An aging star that spits water into space could provide astronomers the clues they need to explain the formation of planetary nebulae, the cloudy remnants of a star's death.
The star, called W43A, is spewing water molecules from a pair of jets as it nears the end of its stellar lifetime. Astronomers believe W43A is on the cusp of forming a planetary nebula, a shell of brightly glowing gas blown off from the outer atmospheres of a star before it dies. A star like the Sun collapses into a dense white dwarf, about the size of the Earth, illuminating the gas around it. Although some nebulae retain the spherical shape of their parent star, most do not.
"The problem for scientists is, how do you get from a star we know is a sphere to a planetary nebula, that is far from being a sphere, yet came from that star," said research team leader Hiroshi Imai, of Japan's National Astronomical Observatory.
The name planetary nebula is a bit of a misnomer, as the object is the product of stars not planets. They were first observed by the French astronomer Charles Messier in 1764, and later named by Uranus-discoverer Sir William Herchel, who thought the nebulae appeared similar to Uranus in the telescope. The name stuck and about 1,600 planetary nebulae have been observed, with many more thought to exist throughout the Milky Way. Astronomers have long known that the intricate, often beautiful structures of nebulae are not spherical, a fact reinforced by Hubble Space Telescope observations in 1997.
The waterspouts observed by Imai and his team bolster theories suggesting that planetary nebulae form from jets of material spat out of old stars. The existence of such jets was never seen until the W43A study, which used the Very Long Baseline Array - a collection of 10 radio telescopes across the United States and Virgin Islands - to make observations. Imai's findings will appear in the June 20 issue of the journal Nature.
W43A is 8,500 light-years from Earth, appearing in the constellation Aquila, the eagle. It emits water molecules from a pair of regions called masers, where the molecules strengthen the star's radio emissions. The streams flow away from the star in two curving lines at about 325,000 miles (523,037 kilometers) an hour.
"The path of the jets is curved like a corkscrew, as if whatever is squirting them out is slowly rotating, or precessing, like a child's top wobbles before it falls down," said Phillip Diamond, a VLBA researcher and director of the MERLIN radio observatory at Jodrell Bank in England. The spinning water jets, he added, could be one mechanism for producing the structures seen in planetary nebulae.
The source of the water jets, however, has yet to be explained.
"Traditional wisdom says that it takes a disc of material closely orbiting the star to produce jets, but we don't know how such a disc could be produced around such an old star," Diamond said.
Imai believes his team may have been lucky to even observe the jets, since W34A appears to be in a short transitional stage of its stellar life.
"Our analysis of the water jets indicates that they are only a few decades old," he said. "Once the star collapses under its own gravity into a dense white dwarf, its intense ultraviolet radiation will rip apart the water molecules, making observations such as ours impossible."
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