Astronomers discover "greenest" galaxy ever seen

WASHINGTON, April 23 (Xinhua) -- Astronomers said Tuesday that they have spotted the most environmentally friendly galaxy ever seen, one that converts fuel into stars with almost 100-percent efficiency.

Stars are formed out of collapsing clouds of gas in galaxies. In a typical galaxy, like the Milky Way, only a fraction of the total gas supply is actively forming stars, with the bulk of the fuel lying dormant. The gas is distributed widely throughout the galaxy, with most of the new stars being formed within discrete, dense 'knots' in the spiral arms.

In the galaxy, called SDSSJ1506+54, nearly all of the gas has been driven to the central core of the galaxy, where it ignited in a powerful burst of star formation.

The finding was reported on the latest issue of the Astrophysical Journal Letters.

"It's converting its gas supply into new stars at the maximum rate thought possible," said Jim Geach of McGill University in Canada, lead author of the study. "We are seeing a rare phase of evolution that is the most extreme -- and most efficient -- yet observed."

Geach said the results will provide a better understanding on how the central star-forming regions of galaxies take shape.

SDSSJ1506+54 jumped out at the researchers when they analyzed data from U.S. Wide-field Infrared Survey Explorer (WISE) telescope. Infrared light is pouring out of the galaxy, equivalent to more than a thousand billion times the energy of the Sun. It took the light nearly six billion years to reach the Earth.

The team then used the IRAM Plateau de Bure Interferometer in the French Alps to measure the amount of gas in the galaxy. The ground-based telescope detected millimeter-wave light coming from carbon monoxide, an indicator of the presence of hydrogen gas, which is fuel for stars.

Combining the rate of star formation derived with WISE, and the gas mass measured by IRAM, researchers get a measure of the star-formation efficiency.

The researchers believe they're catching the galaxy in a short-lived phase of evolution, possibly triggered by the merging of two galaxies into one.

The star formation is so prolific that in a few tens of millions of years, the blink of an eye in a galaxy's life, the gas will be used up, and SDSSJ1506+54 will mature into a massive elliptical galaxy.