Did Star Cluster Death Rays Zap Earth?

A blast of radiation from a passing star cluster could turn out to be the cause of a mass extinction on ancient Earth.

In 2003, a team led by Adrian Melott of the University of Kansas in Lawrence suggested that a gamma-ray burst within a few thousand light years of Earth triggered a mass extinction 440 million years ago. But proof has been elusive. Because these bursts occur when a single star explodes or two stellar corpses merge, there is little left to identify the culprit.

Unless, of course, the gamma-ray burst occurred in a massive swarm of stars called a globular cluster, which hosts many pairs of dead stars that might merge, says Wilfried Domainko of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Based on the number of star clusters in the Milky Way and the rate of gamma-ray bursts in them, Domainko calculates one probably exploded within striking distance of Earth at least once in the past billion years.

The European Space Agency’s Gaia star-mapper, expected to launch in 2013, could track the guilty cluster down. Gaia will pinpoint the position and speed of such clusters, so we can see if any coincide with extinctions.

Rhino’s end

From now on, the only place you’ll see this subspecies of black rhino from western Africa is in photographs or stuffed in museums. That’s because this year, the western black rhino (Diceros bicornis longipipes) is officially extinct, and others are clinging on by a thread. In all, the International Union for Conservation of Nature says that a quarter of all mammals are at risk of extinction. It’s not all bad news though. One of conservation’s success stories is (Ceratotherium simum simum), a subspecies of the African southern white rhino, which has soared in number from less than 100 individuals to 20,000 since the end of the 19th century.