Final answer:
The heavier elements in the interstellar medium are primarily found in stars and planetary systems. Stars fuse lighter elements into heavier ones, which are released back into the interstellar medium when stars mature and die. These heavier elements, along with dust grains, can be incorporated into new stars and planetary systems.
Step-by-step explanation:
The heavier elements in the interstellar medium are primarily found in stars and planetary systems.
Stars are responsible for fusing lighter elements into heavier ones, producing energy in the process. As stars mature and eventually die, they release these heavier elements back into the interstellar medium.
These heavier elements, along with dust grains that are made in the outer regions of stars, can then be incorporated into new stars and planetary systems that are forming out of the interstellar medium.