The Bubble at the Heart of Time blocked time travel across realities and before and after the time of its formation. The Council of Cross-Time Kangs learned of its existence and believed that it was the home of a renegade Celestial who had created a great weapon within it. The traitorous Kang Nebula tried manipulating the Avengers into penetrating the bubble so she could claim the weapon for herself but her attempt ultimately failed. Eventually, Reed Richards learned of the bubble's existence, and built a timesled to pierce the bubble. With the help of Iron Man (Tony Stark), Thor, Gladiator of that reality, and the rest of the Fantastic Four, the time bubble was destroyed.
The Bubble at the Heart of Time formed as the result of a warp in space-time from Galactus of Earth-8810 consuming a large amount of matter. After Galactus lay dying on Earth as a result of his battle with Terrax and the Fantastic Four, the Black Celestial restored him to full health but increased his hunger. As a result, Galactus created a black hole to draw enough matter to him to satisfy his hunger. Twenty years later, Galactus had gathered so much mass that he warped space and time around him to such an extent that it created a time bubble. The time bubble prevented time travel before and after, extended across other time lines, and threatened to destroy the entire universe. The Black Celestial created a device that would ensure his own survival and would allow him to start a new universe. Eventually, the Fantastic Four discovered the time bubble and enabled Galactus to use the Ultimate Nullifier to destroy both himself and the time bubble.
Galan of Earth-8810 (deceased)