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 2002 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.