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'87 Supernova Offers Science Unique Look at Sun's Origin

January 24, 1988|WILLIAM HARWOOD | United Press International

CAPE CANAVERAL, Fla. — About 160,000 years ago, the unstable iron heart of a giant sun suddenly collapsed, triggering a devastating shock wave in less than a second that blew the star to pieces and, for an instant, generated more energy than all the starlight in the universe.

In less than 10 seconds, a torrent of subatomic particles called neutrinos blasted away from the collapsed core, by then probably an ultra-dense neutron star just 30 miles across, carrying news of the stellar catastrophe across the universe at or near the speed of light.

The titanic shock wave created a blinding flare of light that followed close behind. Showers of high-energy gamma rays, reduced to visible light and delayed by collisions with material in the expanding cloud of stellar debris, ultimately followed.

Difficult to Detect

The energy generated in the explosion--temperatures reached more than 10 billion degrees--created heavy metals out of lighter elements. Thus the star's wreck seeded that region of the universe with the building blocks of future solar systems.

About 160,000 years later, on Feb. 23, 1987, the flood of penetrating neutrinos, which can pass through light-years of solid lead without being stopped, reached Earth's solar system.

A light-year is the distance light travels in a year at a speed of 186,000 miles per second. By this yardstick, the explosion occurred 160,000 light-years from Earth.

Neutrinos are electrically neutral subatomic particles that have virtually unmeasurable mass, if they have mass at all. They seldom interact with other particles--hence their great penetrating power--and are thus extremely difficult to detect.

Nonetheless, 19 of the elusive particles were detected by sophisticated instruments in the United States and Japan, along with another five detected in Italy that may be associated with the explosion, but no one noticed at the time. And then, three hours later, the light arrived.

On a cold mountaintop in Chile, Canadian astronomer Ian Shelton noticed a star in the Large Magellanic Cloud, a satellite galaxy to Earth's Milky Way, that was far brighter than any star he could remember in that area.

He quickly realized he had stumbled onto a magnificent discovery. Telegrams were sent to observatories around the world announcing what turned out to be the closest supernova visible from Earth in nearly 400 years.

It was Feb. 24, 1987, and the telegrams marked the event of the year, if not the century, for astronomy.

Unprecedented Detail

Even though about 620 supernovae have been observed throughout recorded history, the vast majority were so far away that it has been extremely difficult to study more than their general behavior. Supernova 1987A is in a class by itself in that regard and, as exciting as its discovery was, the best was yet to come.

Because the supernova is so relatively close as astronomical distances go, scientists have been able to study the rare celestial phenomenon in unprecedented detail using the full array of modern instruments both on the ground and in space.

For the first time, astronomers have been able to identify the original, or "progenitor," star that exploded--Sanduleak-69 202--which is crucial to understanding what kinds of stars can experience such devastating deaths.

They have detected the neutrino burst that signified the original collapse of the star's unstable iron core and, as 1987 came to a close, gamma rays were observed for the first time, confirming the creation of heavy metals like iron through a process called "explosive nucleosynthesis."

Edward Chupp of the University of New Hampshire is the principal investigator of a joint U.S.-West German experiment aboard NASA's Solar Maximum Mission satellite. The instrument detected gamma rays from the supernova in August.

"The idea is that our sun, when it was formed, was formed out of material debris that was the result of explosions of other stars that were dispersed throughout space," he said. "So, in a sense, we're finding out our own origins."

The discovery was a triumph for modern astronomy.

'A Long Time to Come'

Astrophysicist Stan Woosley of the University of California at Santa Cruz and M. M. Phillips of the Cerro Tololo Inter-American Observatory in Chile wrote in a paper for the journal Science: "The great beauty of this supernova is that . . . we will be able to observe it at all wavelengths for a long time to come."

"But the most important and exciting events will come unforetold as supernova 1987A continues to be the answer to an astronomer's prayer--'Surprise me!' "

Supernovae have long fascinated astronomers because they represent the most violent events in the universe. When Sanduleak's core collapsed, the neutrinos that were emitted in one second carried away 100 times the entire energy output of Earth's sun over the 5 billion years it has been in existence.

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