The light we can see with our own eyes is only a small fraction of the electromagnetic spectrum. Since the discovery of infrared radiation over 200 years ago, we have employed ways to make the invisible visible, allowing us to look at the universe in a completely different way.
The European Space Agency (ESA) launched the Herschel Space Observatory in 2009 with the goal of providing the best view of the infrared universe. Although it concluded operations in 2013, scientists have been busy processing the data and have now released the first part of the Herschel Infrared Galactic Plane Survey (Hi-GAL), which consists of 70 maps of extraordinary quality and resolution.
"These maps are not only stunning from an aesthetic point of view, but they represent a rich data set for astronomers to investigate the different phases of star formation in our Galaxy," explains Sergio Molinari from IAPS/INAF, Italy, principal investigator for the Hi-GAL Project, in a statement.
Hi-GAL is Herschel's largest observing program in terms of both sky coverage – 2 percent of the whole sky – and observing time, with over 900 hours of observation. The images allow us to see the interstellar matter and stellar nurseries, giving us insight into how stars form.
Using infrared light allowed astronomers to look at some of the coldest objects in the universe, but obtaining the maps was not easy as often proto-stellar objects and diffuse gas clouds have similar temperatures. The team had to develop a special technique to maximize the contrast between the individual sources and the background.
The result can be seen in this spectacular video of the plane of the Milky Way. It spans almost 40 percent of the central plane, where most of the stars reside. The view is a composite of three wavelengths – 70 (blue), 160 (green), and 350 (red) microns – which correspond to objects at a temperature of 40, 18, and 8 Kelvin (-385°F, -427°F, and -444°F), respectively.