Following my Coursera course "Analyzing the Universe" in week five there was a fun part to separate x-rays with different energies into a RGB energy spectrum.

It is believed that the point-like light source in the middle of the remnant is a neutron star.

Red was assigned to energies between 0.1 and 1.5 keV, green between 1.5 and 2.2 keV and blue between 2.2 and 10 keV. I loved the result so I abused this scientific work in Photoshop and transformed it into something more artistic ;) Hope you enjoy it.

Remember these are not red, green or blue photons, just x-rays with different energies assigned to the according color.

If you are interested I think you can still access this course here: https://www.coursera.org/learn/analyze/

Wikipedia:

Cassiopeia A (Cas A) is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away within the Milky Way.[2][3] The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective. In wavelengths of visible light, it has been seen with amateur telescopes down to 234mm (9.25 in) with filters.[4]

It is estimated that light from the stellar explosion first reached Earth approximately 300 years ago, but there are no historical records of any sightings of the supernova that created the remnant. Since Cas A is circumpolar for mid-Northern latitudes, this is probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth (although it is possible that it was recorded as a sixth magnitude star 3 Cassiopeiae by John Flamsteed on August 16, 1680[5]). Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and re-absorbed much of the light released as the inner star collapsed.

Cas A was among the first discrete astronomical radio sources found. Its discovery was reported in 1948 by Martin Ryle and Francis Graham-Smith, astronomers at Cambridge, based on observations with the Long Michelson Interferometer.[6] The optical component was first identified in 1950.[7]