How to extend an Image from side to side softening the hard edge of image

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I use Gimp and Blender to make my Videos, I have an Animation of the Sun Series: 
see https://www.youtube.com/playlist?list=PL...fvNkVm3m6c

As you can see from the Image below Original 



The Corona or Radiating Fire of the Sun has a hard edge on both sides sometime, sometimes they extend up and down, but not much, and the few times this did happen I fixed them by hand, but the side ones do not look good. 

This is a NASA public domain images of the Sun in AIA 193 4096x4096 format, with an Environment image texture of the Stars as background using Blender. 

What I want to do is soften the hard line so it looks more like this:



I just did a fast Smudge by hand in GIMP, this was originally a Blender question.

There are over 33,333 images for one Year and I have over 6 years of images that I am working with, that is over 200,000 images, so I can not do this by hand in my lifetime since I am dying of Cancer my time is limited, I am old and have Arthritis as well, so it would be a very painful way to go out, and I might not finish it, so why start, but I wanted to finish this series, and go back and do years before the series started, which is 2010, so people can view the sun over a decade, but the hard edge looks bad, and I know there is a way to fix this, but I am not good enough at blender or Gimp to figure it out, I think I ask once a year, and try to figure out how to fix it, my guess is that I need to write a script that takes the edges of the images and blurs or smudges it side ways in an oval shape, but I know even less about it when it comes to automating edits in gimp, then I do about Blender, not even sure it can be done, no idea how to do that, anyone have any ideas?

I originally did the video in 1080, now I want to render it in 2160, since the originals are larger then the 3840, it should look good at 4k, but I want to fix this issue since it will take a long time to render all these images in Blender.

Thanks