When hot hydrogen cooled to form galaxies in the early universe, intense far-ultraviolet radiation was emitted as electrons in the atoms fell from excited states to the ground state. This so-called Lyman alpha emission is a tell-tale signature of galaxy formation and has a characteristic wavelength of 121.6 nanometres. However, this radiation has been red-shifted to longer wavelengths by the expansion of the universe, and astronomers can calculate the age of a galaxy by measuring the red-shift of its Lyman alpha line.

Roser Pelló of the Observatoire Midi- Pyrénées in France, Daniel Schaerer of the Geneva Observatory in Switzerland and colleagues took images of the galaxy cluster Abell 1835 with the ISAAC instrument on the Very Large Telescope in Chile. This cluster behaves as a gravitational lens and allows astronomers to study galaxies otherwise too faint to be seen.

The French-Swiss team detected a weak but clear feature in the spectrum of Abell 1835 IR1916 that they believe is the Lyman alpha line red-shifted to a wavelength of 1337 nanometres in the near-infrared region of the spectrum. This corresponds to a red-shift of 10, which is significantly higher than the previous record of 6.6.

Moreover, Pelló, Schaerer and co-workers calculated that the galaxy is undergoing a period of intense star formation and that it has produced some 10 million solar masses worth of stars. The team says that these stars - which may have been the “building blocks” of today’s large galaxies - could have provided the first light sources that put an end to the dark ages in the early universe.