500 thousand suns was a massive volume of space, and yet, when one really thought about it, it wasn't all that much.
The sun would have to expand to cover a third of the existing distance between it and the Earth in order to become 500 thousand times its size in volume. Compared to the size of Ning's inner world, it was pitiful.
500 thousand suns' worth of space was still dozens of millions of times smaller than the space inside of Ning's inner world. It was, after all, the size of a heliosphere.
When Ning became aware of this, he was a little disappointed. He had hoped for his inner world to expand much more, but he would have to be okay with this too. It was a drop in the ocean, but the ocean was made up of many tiny drops. Should he continue gathering more drops, he would soon form an ocean.
And thankfully, he didn't have a time limit. He was an Immortal, so he could take his entire life improving its size.