A White Dwarf Was Observed 'Switching On and Off' for the First Time

And something might be interfering with its food supply.
Chris Young
An artist's impression of a white dwarf.Helena Uthas/Durham University

Astronomers from Durham University in the United Kingdom observed a dying star, also known as a white dwarf, abruptly flicker as it slowly fades away in the night sky, a press statement revealed.

The event "has never been seen in other accreting white dwarfs," explained Simone Scaringi, an astronomer at Durham University's Centre for Extragalactic Astronomy and the lead author on a study detailing the observation. "It appears to be switching on and off."

When a star gets to the final phase of its life cycle, it usually becomes a white dwarf, a type of star that is typically approximately the size of the Earth but with a mass comparable to the Sun.

While analyzing data from NASA's Transiting Exoplanet Survey Satellite, or TESS, the Durham University astronomers made a world-first observation of a white dwarf losing brightness in only 30 minutes. The fastest time scientists had previously observed a white dwarf lose its brightness was over a period of several days. The white dwarf in question is accreting, or feeding, off of an orbiting companion star and the Durham University astronomers say this is at the heart of the event behind the unprecedented observation.

Cutting off a white dwarf's food supply

Accreting white dwarfs are affected in several ways by the amount of material on which they feed. The bright reactions caused by the accretion process are highly visible through advanced telescopes and can teach us a great deal about some of the oldest celestial objects in the night sky. This week, for example, we also reported on a white dwarf that rotates once every 25 seconds due to the effects of a neighboring red dwarf.

For the new observation, the Durham University researchers believe that something may be interfering with the "food supply" of the white dwarf they observed, which in turn affected the brightness of the dying star. The astronomers observed a white dwarf binary system about 1,400 light-years away, called TW Pictoris, abruptly rise and fall in brightness over short periods. They believe the shift in brightness might be caused by reconfigurations of the white dwarf's surface magnetic field. When the white dwarf is "off", the magnetic field is spinning so quickly that it causes a centrifugal barrier, stopping the fuel from its neighboring star. 

"This really is a previously unrecognized phenomenon," said Scaringi, "and because we can draw comparisons with similar behavior in the much smaller neutron stars it could be an important step in helping us to better understand the process of how other accreting objects feed on the material that surrounds them and the important role of magnetic fields in this process."

The researchers, who published their article in the journal Nature Astronomy, hope their new observation will help them learn more about the phenomenon of accretion, where objects such as black holes and white dwarfs feed on colossal amounts of surrounding materials from nearby stars in cataclysmic events that are observable from thousands of light-years away. 

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