Astronomers catch a white dwarf turning itself on and off for the first time

A white dwarf accreting material from its partner star
(Image credit: NASA/CXC/M.Weiss)

White dwarfs are among the most studied and understood celestial objects in the universe, but they are still capable of surprising us when we least expect it.

Astronomers using NASA's Transiting Exoplanet Survey Satellite (TESS) were studying a white dwarf in a binary star system when they suddenly caught it turning itself "on and off" over the course of as few as 30 minutes.

The researchers, lead by Dr. Simone Scaringi at the Centre for Extragalactic Astronomy, at Durham University, UK, were studying how the white dwarf accreted material – a fancy way of saying gobbling up – from its stellar partner when they observed the brightness of the white dwarf suddenly plummet. The observations were published this week in the journal Nature Astronomy.

"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 and is totally unexpected from our understanding of how these systems are supposed to feed through the accretion disc," Scaringi said. "It appears to be switching on and off."

This kind of shift isn't unusual in other objects like neutron stars, but it is the first time it has been observed in a white dwarf, which makes it especially interesting to astronomers studying the physics of 'accretion'.

Accretion is the process by which vast amounts of material accumulates from a source into a rotating disc around a center of gravity that slowly absorbs the material. Most famously, Saturn's rings are a form of accretion disk, as is the disk surrounding the supermassive black hole in the heart of the galaxy M87, which was the first black hole ever directly imaged back in 2019.

Much like the accretion disk around M87's supermassive black hole, the accretion disk around a white dwarf star also causes it to shine brightly as the rapidly accelerating material on the inner edge of the disk generates radio waves that astronomers are able to detect. It is these radio waves that Scaringi has been studying in order to understand the physics behind this process as it plays out throughout the universe.

"In general the accretion process does not have any short-term 'gaps'," Dr. Scaringi told TechRadar in an email. "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 (for yet unclear reasons)," Dr. Scaringi told us. "When this happens the disk is still bright as it 'drains' material that was previously still 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.

"Once the amount of material has nearly drained out entirely, this is when so-called 'magnetic-gating' acts: the spinning magnetospheric barrier of the white dwarf prevents left-over disk material from simply accreting smoothly, but instead regulates the amount that lands onto the white dwarf in 'fits and starts'. 

"As it takes months to drain a disk out, seeing TW Pictoris drop in brightness in 30 minutes was totally unexpected," Scaringi told us. "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."

These observations may turn out to be a critical step in our understanding of accretion behavior, since white dwarfs are far more common in the universe than neutron stars or black holes, which are also well know but little understood accretors. 

This phenomenon should thus be easier to study around white dwarfs, and since the physics behind accretion are essentially the same as it is with neutron stars and black holes, we should be able to extrapolate what happens around a white dwarf to these more exotic accretors.

"This really is a previously unrecognized phenomenon" Scaringi said, "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."


Analysis: White dwarfs still have secrets to share 

White dwarfs are some of the most common objects in the night sky, even if they are among the tiniest. Usually found at the center of so-called planetary nebulae – a type of smaller nebula that doesn't result from a supernova but rather a gradual shedding of outer material from a dying star – these kinds of stellar corpses are easier to spot and thus study than more elusive neutron stars or black holes.

As such, we know a lot about white dwarfs, but clearly there is even more to learn about them. The processes at work in these remnant cores of dead stars are the product of forces beyond anything we've ever encountered in our own solar system – thankfully – so objects like TW Pictoris are especially interesting for us. 

Studying their environment and how they interact with the space around them can give us real insight into their inner workings, with implications for our own sun, which is one day destined to become a white dwarf some five to eight billion years from now.

How this magnetic gating mechanism works is still a matter of study, but clearly we aren't even close to fully understanding these remarkable objects.

John Loeffler
Components Editor

John (He/Him) is the Components Editor here at TechRadar and he is also a programmer, gamer, activist, and Brooklyn College alum currently living in Brooklyn, NY.

Named by the CTA as a CES 2020 Media Trailblazer for his science and technology reporting, John specializes in all areas of computer science, including industry news, hardware reviews, PC gaming, as well as general science writing and the social impact of the tech industry.

You can find him online on Bluesky @johnloeffler.bsky.social

Read more
Mavic Air 2 Drone over water
Don't panic – those mystery drones over New Jersey might not be so mysterious after all
Beaverlabs TW2
I tried an entry-level AI telescope and all I learned is that tech doesn’t make everything better
Twitter social media application change logo to X. Elon Musk CEO of twitter rebranded Twitter to 'X'. Social media application technology concept.
X is back – here's what we know about the 'massive cyberattack' that caused Twitter to go down multiple times
A woman standing next to a telescope looking up at the moon
How to step up your stargazing game in 2025 on the cheap, according to space experts
Spider-Man next to an RTX 5090 and the DeepSeek logo.
ICYMI: the week's 7 biggest tech stories from DeepSeek rocking the AI world to Garmin's major outage
A look at the Disney Treasure at sea.
'There’s nothing like this in any land-based themed park that’s out there' – a Disney Imagineer on how the Treasure cruise ship's Haunted Mansion Parlor came to be
Latest in Tech
Apple iPhone 16e
Which affordable phone wins the mid-range race: the iPhone 16e, Nothing 3a, or Samsung Galaxy A56? Our latest podcast tells all
The Apple MacBook Air next to the Dyson Supersonic R and new AMD GPU
ICYMI: the week's 7 biggest tech stories from the best tech at MWC to Apple's new iPads and MacBooks
A triptych image featuring the Bose Solo Soundbar 2, Nothing Phone 3a Pro and the Panasonic Lumix S1R II.
5 trailblazing tech reviews of the week: Nothing's stylish, affordable flagship and why you should buy AMD's new graphics card over Nvidia's
The best tech of MWC 2025 examples, including the Nothing Phone 3a Pro, the Nubia Flip 2, and the Lenovo Solar PC
Best of MWC 2025: the 10 top tech launches we tried on the show floor
Toy Fair 2025 Primal Hatch
The 7 best toys we saw at Toy Fair 2025, from a Lego boat to a hatching, robotic dinosaur
ICYMI
ICYMI: the 7 biggest tech stories of the week, from a next-gen Alexa to the new iPhone 16e
Latest in News
Data leak
Hacked Tata Technologies data leaked by ransomware gang
Ryzen 9000 promotional material
AMD's most powerful processor ever actually runs better on Windows 10 than Windows 11
Intel CEO Lip-Bu Tan
Intel reveals its new CEO
The SAG-AFTRA San-Fransisco-North California Local
SAG-AFTRA union and video game industry bargaining group remain at odds as agreements on AI protections still 'frustratingly far apart'
Data center racks with cables and servers
Data centers are being pushed to their limits, but digital twins could help
A collage of Tom Holland's unmasked Spider-Man and Sadie Sink's Max in Stranger Things season 4
Marvel reportedly casts Stranger Things star Sadie Sink in Spider-Man 4, but I don't want her to tackle the roles she's rumored to play