Royal Astronomical Society | 2018 Nov 07
Solving a decades-old mystery, an international team of astronomers have discovered an extremely hot magnetosphere around a white dwarf, a remnant of a star like our Sun. ...
White dwarfs are the final stage in the lives of stars like our Sun. At the end of its life, these stars eject their outer atmospheres, leaving behind a hot, compact and dense core that cools over billions of years. The temperature on their surfaces is typically around 100,000 degrees Celsius (in comparison the surface of the Sun is 5500 degrees).
Some white dwarfs though challenge scientists, as they show evidence for highly ionised metals. In astronomy ‘metals’ describe every element heavier than helium, and high ionisation here means that all but one of the outer electrons usually in their atoms have been stripped away. That process needs a temperature of 1 million degrees Celsius, so far higher than the surface of even the hottest white dwarf stars.
Reindl’s team used the 3.5-metre Calar Alto telescope in Spain to discover and observe a white dwarf in the direction of the constellation of Triangulum, catalogued as GALEX J014636.8+323615, located 1,200 light-years from the Sun. Analysing the light from the white dwarf with a technique known as spectroscopy, where the light is dispersed into its constituent colours, revealed the signatures of highly ionised metals. Intriguingly these varied over a period of six hours -- the same time it takes for the white dwarf to rotate.
Reindl and her team conclude that the magnetic field around the star -- the magnetosphere -- traps material flowing from its surface. Shocks within the magnetosphere heat the material dramatically, stripping almost all the electrons from the metal atoms. ...
Unravelling the Baffling Mystery of the Ultra-hot Wind Phenomenon in White Dwarfs ~ Nicole Reindl et al
- Monthly Notices of the RAS: Letters 482(1):L93 (Jan 2019) DOI: 10.1093/mnrasl/sly191