Galaxies stripped bare

Raging torrents of molecular gas, detected coming from galaxies for the first time by ESA's Herschel space observatory, could be the culprit behind galaxies that have lost the ability to form new stars.

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For the first time, ESA’s Herschel infrared space observatory has detected raging winds of molecular gas streaming away from galaxies at speeds of more than 1,000 km/s, 10,000 times faster than the wind in a hurricane here on Earth.

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These outflows may have the power to strip galaxies of gas and halt star formation in its tracks, since they are robbing galaxies of the raw material they need to make new stars – molecular gas.

If the outflows are powerful enough, they could even halt star formation altogether.

Scientists at the Max-Planck-Institut für extraterrestrische Physik in Germany used Herschel’s Photoconductor Array Camera and Spectrometer to study 50 galaxies.

In galaxies with the most vigorous outflows, they found that 1,200 times the mass of the Sun is being lost each year.

At these rates some galaxies could completely lose their star-forming gas in as little as a million years.

The extraordinary winds could be generated by the intense emission of light and particles from young stars, by shockwaves from the explosion of old stars, or by the radiation given off as matter swirls around a black hole at the centre of a galaxy.

The fastest winds appear to be coming from galaxies that contain the brightest ‘active galactic nuclei’ – where a giant black hole is feeding from its surroundings.

The results could be a step towards explaining how some elliptical galaxies are formed.

In these galaxies, no new stars are being formed because there is no molecular gas left.

As smaller galaxies interact and merge with each other, more food is supplied to the central black hole in the combined nucleus, making it larger and more active.

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This could mean a more powerful wind, which removes the molecular gas and prevents any further star formation taking place.