What was the letter from Cygnus ten thousand years ago?

Cygnus wrote in a letter 10,000 years ago: High-energy gamma rays were detected at the high-altitude cosmic ray observatory in Haizishan, Daocheng County, Sichuan Province, China.

This ray may be emitted by the poles of a supermassive black hole, may be the product of a supernova explosion, or may be a pulsar signal. The discovery of this observatory has broken through the existing cognition of human beings. The photon energy of gamma rays discovered this time is as high as 1.4 eV, which is the highest energy gamma photon recorded by human beings so far.

Introduction to cygnus:

Cygnus, one of the northern constellations, is a mysterious constellation. At 20 o'clock on September 25th every year, Cygnus rises to the sky. Summer and autumn are the best time to observe Cygnus. Interestingly, the rise and fall of Cygnus is really like a flying swan: it rises obliquely from the northeast to the sky, and when it reaches the zenith, its head points to the west. When it moves to the northwest, it turns head down, tail up and disappears on the horizon.

The main star of Cygnus is arranged in a big cross, so it used to be called "Northern Cross". It's easy to imagine the cross as a swan. A long vertical cross is a swan's long neck and its wings are spread horizontally.

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