NASA’s Kepler Space Telescope has observed the flashy process by which a white dwarf is devouring its companion star. Brown dwarfs are sub-stellar objects that failed to sustain hydrogen fusion, warranting the moniker ‘failed stars’. The system observed by astronomers consists of a brown dwarf that orbits the white dwarf star at about 400,000 kms away from the star in 83 minutes. The distance is about as much as the distance between the Moon and the Earth.

The close proximity allows the white dwarf’s strong gravity to gradually strip its companion of the material. This material gravitated towards the star forms a spiral around it - an accretion disk. The white dwarf is about the size of the Earth and has the same mass as our Sun. Its brown companion star is one-tenth the size and weights as much as 10 to 80 Jupiters.

Astronomers have performed a study based on data from the Kepler Space Telescope. Kepler was able to observe a ‘super-outburst’ in the system as the white dwarf consumed its brown companion star. It is theorized that as an accretion disk grows in size, its outer edge undergoes gravitational resonance with the orbiting brown dwarf.

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The resonance gives rise to thermal instability and the disk is superheated from temperatures of about 2,700–5,300° C to 9,700–11,700°C. The temperature rise is accompanied by increasing brightness which was observed by scientists. It is predicted that the brightness increases rapidly but scientists observed a slow start followed by rapid intensification to 1000 times the brightness.

While dwarf nova systems of this kind are rare, such super-outbursts have been observed in two other systems. It might be years before a system undergoes an outburst, making it difficult to observe these in action. The system was coincidentally observed and stored in Kepler’s archives and was then accidentally found by scientists. Lead researcher, Ryan Ridden-Harper explained, “In a sense, we discovered this system accidentally. We weren't specifically looking for a super-outburst. We were looking for any sort of transient.”

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Image Credit: NASA/ L. Hustak (STScI)