A pulsar orbits about 22,000 light-years from Earth, and its magnetic field dwarfs everything known so far. Its field strength is 1.6 billion Tesla – for comparison: A commercially available horseshoe magnet achieves 0.1 Tesla, a powerful MRI 3 Tesla. A working group led by Ling-Da Kong from the Chinese Academy of Sciences made the extraordinary measurement with the help of subtle changes in the neutron star’s strong X-ray emission, as she writes in the »Astrophysical Journal Letters«.
Swift J0243.6+6124 is a binary star system discovered in 2017 as the cause of a burst of radiation of extreme brightness and energy. Analyzes revealed that the neutron star is an ultra-luminous pulsar: the only X-ray source in our galaxy that falls into this category of ultra-bright sources. Previous theses suggested that they must have equally strong magnetic fields. Swift J0243.6+6124 is also the only example in the Milky Way of an X-ray pulsar with a companion star feeding it fast enough matter to produce jets of radio-emitting matter from its poles.
To study the pulsar more closely, the team pointed the Chinese X-ray telescope Insight-HXMT in its direction. The data showed a prominent absorption line in the X-ray spectrum of the pulsar radiation in the energy range of 146 kiloelectronvolts. In addition, it showed characteristic features of a so-called cyclotron resonance scattering. It occurs when electrons are extremely scattered and accelerated in a celestial body’s magnetic field. If they encounter X-rays, they absorb certain parts of this radiation. From the energy that occurs at this absorption line, one can derive the magnetic field strength in the vicinity of the pulsar.