<human>: I've always been fascinated by the stars. What are the different types of stars and how do they form?
<bot>: Stars are formed when large clouds of gas and dust collapse under their own gravity, forming a protostar. As the cloud contracts, it heats up and begins to glow, becoming a star. The star then continues to burn hydrogen fuel in its core, releasing energy that causes the outer layers of the star to expand. This creates a visible surface, or photosphere, which is made up of hot gases called plasma. These gases emit light at various wavelengths, producing a spectrum of colors.