Why has only the most massive stars are important contributors in enriching the galaxy with heavy elements?

Answer 1

To "enrich the Universe", the heavy elements would need to get back out of the star - and into outer space, where it can eventually become part of new star systems. This "getting out" happens mainly in supernova explosions - i.e., in the case of very massive stars.

Also, stars with very low mass mainly convert hydrogen into helium - they didn't have time yet, given the current age of the Universe, to advance to a later stage, where they convert helium into heavier elements - and the stars with the very lowest masses never will, since they won't get hot enough.

Answer 2

Low to medium mass stars cannot produce elements heavier than oxygen. Higher mass stars can fuse heavier elements up to iron and produce still heavier elements when they explode as supernovae.

Answer 3

The super-huge stars can produce all heavy elements that can even exist. In fact, super huge stars can even indirectly produce lithium, beryllium and boron, 3 very light elements, but only indirectly. (Highly energetic cosmic rays randomly strike existing atoms of heavy elements, and split them into the light elements through a process called 'spallation').

Other than lithium, beryllium, and boron, the lighter elements exist anyway from smaller stars.

Answer 4

Only massive stars produce heavy elements in the first place. Only the most massive stars get hot enough to make those elements.