Crivello's Cauldron was the sentient heart of an artificial sun.
When the Earth's sun began to fail in the 51st century, the scientist Crivello created the Cauldron to make another one. He tried to communicate with it to give instructions, but failed and was aged sixty years as a result. He had his android Marquez throw the Eighth Doctor into the Cauldron, having realised a time traveller would not be affected as he was. The primed Cauldron departed for the Crab Nebula, where it became the centre of a new star system in an unpopulated area in that region. (COMIC: The Keep)
The Doctor and Izzy landed on Icarus Falling in the 53rd century. This was a satelloid orbiting the new sun created by the Cauldron. Daleks led by the Dalek Supreme seized control of the Cauldron soon after. They wanted to destroy Daleks in all other parallel universes. They needed the Cauldron to create a stable time rift to access those other universes.
However, the rift was not one directional, and other universe Daleks poured through the opening. In the chaos, the Doctor got Brother Ptolemy Muttonchops to make the Cauldron's sun go supernova. This destroyed all the Daleks present from all the universes. The sun then returned to normal. (COMIC: Fire and Brimstone)