Astronomers Use Planet-Hunting Satellite To See White Dwarf “Switch On and Off” for First Time - SciTechDaily

An artist’s impression example of a white dwarf – in this image the white dwarf MV Lyrae – accreting as it draws in material from a companion star.

The white dwarf observed by the team is known to be accreting, or feeding, from an orbiting companion star.

With the new observations, astronomers saw it lose brightness in 30 minutes, a process only previously seen to occur in accreting white dwarfs over a period of several days to months.

The brightness of an accreting white dwarf is affected by the amount of surrounding material it feeds on so the researchers say something is interfering with its food supply.

They hope the discovery will help them learn more about the physics behind accretion – where objects like black holes, white dwarfs, and neutron stars feed on surrounding material from neighboring stars.

TW Pictoris is a relatively bright binary system where a white dwarf accretes material from a companion star.

TW Pictoris consists of a white dwarf that feeds from a surrounding accretion disc fuelled by hydrogen and helium from its smaller companion star.

As the white dwarf eats – or accretes – it becomes brighter.

Using the precise observational detail offered by TESS – normally used to look for planets outside our solar system – the Durham-led team saw abrupt falls and rises in brightness never before seen in an accreting white dwarf on such short timescales.

Because the flow of material onto the white dwarf’s accretion disc from its companion star is relatively constant it should not drastically affect its luminosity on such short timescales.

Researchers led by Durham University, UK, used TESS to observe the white dwarf binary system TW Pictoris.

During the “on” mode, when the brightness is high, the white dwarf feeds off the accretion disc as it normally would.

The researchers say that when this happens the magnetic field is spinning so rapidly that a centrifugal barrier stops the fuel from the accretion disc from constantly falling onto the white dwarf.

In this case, the spinning magnetic field of the white dwarf regulates the fuel passing through a “gate” onto the accretion disc, leading to semi-regular small increases in brightness seen by the astronomers.

Simone Scaringi, in the Centre for Extragalactic Astronomy, at Durham University, UK, said: “The brightness variations seen in accreting white dwarfs are generally relatively slow, occurring on timescales of days to months.

“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.

As white dwarfs are more common in the Universe than neutron stars, the astronomers hope to look for other examples of this behavior in future research projects to learn more about accretion.