The Nine Astral Rivers were filled with incredible secrets, there would be some abnormal constellations that had a possibility to appear in any of the Heavenly Layers.
However, there were also some constellations that not everyone would be able to form an innate link with. These types of constellations typically chose their own masters, sending out a powerful attraction to the Stellar Martial Cultivator as the cultivators wandered in the Heavenly Layer. This would direct their consciousness over, allowing them to form innate links and then condense an Astral Soul from that particular constellation.
Chu Tianjiao and Chu Chen, were both people from the Royal Clan, but to think that they both actually had the destiny of an emperor, as evident from the fact that they condensed an Astral Soul from the Amethyst Emperor Star. This caused many in the crowd to be astonished.