July 29, 1999 A gigantic empty void in our own galaxy was caused by a cluster of massive young stars at its centre, says a professor of astrophysics at the University of Toronto.
The so-called "superbubble" in the W4 region in the Perseus spiral arm of the Milky Way galaxy was detected by Canadian astronomers working for the Canadian Galactic Plane Survey in Penticton, B.C. In the superbubble, which measures several 100 light years across, the interstellar medium, the thin gas and dust that permeates the rest of space, is virtually absent. Professor Peter G. Martin says this is because a cluster of recently formed supergiant stars have pushed the interstellar material away from them with their stellar winds, the flow of particles that are shed by these hotly-burning ultraluminous stars. In this case the cluster of stars created is so populous and yet so compact that it has created the largest void in the interstellar medium yet found.
"Around our sun, the stellar winds are fairly weak, but these stars are each 30 to 50 times more massive, and together they have blown all the gas and dust away, forming this cavity," Martin says.
Martin and his colleagues believe that as the galaxy continues to evolve, the stars within will become supernovae, turning the W4 superbubble into a "galactic fountain," a phenomenon more easily witnessed in other galaxies where the enriched, nuclear-processed matter ejected by the dying stars is dispersed widely over the rest of the galaxy. His analysis, coauthored with Shantanu Basu and Doug Johnstone, both research associates at the Canadian Institute of Theoretical Astrophysics, appeared in the Astrophysical Journal.
CONTACT: Bruce Rolston
U of T Public Affairs
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