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Celestial spiral goes viral

We're used to seeing spiral galaxies in deep space, but other types of outer-space spirals are positively spooky. Astronomers say that this whirligig, more than 3,000 light-years away in the constellation Pegasus, has been created by material spewing out from a binary-star system like water from a lawn sprinkler.

The Hubble Space Telescope spotted the swirl around LL Pegasi, also known as AFGL 3068, several years ago. There's a thin spiral pattern of star stuff winding around the central star, which is hidden from view by thick dust. Observations from Hubble as well as the Keck II telescope in Hawaii indicate that LL Pegasi actually consists of two stars in a tight orbit around each other. Astronomers theorized that one of the stars was spewing material outward in the course of making its rounds.

When the astronomers calculated what kind of orbit would produce the spiral pattern, they came up with an estimate of 800 years per orbit — which turned out to be a close match for the time they think it takes the decomposing star to make one circuit.

The spiral of dust, designated IRAS 23166+1655, is known as a pre-planetary nebula. That's not because the nebula is about to form infant planets, but because the phenomenon is seen as the prelude to the star system's death. When a sunlike star nears the end of its life, it puffs away its outer layers of gas and dust, creating beautiful shells in the process. "IRAS 23166+1655 is just starting this process, and the central star has yet to emerge from the cocoon of enveloping dust," the European Space Agency's Hubble team says in Monday's "Picture of the Week" advisory.

Such objects are known as "planetary nebulas" because when English astronomer William Herschel spotted them in the late 18th century, he compared their roundish shape to that of a planet. That's a shape he knew from experience, as the discoverer of Uranus.

The weirdly regular spiral of IRAS 23166+1655 may not be all that similar to a planet's shape, but it does look like a few other pinwheels that have been seen in outer space. One example is WR 104, the so-called "Death Star" that's 8,000 light-years from Earth and just might blow up one of these days. (But don't worry: Astronomers say it won't kill us.)

WR 104

Peter Tuthill / Univ. of Sydney

A near-infrared image from the Keck telescope shows the pinwheel shape created by the WR 104 star system.

The other spiral that comes to mind is the unidentified flying object that was sighted over Norway last December. Some observers wondered if the glowing spiral shape was a warning signal from visiting aliens, or even a tryout for a holographic sky-hoax system dubbed Project Bluebeam. But the spiral pattern turned out to be the result of rocket fuel spewing from a wayward Russian booster.

Russian spiral

Dagfinn Rap via Space.com

Norwegians had front-row seats for last December's space spiral and green streak.

Compared to a Death Star and a runaway Russian missile, a pre-planetary nebula in Pegasus sounds positively charming — and sure enough, the celestial spiral is going viral. Check out these other reports:

 


 

The pinwheel phenomenon in Pegasus is discussed in a paper presented at the International Astronomical Union meeting in 2006, titled "A Binary-Induced Pinwheel Outflow from the Extreme Carbon Star, AFGL 3068." First author is Mark Morris of the University of California at Los Angeles. Other authors include Raghvendra Sahai, Keith Matthews, Judy Cheng, Jessica Lu, Mark Claussen and Carmen Sanchez-Contreras.

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