Michael chose to use the Star Cores for a particular task. They might be worth a lot if converted into something else via Permute, but Michael used Insert on them to merge them with the four Undead Souls he had formed from the billions of Undead Souls he'd acquired with the Volcano God's help.
The Undead Souls were massive Wraths, souls tarnished by their raging emotions, but they didn't look Hyuman. The Undead Souls were made of eerily black fog, which was shaped into a Hyuman upper body with an elongated neck and head and a cloud-shaped lower body. Their appearance was interesting, but nothing to spend hours studying intensely. Michael solidified their abilities by inserting a Star Core into each of the four Undead Souls.