Magnetic fields of massive stars and their compact remnants

• Applicant: Professor Dr. Norbert Langer
• Subject Area: Astrophysics and Astronomy
• Term: from 2011 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 200013763

• Final Report Year: 2016

Final Report Abstract

Our Sun and all comparable stars are known to host a highly variable magnetic field, which is thought to be continuously regenerated through an internal dynamo process. Most of the stars more massive than the Sun, however, appear to show no trace of a magnetic field, which is not surprising since the dynamo known to work for the Sun can not operate in them. Yet, in recent years, it has been found that about 10% of the more massive stars do host large scale stable magnetic fields. The origin of these fields, their effect on the evolution of the stars, and their presence and strengths in their compact remnants, the neutron stars, are the topic of this project. Our team of researchers in Germany and Chile has significantly added to the cumulating evidence that the magnetic fields in massive stars are generated during the merger process of two stars in a compact binary system. We found theoretical models of merged stars to comply with observational properties of observed magnetic stars. Furthermore, in an observational study, we found a high fraction of magnetic massive stars to possess high space velocities, which we interpret as the result of the former presence of a companion star. We shed light on the effect of magnetic fields on the evolution of massive stars, through multi-dimensional magneto-hydrodynamic models, through stellar evolution models which include effects of magnetic fields, and through observational studies of magnetic fields in massive stars. We found evidence for the possible slow decay of the fields in massive stars, on time scales comparable to the life times of the stars. We also found that such decay appears to occur more rapidly the more massive the stars which are considered, consistently from theoretical and observational studies. We found evidence that blue supergiants, like the progenitor of the famous Supernova 1987A, are the descendants of magnetic core-hydrogen burning stars. We were also able to draw a connection between magnetic massive stars and magnetars, the extremely magnetised variety of neutron stars. We show that there is evidence for at least a fraction of the massive magnetic hydrogen burning stars to retain the magnetic fields during their later evolutionary stages. These findings stimulated our interpretation of recently identified so called superluminous supernovae being powered by a central magnetar, and magnetic fields playing a central role in the progenitor evolution of massive merging double black holes, as recently observed through the first direct detection of gravitational waves.

Publications

• 2014, Magnetic Fields throughout Stellar Evolution, IAU S302, Cambridge, UK: Cambridge University Press
  Petit P, Jardine M, Spruit H C (Editors)
  
• 2012, Presupernova Evolution of Massive Single and Binary Stars, Ann. Rev. Astron. Astrophys., 50, 107
  Langer, N
  
• 2013, Exploring the origin of magnetic fields in massive stars. New magnetic field measurements in cluster and field stars, A&A, 551, A33
  Hubrig S, Schöller M, Ilyin I, Kharchenko N V, Oskinova L M, Langer N, Gonzalez J F, Kholtygin A F, Briquet M
  
• , 2015, Magnetic fields in non-convective regions of stars, Living Reviews
  J. Braithwaite, H.C. Spruit
  
• 2015, Blue supergiants as descendants of magnetic main sequence stars, A&A, 584, A54
  Petermann I, Langer N, Castro N, Fossati L
  
• 2015, Instability of magnetic equilibria in barotropic stars, MNRAS, 447, 1213
  Mitchell J P, Braithwaite J, Reisenegger A, Spruit H, Valdivia J A, Langer N
  
• B fields in OB stars (BOB): on the detection of weak magnetic fields in the two early B-type stars β CMa and ∈ CMa: Possible lack of a ”magnetic desert” in massive stars, 2015, A&A, 574, A20
  Fossati, L, Castro N, Morel T, Langer N, Briquet M, Carroll T A, Hubrig S, Nieva M F, Oskinova L M, Przybilla N, Schneider F R N, Schöller M, Simon-Diaz S, Ilyin I, de Koter A, Reisenegger A, Sana H
  
• 2016 Rejuvenation of stellar mergers and the origin of magnetic fields in massive stars, MNRAS, 457, 2355
  Schneider F R N, Podsiadlowski P, Langer N, Castro N, Fossati L
  
• 2016, A hydrostatic MHD code for modelling stellar interiors, 2016, A&A, 585, A127
  Boldt L, Mitchell J, Braithwaite J