The network of interstellar filaments in Polaris


The network of interstellar filaments in Polaris as imaged by ESA’s Herschel space observatory at infrared wavelengths 250, 350 and 500 microns. These filaments are not yet forming stars.

This colour-composite image of the Polaris Flare shows the extended filamentary structure of this quiescent cloud, located at a distance of about 490 light years, and characterised by little or no current star formation activity. A detailed study of this complex has revealed more than 60 filaments, 31 of which have been measured in detail. They all appear to have very similar widths, with a value of about 0.3 light years.

More than 300 compact starless cores have been detected embedded in the filaments in this region, but hardly any of them appear to be gravitationally bound, pre-stellar core candidates, the seeds of future stars. By studying this and other regions, astronomers have inferred that interstellar filaments precede the onset of star formation in molecular clouds.

ESA’s Herschel space observatory has revealed that nearby interstellar clouds contain networks of tangled gaseous filaments. Intriguingly, each filament is approximately the same width, hinting that they may result from interstellar sonic booms throughout our Galaxy.

The filaments are huge, stretching for tens of light years through space and Herschel has shown that newly-born stars are often found in the densest parts of them.

Such filaments in interstellar clouds have been glimpsed before by other infrared satellites, but they have never been seen clearly enough to have their widths measured. Now, Herschel has shown that, regardless of the length or density of a filament, the width is always roughly the same.

The analysis shows that filaments precede star formation and, in some cases, pave the way for it. The Polaris Flare, with its intricate web of interstellar filaments, none of which appear to be above the mass threshold, offers an example of the state of a molecular complex prior to the onset of star formation.

Credits: ESA and the SPIRE & PACS consortia, Ph. André (CEA Saclay) for the "Gould’s Belt survey" Key Programme Consortium, and A. Abergel (IAS Orsay) for the "Evolution of Interstellar Dust "Key Programme Consortium.


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