Artist's impression of a white dwarf. In this image, the white dwarf MV Lyrae is accreting as its draws in material from a partner star. Helena Uthas
Astronomers used a satellite for planet hunting to observe a white dwarf suddenly switching on and off.
Researchers from Durham University in the UK used NASA's Transiting Exoplanet Survey Satellite to observe this unique phenomenon.
After they burn off their hydrogen, white dwarfs are what stars eventually become. They are about the same size as the Earth but have a mass that is closer to the Sun.
The team observed a white dwarf that was accreting from an orbiting companion star.
Astronomers were able to observe the brightness of the object drop in just 30 minutes. This is a phenomenon that was previously only seen in accreting white dwarfs, which can take several days or even months to complete.
The amount of surrounding material that it eats influences the brightness of an accreting White dwarf. Researchers believe something is preventing its food supply.
They hope that the discovery will allow them to learn more about the physics of accretion, where objects such as black holes and white dwarfs feed on surrounding material from nearby stars.
These findings were published in Nature Astronomy.
TW Pictoris, a binary system that is quite bright, where a white dwarf accretes material form a companion star, is very bright. TW Pictoris abruptly and abruptly fades within 30 minutes according to observations made with the Transiting Exoplanet Survey Satellite. This figure shows how TESS observations revealed this transition from a bright blue mode to a faint red mode. Credit: Simone Scaringi
The phenomenon was observed in TW Pictoris, a white dwarf binary system that is located approximately 1,400 light-years from Earth.
TW Pictoris is composed of a white dwarf, which feeds off an accretion disk surrounding it that is fuelled by hydrogen from its smaller companion star. The white dwarf becomes brighter as it eats or accretes.
The Durham-led team observed sudden drops and rises of brightness that were not seen before in an accreting white dwarf. They used the exact observational detail provided by TESS, which is normally used to search for planets beyond our solar system.
The flow of material from the companion star to the white dwarf's disk accretion disc is fairly constant so it shouldn't have a significant impact on its luminosity.
Researchers believe that what they are seeing could be reconfigurations in the white dwarf's magnetic field.
When the brightness is high, when the "on" mode is on, the white dwarf consumes the accretion disc as it would normally. The system abruptly turns off and the brightness drops.
The fully integrated Transiting Exoplanet Survey Satellite, (TESS), was launched in 2018 to discover thousands of planets orbiting other stars. TESS was used by researchers at Durham University in the UK to observe TW Pictoris, a white dwarf binary system. Credit: Orbital ATK/NASA
Researchers believe that this is because the magnetic field spins so fast that the fuel from the disk's accretion disk stops it constantly falling on the white dwarf.
Magnetic gating regulates the amount of fuel that the white dwarf can consume during this phase.
The white dwarf's spinning magnetic field regulates the fuel as it passes through a "gate" onto the accretion disc. This causes semi-regular small brightness increases that are seen by astronomers.
After a while, the system will turn "on" sporadically again and the brightness returns to its original level.
Dr. Simone Scaringi (Center for Extragalactic Astronomy at Durham University, UK) is the lead author. She stated: "The brightness variations in accreting White Dwarfs are generally relatively slow and occur on timescales of days or months.
"Seeing the brightness of TW Pictoris drop in 30 minutes is an extraordinary sight. This is a phenomenon that has not been seen before in any other accreting white dwarfs. It is also completely unexpected given our understanding of how these systems feed through the disk. It seems to be switching between on and off.
NASA's Transiting exoplanet survey satellite (TESS), is being moved within the Payload Hazardous Service Facility at the Kennedy Space Center in Florida. Credit: NASA/Frankie Martin
"This is an amazing phenomenon that was not previously recognized. We can draw parallels with similar behavior in smaller neutron stars. This could help us better understand how other accreting objects interact with the surrounding material and the importance of magnetic fields in this process.
White dwarfs are more common than neutron stars in the Universe, so astronomers plan to search for more examples of such behavior in future research projects in order to learn more about accretion.
The Italian National Institute for Astrophysics, the South African Astronomical Observatory and the University of Cape Town were also part of the research team.
Continue reading Astronomer finds that white dwarfs are magnetic as they age
More information: Simone Scaringi, An Acreting White dwarf that exhibits fast transitional mode switching. Nature Astronomy (2021). www.nature.com/articles/s41550-021-01494-x Journal information: Nature Astronomy Simone Scaringi, An accreting white dwarf displaying fast transitional mode switching,(2021). DOI: 10.1038/s41550-021-01494-x
