初代星・初代銀河研究会（2019年11月11‒13）＠名古屋大学

宇宙最初のrプロセス天体は何か？
What is the ﬁrst r-process
event/star in the universe
Nobuya Nishimura
YITP, Kyoto University

Reviews on r-process studies• Review papers• Horowitz et al. (38 authors), JPhG, (2019)• Cowan et al., Rev of Mod. Phys., submitted (arXiv:1901.01410)• Japanese WSs (in the era of post-GW170817); trilogy(?)
https://sites.google.com/view/rp2018

https://www2.yukawa.kyoto-u.ac.jp/~rp2019

Astrophysics nuclear-physics• GW170817• RIBF experiments• astrophysics• NS-NS mergers• kilonovaeNuclear-physics theory• mass formula• neutron capture• β-decay (and others)• ﬁssion

Nucleosynthesis beyond IronuA,,hT

UPtBaEu

N=126
N=82
N=50

Solar neutron-capture (s/r-process) elements
solar abundances
N=50

N=82

N=126

stellar fusion
standard SNe
may be NO well deﬁned r-process
peak corresponding N = 50

classiﬁcation of s & r process
is based on s-process “theory”
uncertainty of the s-process is due ton-capture on stable nuclei (experimental)(see, NN+2017, Cescutti+NN+2018)

Cowan+2019Cowan&Thieleman(2004)

r-process nucleosynthesis “ﬂow”

Evolution of r-process elements
solar abundances

abundance evolution

Contents• Introduction•

overview of r-process nucleosynthesis• NS mergers as the main r-process site••a brief overview of r-process astrophysical sites
NS mergers, GW170817, kilonova/macronova, GCE etc.

• MR-SNe as alternative r-process sites••

central engine of “r-process jet” cc-SNeconnection to observation• (Nuclear-physics uncertainties)

Neutron-star mergers
as the main r-process site

•Wanajo, Sekiguchi, NN+(2014), ApJL
•Fujibayashi, Kiuchi, NN+(2018), ApJ

Astronomical site(s) of the r-process
neutron star (NS) mergers?
NSBH
NSSupernovae (cc-SNe)?
massive star(10>Msun)

Supernova

Mergerproto-NS
neutrino-driven wind• no direct observation• theoretical diﬃculty• (no very n-rich matter)r-process is observedin Kilonova/Macronova
w/ GW170817

The “kilonova/macronova” with GW

credit NAOJ

The electromagnetic counter part of GW170817 (17. Aug. 2017)
Energy source? ̶> radioactive decay (e.g, β, α & ﬁssion etc.) of
neutron-rich matter during r-process nucleosynthesis
NGC4993 (39.5Mpc)
Sr in the remnant

By Magellan telescope; Drout+2017, ScienceWatson+2019 Nature

“Classic” view: dynamical + post-merger
Freiburghaus, Rosswog & Thielemann (1999)

tidal ejection of “pure” n-rich matter with Ye << 0.1

fission-cycling

Korobkin+ 2012 (e.g., Goriely+ 2011, Rosswog+ 2013)

Modern view: dynamical + post-merger
Fujibayashi et. al. 2018

dynamicalmass ejection

post-merger
lighter r-nuclei(lanthanide poor)
lanthanide
Z=５７­７１

r-proces mechanism
neutron-rich ejecta
in stellar explosion① NSE (> 1 MeV)
(only nucleon and α)

protonneutron③n-capture: A↑(A,Z) → (A+1,Z)high T & ρ② seed formation(α ＋ recombination)
A 〜 100-e⑤ β-decay＋ﬁssion

Low T④β-decay：Z↑(A,Z) → (A,Z+1)

r-proces mechanism
neutron-rich ejecta
in stellar explosion① NSE (> 1 MeV)
(only nucleon and α)

protonneutron③n-capture: A↑(A,Z) → (A+1,Z)high T & ρAstrophysics⑤ β-decay＋ﬁssion

Nuclear physics② seed formation(α ＋ recombination)
A 〜 100-eLow T④β-decay：Z↑(A,Z) → (A,Z+1)

Physical conditions for r-process production- neutronization（low Ye）by e-cap. ( p + e- → n + νe ) + ν-absorption

Ye = Y”p” = Σ(Ai/Zi)Xi 〜 Np/(Nn + Np)
low Ye = neutron-rich- seed formation (see Hoffman et al. 1997)
n/seed > 100 for the 3rd peak production(α + α + n → 9Be; 9Be + α → 12C + n)

(A〜150)A = 140‒160
very n-rich

Details: NS masses & EoS in 3D hydrokm

neutrino Lorbital plane

dynamical ejecta
Ye evolution
based on 3D hydro(Sekiguchi+2015)

νeanti-νeheavy νvertical section (axis)

kmWanajo+NN+2014

Tidal disruption

Shock & neutrino

NS-NS merger: post-merger evolution
Ye: electron faction （green: heavy nuclei; blue：lighter nuclei）

post-merger ejecta
Ye evolution
based on 2D hydro(Fujibayashi+NN+2018)

Simulation models vs Kilonova
Indicated by the simulation is agree with kilonova observation
heavy r-process elements (= lanthanide-rich) w/ high opacity→ peak temperature becomes low (in low density)→ late IR peak(⇆ La-poor -> early “blue” peak)bolometric luminosity
post-merger“blue” (UV) peak
Villar et al. 2018
(La-poor)
dynamical(La-rich)

Shibata et al. 2018

“red” (IR) peaktime, day

Short Summary• NS mergers can produce (all) r-process elements in• based on “Modern” hydrodynamical simulations• dynamical ejecta: lanthanide- and actinide-rich• post-merger ejecta: lanthanide poor

• observations conﬁrmed theoretical models• kilonova w/ GW170817• the light curve: blue -> red• detection of Sr in the remnant?
(indicate “weak” r-process components)

Magneto-rotational SNe
as alternative r-process sites• Winteler+NN+ (2012) ApJL
• NN, Takiwaki & Thielemann (2015) ApJ• NN, Sawai, Takiwaki+(2017) ApJL

Astronomical site(s) of the r-process
neutron star (NS) mergers?
NSBH
NSSupernovae (cc-SNe)?
massive star(10>Msun)

Supernova
another mechanism
magneto-driven jet?

Mergerproto-NS
neutrino-driven wind
• no direct observation• theoretical diﬃculty• (no very n-rich matter)magnetarr-process is observed?
in Kilonova/Macronova
w/ GW170817

r-Process in magneto-rotational supernovae•Magnetar•strong magnetic ﬁeld 〜1015 G(〜1 % of all neutron stars)•Magneto-driven Supernovae?
•GRB central engine•Hypernovae•Super luminous SNe
hypernova/jet-like SN•MR-SNe (magnetar formation)•“the classics”: Symbalisty(1984), Cameron(2003)•2D: Nishimura+NN+(2006); NN+(2012,2015,2017)•3D: Winteler+NN+(2012); Mösta+(2014,2018),
Halevi&Mösta(2018)•“Collapsar model” (BH + disk + jet)
•2D: Fujimoto+(2007); Fujimoto, NN, Hashimoto(2009);•Ono+(2009, 2012)

NN+2015

3D eﬀects on jet-propagationstrong jet in 3D
Winteler+NN+(2012)

deformationby hydro-instability
Mösta+(2018)

misalliance of
B-ﬁled and rotation
Halevi&Mösta(2018)

low Lν
large
misalliance*diﬀerence is due to uncertainty

magnetic-ﬁeld enhancement process?
axi-symmetric (2D); long-term, high-resolution
B-ﬁeld winding
MRI w/ ν-heating
NN+2015
promptdelayed

NN+2017delayedmagnetic-jet
heating
delayedprompt x 4

intermediateDiversity in metal-poor star abundances?
Cowan+2019- many r-rich Galactic halo stars-show the solar r-patternr-process has happened
from the early Galaxy
astrophysical models
reproduce this commonpattern (Z>40; A>90)- However, growing evidence for“weak” r-process patterns(e.g., Honda+2006)
metal-poor stars contain very fast rotator?
(Talk by A. Choplin: s-process in fast rotating massive star)Multiple r-process sources in GCE?
NS mergers cannot explain early chemical evolutionof r-process elements, e.g., Eu?
→ shorter delay time or another sourcecomprehensive GCE analysis after GW170817 (e.g., Côté+2018)
standard DTD cannot explain
Eu evolution? (Côté+2018)
Wehmeyer+(2015,2019):→ single r-process source
diﬀerent event rates for MR-SNe
scenario fails to explain
0.1%NS mergers+ MR-SNeNeed those strong initial B-fields?
CC-SNe with B-ﬁeld ampliﬁcation by MRI
Sawai & Yamada(2014, 2016)

heatingdominatedΔrmin = 100, 50, 25, 12.5 m

Ye

entropy

Entropy + B-ﬁelds(3D)intermediatemagneticallydominatedVarious r-process in several jet SNevery neutron-rich matter in SN core (“proto-magnetar”)
signiﬁcant eﬀect of e--capture (oﬀ β-equilibrium)

Ye = Y”p” = Σ(Ai/Zi)Xi 〜 Np/(Nn + Np)

B12n-richin ν-sphereν-absorption

solar rν-absorption

metal-poor stars
solar-likesolar-liker-process abundances
NN+(2017), based on Sawai models
solar
magnetic

heating

prompt vs delayed(NN+2015,Takiwaki models)

metal poor stars solar-like“intermediate” r-process?

r process“weak” heavy r pattern
HD122563 (Honda+2006)

Alternative r-process sources in early galaxy?

strong jet

weak jet“intermediate” r-process?
nucleosynthesis yields:
github.com/nnobuya/mrsn

Eu evolution by MR-SNe in dSph galaxies
Chemical evolution models
Tsujimoto & NN (2015)
GCE models suggest:- event rate: 0.5 % of CC-SNe- large Eu ejection: 〜10-5 Msun
agree with our MR-SN models(e.g. NN+2015, 2017)

increase of Eu,
which are not explainedby NS-NS mergers

Short Summary• MR-SNe are still possible sites for the r-process• However, strong-magnetic jets are needed to produce
heavier r-nuclei: unavailable so far in “realistic”
progenitor/MHD set-up

We want to discuss possible “observational” properties
of such events: r-process-jet supernovae.

long-term evolution of r-process ejection(propagation of r-process-rich jet in the progenitor)

Strong-magnetic jet: (strong r)
NN, Sawai+2017

x5

temperature

Ejet = 1051 erg
108 cm• hydrodynamics
w/o B-ﬁelds• “jet” injection• Wolf-Rayet(no H-layer)

x 10hydrodynamical simulation
by J. Matsumoto

temperature

Strong-magnetic jet: (strong r)

Evolution of hydro vs r-processstrong r
strong r

0.5 s
weak r

1s5s50 s

weak rElemental distribution in ejecta
based on the nucleosynthesis condition of NN+2017:very n-rich
̶> strong r
medium n-rich ̶> “intermediate r”
weak magnetic jetstronger magnetic jet

̶> Future observation will provide new insights?
“kilonova” due to r-process decay?? (still, just idea … )Summary• NS-NS scenario has no severe problems in GCE• dispersion and event rates agree with Eu evolution• But, some diﬃculties in the early galaxies• several “variations”:
weak r-process and actinide-boost stars• Multiple r-process sources in GCE• rate types of SNe with r-process rich yields• detection of Sr in the remnant?

theoretical interpretation ⇆ observational constraint- merger, SN models - abundances- Galactic evolution - kilonova

Perspective

What is the ﬁrst r-process
event/star in the universe?
• Neutron star mergers?
• diﬃcult?
• large delay time
• can have variation in r-process?
• CC-SNe (but, rare SNe, e.g., MR-SNe)• possible?
• metallicity dependence; active in the early galaxies• variation in the r-process pattern• can be related to “POP III SNe” ?