Light Echoes from Supernova 1987a
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Amateur Detection of the Light Echoes from Supernova 1987a
This image shows what I believe is the first amateur detection of light echoes from SN1987a - 33 years after the event!
The light echoes are produced when the initial flash from SN1987a is subsequently reflected off interstellar dust as light travels outward from the event. Direct light from the supernova was observed on Earth in 1987, and we then see light reflected from dust in the interstellar space arriving later because it has travelled further to reach us.
The image was created by subtracting two Luminance images taken almost 8 years apart, on 24th Oct 2012 and 21st Sep 2020 respectively.
The light areas in the image represent areas that were brighter in 2012, and dark are areas that were brighter in 2020. The light echoes appear as concentric roughly circular arcs, centered on SN1987a's location. This clearly shows how they have expanded during the 8 years.
The echoes also appear to be moving outwards at superluminal speed: With a shift of ~47 pixels in the image, and an image resolution of 0.764"/pixel, the movement corresponds to around 28 light years at the distance of the Large Magellanic Cloud where the supernova occurred (163,000 light years away). This is clearly much faster than the speed of light given there are only 8 years between the images. This apparent superluminal speed is only an illusion though, and does not represent the actual speed of the outward travelling light (see https://en.wikipedia.org/wiki/Superluminal_motion)
To create the difference image I first aligned the 2012 image exactly to the 2020 image, using star alignment and frame adaptation in PixInsight. Afterwards the two images were background subtracted to ensure the best possible comparison and to, hopefully, allow the detection of any faint arcs from the light echoes. Lastly, I subtracted the 2020 image from the 2012 image using PixelMath to reveal the difference that had occurred over 8 years. I was surprised to immediately see very large and prominent light echoes centered around the SN1987a location!
For a final touch, a light noise reduction has been applied to smooth the background.
I'm not sure if Tarantula nebula in the lower right indeed got brighter over the last 8 years, so its presence in the difference image may just be a result of slightly uneven illumination between the two datasets (they were taken with two different telescopes).
