During the extraction process, it’s revealed that the energy within the star fragment consists of bluish white positive energy and the reddish jet-black negative energy. Both energies are cancelling each other due to it’s opposing properties: blue energy is more stable and safe than it’s red counterpart that was unstable and dangerous. This was discovered when the positive energy extracted completely from the star fragment, left the fragment nothing but highly unstable and corruptive red energy. So, they decided to have them inserted into separate cores that must be separated at all costs.