Stellar pinwheels at our Galaxy's core

Astronomers have finally learned the identity of a mysterious “Quintuplet Cluster” of stars situated near the supermassive black hole at our galaxy's core: At least two of the objects are not individual stars, but binary pairs that live fast and die young, forming fiery pinwheels as they spin around one another.

A multinational team led by Peter Tuthill of the University of Sydney in Australia, used the extraordinary resolution of the 10-meter telescope at the W.M. Keck Observatory in Hawaii, to determine the nature of the enigmatic objects. They report their findings in the Aug. 18 issue of the journal Science.

Until these observations, researchers had not known whether the extremely red “cocoon” quintuplets were aging stars surrounded by shells of dust, or young stars accompanied by disks of bright gas. Neither hypothesis was convincing, and neither fully explained the enormous light output: Each quintuplet emits 10,000 to 100,000 times as much radiation as the Sun.

The new findings indicate the quintuplets are members of a rare class called “Wolf-Rayet colliding-wind binaries” — massive, fast-burning star pairs that live only a few million years before exploding in terminal supernovae. By contrast, the Sun is about 5 billion years old and only middle-aged. The pinwheel effect is caused by the way each star's dusty mantle is affected by that of its partner, producing spiral plumes.

“The discovery of spiral plumes, the size of our entire solar system, has solved the enigma of the bright red stars in the Quintuplet Cluster located right next door (within 100 light-years) to the center of our Galaxy,” says study co-author Andrea Ghez of the University of California, Los Angeles. “Within the astronomy world, there has been a surge of interest in these stars. Wolf-Rayets are very massive stars at the very end-point of their normal lives: they are the last stable phase before a supernova explosion. Massive binary systems such as these pinwheel stars will, in fact, explode three times: two explosions as each of the pair separately undergoes a core-collapse supernova, then a third explosion as the two fall into each other in an inspiral-merger event — possibly in the quite-distant future.”