November 17, 2011: Galaxies learned to "go green" early in the history of the universe, continuously recycling immense volumes of hydrogen gas and heavy elements to build successive generations of stars stretching over billions of years. In other words they are more fuel efficient than any hybrid car on the road. This ongoing recycling keeps galaxies from emptying their "fuel tanks" and therefore stretches out their star-forming epoch to over 10 billion years. The catch is that those galaxies that crank up the rate of star formation can blow away their remaining fuel, essentially turning off further star-birth activity. But galaxies like our Milky Way that frugally pace the rate of star birth can go on building new stars at least one billion years into the future.
This conclusion is based on a series of Hubble Space Telescope observations that flexed the special capabilities of its comparatively new Cosmic Origins Spectrograph (COS) to detect otherwise invisible mass in the halo of our Milky Way and a sample of more than 40 other galaxies. The three studies investigated different aspects of the gas-recycling phenomenon in galaxies. The results are being published in three papers in the November 18 issue of Science magazine.See the rest: