|Image courtesy NASA/ESA|
An unusually "perfect" cosmic corkscrew surrounds the binary star system LL Pegasi in a new Hubble Space Telescope picture released this week.
Astronomers think the spiral's evenly spaced rings are being created because one of the stars in the binary pair is dying. Unlike more massive stars that end their lives in explosive supernovae, LL Pegasi is quietly shedding its outer layers of gas and dust to form what's called a planetary nebula.
The dying star itself is still hidden by a dusty cocoon. But it's ejecting material at about 31,000 miles (50,000 kilometers) an hour, the researchers calculate, forming a new ring in the spiral every 800 years.
"If a single star was sitting still, it would eject matter in all directions at roughly the same speed," said Raghvendra Sahai of NASA's Jet Propulsion Laboratory.
Instead the dying star is losing material as it orbits around the center of the binary system. As the star completes an orbit every 800 years, its lost matter winds around the system in a regular geometric pattern.
Published September 9, 2010