Dazzling blobs shed new light on the universe

The Guardian : Lyman-alpha blobs (Lab) are gigantic clouds of hydrogen gas hundreds of thousands of light-years across. Discovered in the 1990s, they emit a bright, ethereal glow when electrons lose energy inside the hydrogen atoms, a process that produces a luminous signature known as the Lyman-alpha line. Although the light is released as ultraviolet radiation, the universe’s expansion stretches the light waves so much on their way to Earth that the light appears green on arrival. Early studies showed that Labs contain clusters of young galaxies, but didn’t reveal why the blobs of gas glow so brightly.To find out, Matthew Hayes of the University of Toulouse in France and colleagues studied Lyman-alpha blob-1, which is about 11.5 billion light-years away and, at about 300 000 light-years across, several times wider than the Milky Way. They report that light from the object is polarized—the electric and magnetic fields that make up the light waves are aligned in a particular direction. It was once thought that the glow came from the hydrogen gas itself as it was pulled by extreme gravitational forces into the heart of the cloud. However, that would produce unpolarized light. The young galaxies inside Labs are stellar nurseries, and some of them have supermassive black holes at their centers. Both will likely heat up the hydrogen gas and cause it to glow. The light then becomes polarized when it’s scattered through the gas cloud over distances of up to 150 000 light-years.