It was realized at the turn of the century that long-duration gamma ray bursts are tied to some massive star explosions. What exactly caused some stars to end their lives as normal supernovae and what caused some to have these associated GRBs and die as hypernovae have been a bit of a mystery, however, and researchers have looked for single-star solutions, such as stellar rotation, that could differ from one star to another.
New research from the International Center for Relativistic Astrophysics Network finds that sometimes even stars need a little help from a friend. Using computational models, they’ve found they can reproduce what is observed if they start from a massive carbon-oxygen burning star and a neutron star companion. When the massive star exhausts its fuel, it collapses into a new neutron star and jettisons a shell of material. The shell of material hitting the companion neutron star can actually be enough to collapse it into a black hole. Material streaming around this newly formed black hole or a souped-up now-larger neutron star can generate a massive magnetic field that in turn generates transitory jets we see as gamma ray bursts.
Let me put that another way – the star that goes supernova as it becomes a new neutron star is not the source of the GRB. Rather a companion star that takes friendly fire is the actual source, and the light curves we see are the combination of the normal supernova explosion and the sudden turn-on of a jet from the companion object’s new magnetic field that fades as the material is used up and pushed away. This new research is published in a trio of papers in The Astrophysical Journal.
This is the kind of science that changes our understanding of an event at a very fundamental level and shows that the solutions to problems large and even hypernova-sized sometimes require fantastical amounts of creativity.
- ICRANet press release
- “Magnetic Fields and Afterglows of BdHNe: Inferences from GRB 130427A, GRB 160509A, GRB 160625B, GRB 180728A, and GRB 190114C,” J.A. Rueda et al., 2020 April 24, The Astrophysical Journal