Starship Asterisk*

COSMIC strings - imperfections in space-time - may be to blame for two unusual bursts of gamma rays in the early universe.

Gamma-ray bursts come in two types. Long-lived, high-intensity bursts are thought to originate from collapsing stars, while shorter, dimmer ones are emitted when neutron stars merge with one another or with black holes.

In 2008 and 2009 two unusual bursts were seen, both short-lived but with the brightness of long bursts. Both occurred within a billion years of the big bang.

K. S. Cheng of the University of Hong Kong and colleagues say the culprit could be cosmic strings - defects in space-time, like streaks in clear plastic, that formed as the early universe cooled.

If a loop of string oscillated in the magnetic fields that pervaded the early universe, it would induce a current within the string, the team's calculations suggest^*. Parts of the string then emit low-frequency radio waves that accelerate the surrounding plasma into generating a burst of gamma rays.

Nial Tanvir of the University of Leicester, UK, whose group discovered the 2009 burst, finds the idea interesting but thinks an unknown property of the first stars is a more likely explanation.

• arXiv.org > astro-ph > arXiv:1005.3427 > 19 May 2010

The high-redshift gamma-ray bursts (GRBs), GRBs 080913 and 090423, challenge the conventional GRB progenitor models by their short durations, typical for short GRBs, and their high energy releases, typical for long GRBs. Meanwhile, the GRB rate inferred from high-redshift GRBs also remarkably exceeds the prediction of the collapsar model, with an ordinary star formation history. We show that all these contradictions could be eliminated naturally, if we ascribe some high-redshift GRBs to electromagnetic bursts of superconducting cosmic strings. High-redshift GRBs could become a reasonable way to test the superconducting cosmic string model, because the event rate of cosmic string bursts increases rapidly with increasing redshifts, whereas the collapsar rate decreases.