White dwarf

White dwarf stars become magnetic with age, new technology told

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We all know that white dwarfs are likely to form only after the stars run out of fuel. At least one in four white dwarfs happens to have the end of their life as a magnetic star. Therefore, magnetic fields are an important part of the physics of the white dwarf. Magnetic analysis of some white dwarfs has found evidence that relates the age of white dwarfs to their magnetism. It is believed that this discovery can help explain the origin and evolution of magnetic fields in white dwarfs.

90 percent of the stars in our Galaxy end up as white dwarfs. Although many of these dwarfs have a magnetic field when this field appears on the surface. Whether it develops during the cooling phase of the white dwarf or its process, is not yet known. Since white dwarfs are dying stars, they also become faint over time as they cool. That’s why more attention is paid to the study of bright white dwarfs that are young and hot.

Heavy white dwarfs are smaller than light white dwarfs, and they are also dimmer. When white dwarfs are selected for observations, younger and less massive stars are selected based on their brightness, and older white dwarfs are ignored. Apart from this, many observations of white dwarfs are done with spectroscopy techniques. These are sensitive to very powerful magnetic fields. Because of this, many magnetic white dwarfs are not studied.

But the sensitivity of spectropolarimetry to magnetic fields is better than spectroscopy. Spectropolarimetry has shown that weak magnetic fields are very common in white dwarfs. Whereas these weak areas cannot be detected through spectroscopy. To conduct a complete spectropolarimetry survey, astronomers from the Armagh Observatory and the University of Western Ontario studied all white dwarfs in a portion of the Giga Catalog together, two-thirds of this portion, about a hundred white dwarfs that had not been previously uncovered. No information or statistics are available.

The researchers made observations using the ISIS Spectrograph and the William Herschel Telescope’s polarimeter and instruments from other telescopes. They found that magnetic fields are rarely found early in the life of white dwarfs. At the time of birth, the feature of this field is not visible separately in white dwarfs. Either it arises later or comes to the surface during cooling.

The researchers also found that the magnetic fields of white dwarfs do not show signs of ohmic fission produced during cooling. But these fields continue to emerge on the surface with the age of the white dwarf. This situation is just opposite to the case of magnetic stars. The strength of the magnetic field rapidly decreases with time. But magnetism in white dwarfs is a completely different phenomenon. In these, the frequency of the magnetic field increases with age. This frequency is related to the mass of the dwarf. This frequency is more visible when the carbon-oxygen core of the star begins to crystallize.

The Dynamo system may explain the weak region of white dwarfs. Compared to the Earth’s magnetic field, the dynamo system can explain a field with a strength of one lakh gauss. But the regions of many white dwarfs with millions of Gauss have been observed. In addition, the dynamo system requires a fast rotation that is not usually seen in white dwarfs. More investigation is needed to resolve this.