Satellites hunting secret nuclear tests found the universe's biggest explosions
On 2 July 1967 two American Vela satellites, launched to catch covert Soviet nuclear tests in space, recorded a flash of gamma rays unlike any bomb. It took decades to learn what they had seen: explosions in far-off galaxies that briefly outshine everything else, surpassed in energy only by the Big Bang.
The Vela programme existed because the United States feared the Soviet Union might cheat on the 1963 Nuclear Test Ban Treaty. After a long analysis, the mysterious bursts were published as science in 1973. Hundreds of explanations followed, including comets smashing into neutron stars, and most early theories assumed the sources lay inside our own galaxy.
That idea collapsed in the 1990s. From 1991 the Compton Gamma Ray Observatory, carrying an extremely sensitive detector called BATSE, showed that bursts arrive evenly from every direction. Sources within the Milky Way would crowd along the galaxy's flat plane. Meanwhile, searches for any matching object at other wavelengths, from pulsars to quasars, kept coming up empty.
The turning point came in 1997, when the Italian-Dutch satellite BeppoSAX caught the fading afterglow of a burst, the glow produced as debris slams into surrounding gas. A later burst that year, GRB 970508, was pinned down within four hours, and its light revealed a distance of roughly 6 billion light years. Bursts can last from milliseconds to hours; most are now thought to mark a massive star collapsing into a neutron star or black hole, while short ones come from two neutron stars merging.
Such distances imply staggering power: a typical burst releases in a few seconds about as much energy as the Sun will over its whole 10-billion-year life. They are also rare, perhaps a few per galaxy every million years, and every one recorded so far has come from beyond the Milky Way. New missions keep watch, including the Chinese-French Space Variable Objects Monitor, launched on 22 June 2024.
Source: Gamma-ray burst
