The 84 million stars of the central Milky Way

  • An international team of astronomers has created a catalogue of more than 84 million stars in the central parts of the Milky Way using a 9-gigapixel image from the VISTA infrared survey telescope.

    According to astronomers, the above-mentioned dataset contains over ten times more stars than previous studies and represents 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," explained Roberto Saito (Pontificia Universidad Catolica de Chile, Universidad de Valparaiso and The Milky Way Millennium Nucleus, Chile).

    "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."

    According to Saito, most spiral galaxies, including our home galaxy the Milky Way, have a large concentration of ancient stars surrounding the centre that astronomers call the bulge. 

Essentially, the bulge of the Milky Way is a large central concentration of ancient stars that is predominantly observed from the southern hemisphere.  
In the bulge of the Milky Way, very faint individual stars can be observed, allowing astronomers to separate stellar populations based on age, kinematics, and chemical composition. 

    However, the bulge is centered on the stellar disk of the Milky Way, where most of the stars, gas, and dust of our Galaxy is concentrated. This makes observations of the bulge very challenging because they are affected by crowding, extinction by interstellar dust, and the depth effect of stars being at a range of distances from us.

    "Observations of the bulge of the Milky Way are very [difficult] because it is obscured by dust," said Dante Minniti (Pontificia Universidad Catolica de Chile, Chile). "To peer into the heart of the galaxy, we need to observe in infrared light, which is less affected by the dust."

    The new color-magnitude diagram of the bulge above 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.

    "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," added Saito.

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