Astronomers have already mapped our galaxy with high precision in visible light – now follows the most detailed map of the Milky Way in the infrared to date. It shows the appearance, behavior and movement of more than 1.5 billion objects in our galaxy, each of which was imaged multiple times over 13 years by the European Southern Observatory’s (ESO) VISTA telescope in Chile. Of particular importance are data from the center of the Milky Way and other dust-shrouded areas of our galaxy that are not visible to optical telescopes. The new infrared mapping has forever changed the view of our home galaxy and will significantly advance the study of the Milky Way and its objects, according to astronomers.
Observing and mapping the sky with telescopes is an important prerequisite for better understanding astrophysical and cosmic processes. Sky surveys in visible light, such as the star catalogs of the Gaia satellite, primarily show the positions, movements and spectral characteristics of stars in the Milky Way and make it possible, for example, to identify star streams or determine the age of stars. Using the Gaia catalogs, astronomers have, among other things, reconstructed the family tree of the Milky Way and solved the “theft” of extragalactic stars. But many processes in the cosmos take place in secret, beyond the wavelengths of light that we can see. Particularly high-energy processes, for example, can only be seen via gamma or X-rays; cool gases and protoplanetary disks can often only be observed more closely in the radio wave range.
Inner Milky Way in infrared
Infrared telescopes, on the other hand, are important because they can also show the objects and processes that are obscured by dense dust, such as most star-forming regions or the dense center of our galaxy. “These inner regions of the Milky Way are the hardest to study and most complex, because they contain a mixture of star populations from the inner disk, bulge and halo, which have very different characteristics,” explain Roberto Saito of the Federal University of Santa Catarina in Brazil and his colleagues. As early as 2010, they began surveying the inner region of the Milky Way with the VISTA telescope (Visible and Infrared Survey Telescope for Astronomy) of the European Southern Observatory at Paranal in Chile. This telescope has a high-resolution infrared camera (VIRCAM), which has a large field of view thanks to its 16 sensors, each comprising 2048 detectors. In the first part of the mapping (VVV), the telescope recorded objects in a 562 square degree area in the center of the Milky Way.
However, the mapping now published also included data from a second VIRCAM survey. “The VVVX survey expanded the area in its galactic longitude and latitude, covering an area of around 480 square degrees in the bulge and around 1170 square degrees in the inner region of our galaxy,” the astronomers report. In total, the new infrared map of the Milky Way includes the results of 420 observation nights and covers an area of the sky that corresponds to 8,600 full moons placed side by side. “Although VVV and VVVX together only cover around four percent of the entire firmament, the mapped region contains the majority of all stars in the Milky Way and the largest concentration of gas and dust in our galaxy,” the team writes. Because each area of the sky was observed several times for the mapping over the course of around 13 years, the infrared data also shows the movements and potential changes in brightness of the celestial bodies recorded. In total, the new infrared map of the Milky Way shows more than 1.5 billion objects – ten times more than the previous version published in 2012.
Star clusters, dust covers and variable stars
The infrared data from this mapping have already revealed numerous previously unknown celestial bodies and processes. “We have made so many discoveries that we have changed the view of our galaxy forever,” says project leader Dante Minniti from Andrés Bello University in Chile. More than 300 scientific articles have already been published based on the data from the VVV and VVVX surveys. Based on this data, astronomers have identified dozens of open star clusters and globular star clusters that are among the oldest components of the Milky Way. Numerous young stars, still embedded in their dusty shells, and variable stars, which are considered important rangefinders and “standard candles” in astronomy, have also now been measured and mapped. Using such data from the VVV and VVVX surveys, researchers have, for example, determined when the bar of our Milky Way was formed, as Minniti and his colleagues report. Brown dwarfs, planets without a parent star and hyper-fast runners have also been examined using infrared data.
“The legacy of the VVVX and VVV surveys will be with us for many years to come,” explain the astronomers. “Although they have already produced a lot of results, the full evaluation of the data will still take years.” At the same time, the infrared map also serves as an aid in planning more precise observations, for example with the James Webb Space Telescope or future large telescopes. In the meantime, the VISTA telescope will be further expanded: it will receive a new, even more powerful infrared spectrometer.
Source: Roberto Saito (Universidade Federal de Santa Catarina, Brazil) et al., Astronomy and Astrophysics, doi: 10.1051/0004-6361/202450584