Sec$on 11.
Neutron star merger
11.1 Neutron star merger
11.2 Observa$ons of gravita$onal wave sourcesCosmic abundances
100-1

H He-2O

1010C-3

Mass
frac$on
質量割合

10Fe“2nd peak”

-4

10-5

10

s-process
sプロセス

10-7

Sr

10-6

r-processrプロセス

r-process
rプロセス
sプロセス
s-processsプロセス
s-processBa-8

10“3rd peak”

-9

Au Pb
Pt

10

10-10

10-11

050

100
150
Mass
number
質量数200250

Neutron-capture nucleosynthesiss (slow)-processr (rapid)-process
nnnnn nnn

Decay

DecayppppppBa, Pb, …

Au, Pt, U, …

Inside of stars

SN? NS merger?

p pOrigin of r-process elements?
Some phenomena related to neutron starSupernova(C) M. Weiss~ 1 event per 100 yr in a galaxy(R ~ 10-2 yr-1)

Neutron star merger(C) NASA~ 1 event per 10,000 yr in a galaxy(R ~ 10-4 yr-1)

Suwa et al. 2011

NS merger => mass ejec$on
Top view

Side viewM ~ 10-3 - 10-2 Msunv ~ 0.1 - 0.2 c

Sekiguchi+15, 16

Why some material are ejected?
(NS has an extremely strong gravity!)r-process in NS merger

Mass number
A=Z+Ns-processr-process(C) Nobuya Nishimura

Radioac$ve decay (Beta decay)
neutronProton

An$Electron neutrino＋＋~20%＋ γ-ray~40%~40%+n ! p + e + ⌫¯e<latexit sha1_base64="Ft2WwY0pDbK8vWaMgY6iQUPp3bw=">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</latexit>

Radioac$vely powered transients similar to SN (56Ni)=> “kilonova”

How to ﬁnd NS merger??

Gravita$onal waves!

(C) LIGO/T. Pyle

Sec$on 11.
Neutron star merger
11.1 Neutron star merger
11.2 Observa$ons of gravita$onal wave sources

The ﬁrst GW detec$on(GW150914)

Merger of binary black hole

LIGO ScienGﬁc CollaboraGon
and Virgo CollaboraGon, 2016, PRL, 061102

2sts a BNS as the source of the gravitational-wave sigl, as the total masses of known BNS systems are beeen 2.57 M and 2.88 M , with components between
17 and ⇠1.6 M [47]. Neutron stars in general have preely measured masses as large as 2.01 ± 0.04 M [48],hereas stellar-mass black holes found in binaries in ourlaxy have masses substantially greater than the componts of GW170817 [49–51].
Gravitational-wave observations alone are able to meare the masses of the two objects and set a lower limit
their compactness, but the results presented here do notclude objects more compact than neutron stars such as
ark stars, black holes or more exotic objects [52–56].
e detection of GRB 170817A and subsequent electroagnetic emission demonstrates the presence of matter.
oreover, although a neutron star–black hole system is not
ed out, the consistency of the mass estimates with thenamically measured masses of known neutron stars innaries, and their inconsistency with the masses of known
ack holes in galactic binary systems, suggests the source
as composed of two neutron stars.

The ﬁrst GW detec$on
From NS merger (GW170817)

DATA

At the time of GW170817, the Advanced LIGO detecs and the Advanced Virgo detector were in observing
LIGO ScienGﬁcode. The maximum
distancesCollaboraGonat which LIGO-Livingstond LIGO-Hanford
could CollaboraGon,
detect a BNS system(SNRand Virgo2017,
PRL= 8),own as the detector horizon [58–60], were 218 Mpc and7 Mpc, while for Virgo the horizon was 58 Mpc. TheFIG. 1. Time-frequency representations [57] of data containing

Search for electromagne$c (EM) counterpart

Coulter+17, Soares-Santos+17, ValenG+17,
Arcavi+17, Tanvir+17, Lipunov+17

Movie: Utsumi, MT+17, Tominaga, MT+18

EM counterpart of GW170817 @ 40 Mpc= “Kilonova”
Day 1

Day 7
Utsumi, MT+17

Op$cal (z) near IR (H) near IR (Ks)

Mej ~ 0.05 Msun
Enough to explain the total mass of r-process elements(if R ~ 10-4 yr-1 Gal-1)Many open issues• Physical origin of the ejecta• Dynamical ejecta and disk ejecta?
• Produc$on rate
• Event rate? => more GW events• Are kilonova (mass ejecGon) always the same?
• Elemental abundances• Which elements are produced?
• How massive elements? Fission?
• Similar to solar abundance raGos?

GW observing runs

We are hereh`ps://www.ligo.org/scienGsts/GWEMalerts.php

GW190425: 2nd NS-NS merger eventh`ps://www.ligo.org/detecGons/GW190425.php

What is the kilonova signal?

Skymap of GW190425~ 10,000 deg2!! (30 deg2 for GW170817)

Abbott et al.

Figure 2. Sky map for GW190425. The shaded patch is the sky map obtained
LVC 2020
from the Bayesian parameter estimation code LALINFERENCE (Veitch et al. 2015)(see Section 4) with the 90% conﬁdence region bounded by the thin dottedcounterpart
was iden$ﬁed…
contour. The No
thickconvincing
solid contour shows
the 90% conﬁdence
region from the lowlatency sky localization algorithm BAYESTAR (Singer & Price 2016).

Summary• NS merger• EjecGon of material by Gdal disrupGon(+ ejecGon from accreGon disk)• r-process => radioacGve decay => kilonova• Observa$ons of GW sources• Kilonova is observed• ProducGon rate fulﬁlls the necessary condiGon• Future• IdenGﬁcaGon of elements or abundance pa`ern• Understanding the variety (producGon rate)• More events with be`er localizaGon

Let’s understand these ques$ons
Knowing = Understanding
with the word of physics• Why do some stars explode?
• Why don’t normal star explode?
• Why do stars show L ~ M ?
• Why do stars evolve?
• Why does the des$ny of stars depend on the mass?
• Why does stellar core collapses?
• Why is the energy of supernova so huge?
•…
4Thermodynamics

Electromagne$sm

Classical
mechanics

Sta$s$cal
mechanics

Astrophysics
Hydrodynamics

Rela$vityQuantum
mechanics
Nuclear physics

Appendix

Relavant $mescales
MergerGW

neutron-capture(r-process)nucleosynthesis

Radioac$ve decay=> kilonova< 1 sec~> days

Mass
ejec$on~< 100 msh`p://www.aei.mpg.de/comp-rel-astro

MT & Hotokezaka 13

Explosive phenomena around the neutron star
Core-collapse supernova

M. Weiss

NS merger

NASA

Moderately neutron rich

Very neutron rich

Ye ~ 0.45 (nn ~ 1.2np)

Ye ~ 0.10 (nn ~ 9 np)

npne=
Ye =
np + nn
np + nn

nn = np
for Ye = 0.50

ら れ る． こ の 加 −熱 は，
νe＋n→p＋e
Core-collapse supernovae ニュートリノ（νe）捕獲および陽子（p）の反電−νe＋n→p＋e

Wanajo, Janka, & M

5Ye, min = 0.466

The Astrophysical Journal Letters, 726:L15 (4pp), 2011 January 101D 2D

mass [10-3 solar]

4＋21Ye, min = 0.404

ν̄ e＋p→n＋e
および陽子（p）の反電3によるものである．超新＋✏ν̄⌫¯＋>✏⌫
e p→ne ＋eeにより，この二つの反Wanajo+11, Wanajo 14によるものである．超新Probably neutron rich
but only moderately
ることが確かめられて
00.40

0.45

Ye

0.500.55<latexit sha1_base64="9GTL7ERUQ10WfAKhvUITSaFhtC4=">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</latexit>

relative to solar

Figure 1. Snapshot of the convective region of the 2D simulation of an ECSN
at 262 ms after core bounce with entropy per nucleon (s; left) and Ye (right).
Mushroom-shaped lumps of low-Ye matter are ejected during the early phase ofthe explosion.
(A color version of this figure is available in the online journal.)

Figure 2. Ejecta masses vs. Ye for the 1D (blue) and 2D (red) explosion m
The width of a Ye -bin is chosen to be ∆Ye = 0.005. The minimum value
are indicated for both cases.
(A color version of this figure is available in the online journal.)

104
103

Ye ~ 0.45 (n ~ 1.2np10) 2

expands continuously, and a neutrino-powered explosion sets inat t ∼ 100 ms p.b. in 1D and 2D essentially in the same way nand with a very similar energy (∼1050 erg; Janka et al. 2008).
In the multi-dimensional case, however, the negative entropy

CaCrTi1D 2DFeNiZnGeSe

KrSrZrMo

により，この二つの反応子と陽子の数はほぼ同1010Neutron star merger
Top view

Side view

Sekiguchi+15, 16

Very neutron rich (Composi$on of neutron starYe ~ 0.10 (nn ~ 9 np)