Hidden views of vast stellar nurseries

"In these images we can detect even the faintest sources of light, like stars far less massive than the Sun, revealing objects that no one has ever seen before," says Stefan Meingast, an astronomer at the University of Vienna in Austria and lead author of the new study published today in Astronomy & Astrophysics. "This will allow us to understand the processes that transform gas and dust into stars."

Stars form when clouds of gas and dust collapse under their own gravity, but the details of how this happens are not fully understood. How many stars are born out of a cloud? How massive are they? How many stars will also have planets?

To answer these questions, Meingast's team surveyed five nearby star-forming regions with the VISTA telescope at ESO's Paranal Observatory in Chile. Using VISTA's infrared camera VIRCAM, the team captured light coming from deep inside the clouds of dust. "The dust obscures these young stars from our view, making them virtually invisible to our eyes. Only at infrared wavelengths can we look deep into these clouds, studying the stars in the making," explains Alena Rottensteiner, a PhD student also at the University of Vienna and co-author of the study.

The survey, called VISIONS, observed star-forming regions in the constellations of Orion, Ophiuchus, Chamaeleon, Corona Australis and Lupus. These regions are less than 1500 light-years away and so large that they span a huge area in the sky. The diameter of VIRCAM's field of view is as wide as three full Moons, which makes it uniquely suited to map these immensely big regions.

The team obtained more than one million images over a period of five years. The individual images were then pieced together into the large mosaics released here, revealing vast cosmic landscapes. These detailed panoramas feature dark patches of dust, glowing clouds, newly-born stars and the distant background stars of the Milky Way.

Since the same areas were observed repeatedly, the VISIONS data will also allow astronomers to study how young stars move. "With VISIONS we monitor these baby stars over several years, allowing us to measure their motion and learn how they leave their parent clouds," explains João Alves, an astronomer at the University of Vienna and Principal Investigator of VISIONS. This is not an easy feat, as the apparent shift of these stars as seen from Earth is as small as the width of a human hair seen from 10 kilometres away. These measurements of stellar motions complement those obtained by the European Space Agency's Gaia mission at visible wavelengths, where young stars are hidden by thick veils of dust.

The VISIONS atlas will keep astronomers busy for years to come. "There is tremendous long-lasting value for the astronomical community here, which is why ESO steers Public Surveys like VISIONS," says Monika Petr-Gotzens, an astronomer at ESO in Garching, Germany, and co-author of this study. Moreover, VISIONS will set the groundwork for future observations with other telescopes such as ESO's Extremely Large Telescope (ELT), currently under construction in Chile and set to start operating later this decade. "The ELT will allow us to zoom into specific regions with unprecedented detail, giving us a never-seen-before close-up view of individual stars that are currently forming there," concludes Meingast.