A PROJECT to map the distant cosmos has turned up a surprise much closer to home: the giant remains of a star, glowing in our own galactic backyard. It is by far the biggest planetary nebula we can see from Earth.
A planetary nebula forms when a star like the sun reaches the end of its life. As its core runs out of fuel, the star鈥檚 outer atmosphere puffs out into space to form a ghostly glowing cloud, and the core shrinks to a white dwarf.
Paul Hewett of the University of Cambridge and his colleagues analysed observations from the Sloan Digital Sky Survey, a mammoth celestial mapping project. They found a huge planetary nebula in the constellation Sextans 鈥� now dubbed Hewett 1 鈥� that appears twice as wide as the sun in the sky (Astrophysical Journal Letters, vol 599, p 37).
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Hewett 1 is either our closest or second closest planetary nebula, lying roughly 450 light years away. It lacks the elegant symmetry of the Twin Jet nebula (pictured); Hewett describes it as 鈥渁 mess鈥�. But it is a unique find because it formed around a helium-rich type of white dwarf never seen with a planetary nebula before.
The finding could help explain why planetary nebulae form. 鈥淲e don鈥檛 really understand in detail why a star decides to hiccup off its outer atmosphere,鈥� says Hewett.