The cosmos is full of strange things, like planets made of diamond, mysterious radio bursts and quasars that shine with the light of 600 trillion Suns. Now astronomers have spotted a bizarre star that may prove to be one of the rarest objects ever, with maybe as few as five or six of them in the galaxy.

The object in question is known as J005311, located in the constellation Cassiopeia about 10,000 light-years from Earth. Found in images from the Wide-field Infrared Survey Explorer (WISE) satellite, J005311 is a bright star nestled inside a gas nebula, which seems to be emitting only infrared radiation and no visible light. That's quite a strange combination, which prompted the team to look into its origins.

By analyzing the spectrum of the radiation coming off the nebula and the star, the team found that the object is even weirder than it appears. It has no hydrogen nor helium, and the star in the center is some 40,000 times brighter than the Sun. Stranger still, it was producing an incredibly strong stellar wind – a zippy 16,000 km (10,000 mi) per second. For reference, the fastest stellar winds coming off hot, huge stars usually top out at about 2,000 km (1,200 mi) per second.

The most likely explanation for all this weirdness is that J005311 is the result of two long-dead stars that merged and reignited. These stars would have been born very Sun-like, but then shrunk and cooled into white dwarfs after they'd burned off all their hydrogen and helium. Only then would they have merged into one white dwarf, which then boosts their mass high enough to kick-start the stellar furnace again, this time fusing heavier elements.

This merged white dwarf accounts for the lack of hydrogen and helium, and the extreme brightness. As for the high-speed winds, it's believed that merged white dwarfs have very strong rotating magnetic fields, which would act like a turbine that accelerates the wind.

But perhaps the most intriguing thing about this object is that it defied the odds to be born in the first place.

"Such an event is extremely rare," says Götz Gräfener, corresponding author of the study. "There are probably not even half a dozen such objects in the Milky Way, and we have discovered one of them."

It turns out that J005311 might not just be rare in space – it's rare in time. The team believes that the two white dwarfs collided only a few thousand years ago – the blink of an eye, cosmically-speaking – and the resulting star probably only has that long left to live. Once it fuses the remaining elements into iron, it will collapse under its own gravity. This will be accompanied by a supernova explosion and leave a neutron star behind at its core.

The research was published in the journal Nature.

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