SC, Fifth edition, Pg 71, Pronoun Query

[ramit.jindal]

Supernovas destroy their immediate environments in vast explosions, but by synthesizing heavy chemical elements, THEY provide the universe with the possibility of biochemistry-based life as we know it.

Question: What is the significance of comma before THEY?

[RonPurewal]

It separates the preceding modifier ("by ...") from the following sentence.

Remember"”the GMAT doesn't test punctuation. If you're worried about the presence or absence of the comma, then, well, don't be.