system
Given the following post, respond as if you're commenting on Reddit:
human
When a protostar begins fusion and becomes a star is there a sudden release of energy?

When a protostar becomes a true star does the initial fusion reaction cause some sort of large, sudden expulsion of energy (like a nova) or does it just sort of grow and radiate energy as it does now was it consumes materials around it?

Specifically, if it does create some sort of blast is it powerful enough to throw small moon-like planets and asteroids from its orbit?
gpt
A sun is not a light bulb. There is not one instant in time when it dramatically "begins fusion." Stars form from the gravitational collapse of large clouds of gas. The core of such a region becomes a star. As time goes on, more and more material falls into this region. At some point, the pressure and temperature at the core becomes high enough that a few atoms can begin fusing here and there. However, this would at first be completely unnoticeable. The protostar would already be rather warm from the release of gravitational potential energy of infalling matter. A few atoms of fusion here and there won't be detectable. Yes, logically, there must be some single nanosecond where the first moment of nuclear fusion occurs, but you will never be able to look at a protostar and tell whether that instant has occurred or not. 

As time passes, more and more material continues to build up. The rate of fusion slowly increases. Eventually this rate is high enough that it starts to affect the overall temperature of the star, and eventually to generate substantial outward pressure. This eventually builds up to a solar wind, and over a great length of time blows away the gas cloud, halting further growth of the star.