Monday, May 09, 2011

Herschel Detects Gigantic Storms Sweeping Entire Galaxies Clean

With observations from the PACS instrument on board the ESA Herschel space observatory, an international team of scientists led by the Max Planck Institute for Extraterrestrial Physics has found gigantic storms of molecular gas gusting in the centres of many galaxies.

Some of these massive outflows reach velocities of more than 1000 kilometres per second, i.e. thousands of times faster than in terrestrial hurricanes. The observations show that the more active galaxies contain stronger winds, which can blow away the entire gas reservoir in a galaxy, thereby inhibiting both further star formation and the growth of the central black hole. This finding is the first conclusive evidence for the importance of galactic winds in the evolution of galaxies.

In the distant and therefore younger Universe, many galaxies show much more activity than our Milky Way today. In commonly accepted evolutionary scenarios gas-rich galaxies merge, which triggers increased star formation as well as the growth of supermassive black holes at their centres. This increased activity, however, seems to cease fairly suddenly, effectively stalling star formation and further growth of the black hole in as little as a few million years' time. What processes could be responsible for removing all the raw material powering this activity -- around a billion solar masses -- in such a short timespan?

The solution to this riddle could be powerful winds that blow gas outwards from the centre of the galaxy. Powered by newly formed stars, shocks from stellar explosions or by the Black Hole in the galaxy's centre, these storms would remove all the gas supply from the galaxy thereby halting the same mechanisms that produced them in the first place.

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