Exploding star to gauge universe's size, age

PHILADELPHIA - New discoveries about a spectacular exploding star will help astronomers pin down the size and age of the universe to an accuracy never before possible.

"This is an achievement of great importance," said Nino Panagia, a scientist with the Space Telescope Science Institute in Baltimore, who used a camera on the orbiting Hubble Space Telescope to make the discoveries. He announced his findings at the annual meeting of the American Astronomical Society in Philadelphia.

Panagia said his team had used the camera to discover a gaseous ring around the remnants of supernova 1987a, a star that exploded on Feb. 23, 1987, in a neighboring galaxy, known as the Large Magellanic Cloud. That explosion was about 1,000 times brighter than any other supernova witnessed in nearly 400 years and helped astronomers confirm key theories about the evolution of the universe.

Panagia said both the discovery of the ring last August and the ability to use the observations to determine the age of the universe were unexpected.

Astronomers believe that the universe is roughly 15 billion years old, with estimates of its age ranging from 10 billion to 20 billion years. Panagia said the space telescope findings should enable astronomers to narrow the estimated age considerably - perhaps to within 15 percent of its actual age.

He said astronomers had used the faint-object camera of the space telescope to estimate the distance to the Large Magellanic Cloud galaxy at 169,000 light-years. Previous estimates had ranged from 143,000 to 179,000 light-years.

A light-year is the distance light travels in a year at a speed of 186,000 miles per second, or about 5.9 trillion miles.

By studying the structure of the ring around the supernova, astronomers were able to estimate the ring's diameter at 1.37 light-years. They then used this to calculate the distance to the Large Magellanic Cloud.

"Within five years we should be able to use this distance as a yardstick for determining the size and age of the universe," Panagia said.