Most distant galaxy detected

Most distant galaxy detected

By Dr David Whitehouse
BBC News Online science editor

The Japanese Subaru Telescope has found a galaxy 12.8 billion light-years away, the most distant galaxy ever observed.

At the edge of the Universe

This discovery is the first result from the Subaru Deep Field (SDF) project which has discovered about 70 distant galaxy candidates by using a special filter to locate galaxies around 13 billion light-years away.

Researchers say the discovery raises hopes that they will be able to find a large number of distant galaxies that will help unravel the early history of the Universe in a statistically meaningful way.

They hope to find out more about the period between the Big Bang and the formation of the first stars and galaxies, after the mysterious so-called "dark ages".

Newborn galaxies

The SDF project's main goal is to detect a large number of the most distant galaxies detectable and to understand their properties and their impact on the evolution of the cosmos.

This is possible because looking for ever more distant galaxies means looking at objects at earlier and earlier times in the history of the Universe.

The SDF observations took advantage of the fact that light from distant galaxies has a characteristic wavelength and shape.

The Subaru Telescope is actually sited in Hawaii

Astronomers believe that the earliest galaxies rapidly formed stars from hydrogen and the light from those stars would have excited any hydrogen remaining around them.

When excited hydrogen returns to lower energy states, it emits light at several distinct wavelengths.

Because of the expansion of the Universe, this characteristic radiation is Doppler shifted to longer, or redder, wavelengths, something that astronomers can use to pick out newborn, distant galaxies.

Extremely faint

To detect these galaxies the SDF team developed a special filter that only passes light within a narrow wavelength range corresponding to a distance of 13 billion light-years.

By observing an area of the sky the size of the Moon, the team was able to detect over 50,000 objects, including many extremely faint galaxies.

By selecting galaxies that were bright only in the special filter and preferentially red, the team found 70 candidates for galaxies at a redshift of 6.6, equivalent to a distance of about 13 billion light-years.

Follow-up observations confirmed that two candidates were distant galaxies with redshifts of 6.58 and 6.54, indicating that the light from them was emitted when the Universe was only about 900 million years old.

The previously observed most distant galaxy, with a redshift of 6.56, was discovered by looking at a large cluster of foreground galaxies that can amplify light from more distant galaxies - a technique known as gravitational lensing.

Astronomers believe that before the first stars and galaxies formed, the Universe was in a so-called dark age. Determining when the dark ages ended is key to understanding the evolution of the cosmos.