As we look up at the starry sky, countless celestial bodies silently peer down upon us. Most of these have been there for billions of years as stellar processes slowly unfold, starting from their birth until their final demise. Light from other celestial objects, though long vanished, has only recently reached us. In other instances, swift changes in the sky occur at timescales as short as seconds or minutes, like when a dwarf star momentarily flares up or when a human satellite crosses the field of view.
My team has been searching for objects that may have vanished. As an unexpected result of our searches, we found cases where multiple star-like objects (transients) appeared and vanished in a small image within an hour, and even more peculiarly, two of our brightest cases happened in July 1952, coinciding in time with the 1952 Washington D.C. UFO flyovers. But what have we actually found, and how do these two events potentially link to one another?
In the Vanishing & Appearing Sources during a Century of Observations (VASCO) project, our team has been dedicated to the search for celestial objects that vanished over the span of 70 years. In the grand scheme of cosmic time and the billions of years needed for a low-mass star to turn into a white dwarf, seventy years is only a fleeting moment in cosmic time. But 70 years is also much longer than the time needed for a satellite to pass through the telescope’s field of view. Our original objective was to search for a star that had vanished, with the hope of detecting instances where a star directly collapses into a black hole (failed supernova), an event predicted by supernova theoreticians. Alternatively, we were intrigued by the prospect of finding a star that vanishes entirely without a trace or explanation; a signature of a highly advanced civilization.
However, this task was far from straightforward. My colleague spent two years developing powerful methods [5] for sifting through the vast terabytes of image data involved. In parallel, we were (and still are) running a citizen science project together with scientists, amateur astronomers, and students primarily in Algeria and Nigeria, to search for these vanishing stars.
For our searches, we employed an object catalog sourced from the US Naval Observatory (USNO) together with archival images dating back to the early 1950s, captured at the Palomar Observatory in California. The images from Palomar predate the dawn of human space exploration. This night sky was pristine, and a far cry from today’s sky that is littered with tens of thousands of debris pieces from human satellites in orbits around the Earth, many producing flashes lasting fractions of a second as they reflect sunlight and tumble through space. These images we compared to the modern databases from Palomar Sky Survey, PanSTARRS, and the Gaia satellite in our quest to find disappearing objects.
We still haven’t found a single failed supernova candidate. However, our exploration has led us to a more intriguing discovery: several images where multiple star-like objects appear in a single snapshot of the sky, never to be seen again. In a specific instance [1], nine faint objects looking like stars were visible in an image captured on April 12, 1950, during a 50-minute exposure. However, they were absent in the image taken just 30 minutes earlier and in another image from six days later. We searched through all available archives in an attempt to locate the nine objects. We directed the world’s largest optical telescope, the Gran Telescopio Canarias, with its 10.4-meter aperture, to the locations where the transients had been. Nothing was found. The objects had simply vanished.
Hellbound and Down 