Hidden Behind Dust: VISTA Discovers Ninty-Six New Stellar Clusters

"We report the discovery of ninety-six new infrared open clusters and stellar groups," opens the 'results' section in the abstract of New Galactic Star Clusters Discovered in the VVV Survey, a research paper explaining the discovery of ninety-six, new stellar clusters. European Southern Observatory's VISTA 'Visible and Infrared Survey Telescope for Astronomy' Telescope, located at ESO's Paranal Observatory in northern Chile, is responsible for making such an advance in the discovery of stellar clusters that have been apparently 'hidden behind dust.'

In comparison with our Sun, stars which have lower mass are most likely to form in groups, which are then labeled 'open clusters.' These stars, or clusters, are vital for galaxy formation and evolution*, as an open cluster is, the foundation of a new galaxy. Nonetheless, on account of these clusters forming in dusty regions, they absorb most visible light that young stars will emit, therefore creating each cluster to become a mystical and invisible 'world.' However, most telescopes cannot see these obscured star-villages. That's when ESO's VISTA can.

The results are amazing. Just after one year of starting the VISTA Variables in the Via Lactea programme (VVV), VISTA has turned out an enchanting find. "This discovery highlights the potential of VISTA and the VVV survey for finding star clusters, especially those hiding in dusty star-forming regions in the Milky Way’s disc. VVV goes much deeper than other surveys," says Jura Borissova, lead author of the study. In order to locate each cluster precisely, the VISTA team used carefully-tuned computer software which could remove foreground stars that were visible in front of each cluster, but not a true member. This was to distinguish the original members, and exclude those who were not. After this task was complete, the team inspected each cluster to make a whole plethora of measurements, like their age and size.

"In order to trace the youngest star cluster formation we concentrated our search towards known star-forming areas. In regions that looked empty in previous visible-light surveys, the sensitive VISTA infrared detectors uncovered many new object," adds Dante Minniti, lead scientist of the VVV survey. "We found that most of the clusters are very small and only have about 10–20 stars. Compared to typical open clusters, these are very faint and compact objects — the dust in front of these clusters makes them appear 10 000 to 100 million times fainter in visible light. It’s no wonder they were hidden," explains Radostin Kurtev, another member of the team.

Throughout the history of the universe, so far, only 2,500 open clusters have been discovered in the Milky Way alone, but astronomers do guess that there could be about 30,000 clusters still hiding behind gas and dust that the clusters have absorbed. This is the first time so many fainter clusters have been found at once: "We've just started to use more sophisticated automatic software to search for less concentrated and older clusters. I am confident that many more are coming soon!," adds Borissova.

The VVV ZY JHKS images and ZJKS true color
image of VVVCL036. The field of view is 2.5×2.5 arcmin,
North is up, East to the left.

*Galactic evolution by no means has to do with 'human' evolution or the 'big-bang' theorem. Galactic evolution is the evolution of galaxies, i.e. how they form...