Stars not massive enough to go supernova will end up as white dwarfs. These stars are no longer fusing atoms to release light, usually growing dimmer and dimmer over time. However, if they can steal some material, they can increase in brightness once again. Astronomers have now caught one such star brightening before dimming again over the space of 30 minutes.
This first incredible observation comes on the tail of other discoveries of white dwarf stars stealing material and brightening over days or months – but for TW Pictoris, as reported in Nature Astronomy, this accretion process happens in a matter of minutes.
TW Pictoris is located about 1,400 light-years from Earth and its peculiar behavior was discovered thanks to NASA's Transiting Exoplanet Survey Satellite (TESS).
The white dwarf has a companion from which it siphons hydrogen and helium. When it is actively accreting, the white dwarf is "on", becoming brighter. Then suddenly the accretion stops, and the white dwarf accretion turns off.
“The brightness variations seen in accreting white dwarfs are generally relatively slow, occurring on timescales of days to months,” lead author Dr. Simone Scaringi, in the Center for Extragalactic Astronomy, at Durham University, said in a statement.
“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 disk. It appears to be switching on and off.”
Current understanding suggests that the strong magnetic field of such stellar objects is key to regulating accretion. As the white dwarf rapidly spins, the magnetism can act as a gate, stopping some of the material from falling into it for a while.
Accretion processes are not exclusive to white dwarfs. Neutron stars and black holes do it too. But White dwarfs are bigger and more common, so studying accretion in these objects could deliver important insights. Especially, if it is discoveries such as this.
“This really is a previously unrecognized phenomenon 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,” Dr Scaringi continued.
1