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Magnetars are neutron stars with extremely strong magnetic fields, created when a supergiant star collapses as a supernova. They produce X-ray pulses and gamma rays, and their magnetic fields can cause starquakes and birefringence. The magnetic field strength is up to 100 gigatesla, and can wipe out credit cards on Earth. Their lifetimes are short, and only nine are known in our galaxy.
A magnetar is a type of supernova remnant; specifically, a neutron star with an extremely strong magnetic field. Magnetars underlie observed astronomical phenomena such as soft gamma repeaters and anomalous X-ray pulsars. Voltages in the crust of the magnetar periodically cause “starquakes” and release electromagnetic radiation in the form of X-rays, producing pulses approximately every ten seconds that can be observed by astronomers on Earth. Gamma rays are also released at irregular and longer intervals.
Magnetars are created when a supergiant star runs out of nuclear fuel and catastrophically collapses as a supernova. To produce a magnetar, the star must have a high rotational speed and magnetic field before collapsing. This only happens in about 1 in 10 cases. Depending on the mass of the star, a neutron star or black hole remains as a supernova remnant.
If the supergiant star rotates very rapidly as it collapses, and is not as massive, collapses into a black hole, an intense natural dynamo is created within the resulting neutron star. If the neutron star rotates fast enough to keep up with the convection period (about once every ten milliseconds), the convection currents are able to operate globally, transferring a significant amount of kinetic energy to a magnetic field . This is the same principle of operation as electric generators, which spin a coiled wire in the presence of a magnetic field to generate electricity. Most of the field building is thought to occur in the first 10 seconds of the neutron star being created.
Through this mechanism, the already impressive magnetic field strength of a typical neutron star, 108 tesla, is increased to 1011 tesla. By comparison, the strength of the Earth’s magnetic field is 30-60 microtesla. The magnetic field strength of a neodymium magnet is approximately 1 tesla, with a magnetic energy density of 4.0 x 105 J/m3. Meanwhile, a magnetar can have a magnetic energy density of up to 100 gigatesla, an energy density of 4.0 x 1016 J/m3, with a mass density E/c2 >105 times that of lead.
A magnetar’s space-bending magnetic field doesn’t last long in astronomical terms — only about 10,000 years, then declines to that of an average neutron star. At this point, their starquakes and gamma-ray emission behaviors cool off. Given their short lifetimes, we only see nine magnetars in our galaxy.
The magnetic field generated by a magnetar is truly astounding. Its magnetic field is so strong that a magnetar 160,000 km (100,000 mi) away could wipe out every credit card on Earth. At less than 1,000km away, the magnetar could tear apart flesh, due to the brief magnetic fluctuations within its water molecules. Near the magnetar, X-rays and other electromagnetic radiation split in two or merge. This phenomenon can be observed in a calcite crystal and is called birefringence. Matter itself is stretched: At a field strength of 105 tesla, an atomic orbital will deform into a cigar-like shape. At 1010 tesla, the hydrogen atoms become like pieces of spaghetti 200 times narrower than their normal diameters.
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