Hubble Probes the Archeology of Our Milky Way’s Ancient Hub

Every star has a story to tell. Study a star and it will give you information about its composition, age and possibly even clues to where it first formed. The stars residing in the oldest structure of our Milky Way galaxy, the central bulge, offer insight into how our pinwheel-shaped island of myriad stars evolved over billions of years. Think of our Milky Way as a pancake-shaped structure with a big round dollop of butter in the middle — that would be our galaxy’s central hub. For many years, astronomers had a simple view of our Milky Way’s bulge as a quiescent place composed of old stars, the earliest homesteaders of our galaxy. A new analysis of about 10,000 normal sun-like stars in the bulge reveals that our galaxy’s hub is a dynamic environment of various ages zipping around at different speeds, like travelers bustling about a busy airport. This conclusion is based on nine years’ worth of archival data from the Hubble Space Telescope. The faster-moving and later-generation stars may have arrived at the hub through our Milky Way cannibalizing smaller galaxies. They mingle with a different population of older, slowing-moving stars. Currently, only Hubble has sharp enough resolution to simultaneously measure the motions of thousands of sun-like stars at the distance of the galaxy’s bulge.