Key Takeaways:
- Astronomers observed a white dwarf star that flickers on and off in just 30 minutes to an hour.
- This rapid fluctuation is unexpected because white dwarfs typically change brightness over days or months.
- The culprit is likely the white dwarf’s rapidly reconfiguring magnetic field, which disrupts the flow of material from its companion star.
- This “magnetic gating” phenomenon is a new discovery and could help us understand how magnetic fields affect feeding in other objects like neutron stars.
- The white dwarf is part of a binary system called TW Pictoris, located 1400 light-years from Earth.
In a recent cosmic phenomenon, astronomers have observed a white dwarf star that exhibits “off and on” behavior, with its brightness fluctuating between 30 minutes to an hour.
Based on data from a NASA spacecraft looking for extraterrestrial planets, the discovery was hailed as “extraordinary” by a group of Durham University astronomers and their international collaborators.
They didn’t anticipate the cause to be as special as it turned out to be; at first, they thought that the fluctuations were something interfering with the white dwarf’s ability to consume energy from a companion star as it is a part of a binary system.
Given that the movement of material from a donor star to the main white dwarf is controlled by gravity, it is unlikely that the star’s luminosity would fluctuate on the short timescales observed.
The surface magnetic field of the white dwarf was rapidly and repeatedly reconfiguring itself, something the researchers had never observed before.
TW Pictoris is a binary system located approximately 1,400 light years from Earth.
The star normally glows brightly into space while its white dwarf is “on,” but occasionally this stops and the star dims, turning “off.”
Although this has happened before, it usually doesn’t happen this quickly.
The reason is that the white dwarf’s exceptionally fast magnetic field is spinning so quickly that it prevents matter from reaching the main star, according to research published in the journal Nature Astronomy.
The Centre for Extragalactic Astronomy at Durham is home to lead author Dr. Simone Scaringi. “The brightness variations seen in accreting white dwarfs are generally relatively slow, occurring on timescales of days to months,” Scaringi said.
“To see the brightness of TW Pictoris plummet in 30 minutes is in itself extraordinary as it has never been seen in other accreting white dwarfs,” he stated.
“In general, the accretion process in accreting white dwarfs is relatively smooth and does not have any short-term ‘gaps’ in brightness variations,” Dr. Scaringi told Sky News.
“What generally happens in these types of systems is that the donor star in orbit around the white dwarf keeps feeding the accretion disk.
“As the accretion disk material slowly sinks closer towards the white dwarf it generally becomes brighter, and eventually makes it onto the white dwarf surface.
“It is known that in some systems the donor stars stops feeding the disk,” he added, although he noted scientists have not yet figured out why this happens, but when it does the disk remains bright for a while as the star “drains” the material that was previously there.
“It then takes the disk about one to two months to drain most of the material, something we saw happen in different accreting white dwarfs,” said Dr. Scaringi.
“The so-called’magnetic-gating’ comes into play once the material has almost completely drained out: the white dwarf’s rotating magnetospheric barrier controls the amount of material that lands on it in ‘fits and starts,’ rather than allowing it to accrete smoothly.
“As it takes months to drain a disk out, seeing TW Pictoris drop in brightness in 30 mins was totally unexpected,” he stated.
“What we think may be happening in TW Pictoris is that instead of the disk being drained out so fast, we are seeing some sort of reconfiguration of the white dwarf magnetic field, which promptly pushes the inner-disk edge outwards, and thus makes it fainter for some time until the disk is able to push back once again,” he said.
Dr. Scaringi declared, “This really is a previously unrecognized phenomenon.”
“Because we can draw comparisons with similar behaviour 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.”
