'Starquake' floods Earth with radiation Brief event Aug. 27 shut down satellites with gamma, X-rays

September 30, 1998|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

WASHINGTON -- Scientists say a blast of X-rays and gamma %% rays swept Earth last month, sending radiation detectors off the scale on seven satellites, temporarily shutting down two of them. %%

%% Astronomers studying the five-minute jolt believe it was triggered by a "starquake" on a tiny but intensely magnetic star, or "magnetar," 20,000 light-years from Earth.

The five-minute battering of Earth's atmosphere is being called the first event outside our solar system known to have caused a significant change in Earth's environment -- electrical changes in the upper atmosphere that briefly altered radio communications over half the globe.

The radiation never reached the planet's surface, and it posed no health threat, scientists said.

"It is astounding, even to somebody like me who thinks daily about neutron stars and black holes," said Jim Cordes, a Cornell University astronomer with no direct connection to the discovery.

The intense wave of radiation struck Earth at 5: 22 a.m. EDT Aug. 27. It arrived from a point high over the night-darkened Pacific Ocean and bathed that half of the planet, reaching as far east as Colorado.

Kevin Hurley, a research physicist at the University of California at Berkeley, said scientists were alerted by seven research satellites, which signaled they were awash in intense X-rays and gamma rays.

One of the two satellites that retreated briefly into a "safe mode" to protect their instruments was the Near Earth Asteroid Rendezvous spacecraft. Launched in 1996 by the Johns Hopkins University's Applied Physics Lab, NEAR is en route to a 1999 meeting with asteroid Eros.

Astrophysicists quickly traced the radiation to a neutron star called SGR 1900+14. Visible only to X-ray telescopes, SGR 1900+14 had been observed since May by astronomer Chryssa Kouveliotou, of NASA's Marshall Space Flight Center. She was drawn by its X-ray glow and repeated five-second bursts of gamma rays.

Neutron stars are the remnants of ordinary stars that have exhausted their nuclear fuel and collapsed, blowing away their outer layers in spectacular explosions called "supernovae."

What remains are tiny orbs barely 12 miles in diameter. They have fluid cores of subatomic particles called neutrons, covered by mile-thick rigid metallic shells. So hot they glow in X-rays, neutron stars are also unimaginably dense. University of Texas astrophysicist Robert Duncan said a tablespoon of SGR 1900+14 would outweigh an aircraft carrier.

In 1992, Duncan and Christopher Thompson, of the University of North Carolina at Chapel Hill, proposed that a rapidly spinning neutron star would have a magnetic field so powerful that it would periodically tear up its metallic crust in a huge starquake, releasing vast amounts of radiation.

They dubbed their theoretical object a "magnetar."

"You would not want this star to be your sun," said Hurley. "It is extremely lethal." Space farers who survived its radiation would find their atoms fatally rearranged by its magnetic field.

Duncan and Thompson believe the power of the Aug. 27 blast -- coupled with Kouveliotou's observations -- constitute strong evidence that SGR 1900+14 is truly a magnetar -- a new addition to scientists' cosmic zoo.

Cordes agreed. More studies are needed to confirm what's been learned so far, he said, but "it looks like they were right on."

Pub Date: 9/30/98

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