Okay, over in the mini-series "Last Planet Standing" it seems that we finally know what Galactus is up to. He figured that since the Big Bang gave birth to him, a second Big Bang will kick-stark his evolution to the next level.
He's put in motion a plan to restart the universe, using the destruction of the Earth as the primer for the event. He's gathered a bunch of powerful items (including Thor's hammer, and Odin's Sword), contained a number of cosmically powered beings, and contained the mystical energies of Asgard.
The destruction of a galaxy in the first issue was a trial run of the process, now he's going to do it on a universal scale using the excess energies he's been gathering, and a new star that's appeared in space.
All this because Thor used Asgard magic to create a "special star" in the sky to honor the death of Captain America. And since the Spider-gril series is coming to an end, Marvel is free to end this anyway they please.
__________________ We're on the side of the demons Cheif. We're evil men in the garden of paradise, sent by the forces of death to bring destruction and devestation wherever we go.