Science

Astronomers have long theorized the existence of the invisible substance because without its mass, galaxy clusters would not have sufficient gravity to keep from flying apart.

The ring is huge, measuring 2.6 million light-years across. It was found in a galaxy cluster 5 billion light-years from Earth. Jee said he was first annoyed when he saw the ring because he assumed it was a distortion or artifact. It took months of checking and rechecking before his team became convinced that the ring was actually a manifestation of dark matter.

-- Marc Kaufman

More Products Being Made From Nanomaterials

Nearly 500 consumer products in 20 countries are being made with nanomaterials -- engineered ingredients a mere 80,000th the width of a human hair that are prized by manufacturers for their extraordinary properties and feared by others for their still uncertain environmental and health effects, a new survey has found.

The inventory includes more than 150 kinds of clothing and cosmetics, including stain-resistant pants and medicinal face creams, and has more than doubled in length since March 2006, when the Project on Emerging Nanotechnologies started compiling the list.

About one in five items in the inventory ( http://www.nanotechproject.org/consumerproducts) contains nanosilver -- microscopic bits of silver that kill bacteria. The Environmental Protection Agency has said it will regulate some but not all nanosilver products, because their disposal may harm beneficial bacteria in the environment.

The United States leads the nanopack with 247 products, but East Asian countries claim 123, a 58 percent increase from last year.

Andrew Maynard, the project's science adviser, has argued for a more organized national approach to assessing the nascent technology's risks, and Bush administration officials have said they are preparing a plan.

The environmental group Natural Resources Defense Council last week released a report ( http://www.nrdc.org/health/science/nano/nano.pdf) calling for a halt to human or environmental exposures to nanomaterials until more safety studies and an adequate regulatory framework are complete.

-- Rick Weiss