Paradoxically, white dwarf stars shrink as they gain in mass

Telescope observations of thousands of slender stars confirm the trend

Telescope observations confirm a strange property of white dwarf stars: when they gain more mass, they retreat.

White dwarfs, the layered nuclei of dead stars, are believed to have this counterintuitive property because they contain a strange material known as degenerate electron gases. The larger a white dwarf, the more its electrons must be squeezed together to create sufficient external pressure to prevent the star from falling under its own weight.

Astronomers have observed evidence of this trend predicted by scientists decades ago by some white dwarfs. Data on thousands of stars shows politics continues with a diverse mass of white dwarfs, Vedant Chandra and colleagues in the Johns Hopkins University report online July 28 on

Understanding how white dwarfs contract as they gain in mass can provide insight into the origin of Type 1a supernovae says astronomer and co-author Hsiang-Chih Hwang. These supernovae are thought to occur when a white dwarf becomes so large and dense that it explodes, but no one knows exactly how white dwarf stars explode (SN: 03/23/16).
The team studied the dimensions and masses of more than 3,000 white dwarf stars observed by the Apache Point Observatory in New Mexico and the European Space Agency’s Gaia Space Observatory. “If you know how far away a star is and how good a star is, you can fully estimate its radius,” says Chandra, an undergraduate physics student. But measuring stars in mass turned out to be more difficult, however, as astronomers typically had to see a white dwarf gravitationally gravitating to another star to get an idea of ​​the white dwarf’s weight.

For the single white dwarf, researchers are studying an effect of the general theory of relativity on starlight, called a gravitational redshift (SN: 07/26/18). When light escapes from a strong gravitational field, such as around a dense white dwarf, its waves are extended to more reddish wavelengths. The greater the mass of a white dwarf in relation to its radius, the greater its length. This property has enabled researchers to estimate the mass of white dwarf stars based on their radii.

The new dimensions of the white dwarf are in close agreement with the theoretical predictions for the smaller dimensions of stronger stars. White dwarfs with about half the mass of the Sun are about 1.75 times the width of the Earth, while those with less mass than the Sun are about 0.75 times the width of the Earth.

It’s exciting to see white dwarfs following the widely anticipated trend of collapse as they gain more mass, says Alejandra Romero, an astrophysicist at the Federal University of Rio Grande do Sul in Porto Alegre, Brazil. Future observations of more white dwarfs will help validate the intricacies of this ray relationship, he says – for example, if white dwarf stars are warmer, according to the predicted theory, they will be modified more than cold stars alike. mass.


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