An example of the artist’s impression of a white dwarf—in this image, the MV Lyrae a white dwarf—is accumulated because the material comes from the co-star. Credit: Helena Uthas
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Astronomers use planet-hunting satellites to see a
Researchers led by Durham University in the UK used
TW Pictoris is a relatively bright binary system in which white dwarfs accumulate matter from companion stars. Observations made using the Transiting Exoplanet Survey Satellite (TESS) revealed how TW Pictoris suddenly faded away in less than 30 minutes. The image shows how TESS observations reveal this transition from a bright mode marked in blue to a dim mode marked in red. Credit: Simon Scaringi
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The team observed the phenomenon in the binary system of the white dwarf, TW Pictoris, which was discovered about 1,400 light-years from Earth.
TW Pictoris consists of a white dwarf fed by an oceanic accretion disk fed by hydrogen and helium from its smaller companion star. When a white dwarf eats – or accumulates – it gets brighter.
Using the finer details of observations provided by TESS – which is often used to search for planets outside our solar system – the team led by Durham saw unprecedented decreases and increases in brightness in white dwarfs accreting in such a short span of time.
Since the flow of matter on the white dwarf’s accretion disk from its companion star is relatively constant, it should not significantly affect its luminosity over a short period of time.
Instead, the researchers believe that what they are witnessing could be a remodeling of the white dwarf’s surface magnetic field.
The Fully Integrated Transiting Exoplanet Survey Satellite (TESS), launched in 2018 to find thousands of new planets orbiting other stars. Researchers led by the University of Durham in the UK used TESS to observe the binary system of the white dwarf TW Pictoris. Credit: Orbital ATK / NASA
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During the operation mode, when the brightness is high, the white dwarf feeds from the accumulator disk as usual. Suddenly and suddenly the system shuts down and the brightness decreases.
When this happens, the researchers say, the magnetic field rotates so fast that a centrifugal barrier prevents the fuel from the accretion disk from falling continuously on the white dwarf.
NASA’s Transiting Exoplanet Survey Satellite (TESS) has flown inside the Payload Hazardous Services Facility at the Kennedy Space Center in Florida. Credit: NASA/Frankie Martin
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During this stage, the amount of fuel the white dwarf can eat is regulated by a process called magnetic gates.
In this case, the white dwarf’s rotating magnetic field regulates the passage of the fuel through the “gate” on the accretion disk, resulting in a small, semi-regular increase in brightness that is visible to astronomers.
After some time, the system “turns on” intermittently, and the brightness increases again to its original level.
Lead author Dr Simon Scaringi, from the Center for Extragalactic Astronomy at the University of Durham, UK, said: “The brightness differences observed in white dwarf accretion are generally relatively slow, occurring over time spans ranging from days to months.
“Seeing a 30-minute decrease in brightness of TW Pictoris is in itself unusual as it has never been seen in any other accretionary white dwarf and was completely unexpected from our understanding of how this system is fed by the accretion disk. It seems to turn on and off.”
“This is truly an unprecedented phenomenon and because we can make comparisons with similar behavior in much smaller neutron stars, it may be an important step in helping us better understand the process by which other accretionary organisms feed on that material. surround them and the important role of magnetic fields in this process”.
Since white dwarfs are more common in the universe than neutron stars, astronomers hope to look for other examples of this behavior in future research projects to learn more about accretion.
Reference: “Accumulated white dwarf displays quick switch in transition mode” Oct 18, 2021, natural astronomy.
DOI: 10.1038 / s41550-021-01494-x
This UK research was funded by Durham University. The research team also included Italy’s National Institute of Astrophysics, South African Astronomical Observatory, University of Cape Town and Free State University, both also South Africa, Radboud University, Netherlands, University of Southampton, UK, and University of Notre Dame, USA.
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