Short-lived neutron stars could account for the intense magnetic fields of black holes and gamma-ray bursts, which are the most powerful explosions in the universe.
A new explanation for how black holes get their extreme magnetic fields could also tell us how the most powerful explosions in the universe are produced.
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| An artist’s depiction of a black hole with gamma ray bursts shooting out into space Marc Ward/Shutterstock |
Gamma ray bursts (GRBs) are intense blasts of radiation produced from cosmic collisions and explosions. Some of the highest-energy GRBs appear to come from stars exploding in a supernova and producing a fast-spinning black hole.
Physicists think the black hole’s spinning weaves its magnetic field into a rope-like structure, which blasts out a jet of matter travelling almost at the speed of light. This then pierces the remains of the parent star and produces the GRB.
But parts of this process are still mysterious, such as how black holes can acquire such a strong and fast-spinning magnetic field from the star that creates them. “When we actually did these calculations, we found that the black holes do not get anywhere close to the magnetic field that we need to launch these relativistic jets from the star itself,” says Ore Gottlieb at Columbia University in New York.
Gottlieb and his colleagues have now found that if a neutron star – the collapsed core of a massive star – forms for a few seconds before it becomes a black hole, this would generate the required magnetic field.
The team ran simulations of a star 40 times the mass of the sun, and tracked how its magnetic field changed over its lifetime until it collapsed and formed a neutron star. They then used a different simulation to track how this magnetic field would change as it became a black hole. “The neutron star is rotating and if its rotation is fast enough, it forms the disc [of material] around the black hole,” says Gottlieb. “This is the most important part that was missing in previous simulations.”
As well as producing the required magnetic field, extra energy from the neutron star also matches the types of supernovae that are associated with the highest-energy GRBs, says Gottlieb.
“What they have provided is a real advancement in getting this complete picture,” says Eric Burns at Louisiana State University.
The idea will be difficult to test with observations because it requires a very rare event, says Burns – such as GRB221009A, discovered in 2022 and dubbed the brightest explosion since the big bang. It would also need extremely sensitive measurements of the GRB’s polarisation, a property that describes how the light rays are twisted, to measure the magnetic fields, he says.
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