Here's why:

* The Big Bang: The universe began with mostly hydrogen and helium.

* Stellar Fusion: Heavier elements are created in the cores of stars through nuclear fusion. This process combines lighter elements into heavier ones.

* Supernovae: When massive stars die in spectacular supernova explosions, they release these heavy elements back into space.

* Building Blocks: These heavy elements are the building blocks for planets, asteroids, and even life itself.

So, while the term "heavy" might seem subjective, in astronomy, it's a convenient way to categorize elements based on their origin and significance.