If during a clear night, we watch toward the center of the Milky Way (in the Sagittarius constellation area), we can notice that it is quite a dense region. Due to this richness, it is one of the most interesting areas for astronomers, but also one of the most difficult to study. With this aim, in recent years several projects have focused on this portion of the sky.
One of the most important is the European Southern Observatory (ESO) public survey VISTA (Visual and Infrared Survey Telescope for Astronomy) Variables in the Via Lactea (VVV) that, after its conclusion, then became VVV eXtended (VVVX).
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Two surveys to discover the Milky Way
As we said, the internal structure of the inner regions of the Milky Way and the details of its formation and evolution are poorly understood, mainly because of the difficult observation conditions (especially in the visible spectrum of light). By using some reference objects of which we know the distance, and by observing in the near-infrared wavelengths, the VVV was able to map the 3D structure of our Galaxy.
In 2016, the legacy of the VVV survey was continued by the VVVX until its end in March 2023, when the VISTA InfraRed CAMera (VIRCAM) was decommissioned. Improving on its predecessor, VVVX was assigned a larger survey area, to provide a more complete picture of the inner Milky Way.
VISTA has dedicated more than 4000 hours to the two projects combined. During this period “only” 4% of the sky has been studied, however, most of the stars in our galaxy were observed. Currently, although there are no other projects like VVV and VVVX, a work complementary to them is done by the James Webb Space Telescope, even if it is not able to cover large areas with such precision.
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The instruments: VISTA and VIRCAM
Both VVV and VVVx wouldn’t be feasible without the VISTA telescope and its VIRCAM instrument.
VISTA is an infra-red ESO telescope, located near the VLT at the Paranal Observatory, at an altitude of 2518 m. Its main mirror has a diameter of 4.1 m and is the most curved mirror ever made of this dimension. To reflect as much infrared light as possible, it is coated with a layer of silver, instead of aluminum. Thanks to its characteristics, VISTA is the ideal instrument to detect very faint objects and rapidly map large areas of the sky.
This is possible also thanks to the VIRCAM camera, an instrument made of 16 detectors, equating to 67 million pixels. Their pairing produces an average of 315 GB of data per observation; equal to a 7-hour-long video with a 4k resolution.
Time to analyze data
VVVX, at the end of its life, produced around 200,000 images of billions of objects. All these data are now available to the scientific community for further studies about our galaxy’s origin, variable stars and exoplanets. Given the amount of data, the researchers themselves defined the survey as a “goldmine for Milky Way studies”.
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