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

metallicity halo stars, suggesting it must be a primary process

• Abundance pattern of second and third

peak r-process elements in low metallicity halo stars is remarkably similar to the pattern found in the sun

• Need lots of free neutrons
• Site is one of the biggest questions of

nuclear astrophysics

• CCSNe have long been implicated as the

site of the r-process

• With GW170817, mounting evidence that

NS mergers may be the site

–2.5 –2.0 –1.5 –1.0 –0.5 0.0 0.5 1.0 80 10–2 10–1 100 101 1 120 1 4 1 6 180 Mass number (A) r-process abundance 200

Neutron number (N) 00 20 40 60 80 100 120

log(T s–1)

140 160 20 40 60 80 100 120

N

r ,

( S i = 1 06 )

Proton number (Z)

From Moeller et al. 2008

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

0.1 0.2 0.3 Ye 10 20 30 s [kB] 10−6 10−5 10−4 10−3 10−2 10−1 M/Mej

Nuclear Evolution of the Ejecta

τ ej ≈10 ms

Dynamical Timescale for the Ejected Material: Ejected Material is neutron rich: Low initial entropy:

see Lattimer & Schramm ’76 and Freiberghaus et al. ’99

Radice, et al. ’16 Which implies a neutron to seed ratio greater than 100

Ye = 1 nneutrons,tot nbaryons

Nuclear Evolution of the Ejecta

T = 7.0 GK ρ = 2.2 × 108 g cm−3 Ye = 0.051

N Z 100 Mass number A 20 40 60 80 100

τ ej ≈10 ms

Dynamical Timescale for the Ejected Material: Ejected Material is neutron rich: Low initial entropy:

Initial distribution will be in NSE, clustered around doubly magic nuclei see Lattimer & Schramm ’76 and Freiberghaus et al. ’99

Which implies a neutron to seed ratio greater than 100

Ye = 1 nneutrons,tot nbaryons

from Lippuner & LR, et al. ‘15

Nuclear Heating Rate

• 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

Day erg g−1 s−1

10

−4

10

−3

10

−2

10

−1

10 10

1

10

2

10

5

10

10

10

15

10

20

log10[n(t=1 day)]

9.5 10 10.5 11 11.5

LR, et al. ‘11

1 2 3 4 5 6 7 8 9 10 10

40

10

41

10

42

Time (days) Bolometric Luminosity (erg s−1)

Electromagne\c displays from nuclear decay

LR, Kasen et al. 2011 Kilpatrick et al. 2017

Assuming ~Fe opacity

Dependence of Nucleosynthesis

• n Ini\al Condi\ons

50 100 150 200 250 −9 −8 −7 −6 −5 −4 −3 −2 −1 Mass number A log Final number abundance Ye =0.01 Ye =0.19 Ye =0.25 Ye =0.50 Solar r-process (scaled) s = 10 kB baryon−1, τ = 7.1 ms s = 10 kB baryon−1, τ = 7.1 ms 5

• Changing the electron

fraction can substantially alter nucleosynthesis in neutron rich outflows

• Neutron rich

nucleosynthesis is most sensitive to Ye

• How far does

nucleosynthesis get before neutron exhaustion?

37 37 38 39 40 41 42 log M✏ skB = 10, ⌧ = 10 ms .5 0.0 0.1 0.2 0.3 0.4 0.5 Ye 37 −5 −5 −4 −3 −2 −1 log Xi, Nf, ¯ Afin

M✏ at 1 day [erg s−1] Nf − 5 final XLa+Ac

Lippuner & Roberts (2015)

Dependence of Nucleosynthesis

• n Ini\al Condi\ons

Neutron-to-Seed Ra\o of ini\al NSE distribu\ons

Can trace Ye cutoff back to the initial conditions

Setting Ye in the Ejecta

where Evolution of the electron fraction is governed by Characteristic Rates:

je~p B je`n B 0.448T MeV 5 s~1 ,

jlen B 4.83L le,51Avle,MeV ] 2*MeV ] 1.2 *MeV 2 vle,MeVBr6 ~2 s~1 , j½ep B 4.83L ½e,51Av½e,MeV [ 2*MeV ] 1.2 *MeV 2 v½e,MeVBr6 ~2 s~1 ,

Weak Interactions in NS Mergers

From summer student Sandra Ning Ye

{νe, e+} + n → p + {e−, ¯

νe}

+

Destroy neutron at early times in hot, neutrino rich environment at early times via: NSE favors more seed nuclei, fewer neutrons, thereby gives lower neutron to seed ratio Incomplete r-process, material builds up at first peak See Wanajo et al. (2014) and Goriely et al. (2015)

• 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

• 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

Neutrino Transport in the Ejecta

see Wanajo, et al. ’14, Radice et al. 16, Palenzuela et al. 16

t (ms) luminosity (1053 erg s-1) 2 4 6 8 10 12 1 2 3 4 electron ν electron anti-ν heavy ν t (ms) mean energies (MeV) 2 4 6 8 10 12 5 10 15 20 25 electron ν electron anti-ν heavy ν

from Wanajo (2014)

Neutrino Transport in the Ejecta

see Wanajo, et al. ’14, Radice et al. 16, Palenzuela et al. 16 Foucart, O’Connor, LR et al. ’16

Number and Energy Energy + Leakage

{νe, e+} + n → p + {e−, ¯

νe}

+

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

0.08 0.16 0.24 0.32 0.40 Ye HY QC LK QC M0 QC

No weak reacs nu reabsorb Only e and p cap

0.05 0.10 0.15 0.20 0.25

Ye

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Mass [M]

Full NSLνe Lνe,52 = 0 Lνe,52 = 0.2 Lνe,52 = 1 Lνe,52 = 5 Lνe,52 = 25

Dynamical Ejecta in BHNS mergers vs NSNS mergers

BHNS NSNS LR, et al. ‘16 Radice, …, LR et al. ’16

50 100 150 200 250

Mass Number

10−7 10−6 10−5 10−4 10−3

Abundance

Lνe,52 = 0 Lνe,52 = 0.2 Lνe,52 = 1 Lνe,52 = 5 Lνe,52 = 25 Solar

50 100 150 200 A Solar HY QC LK QC M0 QC 50 10−5 10−4 10−3 10−2 10−1 Relative abundances

No weak reacs nu reabsorb Only e and p cap

Ejecta Composition

BHNS LR, et al. ‘16 NSNS Radice, …, LR et al. ’16

Weak interactions in BHNS dynamical ejecta

10−2 10−1 100

Time [s]

10−6 10−5 10−4 10−3 10−2 10−1 100 101

λ [s−1]

0.0 0.1 0.2 0.3 0.4 0.5

Ye

λνe λ¯

νe

λe+ λe− Ye

LR, et al. ‘16

⌧ν(r) ⇡ 67.8 ms ⇣ r 250 km ⌘2 L1

νe,53T 1 νe,5

Low entropy tidal ejecta -> small electron/positron capture rates Neutrino reactions are somewhat faster Still to slow to impact Ye significantly, but can impact the first peak nucleosynthesis in the dynamical ejecta

Neutrinos No Neutrinos

νe + n → p + e− 2p 2n 3 n

→

2p + 2n → α

12

→

3α + n →12 C + n

12

→

12C + n...

First r-Process Peak Production in BHNS Mergers

Neutrinos No Neutrinos

νe + n → p + e− 2p 2n 3 n

→

2p + 2n → α

12

→

3α + n →12 C + n

12

→

12C + n...

First r-Process Peak Production Method 2

50 100 150 200 250

Mass Number

10−7 10−6 10−5 10−4 10−3

Abundance

Lνe,53 = 0 Lνe,53 = 1 Lνe,53 = 3 Lνe,53 = 5 Solar

Disk ejecta

• Material in the remnant disk also

experiences a large number of weak interactions, beta- equilibrates

• Broad range of Ye, depending
• n the lifetime of the hyper-

massive neutron star

• Ratio of weak to strong r-

process sensitive to the lifetime

• f the central object

0.1 0.2 0.3 0.4 0.5 0.0 0.5 1.0 1.5 2.0 Electron fraction Ye,5GK Ejected mass in bin [103 M] H000 H010 H030 H100 H300 Hinf from Lippuner, Fernandez, LR, et al. (2017)

see e.g. Metzger & Fernandez 14, Just et al. 15, Siegel & Meter 2018

Disk ejecta

• Material in the remnant disk also

experiences a large number of weak interactions, beta- equilibrates

• Broad range of Ye, depending
• n the lifetime of the hyper

massive neutron star

• Ratio of weak to strong r-

process sensitive to the lifetime

• f the central object

from Lippuner, Fernandez, LR, et al. (2017)

25 50 75 100 125 150 175 200 225 250 10−9 10−8 10−7 10−6 10−5 10−4 10−3 10−2 10−1 100 Mass number A Final MejYA (arbitrary scale) 1st peak 2nd peak rare- earth peak 3rd peak H000 H010 H030 H100 H300 Hinf B070 B090 BF15 solar r-process

see e.g. Metzger & Fernandez 14, Just et al. 15, Siegel & Meter 2018

Jet Driven Supernovae

• Rapidly rotating, magnetized SNe
• Full 3D Dynamics also important

here

• Kink instabilities in jet significantly

change dynamics and impact nucleosynthesis

25

10−2 1 102 104 106 108 0.1 0.2 0.3 0.4 0.5

t − tmap [s] Ye

Lν = 0 erg/s Lν = 1051 erg/s Lν = 1052 erg/s Lν = 1053 erg/s Lν from tracer Original tracer Lν = 0 erg/s Lν = 1051 erg/s Lν = 1052 erg/s Lν = 1053 erg/s Lν from tracer Original tracer

Moesta, LR, et al. (2018) see Winteler et al. 2012, Nishimura et al. 2015, Moesta et al. 2018

25 50 75

charge number Z

10−9 10−8 10−7 10−6 10−5 10−4 10−3

Elemental Abundance

Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi

B13 B12-sym B12 HD122563 CS22892-052

Summary and Outlook

• Ye distribution of the ejecta determining factor in the final composition

and properties of the transient

• Weak interactions play a substantial role in setting the initial conditions

for nucleosynthesis

• Going forward need better treatment of neutrinos during the dynamical

phase -> important to setting the electron fraction distribution via weak interactions

• Sensitivity of r-process nucleosynthesis to input nuclear data of nuclear

reaction network calculations. How well is the lanthanide cutoff Ye known?

• Still some possible SN sites of the r-process
• Hopefully observe a BHNS merger