There are few beings in the Marvel Universe as powerful as the Heralds of Galactus, a fact that Thanos was all too happy to exploit when one of the Heralds died. The resulting cosmic artifact reveals a lot about the Power Cosmic that Galactus wields, but opens up even more questions about its nature.
Galactus’ arrival is almost always preceded by his Heralds, beings he uses as forward scouts to find planets for him to devour. To do so, Galactus imbues his Heralds with the Power Cosmic, a type of seemingly limitless energy that he creates. In Dan Slott and Javier Rodríguez’s Reckoning War: Trial of the Watcher, an alternate Reed Richards identifies the energy as similar to the cosmic radiation that empowered the Fantastic Four, but the exact nature of the Power Cosmic has always remained vague. The first of Galactus’ empowered Heralds is only known as the Fallen One, and is imprisoned after going mad. Despite turning against Galactus, the Fallen One retains the Power Cosmic, but dies during the event Annihilation.
The Fallen One Provides a Path to the Power Cosmic
In Yondu #2 by Zac Thompson, Lonnie Nadler and John McCrea, it’s revealed that after the Fallen One's death, Thanos had his remains turned into an Urn that allows its holder to use the Power Cosmic themselves. Knowing that the Power Cosmic would still reside in the Fallen One’s body, Thanos had the corpse brought to the Dwarves of the Asgardian realm of Nidavellir, the greatest weaponsmiths in the universe. However, Thanos’ own death in Kieth Giffen and Andrea Di Vito’s Annihilation #4 prevents him claiming the Urn, which passes into legend before being found by Yondu.
Even the very framing of the Power Cosmic as a weapon by Thanos is revealing. In Yondu #4, Yondu’s descendent, the classic Yondu of the 1960s Guardians of the Galaxy team, explains that since the Power Cosmic can essentially do anything, it’s only a destructive force in the hands of someone who wants to use it as one, which includes most Heralds. This observation pays off in Yondu #5, the series’ conclusion, when Yondu and the Silver Surfer gift the Herald’s Urn to the survivors of Galador, planet of the Spaceknights, which was thought to have been destroyed in Jonathan Hickman and Jim Cheung’s Infinity #1. Because the surviving Spaceknights only wish to restore their planet, their purity of heart allows them to use the Urn for good, hidden on the overlooked planet. It’s a neat reversal, since Galactus almost always uses the Power Cosmic to aid in destroying planets, and now it’s put to use in healing one.
Interestingly, the classic Yondu mentions in Yondu #2 that the Power Cosmic itself cannot be destroyed, even with its wielder’s death. From a physics perspective this makes some sense. Energy cannot be created or destroyed, only converted into other forms. This does, however, raise the question of what would happen if the body of the Fallen One had been cremated, disintegrated or in some other way totally destroyed. Does the Power Cosmic in itself need to be held in a physical form? What is "energy" when it’s at home? Thanos’ actions have inadvertently raised so many more questions about the nature of Galactus’ power, and it just goes to show that even in a universe with so much history, there will always be some things that remain unknowable.