Supernovas are excellent source of light for investigation of galaxies far away from Earth as well as the excellent probe to discover new properties of light itself. This is because they are very bright and very standard (even if it is not type 1a standard candle, some properties are quite unique). The real size of supernova may be estimated from the well established fact that the maximum luminocity of it is reached at around 20-30 days after explosion (depending upon supernova type and time dilation at high z). The expelled by the explosion star is expanding at the velocity of around 0.03 speed of light [1] what gives the estimation for the diameter of supernova during the maximum brightness (at that moment they are usually discovered) as around 1.2-1.8 light days (3.1*10exp(13) to 4.6*10exp(13) meters). Despite this is much larger than the diameter of star (for example Sun has a diameter of 1.39*10exp(9) meters) the diameter of supernova is still way too small to be resolved at any distinquishable z even with the best resolution space telescope. For example for JWST for wavelength of 2 um (F200W camera) the diffraction limit for the diameter of mirror of 6.5 m is 2*10exp(-6)//6.5=5.38*10exp(-7) rad. Supernova will be observed as exactly one dot in diffraction limit starting at distance of L=4.6*10exp(13)/5.38*10exp(-7)=8.6*10exp(19) meters or ~9000 light years (that would be very small z of 6.5*10exp(-7)).
For already observed supernovas with Z>1 the angular size of it will be much smaller than the resolution of even very futuristic telescope. For example for Z=1 the distance is around 10 billions light years and the resolution necessary is around 5*10exp(-13) radian - 6 orders of magnitude better than JWST. By no means the image of supernova on the photo obtained by space telescope may be larger than exactly one dot in the sense of the diffraction limit of the telescope. The supernova is ultrabright and the angular size of the nearby supernova (like at z=0.004 in [2]) may be looking larger because of the saturation of the detector like in picture in [2] but in this case the obvious mark of saturation is present - the rays due to diffraction like from nearby star on Hubble or JWST. For supernovas at higher z and especially at z>1 the brightness of supernova is hardly enough to be registered (that is why only JWST was able to record multiple supernovas at z higher than 1) and by no means the saturation of the detector can influence the recorded angular size.
In the following photo taken from [3] several supernovas discovered by JWST are shown.
What makes this image is so special is that on the same image close to supernova at z 2.845 and 3.8 the objects with clearly visible smaller size are present (for z=0.655 the smallest objects are have the size comparable to supernova size). But as it was shown by calculation in the case of the complete absence of light scattering the supernova must have the angular size equals to the diffraction limit of telescope (be of the size of the smallest dot on the picture). The only possibility for telescope to see the larger angular size of the supernova is the presence of the light scattering (so the enlarged angular size of supernova has nothing to do with it's real size, this is property of light itself). The objects of the smaller size are inevitable "trespasses" - much closer objects contaminate the image inevitably, like lone stars somewhere on the outskirts of Milky Way - way too far to be resolved even by JWST they will be observed as real diffraction limit dots. This is because according to tired light hypothesis the light scattering is visible only for high z, at the Milky Way or nearby galaxies it is completely unobservable [4,5].
While for relatively small z 0.655 (see also [5] for image with z=0.151) the size of supernova is well below the size of the center of galaxy (where all the stars are blurred together), for the higher Z images (2.845 and 3.8) the angular size of supernova is just a little smaller than the size of the galaxy center - the real size of the object in the absence of light scattering would correspond to ~ 1000 light years (instead of ~ 2 light days), yet this is clearly just supernova because the object is not present on the similar photo taken with separation of one year.
This observation clearly demonstrates that the light itself is responsible for the large angular size of supernovas at high z. The most probably explanation of this behavior is tired light phenomenon with more information outlined in [6].
References.
3.Three JADES galaxies with supernovae (2023 vs. 2022) | ESA/Webb (esawebb.org)
https://esawebb.org/images/JADES8/
https://vixra.org/pdf/2311.0060v1.pdf
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