Astronomers have long thought that the bulge at the center of our Milky Way galaxy is populated with very old stars. But a survey of the area has revealed an unexpected feature: a disk of much younger stars hidden among the veterans. A team of astronomers used survey data taken by the European Southern Observatory’s VISTA telescope at Cerro Paranal in Chile. VISTA is able to observe at infrared wavelengths, which can penetrate the clouds of dust that normally shroud the galactic center. The astronomers were looking for variable stars call Cepheids, which pulse at a rate related to their brightness. This allows astronomers to calculate how far away they are. As the team reports today in Astrophysical Journal Letters, among the 655 Cepheids they found, there were 35 examples of a subset known as classical Cepheids (red dots; the yellow star is our sun), which are typically young stars. The 35 varied in age from 25 million to 100 million years old, striplings compared with the much more elderly stars all around them. Even more surprising, all of the 35 were arranged in a thin disk slicing through the central bulge (see above). The discovery suggests there has been a constant supply of young stars to the galactic center, but where do they come from? The galactic center is thought to have used up its supply of gas from which to make stars long long ago, so astronomers will have to figure out some mechanism by which young stars are moved inward from farther out in the galaxy.
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