How large was the Sun when it first formed as a protostar, perhaps 1000 years after formation?

Question

Quizplus · Accepted Answer

When the Sun first formed as a protostar, it was around 20 times its present diameter. This is because as the Sun formed, it contracted under its own gravity. However, as it contracted, it also became more dense and hotter, which caused it to emit thermal radiation and slow down its contraction. This process continued until the Sun reached a stable state known as the main sequence, where it has remained relatively unchanged for billions of years.

How Large Was the Sun When It First Formed as a Protostar