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The mystery flash that changed astrophysics

Project Vela made one of the biggest space discoveries of the 20th century—cosmic gamma-ray bursts.
July 6, 2020
Gamma-ray burst

Gamma-ray bursts, such as the one illustrated here, are the most powerful explosions in the universe. They emit most of their energy in gamma rays, a form of light more energetic than visible light.CREDIT: NASA

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Scientists expected that there would be some naturally occurring gamma rays in outer space; what they didn’t expect were enormous bursts of them that are about a trillion times brighter than the sun.

By Virginia Grant

In 1967, Los Alamos scientist Ray Klebesadel saw, in data from two Vela satellites, evidence that something extraordinary had happened in outer space. “The instruments on the two satellites had responded to the same event,” Klebesadel says. “It was an electromagnetic phenomenon, but it wasn’t a nuclear event,” which was what the Velas were built to detect. “It was something remarkable.”

Klebesadel had discovered the most powerful explosions in the universe—gamma-ray bursts (GRBs). GRBs are essentially massive space explosions that produce gamma rays, which are a form of radiation. In order to monitor space for nuclear explosions, the detection instruments on the Vela satellites measure x-rays, neutrons, and gamma rays, all byproducts of nuclear explosions. Scientists expected that there would be some naturally occurring gamma rays in outer space; what they didn’t expect were enormous bursts of them that are about a trillion times brighter than the sun.

Declassified, the Vela detection of GRBs was published in 1973, launching a flurry of debates about their origin and nature. We now know that a GRB is produced by the collapse of matter at the formation of a new black hole, but scientists at the time could only speculate about what was causing them. Los Alamos scientist Ian Strong gave a 1973 lecture about gamma-ray bursts, after which he found physicist Stephen Hawking waiting to talk with him. Hawking, like many other scientists of the time, was interested in discussing the mysterious nature of GRBs.

Los Alamos scientists continue to build on the foundational work of Project Vela in studying GRBs with tools such as Los Alamos’ RAPTOR (Rapid Telescopes for Optic Response) robotic observatory system. Recent discoveries about GRBs have come about because of GRB-focused instruments such as the Swift Gamma-ray Burst Explorer, which uses Los Alamos–developed Burst Alert software to find GRBs, and the Fermi Gamma-ray Space Telescope, which was partially developed by Los Alamos scientists. Recently, the Swift and Fermi spacecraft detected GRB 190114C, the first, and so far only, GRB that emits ultra-high-energy photons—teraelectronvolt (TeV) photons. Discoveries like this will help scientists learn even more about GRBs.

Vela’s monumental discovery “generated an enormous amount of excitement, fostering whole new areas of research,” says Richard Belian, a retired Los Alamos physicist who worked on Project Vela. With the continued development of detection instruments for outer space, those areas of research are still being explored at Los Alamos.


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This gamma-ray burst was recorded on August 20, 2005, by the RAPTOR telescope system located at the Fenton Hill Observatory, near Los Alamos.