Comic book power levels never change, prompting countless debates about which character could defeat who or which artifact is more powerful than any other. In the early days of comics, it caused writers a number of headaches -- determining whether adamantium or vibranium was stronger, for instance, or setting popular heroes against each other without angering the fan base of either -- but over time, it’s become an ingrained part of the genre. Such debates can be great fun when undertaken in the right spirit, something the Marvel Cinematic Universe has always taken pains to do.

Thor: Ragnarok quietly slipped a new contender into the mix: the Eternal Flame, locked deep in Asgard’s vault as a preventative against the apocalyptic end of the world. It’s kept there along with some of the most powerful artifacts in the MCU, including an Infinity Stone, and doesn’t seem like much. The film’s central villain thinks differently, however, and when presented the opportunity to claim these other items, she passes them by. The Flame holds much more allure, and while far quieter than the MCU’s other artifacts, its sheer power is not lightly dismissed -- and its presumed destruction is far from assured.

RELATED: Marvel's Eternals Releases Major Information About the MCU Film's Villains

Surtur in Thor Ragnarok

As described in the Marvel Studios Visual Dictionary, the Flame is "a mystical, inextinguishable flame that holds the power of the Fire Demon Surtur." Surtur serves as Thor’s foe in the film’s opening scene when the God of Thunder seems to have things well in hand. He defeats the demon easily, preventing Surtur from destroying Asgard and fulfilling the Ragnarok prophecy for the time being. If the Flame carries his power, then that alone makes it worthy of Hela’s interest.

It goes deeper than that, however. If the Flame truly cannot be extinguished, that makes it a never-ending source of energy, which can be utilized in any number of ways. Hela has a specific purpose in mind when she uses it: the resurrection of the dead, including her wolf companion Fenris. Though the Flame’s abilities bring most of her army back as rotting zombies, Fenris is restored fully to life, which defies the barrier between life and death itself.

RELATED: Where Does Eternals Fall in the MCU Timeline?

As with most comic-book subjects around death, bringing someone back from the dead is tricky: depending largely on the needs of a given story at the time. But at the very least, it suggests a power on par with the Infinity Stones, which could similarly bring the dead back to life within certain limits. And unlike the Stones -- one of which Hela pointedly dismissed in her quick survey of the vault -- it can’t be destroyed or put out under any circumstances. That means that a figure like Hela could presumably draw upon it constantly, making her all but unstoppable.

Indeed, the only thing that can thwart her is releasing the Flame’s energy by restoring Surtur, which would ensure Ragnarok and destroy Asgard. Thor realizes that it’s the only way to stop Hela and lets Surtur devour the realm she has just inherited with the population evacuated, destroying her in the process. That, too, speaks to the Flame’s power. Hela smashed the previously unbreakable Mjolnir seemingly without effort and killed most of Asgard’s defenders in a similar fashion. Thor only turned to the option as a last resort after he failed to stop her. The kind of power required -- which the Flame produced when Surtur re-appeared -- suggests that it could be capable of nearly anything. And if the MCU Ragnarok is a cycle destined to repeat itself, as it’s often portrayed in the comics, then it can never be destroyed but will return anew over and over.

In fact, had Thor not triggered Ragnarok and destroyed Hela in the process, she would have likely been in possession of the Tesseract when Thanos came for it at the beginning of Avengers: Infinity War. Whether or not he could have claimed it from her is a serious question, and with the Flame, it’s not at all clear whether the Titan would prevail against her. Hela spent her long imprisonment planning a return to power, and she clearly wasn’t interested in waiting for a second longer than she had to. The fact the Flame remained her sole goal at that moment speaks volumes about its actual strength.

KEEP READING: Marvel Boss Kevin Feige Explains MCU Movie Delays