Powerful jet of the wrong kind of star | Space

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In recent decades, jets have been a key part of the cosmic landscape. Astronomers see jets emanating from different types of star systems, and from the region of massive, supermassive black holes, but they are far from comprehending them completely. On September 26, 2018, astronomers announced that they were using the Very Large Array (VLA) in the west of Socorro, New Mexico, to discover a jet of fast material propelled by a kind of radioactive material. neutron star deemed unable to launch such a jet. The discovery, said the scientists, requires a fundamental revision of their ideas about the origin of these jets.

Neutron stars are evolved stars – now superdense – what remains when a massive star explodes into a supernova. Jets from such stars appear in a generally observed pattern of objects, where the very dense neutron star is associated with another star and gravitational pulls on the other star. Material flowing from the other star forms a disc around the neutron star. The jets are seen perpendicular to the disc, propelled outward by a mechanism still unknown at the speed of light.

Jakob van den Eijnden, of the University of Amsterdam, is the first author of the new study published in the peer-reviewed journal. Nature. He said:

We have seen jets from all types of neutron stars that extract material from their companions, with one exception. We have never seen a jet coming from a neutron star with a very strong magnetic field before.

This led to a theory that strong magnetic fields prevent the formation of jets.

Now this theory needs to be revised.

The scientists said:

… studied an object called Swift J0243.6 + 6124 (Sw J0243), discovered on October 3, 2017 by the observatory in orbiting Neil Gehrels of NASA, when the object emitted a burst of X-rays. object is a slowly rotating neutron star pulling the material of an associated star that is probably much more massive than the sun.

VLA observations began a week after the discovery of Swift and continued until January 2018.

Both the fact that X-ray emission and radio wavelengths have weakened over time, and the characteristics of the radio show convinced astronomers that they saw radio waves produced by a radio. jet.

Van den Eijnden said:

This combination is what we see in other jet production systems. Alternative mechanisms do not explain it.

Current theories on jet formation in systems such as Sw J0243 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. Van den Eijnden said:

Our clear discovery of a jet in Sw J0243 refutes this longstanding idea.

Or, there is another possibility:

… Scientists suggest that the launch region of Sw J0243's accretion jet could be much farther away than in other types of systems, where the magnetic field of the star is weaker.

According to another idea, the jets can be fed by the rotation of the neutron star, instead of being launched by magnetic field lines in the internal accretion disk.

Nathalie Degenaar, also from the University of Amsterdam, said:

It is interesting to note that the idea of ​​rotational feeding predicts that the jet will be much smaller compared to slower rotating neutron stars, which is exactly what we see in Sw J0243.

The new discovery also implies that Sw J0243 could represent a large group of objects whose radio emission was too weak to be detected until new features provided by the VLA's major update, completed in 2012, are available. If more of these objects are found, the scientists said they could test the idea that the jets are produced by the neutron star.

Astronomers have added that a jet of SwJ0243 could mean that another category of objects, called ultra-bright X-ray pulsars, also highly magnetized, could produce jets. Degenaar said:

This discovery not only means that we need to revisit our ideas about the throws of these systems, but also opens exciting new areas of research.

Bottom line: Astronomers have theorized that strong magnetic fields prevent jets from forming. They then studied an object called Swift J0243.6 + 6124 (Sw J0243) – a highly magnetized neutron star – with a jet.

Via NRAO

Source: A scalable jet from a highly magnetic boosting X-ray pulsar