The magnetic field of white dwarfs and the Earth is created by one dynamo mechanism

One of the most striking phenomena in astrophysics is the presence of magnetic fields. Like Earth, stars and stellar

remnants such as white dwarfs have onlyone magnetic field. It is known that the magnetic fields of white dwarfs can be a million times stronger than those of the Earth. However, their origin has remained a mystery since the discovery of the first magnetic white dwarf in the 1970s. Several theories have been proposed, but none have been able to explain the varying frequencies of magnetic white dwarfs, both as individual stars and in different binary star environments.

This uncertainty can be resolvedthanks to research by an international group of astrophysicists. Thus, it was discovered that a dynamo mechanism similar to the one that generates magnetic fields on Earth and other planets can also work in white dwarfs and create much stronger fields.

“We have long known that in our understandingThe magnetic fields of white dwarfs were missing something because the statistics derived from observations simply did not make sense. The idea that in at least some of these stars the field is generated by an electric current generator may resolve this paradox. Some of you may remember dynamos on bicycles: rotating a magnet produces an electric current. Here everything works the other way around: the movement of the material gives rise to electric currents, which in turn create a magnetic field.”

Professor Boris Hansicke, University of Warwick

According to the proposed dynamo mechanism,the magnetic field is created by electric currents caused by convective motion in the core of the white dwarf. These convective currents are caused by the release of heat from the solidifying core. The main component of the dynamo is a solid core surrounded by a convective mantle, in the case of the Earth, it is a solid iron core surrounded by convective liquid iron. A similar situation occurs with white dwarfs when they have cooled down enough.

In the beginning, after the star has thrownenvelope, the white dwarf is very hot and consists of liquid carbon and oxygen. However, when it cools enough, it begins to crystallize at the center, and the configuration becomes similar to that of the Earth: a solid core surrounded by convective fluid. Since the velocities in liquids can become much higher in white dwarfs than on Earth, the fields generated are potentially much stronger. This dynamo mechanism could explain the frequency of occurrence of highly magnetic white dwarfs in many different contexts, especially white dwarfs in binary stars.

The mechanism for generating the magnetic field is the same asand on the planets. This study explains how magnetic fields are generated in white dwarfs and why these magnetic fields are much stronger than on Earth. The next steps in this study will be the implementation of a more detailed model of the dynamo mechanism and experimental verification of additional predictions of this model.

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