On July 19, 1952, the Palomar Observatory was conducting a photographic survey of the night sky. Part of the project was to take multiple images of the same area of the sky, to help identify things like asteroids.
At approximately 8:52 that evening, a photographic panel captured the light of three stars clustered together. At 15 power, it was reasonably bright in the photo.
At 9:45 p.m., the same area of the sky was captured again, but this time the three stars were nowhere to be seen. In less than an hour, they disappeared completely.
Stars don’t just disappear. They can go out, or experience a brief period of brightness, but they don’t go away. However, photographic evidence was there. The three stars are clearly in the first photo, and clearly not in the second photo.
The assumption then is that they must have suddenly died down, but even this is difficult to accept. Subsequent observations found no evidence of stars brighter than 24 magnitude. This means they are likely to be dimmer by a factor of 10,000 or more.
What could cause stars to dim by such an astonishing amount so quickly?
One idea is that they are not three stars, but one star. Perhaps a star brightened briefly, such as a fast radio burst from a magnetar. While this was happening, a stellar-mass black hole may have passed between us, causing the gravitational lensing flare to briefly become three images.
The problem with this idea is that such an event would be extremely rare, but other photographs taken during the 1950s show similarly rapid disappearances of multiple stars. In some cases, the stars are separated by arcminutes, which is difficult to reproduce by gravitational lensing.
Another idea is that they were not stars at all. The three bright spots are located within 10 arc seconds of each other. If they were three individual objects, something must have caused them to brighten. Given a time period of about 50 minutes, the causal relationship with the speed of light requires that they be no more than 6 astronomical units apart. This means that they should not be more than two light years away.
It is possible that these objects are Oort Cloud objects as some events caused them to brighten around the same time. Subsequent observations were unable to find it because it had since drifted along its orbits.
The third idea is that they were not objects at all. Palomar Observatory is not too far from the deserts of New Mexico where nuclear weapons testing took place. It is possible that radioactive dust from the tests contaminated the photographic plates, causing bright spots to appear in some images but not others.
Considering similar fades seen on other photographic plates of the 1950s, this seems entirely possible.
At this point, we can’t be sure. What we really need is to capture a few of these events in modern sky surveys, where we can quickly go back and make additional observations. For now, it’s a mystery waiting to be solved.
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