Herschel links star formation to sonic booms
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 as much as a hundred of newly-born stars are often found in the densest parts of them. Herschel shows that, regardless of the length or density of a filament, the width is always roughly the same. Astronomers analysed 90 filaments and found they were all about 0.3 light years across, or about 20 000 times the distance of Earth from the Sun.
The filaments are probably formed when slow shockwaves dissipate in the interstellar clouds. These shockwaves are mildly supersonic and are a result of the copious amounts of turbulent energy injected into interstellar space by exploding stars. They travel through the dilute sea of gas found in the Galaxy, compressing and sweeping it up into dense filaments as they go.
Interstellar clouds are usually extremely cold, about 10 degrees Kelvin above absolute zero, and this makes the speed of sound in them relatively slow at just 0.2 km/s. These slow shockwaves are the interstellar equivalent of sonic booms. As the sonic booms travel through the clouds, they lose energy and, where they finally dissipate, they leave these filaments of compressed material.
Above: Dense filaments of gas in the IC5146 interstellar cloud.
