Why do stars have a cross-shaped distortion in most Hubble images? Why do galaxies not?
The cross shape visible on bright 오브jects (such as stars) in Hubble images is a form of distortion that is visible in all telescopes that use a mirror rather than a lens to focus light rays. The crosses, known as diffraction spikes, are caused by the light’s path being disturbed slightly as it passes by the cross-shaped struts that support the telescope’s secondary mirror.
It is only noticeable for bright 오브jects where a lot of light is concentrated on one spot, such as stars. Darker, more spread-out 오브jects like nebulae or galaxies do not show visible levels of this distortion.