This week, astronomers announce the discovery of the most distant galaxy yet seen from Earth. In doing so, they provide fresh clues about the early history of the Universe and seize a hotly contested record. But for some in the field, the competition to bag the record for the most distant object is losing its sparkle.

The new galaxy, dubbed IOK-1, is so far away that the light by which it was detected was emitted only 750 million years after the Universe was born (see page 186). This is just a few hundred million years after the first stars are thought to have switched on.

Other teams have claimed galaxies even farther back in time, although these are awaiting confirmation — or have turned out to be wrong (see 'The galaxy that wasn't'). But the latest detection is not in doubt. “Most people would agree that this is the most convincing, most distant object that has been published,” says Richard Ellis of the California Institute of Technology in Pasadena, who also hunts for distant galaxies.

To find the object, Masanori Iye of the National Astronomical Observatory in Tokyo and his colleagues used the 8.2-metre Subaru Telescope in Hawaii to look for the characteristic radiation emitted by hydrogen in hot, star-forming regions. This emission, known as Lyman-α radiation, has a wavelength that puts it in the ultraviolet part of the spectrum. But light reaching us from distant galaxies has been stretched, or 'redshifted', by the expansion of the Universe, so Iye's team looked for the line at longer wavelengths — the larger the redshift, the older the emitting object. They identified a Lyman-α emitter with a redshift of 6.96, then confirmed it was a galaxy by studying the spectrum of its light in more detail. The identity of a second emitter remains uncertain.

The redshift of the most distant galaxies known has crept up from a neighbourly 1–2 in the early 1980s to the latest value obtained by Iye (see graph, below). Each new record has drawn much interest. “This is one of the few areas in observational astronomy where you can get your name in the Guinness Book of Records,” notes Richard McMahon of the University of Cambridge, UK, who used to hold the record himself.


But some hope to move on from merely claiming records. “I think the field is changing from being simply record-driven, to finding out whether we can reach times where we can see very different properties in the early Universe,” says Esther Hu, of the University of Hawaii in Honolulu, who championed early efforts to find Lyman-α emitters.

In this respect, the more interesting aspect of Iye's paper is that the team found fewer galaxies than it expected. This matches a survey by Rychard Bouwens and Garth Illingworth of the University of California, Santa Cruz (see page 189). They analysed data from the Hubble Space Telescope and suggest that the number of detectable galaxies drops off above a redshift of 7.

This decline might mean that astronomers are getting close to the point when the first galaxies formed. Earlier galaxies may have been smaller, fainter objects that later merged to form brighter beacons. Such information could be fed into simulations of how hydrogen in the early Universe clumped together (see page 151). “What we've done is provide key data that can provide the constraints or inputs to the models,” says Illingworth.

Turning back time: the search for distant galaxies is giving astronomers a clearer picture of how the early Universe behaved. Credit: ESA/NASA/J.-P. KNEIB/R. ELLIS

That doesn't mean astronomers have given up on going farther back in time. New instruments, including an infrared camera to be installed on the Hubble Space Telescope — if the space shuttle makes another servicing trip — and the James Webb Space Telescope, due to fly in 2013, should find a flood of more distant objects.

In the meantime, new techniques are pushing back the limits. Ellis, for example, is searching for distant galaxies whose faint light has been amplified by the gravitational fields of closer galactic clusters. He is preparing a paper that claims six candidates around a redshift of 10 — dating from when the Universe was between 400 million and 500 million years old.

Some prefer to investigate closer, brighter galaxies, about which more can be learnt. “Unless you can measure something else in the galaxy, it's not very useful,” says Illingworth.

But going for the record does get you attention. A story featuring Ellis's search for the oldest objects made the cover of Time magazine's 4 September issue. Illingworth, an old friend and collaborator, jokes: “It's good for astronomy to have these articles, but I'll kick Richard in the butt sometime for not mentioning the other things we're doing.”