Polarized X-ray light from a magnetar has been observed for the first time ever and the results have been published in a paper in Science. The X-ray light emitted by this star suggests that it has a solid surface and no atmosphere.
A team of astronomers used data from NASA’s Imaging X-ray Polarimetry Explorer (IXPE) to look at the magnetar 4U 0142+62. This magnetar is 13,000 light-years from Earth in the direction of the Cassiopeia constellation. IXPE measures how much X-ray light is emitted by an object and how that light is directed, or polarized. In general, light is oriented in random directions, but if light is oriented in the same direction it is said to be polarized.
Magnetars are a special type of neutron star. Neutron stars are very dense cores of massive stars at the end of their lives. The cores are left over after these stars have gone supernova and blown off their outer envelopes of material. The big distinction between neutron stars and magnetars are that magnetars have strong magnetic fields. The magnetic fields can be 100-1,000 times stronger than the magnetic fields of normal neutron stars, making them the most powerful magnetic fields in the entire Universe. These strong magnetic fields drive activity, such as the emission of X-rays and periods of erratic bursts and flares that release an immense amount of material and energy. How much energy? In just one second, these stars can emit an amount of energy that is millions of times greater than our Sun emits in one year.
An atmosphere works as a filter, and would preferentially choose one polarization state for light passing through it. The observations show a much lower proportion of polarized light than would be expected if the X-rays passed through an atmosphere. Theoretical models predict this type of polarization if the magnetar has a solid crust surrounded by a strong magnetic field. In the presence of such a strong magnetic field the gas in the atmosphere of the star has likely reached a tipping point and turned into a solid or a liquid. This is known as magnetic condensation. The solid crust of the star is believed to be made up of a lattice of ions, held together by the strong magnetic field.
Source: University College London