Is a proto star bigger than a star?

Answer 1

Short answer: Yes

The latin root "proto-" means early, or earliest. As a star is an approximately spherical mass of matter undergoing a fusion/fission reaction due to the enormous pressures created at the center of the star due to its massive density. By this logic, we know that a protostar or "early star" is something which isn't yet, but will become a star in the future. By observing the universe and understanding the composition of stars, we've theorized that stars (and their solar systems) are usually formed by nebulae. As the nebulous cloud condenses under its own gravitational pull. Eventually the density reaches a point where the fission/fusion reaction can occur. So it follows that the nebula, is less dense (and by requirement), more voluminous. So a protostar takes up a much greater space, and would appear larger, but it would be less dense. We also have to remember that the size of stars varies. You could compare one protostar to another existing star, but the comparison wouldn't tell you anything about the relative sizes of the two different objects. IE: a big star would've been an even bigger protostar, and a small star would have been a smaller protostar.

Answer 2

A protostar is not bigger than a star. A protostar is a young stellar object that is still in the process of accumulating mass and undergoing gravitational collapse to become a full-fledged star. Once it reaches a critical point where nuclear fusion ignites in its core, it becomes a true star.