October 7, 2010: If you think global warming is bad, 11 billion years ago the entire universe underwent, well, universal warming. The consequence was that fierce blasts of radiation from voracious black holes stunted the growth of some small galaxies for a stretch of 500 million years. Astronomers used the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) to identify an era, from 11.7 to 11.3 billion years ago, when the universe burned off a fog of primeval helium. This heated intergalactic gas was inhibited from gravitationally collapsing to form new generations of stars in some small galaxies.
The telltale helium spectral absorption lines were measured in the ultraviolet light from a quasar — the brilliant core of an active galaxy. The quasar beacon shines light through intervening clouds of invisible gas, like a headlight shining through a fog. The beam allows for a core-sample probe of the clouds of gas interspersed between galaxies in the early universe. The universe was a rambunctious place back then. Giant galaxies frequently collided. This engorged supermassive black holes in the cores of galaxies with infalling gas. The black holes furiously converted some of this mass to powerful far-ultraviolet radiation that would blaze out of galaxies. This heated intergalactic helium from 18,000 degrees Fahrenheit to nearly 40,000 degrees. Only after the helium cooled down could small galaxies resume normal assembly.See the rest: