No, most stars in space tend to grow in their lumosity. But cutting to the chase its because the sun is burning hydrogen into helium at its core, the core breaks down and warms up or heats up, making the outer layers of the sun to grow to a certain amount. This has been happening for a while now, basically since it was 'born'. That's the explanation to why it is not bigger than it was 1,000 years ago. Hope this helped to y'all.