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In 1952, A Group of Three “Stars” Vanished. Astronomers Still Can’t Find Them
On July 19, 1952, Palomar Observatory was undertaking a photographic survey of the night sky. Part of the project was to take multiple images of the same region of sky, to help identify things such as asteroids. At around 8:52 that evening a photographic plate captured the light of three stars clustered together. At a magnitude of 15, they were reasonably bright in the image. At 9:45 pm the same region of sky was captured again, but this time the three stars were nowhere to be seen. In less than an hour they had completely vanished.
Stars don’t just vanish. They can explode, or experience a brief period of brightness, but they don’t vanish. And yet, the photographic proof was there. The three stars are clearly in the first image, and clearly not in the second. The assumption then is that they must have suddenly dimmed, but even that is hard to accept. Later observations found no evidence of the stars to dimmer than magnitude 24. This means they likely dimmed by a factor of 10,000 or more. What could possibly cause the stars to dim by such an astounding amount so quickly?
One idea is that they are not three stars, but one. Perhaps a star happened to brighten for a short time, such as a fast radio burst from a magnetar. While this happened, perhaps a stellar-mass black hole passed between it and us, causing the flare to gravitationally lens as three images for a brief time. The problem with this idea is that such an event would be exceedingly rare, but other photographic images taken during the 1950s show similar rapid disappearances of multiple stars. In some cases, the stars are separated by minutes of arc, which would be difficult to produce by gravitational lensing.
Another idea is that they weren’t stars at all. The three bright points are within 10 arcseconds of each other. If they were three individual objects, then something must have triggered their brightening. Given the timespan of about 50 minutes, causality and the speed of light would require they were no more than 6 AU apart. This means they would have to be no more than 2 light-years away. They could have been Oort Cloud objects where some event caused them to brighten around the same time. Later observations couldn’t find them because they had since drifted on along their orbits.
A third idea is that they weren’t objects at all. Palomar Observatory isn’t too far from the New Mexico deserts where nuclear weapons testing occurred. Radioactive dust from the tests could have contaminated the photographic plates, creating bright spots on some images and not others. Given similar vanishings seen on other photographic plates of the 1950s, this seems quite 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.
注释：
magnetar：n
表示" 磁星"，如：More thorough tests of the magnetar model would require a second giant flare. 对超强磁星体理论更彻底的检验，需要第二次的大爆发。
gravitationally: adv
表示"就重力的观点而言"，如：Gravitationally, dark matter behaves just like ordinary matter. 但就重力的观点而言，暗物质与普通物质的特性完全相同。
arcsecond: n
表示"弧度秒"，means "a 60th part of a minute of arc"，如：A 100-meter telescope should be able to see features 0.001 arcsecond across, which is 40 times better than Hubble can manage. 100米的望远镜应该看得见0.;001弧秒的东西，胜过哈伯望远镜40倍。
causality: n
表示" 缘由；因果关系"，means "the relation between causes and effects"，如：There is no causality between financial structure and real economy. 金融结构和实体经济之间并不存在因果关系。
中文简要说明：
1952 年 7 月 19 日，颇负盛名的加州帕洛玛天文台(Palomar Observatory)正在进行夜空摄影观测，当天的计划是拍摄同一天空区域的多张照片，以帮助识别小行星等物体。晚上 8 点 52 分，一张照片捕捉了三颗星聚集在一起，它们在图像中相当明亮。然而，到了晚上 9 点 45 分，再到同一天区拍摄时，三颗明星却不见了。
今日宇宙(UniverseToday)报导，星星不会凭空消失，它们或许或许出现短暂的高亮度，出现瞬间的猛烈光亮，但它们不会消失，璀璨之后仍然会有余波。然而当天的情况就是如此异常，三颗星星清楚地出现在第一张照片中，但显然不在第二张图片中。如果设它们是突然变暗，但是这也说不过去，因为在该区域的恒星的亮度没有超过 24等，这意味着它们可能亮度降低了 1万倍，甚至更多。
在不考虑非自然现象的前题，天文学家提出一些假设：
第一种看法是：它们不是三颗星，而是一颗。也许一颗恒星刚好短暂地变亮，例如有个磁星正对对地球发出强大脉冲，同时有一个恒星质量的黑洞，从磁星和我们之间经过，导致一场短暂的重力透镜现象出现，造成3个极亮的影像。
然而，这样的事件极为罕见，尤其是这3个明亮恒星之间的距离为数弧度，这很难透过重力透镜效应产生。
第二种看法是：它们根本不是恒星，而是奥尔特云的突然增亮。三个亮点彼此之间的距离在 10 弧秒以内。如果它们是三个单独的物体，那么一定有什么东西触发了它们的亮度。考虑到大约 50 分钟的时间跨度，那么它们之间的距离不得超过 2 光年。它们可能是奥尔特云天体，一些事件导致奥尔特云在大约同一时间被点亮，后来的观测无法找到它们，因为它们已经漂流走了。
这种说法没有任何实际现象左证，我们从未真正看过奥尔特云，更没看过奥尔特云被点亮的事件。
第三个种看法：地球上的核武试爆，造成观测出错。帕洛马天文台距离核武试验的新墨西哥州沙漠不太远。核武测试中产生的辐射尘可能会污染照相底片，辐射尘会使底光感光，造成不明亮点。
鉴于 20 世纪 50 年代其他摄影底片上也出现过类似的相纸污染现象，这被认为是最可能的假说。
然而，我们还不能确定「3明星事件」的真相。天文学家只能持续的观测，累积更多的数据与数据，或许哪一天会知道答案。
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