the astrophysical formation of the elementsbrown/Uio-MSU-ORNL-UT-2011/RSurman5.pdf · the...

the astrophysical formation of the elements

Rebecca Surman Union College

Second Uio-MSU-ORNL-UT School on

Topics in Nuclear Physics

3-7 January 2011

lecture 1: some preliminaries

lecture 2: big bang nucleosynthesis

lecture 3: fusion in main sequence stars

lecture 4: explosive nucleosynthesis

lecture 5: neutron-capture nucleosynthesis


R Surman, Union College Introduction to Nuclear Astrophysics, Lecture 5 7 January 11

Chart of the Nuclides

pro

ton

nu

mber

Z

neutron number N

Big bang nucleosynthesis

~3/4 H

~1/4 He

some Li, Be, B




pro

ton

nu

mber

Z

neutron number N

Fusion in Stars, Explosive burning

H → He

He → C, O

C,O → Si

Si → Fe group




pro

ton

nu

mber

Z

neutron number N



heavy element synthesis


N = 50 N = 82 N = 126

neutron capture nucleosynthesis


separating s- and r-process abundance patterns


Käppeler et al (2010)

the classic s-process


For a recent review, see, e.g. Käppeler et al (2010)

the astrophysical site of the s-process


main component – low mass AGB stars



12C(p,γ)13N(β+ν)13C 13C(α,n)



14N(α,γ)18F(β+ν)18O(α,γ)22Ne 22Ne(α,n)25Mg

Weak component – core He burning in massive stars

nuclear data for the s-process


need beta decay rates and neutron capture rates

Käppeler et al (2010)

r-process basics


from Seeger et al (1965) Solar r-process abundances

data from Käppeler et al (1989)

€

Sn (Z,Apath ) ~ −kT lnnn2

2π2

mnkT

3 / 2

r-process basics


from Seeger et al (1965)

(n,γ)-(γ,n)

€

Sn (Z,Apath ) ~ −kT lnnn2

2π2

mnkT

3 / 2

β (or νe)

Astrophysics

What is the astrophysical site of the r process?

Some possibilities:

supernovae e.g., Meyer et al (1992), Woosley et al (1994), Takahashi et al (1994)

neutron star mergers e.g., Meyer (1989), Frieburghaus et al (1999), Rosswog et al (2001)

shocked surface layers of O-Ne-Mg cores e.g., Wanajo et al (2003), Ning et al (2007)

gamma-ray bursts e.g., Surman et al (2005)

Nuclear Physics

What are the nuclear properties of neutron-rich nuclei far from

stability?

We need:

masses

beta decay rates

neutron capture rates

neutrino interaction rates

fission probabilities and daughter product distributions

the r-process: open questions


Cowan et al (2006)

halo star observations of r-process nuclei


Cowan et al (2006)



Main r-process

Cowan et al (2006)



Main r-process

⇒  a universal process? (e.g., Roederer et al 2009)

⇒  site within core-collapse supernovae?

Weak r-process

Important parameters ⇒

outflow timescale

entropy

electron fraction

€

ρ ~ e−t / 3τ ; τ ~ 0.01 s to ~ 1 s

€

s /k ~ 100 to 400

€

Ye =1

1+ n / p; Ye ~ 0.3 to ~ 0.5

p, n → 4He + n → seed nuclei + n → r process

PNS

shock

ν

€

p + ν e ↔ n + e+

n + ν e ↔ p + e−

€

Tv e> Tve

supernova neutrino-driven wind


Neutrinos influence every stage of the nucleosynthesis

initial neutron-to-proton ratio

seed assembly: alpha effect

r process

€

Yeeq =1

1+ λν e p/λν en( )

PNS

shock

ν

€

p + ν e ↔ n + e+

n + ν e ↔ p + e−

€

Tv e> Tve

€

n + ν e → p + e−AZ + ν e→

A (Z +1) + e−, AZ + ν x→A−1Z + n

binds into additional α’s

€

p + ν e ↔ n + e+

n + ν e ↔ p + e−

neutrinos and a supernova r-process


How is a consistent pattern achieved?

Ye = 0.27 Ye = 0.26 Ye = 0.25

R. Surman, unpublished

the main r-process in supernovae


fission cycling

Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008)

fission cycling in a supernova r-process


calc by R. Surman

Halo star data Solar

Simulations with fission cycling

but the big problem is…


Initial studies were very promising…. e.g., Meyer et al (1992), Woosley et al (1994)

…but it was found to be more difficult to produce the requisite conditions than first thought e.g., Takahashi et al (1994), Witti et al (1994), Fuller & Meyer (1995), McLaughlin et al (1996), Meyer et al (1998), Qian & Woosley (1996), Hoffman et al (1997), Otsuki et al (2000), Thompson et al (2001), Terasawa et al (2002), Liebendorfer et al (2005), Wanajo (2006), Arcones et al (2007), etc., etc.

The most recent calculations of proto-neutron star evolution predict no robustly neutron-rich outflows Huedepohl et al (2010), Fischer et al (2010)

Several environments within neutron star-neutron star mergers have been found to be attractive r-process sites e.g., Lattimer & Schramm (1974, 1976), Meyer (1989), Frieburghaus et al (1999), Goriely et al (2005), Oechslin et al (2007)

…but the timescale for mergers to develop is inconsistent with the data e.g., Sneden et al (1996), Ryan et al (1996), Truran et al (2002), Argast et al (2004), Wanajo & Ishimaru (2006)

compact object mergers instead?


Orbit of a black hole - neutron star binary decays by gravitational wave emission

Tidal disruption of the neutron star produces a rapidly accreting disk around the black hole (AD-BH)

⇒ possible engine for a short gamma-ray burst

animation credit: NASA/SkyWorks Digital

black hole – neutron star merger


accretion disk

PNS BH

jet (?)

shock outflow

ν

ν

protoneutron star/AD-BH comparison


accretion disk

PNS BH

jet (?)

shock outflow

ν

ν

neutrino scattering and emission

nucleosynthesis

nucleosynthesis

nuclear physics of disk

nuclear physics of core

protoneutron star/AD-BH comparison


3D BH-NS merger model 1.6 M neutron star + 2.5 M black hole with a = 0.6 (M. Ruffert and H.-Th. Janka)

r process in BH-NS merger outflows


solar calculation HD122563

(Honda et al 2006)

Surman, McLaughlin, Ruffert, Janka, and Hix, ApJ, 679, L117 (2008), and Surman, McLaughlin, Ruffert, Janka, and Hix, PoS(NIC X)149

Astrophysics

What is the astrophysical site of the r process?

Some possibilities:

supernovae e.g., Meyer et al (1992), Woosley et al (1994), Takahashi et al (1994)

neutron star mergers e.g., Meyer (1989), Frieburghaus et al (1999), Rosswog et al (2001)

shocked surface layers of O-Ne-Mg cores e.g., Wanajo et al (2003), Ning et al (2007)

gamma-ray bursts e.g., Surman et al (2005)

Nuclear Physics

What are the nuclear properties of neutron-rich nuclei far from

stability?

We need:

masses

beta decay rates

neutron capture rates

neutrino interaction rates

fission probabilities and daughter product distributions

the r-process: open questions


New rate determined by Arnold et al


assembly of r-process seeds and the ααn rate

calculations by R Surman

beta decay rates


Möller et al (2003)


Möller et al (2003) + experimental rates

A sample neutrino-driven wind trajectory, with the element synthesis calculated with three different sets of β-decay rates

calculation by R Surman

beta decay rates




Möller et al (2003) + experimental rates

A sample BH-NS merger trajectory, with the element synthesis calculated with three different sets of β-decay rates


measured r-process beta decay rates


http://www.nndc.bnl.gov/chart/

= half-life measurements since 2000 (6th ed)

(neutron-rich nuclei only)

Only a few measurements along r-process path

schematic r-process path

slide from J. Blackmon


fission probabilities + daughter product distributions

symmetric fission

asymmetric fission



mass models versus neutron capture rates

Neutron capture rate variation

Mass model variation

Surman, Beun, McLaughlin, and Hix, PRC, 79, 045809 (2009)

Surman, Beun, McLaughlin, and Hix, PRC, 79, 045809 (2009)

€

σv 131Cd ×10

€

σv 131Sn ×100

130 peak rare earth region + 195 peak

nonequilibrium effects of neutron capture rates


We still don’t know where the r-process takes place

⇒ evidence increasingly points to core collapse supernovae for the site of the main r-process (fission cycling may help)

⇒ list of potential sites should include hot outflows from black hole-neutron star mergers, particularly for the weak r-process

The importance of nuclear masses and beta decay rates has long been recognized. In addition,

⇒ light element charged-particle reactions,

⇒ individual neutron capture rates, and

⇒  fission probabilities and fragment distributions

are also of key importance.

r-process summary


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