Nucleosynthesis and Electromagnetic Transients from Neutron Star - PowerPoint PPT Presentation

Nucleosynthesis and Electromagnetic Transients from Neutron Star Mergers Luke Roberts NSCL, Michigan State University

What is the source of the r- process nuclei? r -process elements present in very low • 120 metallicity halo stars, suggesting it must be r -process abundance a primary process 100 Abundance pattern of second and third • 200 peak r -process elements in low metallicity 180 80 Proton number ( Z ) 0 halo stars is remarkably similar to the 10 1 6 1 Mass number ( A ) 0 pattern found in the sun 4 1 N 10 0 r 120 , 60 ( S i 10 –1 log( T s –1 ) = 0 0 1 1 Need lots of free neutrons • 0 6 ) 1.0 80 10 –2 Site is one of the biggest questions of 40 0.5 • 0.0 nuclear astrophysics –0.5 –1.0 CCSNe have long been implicated as the • 20 –1.5 site of the r -process –2.0 From Moeller et al. 2008 –2.5 With GW170817, mounting evidence that • 00 NS mergers may be the site 20 40 60 80 100 120 140 160 Neutron number ( N )

Merger Mass Ejection • Dynamical Ejecta • Tidal Ejecta (BHNS) • GR -> matter ejected from collision region (NSNS) • Disk winds (e.g. Surman et al. ’08, Wanajo et al. ’11) • Disk outflows from viscous heating and alpha recombination (e.g. Fernandez & Metzger ’13, Just ’14) Radice, et al. ’16

Nuclear Evolution of the Ejecta Dynamical Timescale for the Ejected Material: τ ej ≈ 10 ms 10 − 1 Ejected Material is neutron rich: 10 − 2 30 10 − 3 M/M ej s [k B ] 20 Low initial entropy: 10 − 4 10 10 − 5 Which implies a neutron to seed ratio greater than 100 10 − 6 0 0 . 1 0 . 2 0 . 3 Y e Y e = 1 � n neutrons , tot n baryons Radice, et al. ’16 see Lattimer & Schramm ’76 and Freiberghaus et al. ’99

Nuclear Evolution of the Ejecta T = 7 . 0 GK Dynamical Timescale for the Ejected Material: ρ = 2 . 2 × 10 8 g cm − 3 Y e = 0 . 051 τ ej ≈ 10 ms Ejected Material is neutron rich: Z Low initial entropy: Initial distribution will be in NSE, clustered around doubly magic nuclei N Which implies a neutron to seed ratio greater than 100 Y e = 1 � n neutrons , tot n baryons 100 0 20 40 60 80 100 Mass number A see Lattimer & Schramm ’76 and Freiberghaus et al. ’99

from Lippuner & LR, et al. ‘15

Nuclear Heating Rate 20 10 log 10 [n(t=1 day)] 15 9.5 10 10.5 11 11.5 10 erg g − 1 s − 1 10 10 5 10 − 4 − 3 − 2 − 1 0 1 2 10 10 10 10 10 10 10 Day LR, et al. ‘11 • Power law heating rate (Metzger et al. ’10, Roberts et al. ’11, …) • Larger number of isotopes involved, sum of numerous individual decays • Beta-decays, alpha decays and fission

Electromagne\c displays from nuclear decay LR, Kasen et al. 2011 42 10 Bolometric Luminosity (erg s − 1 ) Kilpatrick et al. 2017 41 10 Assuming ~Fe opacity 40 10 0 1 2 3 4 5 6 7 8 9 10 Time (days)

Dependence of Nucleosynthesis on Ini\al Condi\ons • Changing the electron − 1 fraction can substantially Y e =0 . 01 Y e =0 . 19 Y e =0 . 50 Y e =0 . 25 alter nucleosynthesis in Solar r-process (scaled) − 2 log Final number abundance neutron rich outflows s = 10 k B baryon − 1 , τ = 7 . 1 ms s = 10 k B baryon − 1 , τ = 7 . 1 ms − 3 • Neutron rich − 4 nucleosynthesis is most − 5 sensitive to Y e − 6 • How far does − 7 nucleosynthesis get before neutron − 8 exhaustion? − 9 0 50 100 150 200 250 0 5 Mass number A

Dependence of Nucleosynthesis on Ini\al Condi\ons M ✏ at 1 day [erg s − 1 ] final X La+Ac N f − 5 − 5 37 s k B = 10, ⌧ = 10 ms 0 42 A fin − 1 41 log X i , N f , ¯ log M ✏ − 2 40 − 3 39 − 4 38 37 − 5 37 . 5 0 . 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 Lippuner & Roberts (2015) Y e

Neutron-to-Seed Ra\o of ini\al NSE distribu\ons Can trace Ye cuto ff back to the initial conditions

Setting Y e in the Ejecta Evolution of the electron fraction is governed by Characteristic Rates: where j e ~ p B j e ` n B 0.448 T MeV 5 s ~1 , j l e n B 4.83 L l e ,51 A v l e ,MeV ] 2 * MeV ] 1.2 * MeV v l e ,MeV B r 6 2 ~2 s ~1 , j ½ e p B 4.83 L ½ e ,51 A v ½ e ,MeV [ 2 * MeV ] 1.2 * MeV v ½ e ,MeV B r 6 2 ~2 s ~1 ,

Weak Interactions in NS Mergers See Wanajo et al. (2014) and Goriely et al. (2015) Destroy neutron at early times in hot, From summer student Sandra Ning neutrino rich environment at early times via: { ν e , e + } + n → p + { e − , ¯ ν e } + NSE favors more seed nuclei, fewer neutrons, thereby gives lower neutron to seed ratio Y e Incomplete r-process, material builds up at first peak

Neutrino Transport in the Ejecta see Wanajo, et al. ’14, Radice et al. 16, Palenzuela et al. 16 • Large neutrino luminosities provided by central remnant of the NS merger • Hierarchy of neutrino energies similar to proto-NS neutrino emission because neutrino decoupling physics is similar Foucart, O’Connor, LR et al. ’16

Neutrino Transport in the Ejecta see Wanajo, et al. ’14, Radice et al. 16, Palenzuela et al. 16 luminosity (10 53 erg s -1 ) 4 electron ν electron anti- ν 3 heavy ν • Large neutrino luminosities provided 2 by central remnant of the NS 1 merger 0 0 2 4 6 8 10 12 t (ms) • Hierarchy of neutrino energies 25 mean energies (MeV) electron ν electron anti- ν similar to proto-NS neutrino 20 heavy ν emission because neutrino 15 decoupling physics is similar 10 5 0 2 4 6 8 10 12 t (ms) from Wanajo (2014)

Neutrino Transport in the Ejecta see Wanajo, et al. ’14, Radice et al. 16, Palenzuela et al. 16 Number and Energy Energy + Leakage Foucart, O’Connor, LR et al. ’16

Neutrino Transport in the Ejecta see Wanajo, et al. ’14, Radice et al. 16, Palenzuela et al. 16 { ν e , e + } + n → p + { e − , ¯ Foucart, O’Connor, LR et al. ’16 ν e } +

Dynamical Ejecta in BHNS mergers vs NSNS mergers 0.08 No weak Full NS L ν e HY QC 0.07 reacs L ν e , 52 = 0 NSNS Only e and L ν e , 52 = 0 . 2 LK QC p cap 0.06 L ν e , 52 = 1 nu reabsorb M0 QC L ν e , 52 = 5 0.05 L ν e , 52 = 25 Mass [ M � ] BHNS 0.04 0.03 0.02 0.01 0 0 . 08 0 . 16 0 . 24 0 . 32 0 . 40 0 . 05 0 . 10 0 . 15 0 . 20 0 . 25 Y e Y e LR, et al. ‘16 Radice, …, LR et al. ’16

Ejecta Composition 10 − 1 10 − 3 NSNS BHNS Relative abundances 10 − 2 10 − 4 Abundance 10 − 3 10 − 5 Solar 10 − 4 10 − 6 No weak HY QC reacs L ν e , 52 = 0 L ν e , 52 = 5 LK QC Only e and L ν e , 52 = 0 . 2 L ν e , 52 = 25 10 − 5 10 − 7 p cap M0 QC L ν e , 52 = 1 nu reabsorb Solar 50 100 150 200 250 50 50 100 150 200 Mass Number A LR, et al. ‘16 Radice, …, LR et al. ’16

Weak interactions in BHNS dynamical ejecta 10 1 λ ν e λ e + Y e Low entropy tidal ejecta -> small 0 . 5 10 0 λ ¯ λ e − electron/positron capture rates ν e 0 . 4 10 − 1 Neutrino reactions are λ [s − 1 ] 10 − 2 0 . 3 Y e somewhat faster 10 − 3 0 . 2 10 − 4 r ⌘ 2 ⇣ L � 1 ν e , 53 T � 1 ⌧ ν ( r ) ⇡ 67 . 8 ms 0 . 1 ν e , 5 250 km 10 − 5 10 − 6 0 . 0 Still to slow to impact Y e significantly, 10 − 2 10 − 1 10 0 Time [s] but can impact the first peak LR, et al. ‘16 nucleosynthesis in the dynamical ejecta

First r-Process Peak Production in BHNS Mergers Neutrinos No Neutrinos → → → 3 α + n → 12 C + n 12 C + n ... ν e + n → p + e − 2 p + 2 n → α 12 12 2 p 2 n 3 n

First r-Process Peak Production Method 2 10 − 3 Neutrinos 10 − 4 Abundance 10 − 5 10 − 6 L ν e ,53 = 0 L ν e ,53 = 5 L ν e ,53 = 1 10 − 7 Solar No Neutrinos L ν e ,53 = 3 50 100 150 200 250 Mass Number → → → 3 α + n → 12 C + n 12 C + n ... ν e + n → p + e − 2 p + 2 n → α 12 12 2 p 2 n 3 n

Disk ejecta see e.g. Metzger & Fernandez 14, Just et al. 15, Siegel & Meter 2018 • Material in the remnant disk also H000 2 . 0 Ejected mass in bin [10 � 3 M � ] experiences a large number of H010 weak interactions, beta- H030 1 . 5 equilibrates H100 H300 • Broad range of Y e , depending Hinf 1 . 0 on the lifetime of the hyper- massive neutron star 0 . 5 • Ratio of weak to strong r- 0 . 0 process sensitive to the lifetime 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 of the central object Electron fraction Y e, 5GK from Lippuner, Fernandez, LR, et al. (2017)

Disk ejecta see e.g. Metzger & Fernandez 14, Just et al. 15, Siegel & Meter 2018 • Material in the remnant disk also 2nd peak 10 0 experiences a large number of Final M ej Y A (arbitrary scale) rare- 10 − 1 weak interactions, beta- earth 3rd peak peak 10 − 2 equilibrates 10 − 3 1st peak • Broad range of Y e , depending 10 − 4 10 − 5 on the lifetime of the hyper solar r-process massive neutron star 10 − 6 H000 H100 B070 10 − 7 H010 H300 B090 • Ratio of weak to strong r- 10 − 8 H030 Hinf BF15 process sensitive to the lifetime 10 − 9 0 25 50 75 100 125 150 175 200 225 250 of the central object Mass number A from Lippuner, Fernandez, LR, et al. (2017)