/ at Columbia University on October 8, 2016 r-process nucleosynthesis from NS mergers ach panel) of the ejecta for the LK_QC (upper panel) and M0_QC at radius r = 200 M 295 km and only considers the unbound ch we do not measure any outflow of unbound matter (i.e. where road 60 angle from the equator. The material at low altitudes is ms for the different componentsradice+ of the outflow dynamical ejecta: Fig.:normalized production elements from with early e yields are withof ther-process total abundance of elements escriptiona (pure HY or leakage only cooling, BNS hydrodynamics, merger (dynamical ejecta,with neutrino-driven! 120 is very robust and in overall good agreement with the Solar ejecta of winds) Post-merger accretion disk outflows: 1st peak 2nd peak 3rd peak rare-earth peak Fig.: production of all r-process elements from outflows of post-merger accretion disk Overall ejecta mass per event: Radice h three different levels of microphysical description (HY,Sekiguchi M0). The dynamical ejecta 3from all our simulations ispalenzuela+2015 disk rich with mass-averaged electron fractions Ye! 0.2 (seelehner+2016 strongly depends on EOS entropy perciolfi+2017 We show the joint distribution of Ye and specific robust lower for simulation QC_M0 inand Fig.mass 10. There is an approximate ratio! shock heated on between Ye and s, due to the fact NSthat post-merger simulations: origin of kilonovae and the heavy elements M & 0.4 M & 10 2 M limit 9/10

13 Conclusions Simulations of NS post-merger accretion disks Siegel & Metzger 2017b, i. prep. GRMHD with weak interactions and approx. neutrino transport first fully self-consistent study of its kind evidence for hot coronae that launch thermal outflows first identification of self-regulation in neutrino-cooled accretion disks, implying conditions of neutron richness disk ejecta can be higher than dynamical ejecta from the merger main fuel to power kilonova main site of the r-process suggest NS post-merger systems are robust site of the r-process can produce all r-process elements NS post-merger Short gamma-ray simulations: bursts origin in of thekilonovae time-reversal and thescenario heavy elements 10/10