Posted by Sara Gil-Casanova on April 28, 2011
The combined analysis of the data in different wavelengths revealed that these four bright sources are, in fact, extremely massive stars. All of these stars are thought to be at least 25 times more massive than the Sun and lie between 7,500 and 18,000 light years from Earth. They are rather rare, and are expected to last only a few million years before they end their lives with supernova explosions.
Finding these very massive stars is not easy. Dust and gas throughout the Milky Way obscures much of the view from optical telescopes. Infrared images suffer less obscuration but are extremely crowded with stars. However, these stars shine brightly in X-ray light and easily stand out from their neighbors.
Why are these massive stars so bright in X-rays? Some massive stars have winds that blow material away from their surface at over 2 million miles per hour. If this high-speed material collides with the wind from a companion star, it is decelerated so suddenly that acts like it has collided with a Solar System-sized brick wall. The shock waves resulting from this enormous collision generate temperatures up to 100 million degrees, and produce copious amounts of X-rays. There are many other unidentified Galactic X-ray sources with X-ray properties similar to these four sources, so a large population of massive stars may remain to be discovered with future Chandra observations.