Using a sensitive, new X-ray telescope, astronomers have identified the origin of the high-energy part of the X-ray background and found that supermassive black holes at the cores of galaxies are far more numerous than visible-light surveys indicate. (p. 36)

A new method of disrupting genes, called RNA interference, works in mouse cells. (p. 36)

Fragments of viral genetic material show up with unusually high frequency in nerve tissue of patients with ALS, or Lou Gehrig's disease, suggesting a link between the virus and this lethal illness. (p. 37)

Researchers have linked a recent outbreak of illness at a Tennessee high school to psychological factors rather than toxic gas exposure, as originally suspected. (p. 37)

In butterfly populations afflicted by male-killing bacteria, females gather in frantic swarms to mate. (p. 38)

A bit of fossil fakery snookered a team of paleontologists (p. 38)

Several experimental findings that conflict with predictions of the prevailing standard model of particle physics suggest that nature may include another force beyond the four known ones. (p. 39)

A new understanding of the basic chemistry of plutonium could affect the way nuclear waste is stored. (p. 39)

Biologists have discovered a mechanism for communication between two types of bone cell, and they're exploring the possible bone-growth-stimulating effect of popular cholesterol-lowering drugs called statins. (p. 41)

By coordinating measurements from telescopes, planes, balloons, and a battery of instruments, terrestrial and space scientists have now placed themselves on almost intimate terms with sprites—luminous shapes that fleetingly appear high above lightning storms. (p. 45)

A female blue tit with a particularly dashing mate is more likely to have sons than is a female matched with a ho-hum guy. (p. 40)

A survey of 166 hummingbird species links sex differences in bill length to sex differences in plumage and to breeding behavior. (p. 40)

People allergic to milk products could face potentially life-threatening risks by eating casein-treated fish. (p. 40)

Scientists discovered a potent, new form of vitamin E, an antioxidant, in fish adapted for life in cold water. (p. 40)

The federal government approved food irradiation, the only technology known to kill an especially lethal strain of bacteria, for use on raw meats. (p. 40)

Two games of chance, each guaranteed to give a player a predominance of losses in the long term, can add up to a winning outcome if the player alternates between the two games. (p. 47)

Mathematicians have proved the so-called local Langlands correspondence, a broad generalization of a surprising connection between prime numbers and perfect squares. (p. 47)