Astronomers from ESA’s Herschel mission have released a series of stunning maps of star-forming regions in the Milky Way’s Galactic plane.
The emission nebula RCW 120 seen by Herschel. It lies about 4,300 light-years away. A star at the center, not visible at these infrared wavelengths, has blown a beautiful bubble around itself with the mighty pressure of the light it radiates. The pressure is so strong that it has compressed the material at the edge of the bubble, causing it to collapse and triggering the birth of new stars. Image credit: ESA / Herschel / PACS / SPIRE / Hi-GAL Project / G. Li Causi, IAPS / INAF.
The newly-released maps show a wealth of bright sources, wispy filaments and bubbling nebulae against the background of diffuse gas and dust, marking the spots where stars are being born in our Galaxy.
The maps cover the inner part of the Milky Way, towards the Galactic center as seen from the Sun, with Galactic longitudes between +68 degrees and -70 degrees.
They were compiled by stitching together several hundred hours of observations taken by ESA’s Herschel Space Observatory as part of the Herschel infrared Galactic Plane Survey (Hi-GAL), the largest of all observing programs carried out with Herschel.
“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,” said Dr. Sergio Molinari from IAPS/INAF in Italy, Principal Investigator for the Hi-GAL Project.
The new Herschel maps are accompanied by a set of catalogues listing hundreds of thousands of compact sources that span all phases leading to the birth of stars in our Galaxy.
The War and Peace Nebula, also known as NGC 6357 (left), and the Cat’s Paw Nebula, also known as NGC 6334 (right), seen by Herschel. The War and Peace Nebula hosts several clusters of young, bright and very massive stars that are energising the mixture of gas and dust, making it glow, and carving cavities within the cloud. It lies about 8,000 light-years away. The Cat’s Paw Nebula is one of the most prolific stellar nurseries in the Galaxy. It lies about 5,500 light-years away and owes its name to its appearance at visible wavelengths. Image credit: ESA / Herschel / PACS / SPIRE / Hi-GAL Project / G. Li Causi, IAPS / INAF.
The center of our Milky Way Galaxy, about 25,000 light-years away. Clouds of gas and dust appear distributed along a giant, twisted ring, over 600 light-years wide, which encompasses the supermassive black hole sitting at the Galaxy’s core. Image credit: ESA / Herschel / PACS / SPIRE / Hi-GAL Project / G. Li Causi, IAPS / INAF.
The Eagle Nebula, also known as Messier 16. The nebula lies about 6,500 light-years away. A group of young, bright stars, not visible at these infrared wavelengths, are located near the center of the image. The powerful light emitted by these stars is setting the surrounding gas ablaze, causing it to shine; the stars also drive mighty winds that are carving the giant cavities in the cloud. At the borders of these cavities, the interstellar mixture of gas and dust becomes denser, eventually collapsing and giving rise to a new generation of stars. Image credit: ESA / Herschel / PACS / SPIRE / Hi-GAL Project / G. Li Causi, IAPS / INAF.
This Herschel image shows Vulpecula OB1, a star-forming region about 8,000 light-years away in the constellation Vulpecula. It is a ‘stellar association’ in which a batch of truly giant OB stars (the largest stars that can form) is being born. The giant stars at the heart of Vulpecula OB1 are some of the biggest in our Galaxy. Containing dozens of times the mass of the Sun, they have short lives, astronomically speaking, because they burn their fuel so quickly. At an estimated age of 2 million years, they are already well through their lifespans. When their fuel runs out, they will collapse and explode as supernovae. The shock this will send through the surrounding cloud will trigger the birth of even more stars, and the cycle will begin again. Image credit: ESA / Herschel / PACS / SPIRE / Hi-GAL Project / G. Li Causi, IAPS / INAF.
“It is not straightforward to extract compact sources from far-infrared images, where pre-stellar clumps and other proto-stellar objects are embedded in the diffuse interstellar medium that also shines brightly at the same wavelengths,” said Dr. Molinari, who is the lead author of a recently published study in the journal Astronomy & Astrophysics.
“For this reason, we developed a special technique to extract individual sources from the maps, maximizing the contrast in order to amplify the compact objects with respect to the background.”
“The Hi-GAL maps and catalogues provide a complete census of stellar nurseries in the inner Galaxy,” said co-author Dr. Göran Pilbratt, Herschel project scientist at ESA.
“These will be an extremely useful resource for studies of star formation across the Milky Way, helping astronomers to delve into the Galactic plane and also to identify targets for follow-up observations with other facilities.”
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S. Molinari et al. Hi-GAL, the Herschel infrared Galactic Plane Survey: photometric maps and compact source catalogues. First data release for Inner Milky Way: +68° > l >-70°. Astronomy & Astrophysics, published online April 20, 2016; doi: 10.1051/0004-6361/201526380
