CCD artefact. In CCD charge from one pixel is carried to the edge of the chip to be read, when the signal is too strong it bleeds into neighboring pixels.

This is how CCD works: https://upload.wikimedia.org/wikipedia/commons/thumb/6/66/CC...

Big diffraction spikes for oversaturated stars.

Here's an example where you get to see lots of the optics in the telescope along with the sky: https://viewer.legacysurvey.org/?ra=165.4455&dec=56.3941&lay...

Diffraction spikes are different from saturation trails. The saturation goes preferentially along CCD columns/rows, while diffraction spikes are oriented like the support of the secondary mirror.