UCL News


Cosmic confusion

21 December 2006

A mysterious cosmic explosion detected by NASA's Swift telescope has caused such a flutter in the space science community it is the subject of four reports in the current issue of 'Nature' magazine.

Gamma rays

The mysterious gamma-ray burst happened 1.6 billion light years away, and is suspected to signal the birth of a black hole. However, this type of explosion defies the current categories for these events and experts cannot figure out what caused the explosion.

Gamma-ray bursts fall into two categories, long and short. The long bursts last for more than two seconds and appear to be from the core collapse of massive stars forming a black hole. The surrounding star can feed the newly formed black hole for many seconds leading to a long period of energy release. Most of these bursts come from near the edge of the visible universe. 

The short bursts, less than two seconds long and often lasting just a few milliseconds, appear to be caused by the merger of two neutron stars or a neutron star with a black hole, which subsequently creates a new or bigger black hole. The small amount of remaining merger material can only feed the black hole for about a second and hence gives a short period of energy release.

This particular burst - named GRB 060614 - lasted 102 seconds, but lacked the hallmark of a supernova, or star explosion, commonly seen shortly after long bursts.

Miss Patricia Schady (UCL Mullard Space Science Laboratory) said: "Everyone was happy that there were two kinds of gamma-ray bursts but this throws a spanner in the works."

Dr Mat Page (UCL Mullard Space Science Laboratory) added: "The lack of a supernova from this relatively nearby event was so puzzling, that some astronomers tried to explain it by proposing that the burst was actually at a great distance behind the galaxy it was found in - a cosmic coincidence. However, the images from the UK-built UltraViolet-Optical Telescope on Swift prove conclusively that this is not the case."

Image: Gamma-ray bursts are common, yet random, and fleeting events that have mystified astronomers since their discovery in the late 1960s. Shorter bursts (less than two seconds in duration) are thought to be caused by mergers of binary systems with black holes or neutron stars. Credit: NASA/Dana Berry, Skyworks Digital