Close-up of the Aquila / W40


A previously unseen stellar nursery comes into view in this Herschel image. Six hundred newly forming stars are estimated to be crowded into these colourful filaments of dust. The complex is part of a mysterious ring of stars called Gould’s Belt.

This image shows a dark cloud located 1000 light years away in the constellation Aquila, the Eagle. It covers an area 25 light years across and is so shrouded in dust that no previous infrared satellite has been able to see into it. Now thanks to Herschel’s superior sensitivity at the longest wavelengths of infrared, astronomers have their first picture of the interior of this cloud.

It was taken on 24 October 2009 using two of Herschel’s instruments: the Photodetector Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE).

The blue area, also known as W40 or Sharpless 2-64, is an HII region, where at least three young massive OB stars illuminate the ionised hydrogen gas, causing it to shine. The bright nebula is expanding into the surrounding medium, compressing the ambient gas on its way. This has created a second generation of very young protostars which are only seen at the far-infrared wavelengths accessible to Herschel.

Altogether, about 600 condensations of dust and gas have been identified with Herschel in the field covered by this image. Astronomers estimate that about 150 of these are protostars, celestial objects in the final stages of formation. Each one just needs to ignite nuclear fusion in its core to become a true star. The other 450 objects are insufficiently developed to be considered protostars, but these too will eventually become stars.

This cloud is part of Gould’s Belt, a giant ring of stars that circles the night sky because the solar system just happens to lie near the centre of the belt. For more than a hundred years, astronomers have puzzled over the origin of this ring, which is tilted to the Milky Way by 20 degrees.

Gould’s Belt supplies bright stars to many constellations such as Orion, Scorpius and Crux, and conveniently provides nearby star-forming locations for astronomers to study. Observing these stellar nurseries is a key programme for Herschel, which aims to uncover the demographics of star formation and its origin. In other words, the quantities of stars that can form and the range of masses that such newborn stars can possess. As well as this region of Aquila, Herschel will target fourteen other star-forming?regions as part of the Gould’s Belt Key Programme.

Credits: ESA and the SPIRE & PACS consortia, Ph. André (CEA Saclay) for the Gould’s Belt Key Programme Consortia


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