A gamma-ray burst (GRB) is an extremely luminous event flash of gamma rays that occurs as the result of an explosion, and is thought to be associated with the formation of a black hole. GRBs are far away (1 billion light years or further) from Earth. A few bursts, such as GRB 050904, GRB 080913 and GRB 090423, have been detected at redshifts z>6. For the particular burst GRB 090423 with a low signal to noise spectrum, a redshift z~8.2 was derived. The universe was only 630 million years old, much younger than the current universe, when the light from GRB 090423 was emitted. For some “nearby” GRBs a massive star origin has been established and the GRB rate is a good indicator of the star formation. However the rate of the high redshift GRBs is remarkably higher than the formation rate of the stars in the early universe, possibly implying a new physical origin. An attractive suggestion is that these high redshift bursts are due to superconducting cosmic strings rather than the regular astrophysical processes.

Cosmic strings are hypothetical 1-dimensional topological defects which may have formed during a symmetry breaking phase transition in the early universe. Cosmic strings have long string and short loop structures, vibrate periodically and give rise to gravitational radiation. Recent work indicates that cosmic strings may conduct great amounts of electrical current and perform as superconducting wires. The superconducting cosmic strings moving in the magnetized plasma may give rise to energetic electromagnetic radiation, for example, gamma-ray bursts.If detected it would be a great breakthrough in modern physics.Therefore it is crucial to re-examine the possible link between superconducting cosmic strings and high redshift GRBs. 　

A group of astrophysicists at Purple Mountain Observatory carried out a further research on the superconducting cosmic string GRB model. They found out that the half-opening angle of the superconducting-cosmic-string driven outflow is as narrow as 0.001 rad, which is about two or more orders of magnitude smaller than that inferred from the afterglow modeling. They also investigated the other possibility that the superconducting-cosmic-string driven outflow is very wide but extremely structured. The resulting afterglow emission, however, is still at odds with the data. They then concluded that the superconducting cosmic string model for high redshift GRBs is not supported by current afterglow data unless a prompt process, unclear so far, can broaden the half-opening angle of the initial outflow considerably. The work by WANG Yu, FAN Yizhong (corresponding author) and WEI Daming has been published in Phys. Rev. Lett. as a Comment (http://prl.aps.org/pdf/PRL/v106/i25/e259001).