Astronomers have spent five weeks studying a very strange star--one that is 10 times as massive as our sun and spews 100 trillion tons of gas into space each second--and have found a method to its mad behavior. Presenting their results yesterday at a meeting of the Canadian Astronomical Society in Montreal, the researchers report that the object, WR123, undergoes a stable variation that repeats every 10 hours.

Located about 19,000 light-years from Earth, WR123 belongs to a class of stars known as Wolf-Rayet stars, which are known for complex, irregular patterns in their brightness. An international team used the Microvariability & Oscillations of Stars (MOST) space telescope to observe the star continuously for five weeks. Instead of chaotic behavior, the scientists uncovered a pattern within the data. "Finding a clock in a star like WR123 is like finding the Rosetta stone for astronomers studying massive stars," says team member Laure Lefevre of the University of Montreal. "However, although WR123 may vary like clockwork, it must be a very strange mechanism indeed."

According to the researchers, there are three possible causes of WR123's habitual behavior: The star's own rotation could be to blame, although the speeds required would have the surface of WR123 moving at nearly 2,000 kilometers a second. The gravity from a closely orbiting star might cause regular fluctuations, but the object would have to be so close to WR123 that it would reside in the latter's own gas envelope. Finally, vibrations within the star's interior structure could be responsible for the variations in brightness, but if that's the case, many other theories about Wolf-Rayet stars would have to be reconsidered.