Gamma ray burst may have been two supernovae in one

Gamma ray bursts are typically released from the collapse of massive stars

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On New Year’s Day in 2022, the Neil Gehrels Swift Observatory detected a massive burst of gamma rays from a distant galaxy. After four years of analysis, a group of astronomers has proposed a dramatic story for the burst of light – known as GRB 220101A – in which a collapsing star triggered the formation of both a pulsar and a black hole.

The event began, according to a team led by Remo Ruffini, an astronomer at the International Center for Relativistic Astrophysics Network in Italy, with the collapse of the core of a massive older star, which had earlier been transformed via nuclear reactions into a mix of carbon and oxygen.

When the carbon-oxygen core exploded, the researchers argue that an accelerating cloud of electrons and positrons was released in a hypothetical event that they call an “HB supernova” after the late physicist Homi Bhabha, who studied collisions of those particles. This cloud then ran into a nearby white dwarf, causing it to collapse and become a neutron star. The white dwarf’s collapse triggered a second supernova blast 3.5 seconds after the first.

Then, this second blast hit a third nearby stellar object, another neutron star. As a consequence, the neutron star released a further dramatic burst of energy, the brightest of the entire event, before collapsing to become a black hole.

Meanwhile, fast-moving material continued to fall onto the new neutron star, causing it to spin faster and faster, until it was twirling around in a matter of milliseconds, becoming a pulsar, a star whose fast spin and magnetic field produce regular beams of light. “It’s the most complex system ever observed in astrophysics,” says Ruffini.

Other experts aren’t so sure, though.

“Ruffini et al., put forward a fascinating idea for the origin of GRB 220101A. However, as always, extraordinary claims require extraordinary evidence,” says Ryan Ridden at the University of Canterbury in New Zealand. “Even with the fantastic data available for GRB 220101A, the observations don’t definitively support this novel model”, and could equally well fit a story that ends with a single black hole and no neutron star.