WD 0137-349

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WD 0137-349 is a binary star 300 light years from Earth. It is composed of a white dwarf and a brown dwarf in orbit about it. The orbital period is 2 hours. The orbit of the brown dwarf is slowing decaying.

It is thought that the red giant phase of the current white dwarf was dramatically shortened from around 100 million years on average, to a few decades, because of the actions of the brown dwarf. The brown dwarf was swallowed into the envelope of the red giant, and hastened the expulsion of matter during this phase by rapidly heating gas and accreting a portion of it. During this phase, the gas drag also decreased the orbit of the brown dwarf.

In about 1.4 billion years, it is thought that the orbit of the brown dwarf will have decayed sufficiently to allow the white dwarf to draw matter away and accrete it on its surface, leading to a recurrent nova. If sufficient mass can be accumulated from the brown dwarf, a Type Ia supernova may destroy both stars.

As of 2006, this brown dwarf is the smallest object known to survive being engulfed by a red giant phase. Previously, only red dwarfs had been known to survive being enveloped during a red giant phase. It is thought that objects smaller than 20 Jupiter masses would have evaporated.