Solar systems like ours with heavy elements are formed from the materials after old supernova explosions. After a supernova explosion, there is a dense core left (e.g. neutron star). Why have we not observed the remnants or dense core to the parent of our solar system?
You are correct when you say that the presence of heavy elements in our solar system and on Earth can only be explained from supernova explosions. From what my advisor told me, astronomers have determined that about a million or so years after the supernova (or perhaps multiple supernovas), the remnants settled into the solar nebula from which our Solar System was forming and thus later formed the Earth and Sun and other planets from these raw elements. This supernova would probably have left behind a neutron star or perhaps even a black hole, but there is no way we can determine that.
The reason we cannot observe whatever is left from the "parent supernova" of our solar system is simply because 4.5 to 5 billion years [the age of our Solar System] is a pretty significant time in the universe, and there is no way we can determine what our Galaxy looked like that long ago, and there is no way we can determine what significant events have happened within our galactic neighborhood between now and 5 billion years ago. I know it sounds like a cop-out answer, but it is simply too difficult. Keep in mind that in those 5 billion years, the Sun has travelled around the galaxy about 20-30 times. Many different things could have happened to this parent supernova core remnant in this time. Stars generally move around the Galaxy but also move relative to each other, and there's no way we can determine the precise motion that the supernova and its remnants had 5 billion years ago. Who knows... it may have even travelled outside our Galaxy in this time... we just don't know.
This page was last updated June 28, 2015.