An international team of astronomers has created a catalogue of more than 84 million stars in the central parts of the Milky Way. Colour–magnitude diagrams are very valuable tools that are often used by astronomers to study the different physical properties of stars such as their temperatures, masses and ages. This gigantic dataset is a major step forward for the understanding of our home galaxy. By studying this monumental image, astronomers hope to gain a better understanding of how galaxies form and evolve. This plot contains more than ten times more stars than any previous study and it is the first time that this has been done for the entire bulge.
Taken by the VISTA survey telescope at the ESO's Paranal Observatory in Chile, the 9-gigapixel photo is the result of thousands of individual images being meshed together. Using three separate infrared filters, VISTA is able to see through dust fields that normally obscure the view of an optical telescope. To help analyse this huge catalogue the brightness of each star is plotted against its colour for about 84 million stars to create a colour–magnitude diagram.
The image gives viewers an incredible, zoomable view of the central part of our galaxy. It is so large that, if printed with the resolution of a typical book, it would be a mind-boggling 9 metres long and 7 metres tall. The image used here required a huge amount of data processing, which was performed by Ignacio Toledo at the ALMA OSF. It corresponds to a pixel scale of 0.6 arcseconds per pixel, down-sampled from the original pixel scale of 0.34 arcseconds per pixel.
"Each star occupies a particular spot in this diagram at any moment during its lifetime. Where it falls depends on how bright it is and how hot it is. Since the new data gives us a snapshot of all the stars in one go, we can now make a census of all the stars in this part of the Milky Way," explains Dante Minniti, Pontificia Universidad Catolica de Chile, Chile who co-author of the study.
This research was presented in a paper "Milky Way Demographics with the VVV Survey I. The 84 Million Star Colour–Magnitude Diagram of the Galactic Bulge" by R. K. Saito et al., which was published in the journal Astronomy & Astrophysics (A&A, 544, A147).
The team is composed of R. K. Saito (Pontificia Universidad Católica de Chile, Santiago, Chile; Universidad de Valparaíso, Chile; The Milky Way Millennium Nucleus, Chile), D. Minniti (Pontificia Universidad Católica de Chile; Vatican Observatory), B. Dias (Universidade de São Paulo, Brazil), M. Hempel (Pontificia Universidad Católica de Chile), M. Rejkuba (ESO, Garching, Germany), J. Alonso-García (Pontificia Universidad Católica de Chile), B. Barbuy (Universidade de São Paulo), M. Catelan (Pontificia Universidad Católica de Chile), J. P. Emerson (Queen Mary University of London, United Kingdom), O. A. Gonzalez (ESO, Garching, Germany), P. W. Lucas (University of Hertfordshire, Hatfield, United Kingdom) and M. Zoccali (Pontificia Universidad Católica de Chile).