The archaeology of galaxies in the local group

点击翻译按钮获取中文摘要

Over the past decade I ( and my research team) have been major users of the Hubble Space Telescope. We have been extremely successful in obtaining very large amounts of time (in open competition) to survey a number of ancient star clusters in our Galaxy. The main focus of the research is to determine the ages of these systems and then use that information to glean clues as to when and how our Milky Way Galaxy was formed. We have developed a new age-dating technique that involves measuring precisely the cooling rate of "dead" stars and using this as a clock. Thus far we have explored two clusters in the halo of our Galaxy and have determined that both are about the same age and very old (12 billion years). Since we are quite sure that the Universe itself is only 13.7 billion years old, we now know that our Galaxy (and likely most others) formed rather soon after the Big Bang. We have also applied our chronometer to the disk of our Galaxy which contains its magnificent spiral arms. Here we learned that this Galactic component is significantly younger - by about 4 billion years. Currently we are in the process of obtaining a new set of Hubble data on a star cluster that contains stars similar to those in the central bulge of our Galaxy. An age for this system will provide evidence on whether our Galaxy formed inside out (bulge is older) or from the outside in (bulge is younger). In addition to this stellar chronology we are pursuing a large number of other research programs with these and other data. We are exploring for planets in these clusters by searching for planetary transits across their parent stars and examining whether normal stars have excess infrared light which could indicate a cool planet or planetary disk. We have been observing a number of old star clusters for almost a decade now and the data are precise enough that we can use their positions over a period of time to resolve the INTERNAL motions within the cluster. This allows us to examine in exquisite detail the dynamics of the stars and this is revealing new and interesting phenomena, such as stars given a "kick" when they die, or evidence for a central black hole.