Stars are known to be huge balls of hot boiling plasma. But recently astronomers discovered one of the stars that is quite unlike anything they have encountered before, its own magnetic field is so strong that its effect is enough to counteract the thermal motion at ultra-high temperatures and "freeze" the outer layers to a solid shell.
This discovery was made by scientists studying data collected by the X-ray observatory IXPE (Imaging X-ray Polarimetry Explorer), whose equipment is capable of measuring the polarization of X-ray photons emitted somewhere far in the depths of space. Recall that polarization is the direction of oscillation of electromagnetic waves, its value contains a lot of additional information about the source of radiation, its nature, etc.
In this case, astronomers have examined data relating to the magnetar 4U 0142 + 61, located at a distance of 13 thousand light-years in the constellation Cassiopeia. A magnetar is a type of neutron star that has its own strongest magnetic field.
Analysis of the data revealed something unusual. Scientists had expected that magnetar 4U 0142+61, like other magnetars, would be surrounded by an atmosphere that polarizes radiation in a certain direction. However, such polarization was not observed, indicating the complete absence of an atmosphere.
And what is even stranger is that at higher X-ray energies, the polarization angle changed sharply by 90 degrees. Such a signal would be expected if the magnetar had a solid surface surrounded from the outside by a strong magnetic field. Such a solid shell would be a crystal lattice of ions held together not by interatomic chemical bonds, but by an external magnetic field.
"This was completely unexpected," the scientists write, "We expected the magnetar to have an atmosphere. But under the influence of the magnetic field, the gas overcame a critical point and solidified, just as water turns into ice."
Scientists admit that the anomalies they observe may have other explanations, but the solid surface of the magnetar is the most suitable and viable hypothesis. And in their future research, scientists will pay close attention to how temperature and magnetic field strength affect the changing nature of the surface of neutron stars.