New Delhi: NASA has used its Imaging X-ray Polarization Explorer (IXPE) spacecraft to study a white dwarf star for the first time. A white dwarf is the remnant
core of a dead star, that violently shed its outer layers, leaving behind a dense object about the size of the Earth, containing as much mass as the Sun. EX Hydrae is a system with a white dwarf star and a binary companion at a distance of about 200 lightyears from the Earth in the constellation of Hydra. The binary companion of the white dwarf is a main sequence star, that the white dwarf is feeding on.
Here, the white dwarf is accreting material from its binary companion. The hot gas in the outer atmosphere of the main sequence star is falling into the white dwarf because of its gravitational influence. The strength of the magnetic field of the white dwarf determines the accretion process. The white dwarf in the EX Hydrae system does not have a sufficiently strong magnetic field to focus the matter completely at the poles of the star, while still adding mass to the accretion disk, resulting in the classification of an intermediate polar system. The material is forming an accretion disk, while being pulled towards its magnetic poles.
The tortured material glows energetically
The extreme friction and heat of the infalling material causes temperatures to reach millions of degrees, resulting in an outward pressure that restricts the amount of infalling material. This results in large columns of gas that emit energetic X-rays, something that the IXPE instrument is fine-tuned to observe. IXPE was used to determine that the infalling material forms an accreting column 3,200 km high. The detected X-rays are likely to have been scattered by the surface of the white dwarf itself. The observations of EX Hydrae will help scientists better understand energetic binary systems. A paper describing the research has been published in The Astrophysical Journal.
