# Elements of a Planet reveals nearby supernova remnant?

During a random reading through this site, I found this one: Origin of elements heavier than Iron (Fe)

There was an answer mentioning that "the formation of many elements in earth was due to supernova nucleosynthesis" as told by someone. Hence, a question crosses my mind...

If the elements were formed due to the explosion of a supernova, then there should be a remnant like a black-hole or a neutron star nearby. Were there any nearby?

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'nearby' is a long way in astronomical terms. Roughly a Planet will form from a cloud of gas and dust that differentiates by element. Where a planet forms and what it forms from will determine a planets composition. – Nic Aug 29 '12 at 15:41
the gaseous elemnts are there in the beginning, very little chemistry happens on a planet (unless there's life!). Planets form from the same material as the host star. The central star will blow lighter material away so you end up with more heavy stuff nearer in. – Nic Aug 29 '12 at 15:50

I'm not sure all the details of the Solar System formation are understood, but the general principles are well established. The dust cloud from which the Solar System formed was probably roughly homogenous. However once the Sun began to form, the dust cloud around it rapidly became differentiated. The heavier non-volatile elements stayed near the Sun while the lighter more volatile elements were blown outwards. That's why the inner planets are rocky while the outer planets are gaseous or icy. Incidentally, the water on Earth probably came from comets after Earth was formed, though views are mixed on this subject.

The dust cloud was probably formed by supernovae of Population II stars, and you're correct that these would have left remnants of some form. However dust clouds are big, and were even bigger when first formed. The nebulae where we see star formation have had time to contract and become more dense since the supernovae that formed them. In addition, it's been (at least) 4.5 billion years since the last nearby supernova. There has been plenty of time for the supernovae remnants to wander around, so it's no surprise we don't have one next door.

Having said that, I've never seen an estimate for the density of Population II supernovae remnants, and I'd be interested to know if there's a firm number for this.

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Yes, the heavy elements were formed in supernova explosions that happened before the birth of the solar system. These elements come from not one but many supernovas that happened at different times during the life of the galaxy.

The sun goes around the centre of the galaxy about once every 200My. Hence, during the sun's life (~5 Gy) we have circled the galaxy about 25 times. So have all the other stars in our neighbourhood, but their orbital period varies with the distance of the star from the centre of the galaxy. See http://en.wikipedia.org/wiki/Milky_Way for more details. As a result, stars that were close to each are gradually drifting apart, and there is no way of telling which supernova(s) our elements come from.

It's also likely that the collapse of the solar nebula was triggered by a supernova. That supernova would have exploded only a short time before the birth of the sun, but again there is no way of finding it.

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The materials that made up the solar system can be studied through the analysis of pre-solar grains and the abundances of various isotopes in primitive meteoritic material.

Pre-solar grains were formed in the photospheres of stars pre-dating the Sun. These grains were then expelled into the interstellar medium (ISM) in stellar winds and also in supernova explosions. The grains are found inside meteoritic material and typically consist of minerals like silicon carbide. The analysis of isotopic ratios of a wide variety of elements betrays the origins of the material.

It is generally found that the material that makes up the solar system (and Sun) comes from many stars and via many routes, not just supernovae. In fact many of the elements n the solar system, contrary to a common misconception, are not produced in massive stars and disseminated into the ISM via supernovae. Elements like C, N, F, a variety of heavier elements like, Ba, Rb, Sr, Pb and many others are dominantly made in intermediate mass asymptotic giant branch stars and enter the ISM through convective mixing followed by mass loss in stellar winds. Other sources of elements include type Ia supernovae, novae, cosmic ray spallation, neutron star mergers...

So, the solar system is not really the product of one or even a few events., but many such events that have all become mixed in the ISM over billions of years.

Now having said that, some think that there is evidence that the Sun formed in a large cluster of stars and the protosolar nebula was contaminated by the debris from a nearby (within a light year) supernova event (see the excellent review on the birth environment of the Sun by Adams 2010). The evidence for this comes in the form of short-lived extinct radionuclides such as 60Fe found in meteorites. This has a half-life of about 2 million years and decays to 60Co and then 60Ni. By checking the abundances of 60Ni vs other iron isotopes it has been claimed that the solar system was polluted with 60Fe by a blast from a supernova more-or-less at the time of formation. The interpretation is still keenly disputed.

Even if it were the case that a single supernova remnant has left its "fingerprints" on the solar system composition, it is hard to see how we would find the remnant (black hole or neutron star) it left behind. Firstly, over 4.5 billion years, the Sun has travelled many times around the Galaxy, so it is (probably) nowhere near where it was born; so it is no good looking nearby for anything. Secondly, supernova remnants (i.e. the nebulae) are comparatively shortlived (a million years or so) and the compact black hole or neutron stars that are produced often have very sizeable velocities imparted by the supernova and swiftly depart the centre of their nebular remnants. Thus we wouldn't know where to look and there is every chance that the neutron star or black hole could even have escaped the Galaxy or could be on a highly elliptical Galactic orbit and be nowhere near the Sun. Finally, looking for old neutron stars and black holes is difficult. They are not pulsars and will not emit much in the way of electromagnetic radiation unless they are still in a close binary system and accreting from a normal star.

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