When a U.S. spy satellite first detected bursts of gamma radiation
in 1967, analysts took the readings to be evidence of Soviet nuclear
tests, which is what the satellite was looking for. Today's astronomers
know that gamma ray bursts come from outer space, not Asia. But
back then the equipment wasn't capable of pinpointing the source
of the radiation, so suspicion was wrongly cast in the Russians'
direction.
Not until 1997 was there equipment in orbit capable of locating
the direction from which gamma ray bursts were coming. And it
wasn't until May of last year that a team of astronomers led by
Notre Dame physicist Peter Garnavich could claim to have determined
the source of at least some of the gamma ray bursts -- the explosion
of giant stars.
By comparing readings from an Italian satellite with views from
a telescope in Chile, the team showed that a burst of gamma radiation
detected in November 2001 coincided with and came from the same
location as a massive star exploding more than 6 billion light
years away. That means light from the supernova started moving
toward Earth before there even was an Earth.
Although gamma rays are at least 100,000 times more energetic
than light, Earth's thick atmosphere of oxygen and nitrogen protects
us from harm, according to Garnavich. A star explosion big enough
and close enough to harm Earth may have already occurred, but
we won't know about it until the light and other radiation gets
here. That could take thousands of years.
