Huge White Dwarf Magnetic Fields

Illustration of the origin of magnetic fields in white dwarfs in shut binaries (to be learn counter clockwise). The magnetic discipline seems when a crystallizing white dwarf accretes from a companion star and as a consequence begins to spin quickly. When the white dwarfs discipline connects with the sphere of the secondary star, mass switch stops for a comparatively brief interval of time. Credit: Paula Zorzi

  • University of Warwick astronomer co-authors new research in Nature Astronomy that proposes an answer to long-running query of how white dwarf stars generate magnetic fields
  • A dynamo mechanism, comparable to how Earth generates its magnetic discipline, might be the reply
  • This analysis reveals that typically very comparable mechanisms can work in very totally different astronomical objects.

A dynamo mechanism may clarify the extremely robust magnetic fields in white dwarf stars in accordance to a global crew of scientists, together with a University of Warwick astronomer.

One of probably the most putting phenomena in astrophysics is the presence of magnetic fields. Like the Earth, stars and stellar remnants akin to white dwarfs have one. It is understood that the magnetic fields of white dwarfs generally is a million occasions stronger than that of the Earth. However, their origin has been a thriller because the discovery of the primary magnetic white dwarf within the Nineteen Seventies. Several theories have been proposed, however none of them has been in a position to clarify the totally different incidence charges of magnetic white dwarfs, each as particular person stars and in numerous binary star environments.

This uncertainty could also be resolved thanks to analysis by a global crew of astrophysicists, together with Professor Boris Gänsicke from the University of Warwick and led by Professor Dr. Matthias Schreiber from Núcleo Milenio de Formación Planetaria at Universidad Santa María in Chile. The crew confirmed {that a} dynamo mechanism comparable to the one which generates magnetic fields on Earth and different planets can work in white dwarfs, and produce a lot stronger fields. This analysis, part-funded by the Science and Technology Facilities Council (STFC) and the Leverhulme Trust, has been printed within the prestigious scientific journal Nature Astronomy.

Crystallizing Magnetic White Dwarf

A crystallizing magnetic white dwarf accreting from the wind of its companion star. Credit: Paula Zorzi

Professor Boris Gänsicke of the Department of Physics on the University of Warwick mentioned: “We have known for a long time that there was something missing in our understanding of magnetic fields in white dwarfs, as the statistics derived from the observations simply did not make sense. The idea that, at least in some of these stars, the field is generated by a dynamo can solve this paradox. Some of you may remember dynamos on bicycles: turning a magnet produces electric current. Here, it works the other way around, the motion of material leads to electric currents, which in turn generate the magnetic field.”

According to the proposed dynamo mechanism, the magnetic discipline is generated by electrical currents brought on by convective movement within the core of the white dwarf. These convective currents are brought on by warmth escaping from the solidifying core.

“The main ingredient 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 in white dwarfs when they have cooled sufficiently,” explains Matthias Schreiber.

The astrophysicist explains that initially, after the star has ejected its envelope, the white dwarf may be very sizzling and composed of liquid carbon and oxygen. However, when it has sufficiently cooled, it begins to crystallize within the middle and the configuration turns into comparable to that of the Earth: a strong core surrounded by a convective liquid. “As the velocities in the liquid can become much higher in white dwarfs than on Earth, the generated fields are potentially much stronger. This dynamo mechanism can explain the occurrence rates of strongly magnetic white dwarfs in many different contexts, and especially those of white dwarfs in binary stars” he says.

Thus, this analysis may resolve a decades-old drawback. “The beauty of our idea is that the mechanism of magnetic field generation is the same as in planets. This research explains how magnetic fields are generated in white dwarfs and why these magnetic fields are much stronger than those on Earth. I think it is a good example of how an interdisciplinary team can solve problems that specialists in only one area would have had difficulty with,” Schreiber provides.

The subsequent steps on this analysis, says the astrophysicist, are to carry out a extra detailed mannequin of the dynamo mechanism and to take a look at observationally the extra predictions of this mannequin.

Reference: “The origin and evolution of magnetic white dwarfs in close binary stars” by Matthias R. Schreiber, Diogo Belloni, Boris T. Gänsicke, Steven G. Parsons and Monica Zorotovic, 29 April 2021, Nature Astronomy.
DOI: 10.1038/s41550-021-01346-8

The analysis additionally obtained assist via an STFC Ernest Rutherford Fellowship.

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