Study Suggests It Takes Two Stars To Create Gamma-Ray Bursts

Artist’s impression of a gamma-ray burst with an orbiting binary star. University of Warwick/Mark Garlick

Gamma-ray bursts (GRBs) are the brightest explosions in the universe and, just like it takes two to tango, researchers think that two stars are required to produce the right conditions for a GRB to form.

The team's work focuses on the so-called long gamma-ray bursts, which make up about 70 percent of all the GRB events observed. These are generated when massive stars go supernova, with gamma ray emissions coming from the jet of material fired by the star at velocities close to the speed of light. The formation of the jet is dependent on a star spinning very quickly. This is because stars, especially massive ones, can lose such property easily. The team reports in Monthly Notices of the Royal Astronomical Society that having a companion guarantees that the spin doesn’t slow down. Quite the opposite in fact.

“What we have determined is that the majority of stars are spinning fast precisely because they’re in a binary system,” lead author Ashley Chrimes, a graduate researcher at the University of Warwick, said in a statement. “The question has been how a star starts spinning or maintains its spin over time. We found that the effect of a star’s tides on its partner is stopping them from slowing down and, in some cases, it is spinning them up. They are stealing rotational energy from their companion, a consequence of which is that they then drift further away.”

The team simulated thousands of binary system models. In some of these, the tidal forces of the two stars influence the spin of the companion going supernova. According to the work, there are enough binary stars with the right characteristics to explain the number of GRBs emitted. Only 10 to 20 percent of all GRBs are observed because the jet of material needs to be pointed towards us to be seen.

The model was developed by researchers from the University of Warwick and Dr J J Eldridge, an assistant professor at the University of Auckland. The team hopes to use a similar approach to see if they can explain other transient events, such as the mysterious fast-radio bursts.

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