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While admiring this beautiful image (Spiderweb protocluster field) https://esawebb.org/news/weic2428/ captured by the James Webb Space Telescope (JWST), I noticed several (more than five) circular objects scattered randomly across the image. Each of these objects has a circular shape and appears to be quite distant from nearby galaxies. What are these objects?

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  • $\begingroup$ Original picture esawebb.org/media/archives/images/original/weic2428a.tif $\endgroup$
    – Norman
    Commented Dec 8 at 20:05
  • $\begingroup$ If there would be no other options,- I would choose primordial black holes explanation, blue region around them could be short-wavelength EM waves emitted from accretion disk. $\endgroup$
    – Agnius Vasiliauskas
    Commented Dec 8 at 20:54
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    $\begingroup$ @AgniusVasiliauskas i imagine there's a size argument or two that could be made here that would almost certainly exclude PBHs. OP: My first guess would be foreground stars that were (partially) removed when processing the image. $\endgroup$
    – Kyle Kanos
    Commented Dec 8 at 21:26
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    $\begingroup$ @KyleKanos Maybe... Just two questions for you : 1. How you would explain blue corona around these "removed objects from background" ? I mean, why is it only blue color of corona? Was it some sort of blue giant stars depicted before removal ? And 2. Why the hell to remove some blue background stars from the picture ? Was it some sort of evil needed to be removed to pleasure arbitrary observer ? P.S. As an additional note,- this "effect" can't be diffraction patterns of telescope,- they are seen as a sharp edges having $\large \star$ shape. $\endgroup$
    – Agnius Vasiliauskas
    Commented Dec 9 at 15:52
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    $\begingroup$ Yet another hypothesis is that maybe these effects are simply some defects of JWST telescope,- maybe some microscopic dust particles on the mirror or damage from HE cosmic rays at some pixel locations or something similar. $\endgroup$
    – Agnius Vasiliauskas
    Commented Dec 9 at 16:03

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These might be snowball artifacts caused by large cosmic rays that oversaturate central pixels or ghosts caused by imperfect removal of internal reflections. As discussed in "How Are Webb’s Full-Color Images Made?", however, these images go through a lot of processing so we should be very cautious in their interpretation.

Note that this question might get a better answer on Astronomy Stack Exchange, and it would be best to also give the full image with the objects circled.

Snowballs

Below is a is a very large example of a "snowball" and a CEERS NirCam Image that shows several faint snowball artifacts.

Snowball artifact from JWST documentation

Snowball artifacts identified in a NIRCam image

Ghosts

Bright objects can produce faint secondary images from internal reflections in the JWST optical systems. Such ghosts can be mitigated by processing dithered images but can still leave behind artifacts such as those shown below.

Residual ghost images after processing

"Dithering is performed by moving the telescope slightly between exposures using small angle maneuvers (SAMs), so that the astronomical scene is offset to different locations on the detector in the different exposures."

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