February 11, 1998 in Nation/World

Supernova’s Blast Sets Off Stellar Display Ring Of Fire Draws Telescopes To Distant Galaxy

Paul Recer Associated Press
 

An exploding star that lighted up the southern sky in 1987 and then dimmed is starting to brighten again as its high-speed blast wave creates a ring of fire.

Though not visible from the ground, astronomers said Tuesday, the increasing brightness of the supernova remnant is clearly visible in images taken by the Hubble Space Telescope. They said light from the ring of fire should intensify over the next 10 years.

“This is the first spark of some stellar fireworks that will take place over the next few years,” said Robert P. Kirshner, a Harvard astronomer.

The exploding star, known as Supernova 1987A, was first sighted on Feb. 23, 1987, in ground telescope photo images of the Large Magellanic Cloud, a small galaxy of stars 167,000 light-years from Earth. The star is visible only from the Southern Hemisphere.

It’s believed the star was a red supergiant, 20 times the mass of Earth’s sun, that reached the end of its lifetime and exploded, heating instantly to 10 billion degrees.

High-speed particles, called neutrinos, raced out from the explosion and lighted up a disk of gas that is thought to have formed a ring around the star.

The glow from the explosion faded slowly, but a shock wave of energy, moving at about 40 million miles an hour, is now beginning to smash into the ring of gas. The violence of the collision is heating the gas to millions of degrees and setting it aglow.

Supernova 1987A is the brightest exploding star seen from Earth since 1604. By following each step of the violent process, astronomers say they will learn more about the final stages of stellar evolution.

“We get to be witnesses to an event that promises to tell us a lot about the death throes of a star,” said Kirshner.

Richard McCray, an astronomer at the University of Colorado, Boulder, said that what became Supernova 1987A probably evolved from a twin-star system that merged into a single object. The merger process caused the formation of the invisible ring of gas that is being lighted up by the explosion’s shock wave, he said.

“The ring is putting on a display the likes of which have not been seen for centuries,” said McCray.

In the center of the ring is what Kirshner called “the shredded remains of a massive star.”

Anne L. Kinney of the Space Telescope Institute said astronomers are fascinated by the inner workings of a supernova because it is believed that such explosions helped create and distribute all the heavy elements.

Early in the universe, she said, there were only hydrogen and helium, the elements that burn in the nuclear fusion fires of stars. As a star burns and evolves, it creates heavier elements, such as iron, oxygen and carbon, which are essential to life. When a large star burns all its hydrogen and helium, it can collapse and explode into a supernova that spews out the heavy elements.

“Supernovae fertilize the galaxies with this enriched material,” she said.


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