Dazzling blobs shed new light on the universe

Scientists solve mystery of why Lyman-alpha blobs shine so brightly
A Lyman-alpha blob
Astronomers looked to Lab-1, the largest Lyman-alpha blob, to find a more accurate picture of how the universe formed. Photograph: ESO/M. Hayes/PA

Astronomers have discovered why vast blobs of matter many times the size of a galaxy discovered in their snapshots of the early universe glow the way they do.

The rare, ethereal objects, first seen in the 1990s, came to be known as Lyman-alpha blobs (Lab), their place instantly secured among the most mysterious phenomena in the heavens. Early studies revealed the blobs to be gigantic clouds of hydrogen gas that contained clusters of fledgling galaxies, but scientists could not explain why the blobs glowed so brightly.In new research, astronomers turned the European Southern Observatory's Very Large Telescope in Paranal, Chile, to face the enormous Lyman alpha blob-1, to find an answer.

The blob is one of the largest known, about 300,000 light years across, several times wider than the Milky Way, and so distant that its light has taken 11.5bn years to reach the Earth. All Labs glow with light emitted when electrons lose energy inside hydrogen atoms, a process that produces a luminous signature known as the Lyman alpha line.

Although the light is released as ultraviolet radiation, the expansion of the universe stretches the waves so much that by the time it has crossed the cosmos to reach Earth, the light appears green.

A team led by Matthew Hayes, a cosmologist at the University of Toulouse, reported in the journal Nature that light from the giant blob was polarised, meaning the electric and magnetic fields that make up the lightwaves were aligned in a particular direction.

"We wanted to know what was powering these systems and this helps us understand that. If the light is polarised, it has to come from within the galaxies themselves," Hayes said. The study appears in the journal, Nature.

One earlier school of thought held that the glow came from gas in the cloud as it was pulled by extreme gravitational forces into the heart of the blob. But this would produce unpolarised light, Hayes told the Guardian.

The young galaxies inside Labs are birthplaces for stars and some galaxies have supermassive black holes at their centres. Both of these are likely to contribute to heating up the gas cloud and causing it to glow, Hayes said. The light becomes polarised as it is scattered through the gas cloud over distances of up to 150,000 light years. "This helps us build a more accurate picture of how the universe formed."