Suicide Linked to Sunlight

Unemployment, poverty, disability -- and, surprisingly, even spring -- are powerful risk factors for suicide, researchers say.

Although psychiatric disorders such as depression remain the most potent predictors of suicide, two large studies in Denmark and Australia indicate that a host of environmental and social factors influence people's decision to end their lives, according to papers published this month in the American Journal of Psychiatry.

The effects of social and environmental factors appeared to differ for men and women: Living in urban areas appeared to decrease the risk of suicide among men but increase it among women. Economic stress appeared to affect men more than women, and psychiatric disorders were more likely to increase the risk among women.

Being the parent of a young child seemed to provide more protection for women, while marriage seemed to provide more protection for men, said researchers at Aarhus University in Denmark.

A second study examined the link between suicide and the weather over nine years in the state of Victoria in Australia. By tracking when suicides occurred from 1990 to 1999, researchers at the Baker Medical Research Institute in Melbourne found that suicides peaked during spring and summer.

It is the latest in a series of contradictory studies on the links between mood and weather. Some have suggested that disorders such as depression are adversely influenced by the gloom of winter, but the Australian researchers said increased sunlight increased the risk of suicide, especially violent suicide.

"Our observation of a strong association between suicide and sunlight hours and other reports documenting higher rates of suicide in springtime raise concerns about a possible link between suicide and bright light exposure," they wrote.

-- Shankar Vedantam

A Step Toward Nuclear Fusion

Scientists at Sandia National Laboratories have used high-energy X-ray pulses to produce free neutrons from heavy hydrogen, showing that the laboratories' "Z" machine might one day achieve controlled nuclear fusion.

In an experiment announced last week at the American Physical Society's spring meeting, Sandia scientists used the X-rays to bombard a capsule the size of a pencil eraser holding deuterium at the center of the Z machine, a circular device about 120 feet in diameter.

Deuterium is an isotope of hydrogen containing one proton and one neutron. When the pulse hit the capsule, it created enough heat to cause two deuterium nuclei to fuse into a single helium nucleus containing two protons and a neutron, with the remaining "thermonuclear" neutron a byproduct of the reaction.

Team member Ray Leeper said such experiments had fallen short in the past because engineers had been unable to focus enough power on a small enough target to develop the necessary heat. "Now it seems clear we can do that," he said.

The Sandia achievement is a first step toward achieving a sustainable fusion reaction -- in which the amount of energy produced exceeds the amount applied. Such an application -- capable of creating an energy revolution -- remains far in the future.

-- Guy Gugliotta

Catching Some Gamma Rays

At 6:37 a.m. on March 29, astronomers captured an incredible burst of light from a giant star as it exploded and then collapsed into a black hole.

During the first minute, the explosion "emitted energy at a rate more than a million times the combined output of all the stars in the Milky Way," said Carl W. Akerlof of the University of Michigan, who leads an international team of fast-response astrophysicists who use a network of space- and ground-based telescopes to study these fleeting displays.

The optical brightness of the gamma ray burst was about 100 times more intense than anything seen before, he said.

Gamma ray bursts are the most powerful explosions known, visible across the universe, but they are extremely difficult to study because they are so distant, random and brief.

This one, a mere 2 billion light years away, in the direction of the constellation Leo, was unusually bright and close, so it could be studied in rare detail.

Astronomers have speculated that the dazzling gamma ray bursts are generated by explosive stellar deaths known as supernovas and their flashier cousins known as hypernovas -- which are 10 times as powerful.

But researchers have had a hard time catching a gamma ray burst and the triggering event together. Their observations of the fading afterglow from this nearby burst -- tentatively classified as a hypernova -- have provided the best direct evidence so far, said Thomas Matheson of the Harvard-Smithsonian Center for Astrophysics. "There should no longer be doubt in anybody's mind that gamma ray bursts and supernovae [and hypernovae] are connected."

-- Kathy Sawyer