The Most Distant Explosion in the Universe: A Gamma-Ray Burst at a Redshift of 9.4

25 May 2011

A gamma-ray burst detected by NASAʼs Swift satellite may be the most distant object known in the Universe. The burst marked the explosion of a massive young star at a time when the Universe was only about half a billion years old (compared to its present age of 13.7 billion years). The discovery paper was led by Antonino Cucchiara (formerly Penn State, now at UC Berkeley) and is presented in the Astrophysical Journal by an international team of astronomers, including Oxford astronomers Philipp Podsiadlowski and Christian Wolf.

Gamma-ray bursts are rare events but can be seen throughout the Universe as they are intrinsically very luminous and their gamma-ray radiation is confined into narrow beams, like the beacons of a lighthouse. They are related to supernovae, the more commonly known explosions of massive short-lived stars, although it is still not agreed what special conditions produce these particularly energetic events. As they flash up for only a brief period, their detection requires rapid-response observations.

Reaching us from the edge of the known Universe, the light of this event, GRB 090429B, is redshifted such that it can only be seen with infrared cameras. It is also dimmed to the most extreme degree; even GROND, the successful rapid-response camera at the 2.2-m-telescope at La Silla, Chile, saw nothing more than blank sky. Instead it took the light-gathering power of the 8.1-m Gemini-North telescope in Hawaii (from which the UK will withdraw in 2012) to see the infrared flash and analyse its light.

Unfortunately, Gemini was under clouds for most of the time the burst was visible, so that no spectrum could be taken, which would have allowed a direct measurement of the distance to the burst. Instead, the team had to rely on a less accurate method, where images taken in a number of different colour filters provide a very fuzzy spectrum and thus only a rough location of the main spectroscopic feature that constrains the distance. The burst's redshift was found to be somewhere between 9 and 9.5, with a best estimate of 9.4; this translates into a distance of around 13.1 billion light-years.

It is already the second gamma-ray burst found at a distance of more than 13 billion light-years, occurring at an epoch when the Universe was younger than 700 million years. This early epoch in the life of the Universe is just the period when the first stars and galaxies were forming and is still virtually unexplored. Owing to their brightness, gamma-ray bursts can therefore point to the sites of the earliest star formation ever. With present-day instrumentation, it is possible to find gamma-ray bursts up to a redshift of about 14, when the Universe was less than 400 million years old. Future instruments, such as the next-generation James Webb Space Telescope (to be launched in 2014), will be able to explore these sites in much more detail.

Press Release

Discovery Paper