About 2,700 light years away from Earth, an incredibly rare event is occurring: a white dwarf and brown dwarf are closely orbiting each other in less than an hour and a half.

The white dwarf, which scientists are calling WD 1202-024, was discovered in 2006. WD 1202 became a white dwarf about 50 million years ago when it ran out of usable hydrogen in its core. When a study showed WD 1202 having a consistent change in brightness, astronomers assumed the white dwarf was a variable star. While studying what caused the change in brightness, astronomers were surprised to find that its actually caused by a companion brown dwarf.

The pair is only separated by about 192,625 miles (310,000 kilometers), which is closer than the Moon is to Earth. The white dwarfs gravity is so strong and so fast 62 miles (100 kilometers) per second that it pulls the brown dwarf into an orbit that is completed every 71 minutes.

The brown dwarf, like all brown dwarfs, is too big to be considered a planet, but not big enough to sustain nuclear fusion. This brown dwarf is 67 times the mass of Jupiter and about the equivalent diameter. Because white dwarfs are small husks of former stars, its also wider (though not as massive) as its home dead star. Since its so much bigger than the white dwarf it blocks the light from us when it passes by it.

WD 1202 burns at a scorching 40,352 Fahrenheit (22,000 Celsius), making it bright enough to see, while the brown dwarf is too faint to be seen without the help of its white dwarf companion.

Astronomers believe the brown dwarf was inside WD1202 about 50 million years ago when WD 1202 expanded to become a red giant, becoming bigger than the brown dwarfs orbital distance and engulfing the entire brown dwarf. But the brown dwarf survived when the density of the gas in the red giants outer layers dropped while it expanded, saving the brown dwarf from becoming so hot that it shrunk its orbit.

The brown dwarf is orbiting so closely to WD 1202 that its slowly getting drawn into its host star. Astronomers believe in about 250 million years the brown dwarf will get so close that the white dwarfs gravity will draw material from the brown dwarf and eventually end up a type 1a supernova when theres enough material mixed with intense gravity and the white dwarf will go through sudden catastrophic fusion and explode with a flare in brightness over the system, before cooling and dimming again, to repeat all over again in years to come.

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This brown dwarf used to be inside its white dwarf companion. - Astronomy Magazine