This gigantic dataset contains more than ten times more stars than previous studies and is a major step forward for the understanding of our home galaxy. 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 9 meters long and 7 meters tall. “By observing in detail the myriads of stars surrounding the center of the Milky Way we can learn a lot more about the formation and evolution of not only our galaxy, but also spiral galaxies in general,” explains Roberto Saito (Pontificia Universidad Católica de Chile, Universidad de Valparaíso and The Milky Way Millennium Nucleus, Chile), lead author of the study. Most spiral galaxies, including our home galaxy the Milky Way, have a large concentration of ancient stars surrounding the center that astronomers call the bulge. Understanding the formation and evolution of the Milky Way’s bulge is vital for understanding the galaxy as a whole. However, obtaining detailed observations of this region is not an easy task. “Observations of the bulge of the Milky Way are very hard because it is obscured by dust,” says Dante Minniti (Pontificia Universidad Catolica de Chile, Chile), co-author of the study. “To peer into the heart of the galaxy, we need to observe in infrared light, which is less affected by the dust.” The large mirror, wide field of view and very sensitive infrared detectors of ESO’s 4.1-meter Visible and Infrared Survey Telescope for Astronomy (VISTA) make it by far the best tool for this job. The team of astronomers is using data from the VISTA Variables in the Via Lactea program (VVV),[1] one of six public surveys carried out with VISTA. The data have been used to create a monumental 108 200 by 81 500 pixel color image containing nearly nine billion pixels. This is one of the biggest astronomical images ever produced. The team has now used these data to compile the largest catalog of the central concentration of stars in the Milky Way ever created.[2] To help analyze this huge catalog the brightness of each star is plotted against its color for about 84 million stars to create a color–magnitude diagram. 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. Color–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.[3] “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. The new color–magnitude diagram of the bulge contains a treasure trove of information about the structure and content of the Milky Way. One interesting result revealed in the new data is the large number of faint red dwarf stars. These are prime candidates around which to search for small exoplanets using the transit method.[4] “One of the other great things about the VVV survey is that it’s one of the ESO VISTA public surveys. This means that we’re making all the data publicly available through the ESO data archive, so we expect many other exciting results to come out of this great resource,” concludes Roberto Saito. This pan video gives a closer look at a huge new image of the central parts of the Milky Way made by combining thousands of images from ESO’s VISTA telescope on Paranal in Chile and compares it with the view in visible light. These infrared data, which come from the VVV public survey, have been used to study a much larger number of individual stars in the central parts of the Milky Way than ever before. Because VISTA has a camera sensitive to infrared light it can see through much of the dust blocking the view in visible light, although many more opaque dust filaments still show up well in this picture. Credit: ESO/VVV Consortium/Nick Risinger, Music: Delmo — Acoustic, Acknowledgement: Ignacio Toledo Notes Reference: “Milky Way demographics with the VVV survey – I. The 84-million star colour–magnitude diagram of the Galactic bulge” by R. K. Saito, D. Minniti, B. Dias, M. Hempel, M. Rejkuba, J. Alonso-García, B. Barbuy, M. Catelan, J. P. Emerson, O. A. Gonzalez, P. W. Lucas and M. Zoccali, 23 August 2012, Astronomy & Astrophysics.DOI: 10.1051/0004-6361/201219448
