Re: Where's the neutron star left behind by the supernova that created us?

There are two points to be made here. The first is that not all supernovae leave neutron stars behind at all. In theory, a supernova could leave a neutron star or a black hole. Neutron stars are easier to find than black holes because neutron stars can have magnetic fields, leading to radio emissions as pulsars. Black holes cannot have their own magnetic fields, per the "no hair" theorem. This just means that remnants might be very hard to locate.

That doesn't really directly answer your question, though. So here's the second, more important, half: there isn't just one supernova responsible for our heavy elements. Over the 10 or so billion years that our Galaxy has been around, stars have been born, lived and died. Many stars have come and gone, the larger ones living more quickly than the smaller ones. The large ones have tended to explode as supernovae and send out small amounts of heavy elements into the gas and dust of the Galaxy. Each explosion adds a bit more of these heavy elements so that over time the total fraction of the heavy stuff builds up.

Where are all of these neutron stars and black holes? Everywhere. Over time, many of them have moved away from our location. Some of them were probably sent hurtling out of the plane of the Milky Way thanks to the push they received in the explosion that created them. These neutron stars and black holes move up and down through the plane of the galaxy, like a horse on a merry-go-round. Other remanents have found themselves on orbits about the center of the galaxy which have caused them drift away from out location. Still others might be around us, but most would be too cold and quiet to be detected today.

For more good stuff on planet formation and supernovae, you can check out most any introductory astronomy text. I especially recommend The Cosmic Perspective by Jeff Bennett, Megan Donahue, Nick Schneider and Mark Voit. Also, you might find SNe and SNR Pages on the WWW interesting.

[There is just one wrinkle to add to this answer. Certain kinds of meteorites show evidence of having contained a particular isotope of aluminum, ²⁶Al. This isotope is radioactive and decays quickly. After a few million years, all of the ²⁶Al in a meteorite would have decayed away. ²⁶Al is known to be made during supernovae. However, how did the ²⁶Al get into these meteorites? If some supernova occurred and the material ejected from it was later incorporated into the material from which the solar system, there should be little or no ²⁶Al in these meteorites. That's because the time it would take for material to drift from a supernova remnant into a region where new stars are forming is typically much, much longer than a few million years. Thus, for some time, astronomers have concluded that there must have been a supernova quite close to the region where the Sun formed. In that way, the material blown out during the supernova could have found its way to the young solar system quite quickly, before all of the ²⁶Al decayed.

We are now learning that young stars, like the Sun was five billion years ago, often emit considerable amounts of high-energy radiation. It is not yet clear, but it seems possible that the Sun might have been manufacture some ²⁶Al during its formation. Again, this scenario is by no means certain, but, if correct, it implies that there need not have been a close supernova during the solar system's formation. For more information, you might want to check out this news release describing a recent analysis of a meteorite. Moderator]