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Astronomers using Karl G. Jansky of the NSF's Very Large Array discovered a jet of rapidly moving material propelled outwards from a strongly magnetized neutron star. The discovery, reported in the review Nature, forces to rethink a long-standing theory on the origin of these jets.
An artist's impression of the powerful neutron star Swift J0243.6 + 6124 that launches a jet. Image Credit: ICRAR / University of Amsterdam.
Neutron stars are superdense objects, the remains of massive stars that exploded like supernovas.
In binary pairs with "normal" stars, their powerful gravity can move the material away from their companions.
This material forms a disk, called accretion disk, rotating around the neutron star. The jets of matter are propelled at the speed of light, perpendicular to the disc.
"We have seen jets from all types of neutron stars pulling material from their companions, with one exception. Never before have we seen a jet coming from a neutron star with a very strong magnetic field, "said Jakob van den Eijnden, astronomer at the University of Amsterdam.
This led to a theory that strong magnetic fields prevent the formation of jets. The new discovery contradicts this theory. "
van den Eijnden and his colleagues studied an object called Swift J0243.6 + 6124, discovered in October 2017 by NASA's Neil Gehrels Swift observatory, when the object emitted an X-ray explosion.
The object is a slow spinning neutron star that fires a material from an associated star that is probably much more massive than the Sun.
"The magnetic field of the neutron star we studied is about 10 trillion times stronger than that of our own Sun. So we observed for the first time a jet from a star to neutrons with a very strong magnetic field, "said van den Eijnden said.
"The discovery reveals a whole new class of jet production sources to study."
Observations with Karl G. Jansky of the NSF Very Large Array began a week after the discovery of Swift and continued until January 2018.
Both the fact that the emission of the X-ray neutron star and the radio wavelengths have weakened over time, and the characteristics of the radio show convinced astronomers that they saw radio waves being produced. by a jet.
"This combination is what we see in other jet production systems. Alternative mechanisms do not explain it, "van den Eijnden said.
Current theories of jet formation in systems such as Swift J0243.6 + 6124 indicate that the jets are launched by magnetic field lines anchored in the inner parts of the accretion discs.
In this scenario, if the neutron star has a very strong magnetic field, this field is too powerful and prevents the formation of the jet.
According to the team, the launch region of the Swift J0243.6 + 6124 accretion jet could be much farther away than in other types of systems, where the magnetic field of the star is weaker.
Another idea is that the jets can be powered by the rotation of the neutron star, instead of being thrown by magnetic field lines into the internal accretion disk.
"It is interesting to note that the idea of rotation predicts that the jet will be much smaller compared to slower rotated neutron stars, which is exactly what we see in Swift J0243.6 + 6124," explains Dr. Nathalie Degenaar. .
"A Swift Jet J0243.6 + 6124 may mean that another category of objects, called ultra-bright X-ray pulsars, also highly magnetized, could produce jets," astronomers said.
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J. van den Eijnden et al. An evolving jet from a strongly magnetized X-ray pulsar. Nature, published online September 26, 2018; doi: 10.1038 / s41586-018-0524-1
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