In the end of season 2 of Doctor Who (2005), The Doctor needed enormous power to open the rift to the parallel universe to say goodbye to Rose. So, he burned up a star.
I don't know what burning a star means (as a star's already burning), but he also said something about orbiting a supernova, meaning he was drawing power from an exploding star (which can outshine 10 billion suns).
But why would he need that? Doesn't the TARDIS have a more efficient power source?
In the Journey to the Centre of the TARDIS episode, we saw the Eye of Harmony, the power source of TARDIS. It was created by suspending time around an exploding star in the act of becoming a black hole, harnessing the potential energy of a collapse that would never occur. From the episode, there were several exploding stars which were in permanent decaying states. Isn't this some kind of unlimited power source?
The collapse of star would never happen, but yet potential energy of collapse was the output. It looks to me a kind of time loop situation. At any given point of time outside Eye of Harmony, shouldn't Eye of Harmony give literally infinite energy as there'd be infinite number of collapse energy harness cycle by then?
Why exactly did The Doctor need to use an external, less-efficient power source in that case?