The astronomers of European Southern Observatory (ESO) they released the more detailed map ever created of our galaxy, the Milky Way, in the wavelengths ofinfrared. The map was obtained by combining well 13 years of observations carried out with VISTA infrared telescope (Visible and Infrared Survey Telescope) located on the Cerro Paranal, Chilewhere the best skies in the world for astronomical observations are found. Consider that the map is so vast and detailed that it covers an area in the sky equal to 8600 full moons and to contain well 1.5 billion objects! The Earth is located in a rather peripheral position of the Milky Way, about 26,000 light years from its center, and we can see its disk as a bright, milky streak in a night sky not too affected by light pollution. This new map helps us refine our knowledge of our “star city”: it will help astronomers peer towards the central regions of the Milky Way, beyond the dust that prevents optical light from reaching us, and witness the birth of new generations of starslike those in Lobster Nebula NGC 6357 in the video you find below.
How the infrared map of the Milky Way was created
The map released by ESO is the result of a long project 13 years oldfrom 2010 to 2023, led by Dante Minniti (Andrés Bello University in Chile) e Philip Lucas (University of Hertfordshire in the United Kingdom), and also attended by astronomers from the National Institute of Astrophysics in Rome, Bologna, Naples, Padua and Ferra. The project, the largest observation ever conducted by ESO, was made up of 420 nights where astronomers observed the Milky Way in the wavelengths ofinfrared using the room VIRCAM of VISTA telescopeon Cerro Paranal in Chile. Let’s talk about well 200,000 infrared images of the night sky that cover an area of sky equal to 8600 full moons and which occupy disk space equal to 500 terabytes.
Every portion of the sky was observed several times from the VISTA telescope, thus allowing so-called images to be obtained “deeper”i.e. with a longer exposure time, obtained by combining several images of the same area in the sky. By doing so, astronomers were able to capture the fainter stars of our galaxy, reaching a total of 1.5 billion objects recognized in all images. Astronomers estimate that the amount of data is so large that it will take decades to extract every possible scientific result from the new map.
Why infrared is so important
Observe through the disk of the Milky Way using only the optical light (what we are able to see) is a difficult task. In fact, the Earth is not outside the Milky Way, but inside the diskso to be able to look through it, for example towards the center of the galaxy, the light needs to pass through a large amount of gases and dust (small grains of carbon, silicon or polycyclic aromatic hydrocarbons). The latter, in particular, block and scatter optical light, making some regions of the galaxy appear like darkcompletely empty. Actually, this it’s just an effect of the absorption and diffusion of light, analogous for example to when we look through a fog bank and there seems to be nothing behind it.
This effect though depends on the wavelength of light meeting gases and dust. There infrared light has a wavelength such that it can cross unscathed the great clouds of interstellar dust. Therefore building telescopes sensitive to infrared wavelengths is equivalent to remove a smoke screen and finally be able to see what is hidden in the darkest corners (in the optical) of the Milky Way. In addition to this, infrared wavelengths are where most of the light comes from very old stars and small in size, like the red dwarfsis emitted, so observing in these wavelengths is crucial if you want to study this particular class of objects.
The same considerations led to the choice of infrared for the James Webb Space Telescopethe most advanced space telescope ever built.
What new ESO data teach us about our galaxy
ESO has released a series of spectacular images which show an example of what can be studied with this new data. The ESO images open a new window on the regions where the new generation of stars populating the Milky Way is forming. There Lobster Nebula NGC 6357 and the Cygnus Nebula (Messier 17)more than 5500 light years away from Earth, they are in fact gods nursery stellarregions where gravity collapsed interstellar material into an object that triggered nuclear fusion reactions, giving birth to new stars.
Within these extensive clouds of dust and gas we can observe spectacular blue starsi.e. very hot objects (more than 20,000 °C on the surface) and young (less than a handful of million years old), destined to explode in a supernova within a few tens of millions of years. The pictures also show spectacular nebulae made up of gases that are excited by the intense electromagnetic radiation released by young stars. These regions are usually surrounded by the same dust from which they were formedso they would remain invisible if we did not have infrared telescopes available. The energy emitted by stars gradually changes the shape of nebulae through intense radiation and powerful winds of charged particles.
The ESO images also show some wonderful things globular clustersspherical concentrations of millions of very ancient starshelping us understand the formation history of our galaxy. VISTA’s observation of infrared light also allows the detection of very cold objects, which shine at these wavelengths, such as brown dwarfs (“failed” stars that are not sustained by nuclear fusion reactions) or planets which are free floating and do not orbit a star.
