A massive burst of gamma rays from a star that exploded billions of years ago reached Earth on March 19, and clocked in as the brightest burst of gamma rays ever observed, astronomers say. The blast, dubbed GRB 080319B, came from 7.5 billion light years away, more than halfway across the universe. Despite the immense distance, it would have been visible with the naked eye at dark sites on Earth for 40 seconds [New Scientist]. Researchers say they burst was so bright because the jet of matter and energy was pointed directly at Earth.
Gamma ray bursts, the universe’s most luminous explosions, occur when massive stars, perhaps 20 to 30 times the mass of the sun, burn out their nuclear fuel. As a star’s core collapses, it creates a black hole that drives powerful gas jets outward [Reuters]. The collisions of particles within those jets create high-energy gamma rays, which heat up surrounding gas and produce visible light. Nobody knows whether anyone looked up at the right spot in the sky at the right moment on March 19 to see the pulse of light, but NASA’s robotic Swift observatory did what it’s supposed to when it detects a gamma-ray burst, and swung into action [Ars Technica].
The observations of the Swift satellite and telescopes around the world, published in the journal Nature [subscription required], showed that the jet just happened to be pointing directly at our planet, giving astronomers an exceptional view and unprecedented data about the powerful explosion that caused the gamma ray burst. Says researcher Judith Racusin: “We deduce that we happened to view this monster down the barrel of this very narrow and energetic jet” aimed directly at Earth [Science News].
Rarely are these jets so well-aimed at Earth, and it’s only the vast distance of their origins that keeps them from wreaking havoc on Earth’s climate. “If it happened in our galaxy we would actually be in considerable trouble,” said Swift team leader David Burrows of Pennsylvania State University. It could cause chemical changes in our atmosphere that could result in rapid global winters and mass extinction events, he said [Discovery News].
Image: NASA/Swift/Mary Pat Hrybyk-Keith/John Jones