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Evolution of Metal-Poor Massive Stars Towards GRBs

Explore the formation of Gamma-Ray Burst (GRB) progenitors from metal-poor massive stars, focusing on single and binary star models, as well as new evolutionary models of rapidly rotating metal-poor single stars. Discuss the necessary conditions for GRB formation, including the formation of relativistic jets, removal of hydrogen envelope, and angular momentum redistribution. Investigate the role of magnetic fields in J-transport and uncertainties in Wolf-Rayet winds. Consider the homogeneous evolution of single stars in relation to GRB progenitors and examine the Z dependence of GRB progenitor evolution. Future work aims to better understand GRB formation channels and rates based on metallicity variations.

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Evolution of Metal-Poor Massive Stars Towards GRBs

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  1. Evolution of metal poor massive stars towards GRBs Sung-Chul Yoon (Amsterdam) In collaboration with Norbert Langer (Utrecht) Tartu, Aug. 15, 2005

  2. Outline • GRB progenitors • Single star models & problems • Binary models & problems • New evolutionary models of rapidly rotating metal poor single stars • Discussion

  3. GRB progenitors • Some clues • Association with star-forming regions in galaxies • GRB 980425  SN 1998bw (Galama et al. 1998) • GRB 030329  SN 2003dh (eg. Hjorth et al. 2003) • At least, some GRBs are deaths of massive stars! -- especially from massive He stars (or WR stars) • Association with Type Ibc supernovae • Crossing time of jet ~ 10 secs: compact progenitors • GRBs are a subset of SN Ibc? (RGRB/RSNIbc ~ 0.01—0.001)

  4. Necessary Conditions for GRB formation • Formation of relativistic Jets => central engines are rapid rotators • Collapsar scenario (Woosley) – formation of a Keplerian disk around a black hole: j > 1016 cm2/s • Difficult to achieve (Maeder & Meynet 03; Heger et al. 05) • Removal of H envelope • Difficult at very low/zero Z • He core massive enough to form BH

  5. Angular momentum redistribution inside stars • Core contraction/chemical gradient between the core and the envelope • Angular momentum transport by Eddington Sweet circulations, Shear instability, magnetic torques, etc. • Stellar wind mass loss

  6. Angular momentum redistribution Using a hydrodynamic stellar evolution code (e.g. Heger et al. 00; Petrovic et al. 05). Effect of magnetic torques is considered according to Spruit (2002)

  7. Role of magnetic fields in J-transport Models with B-fields are more consistent with observations!!

  8. Binary Evolution Mass accretion will spin up the secondary star.

  9. Mass and J accretion in close binaries Petrovic, Langer, Yoon & Heger (2005) • Spin-up by accretion leads to strong stellar winds. • J-transport during He core contraction is very rapid. • the core becomes slow again – as slow as in single stars. • Spin-up during MS does not help. M1 = 56, Pinit =6 days

  10. Spin-up in WR stages? • Tidal locking of a massive helium star in a very close binary (Izzard et al.03; Podsiadlowski et al.04)? • Orbit should be very short: P < 5 hr • Massive He stars in X-ray binaries? – eg. Cyg X-3 (P ~ 4.8 hr; van Kerkwijk et al. 1992) • He star merger (Fryer & Heger 2005) • BUT: Any evolutionary scenario related to common envelope phase may not work at very low Z

  11. Homogeneous evolution of single stars • Found by Maeder(1987)

  12. Homogeneous Evolution Rapidly rotating helium stars can be made even without removing hydrogen envelope => particularly important at low Z

  13. Homogeneous Evolution Yoon & Langer (2005); see also Woosley & Heger (2005)

  14. Uncertainties in WR winds • Maximun Z for such evolution to GRBs sensitively depends on the WR wind mass loss rate. • With current estimate of WR winds by Vink & de Koter (05): Zmax ~0.001

  15. Observational evidence for homogeneous evolution GRB progenitor? NGC346 in SMC; Bouret et al. (2003)

  16. Z dependence of GRB progenitor evolution

  17. Future Work • Understand better GRB formation channel and its rate as a function of metallicity.

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