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Understanding the Evolution of Massive Stars Leading to Gamma-Ray Bursts

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lenci
15 diapositives · 314 Views · Oct 04, 2014

This work explores the evolution of massive stars and their connection to gamma-ray bursts (GRBs). We analyze GRB progenitors, noting their association with star-forming regions and specific supernovae like SN 1998bw and SN 2003dh. Our findings indicate that at least some GRBs result from the deaths of massive stars, particularly Wolf-Rayet stars. We discuss the necessary conditions for GRB formation, such as the creation of relativistic jets and the role of angular momentum and magnetic fields. The evolutionary pathways, including quasi-chemically homogeneous evolution, suggest that stars may produce GRBs even without hydrogen envelope removal.

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Understanding the Evolution of Massive Stars Leading to Gamma-Ray Bursts
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  1. Evolution of massive stars towards GRBs Sung-Chul Yoon (Amsterdam) In collaboration with Norbert Langer (Utrecht) Santorini, Aug. 29, 2005

  2. 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)

  3. 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 • Removal of H envelope • Difficult at very low Z • He core massive enough to form BH

  4. Angular momentum redistribution inside stars • Stellar wind mass loss  Removal of hydrogen envelope • Core contraction/chemical gradient between the core and the envelope • Angular momentum transport by Eddington Sweet circulations, shear instability, magnetic torques, etc.  Angular momentum condition of j > 1016 cm2/s

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

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

  7. 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

  8. 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 05) • BUT: Any evolutionary scenario related to common envelope phase may not work at very low Z S Fryer & Heger 05

  9. Quasi- Chemically Homogeneous evolution of single stars • Found by Maeder (1987) The envelope cannot spin down the core; The angular momentum redistribution is mainly determined by stellar winds The core is spun down by the slowly rotating envelope

  10. Quasi- Chemically Homogeneous evolution Rapidly rotating helium stars can be made even without removing hydrogen envelope => particularly important at low Z

  11. Quasi- Chemically Homogeneous evolution Yoon & Langer (2005); see also Woosley & Heger (2005)

  12. 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 ~Zsun/10

  13. Observational evidence for homogeneous evolution N enriched blue stars in Magelanic cloulds: GRB progenitor? NGC346 in SMC; Bouret et al. (2003)

  14. Z dependence of GRB progenitor evolution

  15. Conclusion • Quasi-Chemically homogeneous evolution of single stars at low Z • Very rapidly rotating stars (Vinit/VKepler ~ 0.5) with Z < Zsun/10 and 20 < M/Msun < 60 will be able to make GRBs • Consistent with observational indications of low Z of GRB hosts: e.g. GRB 050730, Z ~ Zsun/100 (e.g.Starling et al. 05) • No-need of removal of H envelope by winds: even first stars will be able to produce GRBs • Binary evolution channel: detailed study needed (=> Lecture by Podsiadlowski)