Particle Flow Confirmed--Supernova Is Spewing Them
In what one astronomer termed “the most important event in astronomy” in two decades, scientists around the world have confirmed that the recently detected exploding star more than 150,000 light-years away has bombarded the Earth with neutrinos, offering strong proof for some of the most fundamental theories about the evolution of the universe.
Neutrinos, which are subatomic particles so small that they usually pass through the Earth without hitting anything, were captured in huge underground detectors in Japan and Ohio at almost exactly the same time, scientists said Tuesday. The reports confirm what scientists had been hoping for since last week, when the first report of such neutrinos was made in Italy.
Ironically, that report now appears to be wrong.
Detection of Neutrinos
The detection of the neutrinos, which traveled for 900 quadrillion miles to get here, added to the near state of ecstasy in which many astronomers have found themselves the last two weeks because of the discovery of the supernova in the neighboring galaxy.
The supernova is the closest to the Earth in nearly 400 years, and it was discovered just as the star exploded, allowing scientists to study it during its earliest stages.
Astronomers, however, have been confronted with a few surprises as research that could last decades got under way.
Soon after Canadian astronomer Ian Shelton at the Las Campanas Observatory in northern Chile discovered the supernova, astronomers concluded that the supernova resulted from the explosion of a giant star called Sanduleak-69. That is the only star believed large enough to cause a supernova that shows up in previous photographs of that region of the sky.
However, astronomers from the Goddard Space Flight Center in Maryland and the Smithsonian Center for Astrophysics in Massachusetts were astounded when they studied the supernova with the International Ultraviolet Explorer, the largest telescope now in orbit. Sanduleak-69 was still there, although temporarily dwarfed by the spectacular show from the supernova--meaning that it was another star that had exploded.
Studying Photographs
Astronomers have been studying other photographs in hopes of finding it, but with no success.
So as it stands now, no one is sure which star exploded.
Nothing concerning the supernova has so intrigued scientists as the neutrinos, which were captured on Feb. 23, even before the supernova was discovered the following evening.
“It’s quite a startling event,” said Frederick Reines of the University of California, Irvine, who proved the existence of neutrinos in 1956 when he created antineutrinos in a nuclear reactor.
Although neutrinos emitted by the sun have been detected in the past, these are the first neutrinos ever captured from a source outside the solar system, and they help confirm the theory that exploding stars create the elements from which other stars are born.
‘We are all on a supernova high,” said John Bahcall of the Institute for Advanced Study at Princeton. After the supernova was discovered, he predicted that the neutrinos would be detected, and in what quantities. “We’re very intoxicated.”
The frenzy for astronomers began late last week when scientists at a detection facility at Mont Blanc in the French-Italian Alps reported a sudden burst of five neutrinos within a seven-second period on Feb. 23. Since neutrinos from the sun arrive continuously, and not in bursts, the sudden activity suggested that the burst had come from the supernova, just as the theorists had predicted.
Agonizing Uncertainty
There followed, however, an agonizing period of uncertainty while astronomers around the world awaited reports from other detectors confirming the Mont Blanc finding. Any neutrino detector in the world should have recorded the burst at the same time as Mont Blanc, since the blast from the supernova would have dispersed neutrinos evenly in all directions, but the reports were not forthcoming.
Finally, the reason for the delay began to surface.
Early Tuesday, the report everyone had been waiting for arrived at the International Astronomical Union’s Central Bureau for Astronomical Telegrams in Cambridge, Mass., a clearinghouse for astronomers. The report was from the Kamiokande-II detector in Japan, operated by the University of Tokyo and the University of Pennsylvania. It is by far the largest neutrino detector in the world, where electronic impulses from neutrinos striking electrons in an underground lake deep in a Japanese mine can be detected, thus proving that neutrinos have arrived.
Observed Neutrino Burst
The report stated flatly that the detector had “observed the neutrino burst from Supernova 1987A,” the recently discovered supernova in the Large Magellanic Cloud, the galaxy closest to the Milky Way. Eleven neutrinos were captured during a 13-second period.
However, the Japanese facility detected the neutrinos five hours later than Mont Blanc, an inconsistency that means one--or both--facilities had to be wrong because the wave of neutrinos would have swept across the entire Earth at the same time.
Ohio came to the rescue.
The Ohio detector, operated in part by a team from UC Irvine, had detected eight neutrinos during a 10-second span at precisely the same time as the detector in Japan.
“The accidental probability (of both facilities getting the wrong reading at exactly the same time) is so close to zero that it has to be something for real,” Reines said. “It can’t be just some local glitch.”
The logical conclusion, several astronomers said, is that while the Mont Blanc reading must have been off, it would be too much of a coincidence for both Japan and Ohio to come up with false readings at precisely the same time, so the neutrinos had indeed arrived on Earth, although five hours later than originally thought.
Extremely Important Finding
“In my opinion, that settles the question,” Bahcall said.
The finding is extremely important to astronomers because it confirms that Supernova 1987A did just what theorists said it would do. According to the theory, when a giant star dies, it collapses on itself and then explodes violently, creating the heavy elements that are dispersed to form other stars.
But just before the star explodes, according to theorists, copious amounts of neutrinos should be formed in the star’s highly agitated core, and subsequently ejected by the explosion. Thus if the theory of stellar dynamics is correct, neutrinos should be detectable on Earth about the same time as the first light from the explosion arrives, since they travel at very close to the speed of light.
And that, astronomers said Tuesday, appears to be exactly what has happened.
