Sustained star formation in the central stellar cluster of the Milky Way

THE central stellar bulge of our Galaxy is commonly thought to consist predominantly of a coeval population of very old (similar to 10(10) yr) stars(1-3). But evidence for young(4) and intermediate-age stars(5,6) in the bulge is accumulating. Here we argue that star formation has been occurring in the molecular gas near the centre of the bulge throughout the lifetime of the Galaxy, and that the resulting stellar population is evident as the prominent infrared(7,8) 'r(-2) central star cluster' (a cluster whose space density decreases as the square of the distance from the centre),Although our hypothesis is at odds with the standard view that this central cluster is the innermost part of the more extended and ancient bulge(9-11), sustained star formation is consistent with both the available observational data and simple models of mass inflow and collisionally induced star formation in this region. Even if the central star-formation rate is relatively modest, it appears that the stellar population of the Galactic bulge has been augmented substantially since its birth.