Vanishing Points in Old Sky Photographs express
In the 1950s, telescopes photographed the sky on glass plates. Now those images are digitized, and they can be compared with modern surveys. Astronomers wrote a program that automatically finds bright points on old frames and checks whether they appear in new images. If a point was there but is now gone, it's a candidate for a 'vanished source.'
The program checked 30-minute patches of sky across the entire survey and, after filtering out false positives, found 2.85 million such candidates. Comparison with a catalog of 5,399 previously known 'vanished' objects yielded matches in 3,450 cases: that's 63.9%. The average coordinate discrepancy is only 0.94 arcseconds, meaning the points align almost perfectly.
Next, they checked whether the disappearances were linked to specific observation nights. It turned out that on the day after some nights, there are slightly more candidates than on random days, but the difference is small and could be due to chance. A statistical test gives a 17% probability of randomness, while a stricter model gives 71%. This means no temporal pattern is evident so far.
The main takeaway: the method works and confirms old findings, but more thorough checks are needed to search for rare events. The archival plates remain a treasure trove of mysteries, and now there's a tool to sift through them.
The Palomar Survey plates were digitized in the 1990s, and each image takes up about 1 gigabyte, the entire archive weighs in at tens of terabytes.