Within the main Marvel Universe, Thor has been through a journey that has tested the meaning of godhood. After losing both his arm and Mjolnir, he relinquished his name and became the Odinson. While he continued to fight against villains, this was Thor at his lowest, consumed by the belief that he was unworthy of the power he had wielded for years. While the War of the Realms event saw Thor prove his worthiness to the whole Marvel Universe, Donny Cates and Nic Klein's Thor has made teh God of Thunder stronger than ever.
Thor's latest transformation came at the hands of Galactus. After crashing into Asgard, Galactus revealed that the force that had destroyed his universe, the Black Winter, has returned in all its destructive power. Needing Thor's help to prepare for its eventual attack, Galactus imbued the son of Odin with the Power Cosmic, which upgraded Thor's abilities and gave him a new arm (along with a quick shave). This new form places Thor in a whole new league of cosmic powerhouses. When understanding the true power of the Power Cosmic and Thor's hammer, one finds that Thor could even take down the Mad Titan himself, Thanos.
Serving as the newest herald of Galactus, Thor has become the recipient of one of the most powerful forces of the Marvel Universe, the Power Cosmic. That power's most famous wielder, Norrin Radd, was just an average resident of his planet, Zenn-La, before becoming the Herald of Galactus. As a result, the Silver Surfer has used his power to save reality and even to create a reality in some cases. For those that already have power, like the Cosmic Ghost Rider, the Power Cosmic only adds to their inherent power to create a force that can challenge anyone.
However, the combination of the Power Cosmic and Mjolnir has already been showcased in the "Thanos Wins" storyline from Donny Cates and Geoff Shaw. After being taken to the end of the universe, Thanos joined his future self in preparing for the last and greatest threat to his ultimate victory. Among the hordes of the Annihilation Wave, the transformed Silver Surfer -- now called the Fallen One -- declared his worthiness and prepared to use the former hammer of Thor to end the reign of Thanos.
In this battle, the Silver Surfer proved himself to be a worthy threat to Thanos as he quickly began to defeat him. Unfortunately, he was undermined by his encounter with a broken Bruce Banner, who reminded him of all the heroes that had been killed by the Mad Titan. With this distraction, the younger Thanos surprised Norrin before removing his arm and killing him. Despite that, the Power Cosmic and Mjolnir stood a chance against Marvel's greatest villain at the height of his power, and the elder Thanos even turned to his younger self for help in in defeating the Mjolnir-wielding Surfer.
As this Surfer shows, the power of Galactus and Thor is already considerable, but the main Marvel Universe Thor is also the All-Father. With the powers of that position, he was able to throw Mjolnir across the realms in a feat of strength and a show in power. Taking his rightful place, Thor's power levels have already been increased. Galactus only reinforces Thor's status as one of the most powerful beings in the universe. Already, he has destroyed one iconic Marvel weapon like it was nothing.
In the past, Thor has been one of the few Avengers with the ability to challenge Thanos. While those battles usually tested Thor's power and fighting skill, his the God of Thunder's new abilities have made him strong enough to take out Thanos with ease. Given his experience as a warrior, Thor knows how to wield his power to its most devastating extent. With the threat of King Thanos looming over the main Marvel Universe again, Thor may have to succeed where the Silver Surfer failed.
But before he can turn the attention to the Mad Titan, Thor has to deal with the threat of the Black Winter, which is so serious that Galactus turned to him for help. Even if Thor has enough power to mop the floor with Thanos, the Black Winter will test the Thunder God's powers in a way few things ever have before.