ANN ARBOR—Discovery of pinwheel-shaped dust spirals around two of the mysterious cocoon stars in the Quintuplet cluster tells scientists for the first time that they contain a duo of stars instead of just one.

The spiral shape is a telltale sign of a binary system, which means that it is two lighter-weight stars in orbit around each other, rather than one. Although lighter, these stars are still classified as massive, and will each still become a supernovae and provide giant energy pulses in this cluster located near the center of our Milky Way galaxy.

The finding put to rest the debate among astronomers over these dust-enshrouded stars, said John Monnier, assistant professor of astronomy at the University of Michigan. It also proves that massive stars in this cluster are smaller than previously thought, and it follows that dust cocoons seen elsewhere in the galaxy are likely also harboring two stars instead of one.

The findings will appear Aug. 18 in the journal Science, in the paper ” ‘Pinwheels’ in the Quintuplet Cluster. ” Monnier co-authored the paper with lead author Peter Tuthill, a research astrophysicist in the department of physics at the University of Sydney.

Scientists have debated the nature of the Quintuplet cluster stars for years. The cluster was named after its prominent five bright red stars. However, up until now, the stars have been tough to view because they are quite distant and each hidden in a shroud of dust. Astronomers used the world’s biggest optical telescope, the Keck in Hawaii, to zoom in on the stars, according to Tuthill.

The magnification achieved was five times greater than the best existing images of the cluster. Although still unable to see through the dust completely, the enhanced resolution allowed researchers to see that the dust formed spiral pinwheels, the same type of dust seen in a type of massive star called a Wolf-Rayet star.

Monnier and Tuthill first identified the characteristic dust pinwheels around this type of Wolf-Rayet star in 1999. Wolf-Rayet stars are thought to be immediate precursors to supernova, the explosion at the end of a massive star’s life. Supernovae are rare events, but can be identified across the universe because they produce extremely bright objects made of hot plasma that can be a millions of times brighter than the star that exploded.

The spiral dust that was observed in the Quintuplet stars is caused by colliding stellar winds from two stars near one another, Monnier said. The aftermath of the violent wind collision produces a stream of dust, and this dust stream shows researchers they are actually observing two or more stars, and allow a much better estimate of their actual masses.

Counting and weighing these massive stars correctly are crucial to understanding the history of our galaxy, since the final supernova explosions have a dominant effect on their surroundings, including producing and spreading out much of the heavier elements needed for forming planets around lower-mass stars like the Sun.

Other collaborators included Dr. Angelle Tanner from Jet Propulsion Lab at Caltech, professor Donald Figer from Center for Imaging Science at Rochester Institute of Technology, Andrea Ghez, UCLA professor of Physics and Astronomy, and William Danchi from NASA Goddard Space Flight Center.

Monnier

U-M Department of Astronomy