Astronomers see white dwarf switch on and off

White dwarfs are what most stars become after burning off the hydrogen that fuels them. Now our astronomers have seen one of these galactic objects switching on and off for the first time.

Researchers used a planet-hunting satellite to observe the unique phenomenon in a white dwarf about 1,400 light years from Earth.

This particular white dwarf is known to be accreting, or feeding, from an orbiting companion star.

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

Accreting white dwarf
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 believe what they're witnessing could be changes to the white dwarf's surface magnetic field.

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

Suddenly and abruptly the system turns "off" and its brightness plummets.

Magnetic gating
The researchers say that when this happens the magnetic field is spinning so rapidly it creates a barrier disrupting the amount of food the white dwarf can receive - a process called magnetic gating.

This leads to semi-regular small increases in brightness seen by the astronomers. After some time, the system sporadically turns "on" again, and the brightness increases back to its original level.

They hope their discovery will teach us more about the physics behind accretion - where objects like black holes, white dwarfs and neutron stars feed on surrounding material from neighbouring stars.

Research paper

Related Links
Durham University
Stellar Chemistry, The Universe And All Within It

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