An artist’s impression showing a galaxy with a molecular outflow. Herschel has discovered that such outflows can travel at 1000 km/s, which could deplete the galaxy of the gas needed for further star formation within one million to 100 million years.
Credit: ESA/AOES Medialab
Ariane-5 ECA launch of Herschel and Planck in May 2009 from Europe's Spaceport in French Guiana.
Credit: ESA/CNES/Arianespace-Service Optique CSG
PARIS: Raging winds of molecular gas have been detected streaming away from galaxies. Suspected for years, these outflows may have the power to strip galaxies of gas and halt star formation in its tracks.
The winds, picked up by the European Space Agency's (ESA) orbiting Herschel infrared space observatory, can blow at a speed of more than 1000 km/s, or about 10,000 times faster than the wind in a terrestrial hurricane.
This is the first time that such molecular gas outflows have been unequivocally observed in a sample of galaxies. Because stars form from molecular gas, and these outflows are robbing the galaxy of the raw material it needs to make new stars, they could halt star formation altogether.
"With Herschel, we now have the chance to really study what these outflows mean for galactic evolution," said lead author Eckhard Sturm from the Max Planck Institute for Extraterrestrial Physics in Germany of the paper published in The Astrophysical Journal. "By detecting outflows in the cold molecular gas from which stars are born, we can finally witness their direct impact on star formation."
Stripping galaxies of star-forming gas
While mass outflows driven by stars and active galactic nuclei (AGN) - the core which produces more radiation than the entire rest of the galaxy - are crucial to many current models of galaxy evolution, observational evidence of such feedback processes is scarce.
"Outflows are key features in models of galactic formation and evolution, but prior to our work no decisive evidence of their active role in such processes had been gathered," said Sturm.
The researchers used Herschel's Photoconductor Array Camera and Spectrometer to study 50 galaxies. They inferred that 1200 times the mass of our Sun is being lost each year from the galaxies with the most vigorous outflows.
That is enough to strip them of their entire reserves of star-forming gas within one million to 100 million years. In other words, some galaxies could completely expel their star-forming gas in as little as a million years. Inhibiting star formation in a galaxy is known as negative feedback.
Where the fastest winds come from
These winds could be generated by the intense emission of light and particles from young stars, or by shockwaves from the explosion of old stars.
Alternatively, they may be triggered by the radiation given off as matter swirls around a black hole at the centre of the galaxy.
The fastest winds appear to be coming from the galaxies that contain the brightest AGN, in which a giant black hole is feeding from its surroundings.
