It is over a million light-years away, the farthest star ever observed in the Milky Way.
It is located about halfway from our neighbor, the Andromeda galaxy and is part of a group of more than 200 newly discovered stars, which allow us to trace the outermost boundaries of the Milky Way's stellar halo, which extends far beyond the disk of the galaxy.
The study, led by the University of California at Santa Cruz and presented at the meeting of the American Astronomical Society (AAS) in Seattle, used data collected by the Canada-France-Hawaii Telescope (Cfht), located on the island of Hawaii and managed by the Canadian National Research Council (NRC), the French National Center for Scientific Research (CNRS) and the University of Hawaii.
Graphic representation of the Milky Way's halo, which extends far beyond the galactic disk, up to about one million light-years from the center (source: NASA, ESA, and A. Feild/STScI)
“This study redefines what constitutes the outer limit of our galaxy,” comments Raja GuhaThakurta, co-author of the study led by Yuting Feng.
“The Milky Way and the Andromeda galaxy are both so huge they almost touch.
Precisely for this reason - adds GuhaThakurta - the outer halo is very difficult to study, despite containing a large part of the mass of the entire galaxy".
The very distant stars observed belong to the class of the so-called RR Lyrae: they are old stars that expand and contract in a periodic and extremely regular manner, varying their luminosity.
“The way their brightness changes looks like an electrocardiogram – says GuhaThakurta – they are like the heartbeats of the galaxy”.
These characteristics make them perfect as reference points for calculating galactic distances and have allowed us to confirm that the outermost edge of the Milky Way is about one million light years from the centre.