A team of astronomers from the University of Durham (England) has discovered, thanks to data from NASA’s TESS satellite (commonly used to hunt planets outside the solar system), a white dwarf that “turns on and off” every 30 minutes , a behavior that previously had only been seen every days or months; never so fast.
The star in question is in the TW Pictoris system , located 1,400 light-years distant from Earth.
Why are these abrupt dips and increases in brightness?
White dwarfs are among the most studied and understood celestial objects in the universe because such an outcome awaits our star in about 5 billion years.
The experts, led by researcher Simone Scaringi at Durham University’s Center for Extragalactic Astronomy, were studying how the white dwarf accumulated material from its companion star when they observed that the brightness of the white dwarf suddenly plummeted. Typically, by devouring hydrogen from its companion star, the star becomes brighter. And because the flow of material into the white dwarf’s accretion disk from its companion star is relatively constant, it shouldn’t dramatically affect its luminosity on such short timescales.
“To see the brightness of TW Pictoris plummet in 30 minutes is in itself extraordinary, as it has never been seen in other accumulating white dwarfs and is totally unexpected from our understanding of how these systems are supposed to feed through the accretion disk, “explains Scaringi in his study published in the journal Nature Astronomy. “It seems to go on and off.”
The satellite allowed the team to see abrupt dips and increases in brightness never before seen in a growing white dwarf in such short periods of time. Astronomers believe that what they are witnessing could be reconfigurations of the magnetic field of the white dwarf’s surface as it incorporates more and more hydrogen. During this phase, the amount of fuel the white dwarf can feed on is regulated by a process called magnetic activation. The magnetic field would rotate so rapidly that a centrifugal barrier would prevent fuel from the accretion disk from constantly falling on the white dwarf, causing these small, semi-regular increases in brightness that astronomers see.
These observations can be a very important step in our understanding of accretion behavior, as white dwarfs are much more common in the universe than neutron stars or black holes.
The Transiting Exoplanet Survey Satellite (TESS) launched in April 2018 and since its launch, it has identified 154 planets , with 4,471 additional candidates, according to NASA. He completed his main mission on July 4, 2020 and is now on an extended mission.
Referencia: Simone Scaringi, An accreting white dwarf displaying fast transitional mode switching, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01494-x. www.nature.com/articles/s41550-021-01494-x