Neutron stars are stellar corpses, the extraordinarily dense remains of supernovae. They are complicated, extreme objects and there is a lot that we don’t know about them. Some assumptions we have made have turned out to be incorrect, as a new study demonstrates.
So far astronomers have observed neutron stars producing jets of material only if their magnetic field has been relatively weak, so it was thought that in the most magnetic of these objects material would never get close enough to the star to be propelled into a jet. But new observations, reported in Nature, challenge that idea. An international team of researchers has observed a highly magnetized neutron star producing a jet.
"The magnetic field of the neutron star we studied is about 10 trillion times stronger than that of our own Sun, so for the first time ever, we have observed a jet coming from a neutron star with a very strong magnetic field," lead author Jakob van den Eijnden, from the University of Amsterdam, said in a statement. "The discovery reveals a whole new class of jet-producing sources for us to study."
The object in question is called Swift J0243.6+6124 and was studied in both radio waves, using the Karl G. Jansky Very Large Array (VLA) radio telescope in New Mexico, and X-rays, using NASA’s Swift space telescope. The observations showed that the jet is much fainter than those of other neutron stars. This was only spotted thanks to the new capabilities of the VLA. The researchers suggest that the weakness indicates that the properties of the neutron star play a crucial role in regulating these jets.
It's still unclear what exact mechanism powers the jets. Material from the surrounding environment is captured and then ejected. Most of the time this material comes from a companion star, slowly being pulled apart by the intense gravity of a neutron star or a black hole. Jets are also produced by supermassive black holes and can stretch for millions of light-years.
"Jets play a really important role in returning the huge amounts of gravitational energy extracted by neutron stars and black holes back into the surrounding environment," added study co-author Associate Professor James Miller-Jones, from Curtin University. "Finding jets from a neutron star with a strong magnetic field goes against what we expected, and shows there's still a lot we don't yet know about how jets are produced."
Swift J0243.6+6124 is known as an ultra-luminous X-ray pulsar and the team suspects that many objects in this category could share faint jets like the one just discovered.