1. Aspects of the Astrophysics and Nuclear Physics of r-Process Nucleosynthesis
Rebecca Surman
Union College
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology
July 2008

2. r-process nucleosynthesis
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

3. r-process nucleosynthesis - current challenges
Astrophysics
The astrophysical site(s) not conclusively known; possibilities include:
• core collapse 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
Nuclear properties for ~3000 nuclei far from stability
nuclear masses fission probabilities, distribution of fragments
beta decay rates neutron capture rates (?)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

4. halo star observations
Cowan et al (2006)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

5. halo star observations
Main r process
Cowan et al (2006)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

6. halo star observations
Weak r process
Main r process
core collapse supernovae ?
Cowan et al (2006)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

7. the SN neutrino-driven wind
Important parameters 
outflow timescale
entropy
electron fraction
shock
PNS 
p, n  4He + n  seed nuclei + n  r process
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

8. the main r process How is a consistent pattern achieved? Ye = 0.25
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

9. Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008)
low Ye main r process
Beun, McLaughlin, Surman, & Hix, PRC 77, (2008)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

10. Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008)
low Ye main r process
Fission Cycling
Beun, McLaughlin, Surman, & Hix, PRC 77, (2008)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

11. Surman, Beun, McLaughlin, Kane, & Hix, J Phys G 35, 014059 (2008)
fission cycling and the neutrino luminosities
(1051 erg/s)
(1051 erg/s)
Surman, Beun, McLaughlin, Kane, & Hix, J Phys G 35, (2008)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

12. Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008)
fission cycling: comparison with halo star data
Beun, McLaughlin, Surman, & Hix, PRC 77, (2008)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

13. fission cycling and the main r process
In the SN neutrino-driven wind, the electron neutrino flux determines whether a successful r process is possible
The electron neutrino flux can be reduced by:
 fast outflow
 active-sterile neutrino oscillations
 other new physics
If a sufficient reduction in the electron neutrino flux occurs, fission cycling may insure a stable abundance distribution consistent with the pattern in metal-poor halo stars
Accurate fission probabilities and fragment distributions are required to correctly predict the details of the final abundance distribution for a fission cycling main r process.
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

14. black hole - neutron star merger
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
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

15. PNS – AD-BH comparison jet (?) shock outflow  PNS BH  accretion disk
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

16. PNS – AD-BH nuclear physics
nucleosynthesis
jet
jet (?)
shock
nucleosynthesis
outflow 
PNS BH 
accretion disk
neutrino scattering and emission
nuclear physics of disk
nuclear physics of core
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

17. 3D black hole - neutron star merger model
1.6 M neutron star M black hole with a = 0.6
Evolved until remains of neutron star form an accretion disk
Model by M. Ruffert and H.-Th. Janka
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

18. Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785
neutrino temperatures
Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

19. Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785
our nucleosynthesis calculation
Outflow parameterization
Adiabatic flow with velocity as a function of radial distance:
with v ~ 104 km/s, 0.2 < < 1.4, < s/k < 50
Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

20. Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785
sample nucleosynthetic outcomes
All trajectories from the inner disk region make r-process nuclei
This is a direct consequence of the neutrino physics
Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

21. sample nucleosynthetic outcomes
Example: the importance of beta decay rates
Möller et al (2003)
Möller et al (1997)
Möller et al (2003) + exp
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

22. neutron capture rates and the r process
Do they make any difference?
can influence time until onset of freezeout
e.g., Goriely (1997,8), Farouqi et al, Rauscher (2005)
can shape local details of the abundance distribution
e.g., Surman et al (1998), Surman & Engel (2001)
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

23. Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753
mass model - neutron capture rate comparison
Neutron capture rate variation
Mass model variation
Surman, Beun, McLaughlin, and Hix, arXiv:
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

24. Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753
nonequilibrium effects of individual capture rates
130 peak
rare earth region peak
Surman, Beun, McLaughlin, and Hix, arXiv:
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

25. Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753
influential neutron capture rates
Surman, Beun, McLaughlin, and Hix, arXiv:
Capture rates that affect a 5-40% change in the global r-process abundance pattern for increases to the rate by a factor of: 10 50
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25

26. summary 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 would help)
 list of potential sites should include hot outflows from black hole-neutron star mergers, particularly for the weak r process
Everybody knows we need nuclear masses and beta decay rates
 individual neutron capture rates are also important
 fission probabilities and fragment distributions may be crucial
R Surman, Astrophysics and Nuclear Physics of the r process, SNP /25