Years ago, talking about the persistent rumor that the Hubble Space Telescope was an off-the-shelf spy satellite retrofitted for astronomy*, I told a NASA employee that I was pretty sure academic astronomers were culturally anti-military and they wouldn’t be crossing lines and dealing with spies or the defense department. The NASA employee looked at me and said, “Don’t be naïve.” And ever since, I’ve been interested in the cases of interplay between astronomers and the military. The case I learned about most recently: a hyper-violent explosion called a gamma ray burst, that astronomers are still trying to figure out, was first discovered by satellites flown by the defense department’s Advanced Researth Projects Agency, ARPA, now called DARPA.
Gamma rays are light that carries even more energy than x-rays. You want to stay as far away as possible from anything that makes gamma rays. One of these things is a hydrogen bomb.
By the late 1950’s, both the U.S. and the Soviet Union had been testing bombs of just about every size and had begun thinking that making the earth and sky radioactive might be a bad idea and maybe they should sign a treaty to stop doing that. But first they’d have to figure out how to detect all the ways the other side might cheat.
In 1959, after months of negotiations, the Soviet Union wouldn’t agree to satellites that would monitor the sky for rogue nuclear explosions. A young physicist named Stirling Colgate (of the toothpaste Colgates, “I had had enough of privilege growing up,” he said), who was consulting for the US side, told the Soviets he thought the gamma ray signature of a nuclear explosion could look like the gamma ray signature of a supernova. What if a supernova went off and everybody thought it was a bomb? Two weeks later, everybody agreed to send up satellites that could keep an eye on the situation.
The US’s were called Vela satellites; they carried neutron, and x- and gamma-ray detectors. The gamma detectors were important because if the Soviets exploded a nuclear bomb behind the moon, the only way to see it would be with the gammas blown out of the radioactive cloud.
On July 2, 1967, Vela 4 recorded a burst of gamma rays, but the signature wasn’t exactly that of a nuclear explosion so the people monitoring the Vela’s shelved it. Over the four years, this happened 16 more times, gamma ray bursts that weren’t bombs. The bursts occurred randomly over the sky and seemed to be coming from outside the solar system.
The Vela monitors, government scientists at Los Alamos, published these bursting oddities, oddities that clearly were not in the realm of national security but of astronomy and therefore could be made public. One of the scientists gave a talk at an astronomy conference. The only media that covered the talk was the National Enquirer; the reporter wondered whether the bursts might coming from a nuclear war between space aliens.
The gamma ray bursts continue. Generations of astronomy – i.e., not spy – satellites have recorded them with increasing detail. Astronomers agree they’re coming from as far as 9 billion light years away, they last only seconds, they’re extraordinarily bright, they’re among the biggest explosions in the universe. Astronomer think they’re either from stars blowing up as various kinds of supernovae, or they’re from the merger of two neutron stars — the neutron star merger whose gravitational waves we detected had a burst of gamma rays. But the bottom line is, nobody knows for sure what they are.
An astronomer told me once that astronomers sometimes work with the military because their technology is often the same, but (and I paraphrase), “they’re using it to look down and we’re using it to look up.” In this case of collaboration, the outcome was the 1963 nuclear test ban treaty. And young Stirling Colgate later becoming famous studying supernovae: “I had always loved explosions,” he said.
*I have no idea.
Much of this story came from a nice online archive at the University of Chicago, in this case, a history of gamma ray astronomy written by Stirling Colgate. Other parts of the story came from a short history written by J.T. Bonnell.
Photo of core collapse supernova, one of the kind that probably emits gamma ray bursts: X-ray: NASA/CXC/Drew Univ/S.Hendrick et al, Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSFech