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Aspects of the Astrophysics and Nuclear Physics of r -Process Nucleosynthesis

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. r -process nucleosynthesis.

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Aspects of the Astrophysics and Nuclear Physics of r -Process Nucleosynthesis

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  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 08 2/25

  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 08 3/25

  4. halo star observations Cowan et al (2006) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 4/25

  5. halo star observations Main r process Cowan et al (2006) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 5/25

  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 08 6/25

  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 08 7/25

  8. the main r process How is a consistent pattern achieved? Ye = 0.25 Ye = 0.26 Ye = 0.27 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 8/25

  9. low Ye main r process Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 9/25

  10. low Ye main r process Fission Cycling Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 9/25

  11. fission cycling and the neutrino luminosities (1051 erg/s) (1051 erg/s) Surman, Beun, McLaughlin, Kane, & Hix, J Phys G 35, 014059 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 10/25

  12. fission cycling: comparison with halo star data Beun, McLaughlin, Surman, & Hix, PRC 77, 035804 (2008) R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 11/25

  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 08 12/25

  14. 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 black hole - neutron star merger animation credit: NASA/SkyWorks Digital R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 13/25

  15. PNS – AD-BH comparison jet (?) shock outflow  PNS BH  accretion disk R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 14/25

  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 08 15/25

  17. 3D black hole - neutron star merger model 1.6 M neutron star + 2.5 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 08 16/25

  18. neutrino temperatures Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 17/25

  19. our nucleosynthesis calculation Outflow parameterization Adiabatic flow with velocity as a function of radial distance: with v~ 104 km/s, 0.2 < < 1.4, 10 < s/k < 50 Surman, McLaughlin, Ruffert, Janka, and Hix, arXiv:0803.1785 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 18/25

  20. 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:0803.1785 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 19/25

  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 08 20/25

  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 08 21/25

  23. mass model - neutron capture rate comparison Neutron capture rate variation Mass model variation Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 22/25

  24. nonequilibrium effects of individual capture rates 130 peak rare earth region + 195 peak Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 23/25

  25. influential neutron capture rates Surman, Beun, McLaughlin, and Hix, arXiv:0806.3753 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 50 100-1000 R Surman, Astrophysics and Nuclear Physics of the r process, SNP 08 24/25

  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 08 25/25

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