Seriphia Galaxy

The Seriphia Galaxy, also designated Galaxy 17A53, was a neighbouring galaxy to the one that contained Gallifrey. It was four times the size of the Milky Way and home to over six hundred billion stars.

The Dalek Empire detonated the Apocalypse Element within the galaxy, causing widespread destruction at 18 light-years Gallifrey-relative and would be destroyed over six hours. However, the unpredictable nature of the element sped up the destruction, but the fireball was contained and kept from engulfing the universe through the use of the Eye of Harmony.

The Daleks then accelerated time to ensure that the galaxy reformed, allowing the Daleks to establish a power base within it, with control over a million Skaros. (BFA: The Apocalypse Element)