Supernova Shock Wave And Its Role In Solar System Formation
August 3, 2012

3D Model Helps Explain How A Supernova Explosion Created Our Solar System

April Flowers for - Your Universe Online

It has long been thought that our Solar System was formed by the shockwave from a supernova explosion. According to this theory, the shockwave also injected material from the exploding star into a cloud of gas and dust. The newly polluted cloud formed the Sun and its surrounding planets.

A new study by Alan Boss and Sandra Keiser of the Carnegie Institution for Science, published in The Astrophysical Journal Letters, provides the first full 3D models for how this might have happened.

Short-lived radioactive isotopes (SLRI's) are traces of the supernova's pollution and they can be found in meteorites. SLRI's -- version of elements with the same number of protons, but a different number of neutrons — found in primitive meteorites decay on time scales of millions of years. This decay turns them into different, so-called daughter elements. A million years might sound like a long time, but it is considered short when compared to other radioactive isotopes studied by geochemists and cosmochemists, which have half-lives measured in billions of years.

When these daughter elements are found distributed in telltale patterns in primitive meteorites, it means that the parent SLRI's had to be created just before the meteorites themselves were formed. For scientists, this presents timing problems, as the SLRI's must be formed in a supernova, injected into the presolar cloud, and trapped inside the forming meteorites, all in less than a million years.

It is those telltale patterns, though, that assure scientists they are on the right track and that those daughter elements were not the ones injected. This is because the abundances of the daughter elements in different mineral phases are correlated with the abundances of stable isotopes of the parent elements. Different elements have different chemical behaviors during the formation of these first solids, and the fact that the daughter elements correlate with the parent elements means those daughter elements had to be derived from the decay of unstable parent elements after those solids were formed.

As an example, one of the SLRI's, iron-60, is only created in significant amounts by nuclear reactions in massive stars. Thus, the iron-60 must have come from a supernova, or a giant star called an AGB star. An AGB, or Asymptotic Giant Branch star is a low to medium mass star late in its evolution. Boss and Kieser's previous modeling showed that it was likely that a supernova triggered our Solar System's formation, as an AGB star's shocks are too thick to inject the iron-60 into the cloud.  Supernova shockwaves are hundreds of times thinner.

With this new study, Boss and Kieser have extended those original models to 3D so that they can see the shock wave striking the gas cloud, compressing it and forming a parabolic shock front that envelopes the cloud and creates finger-like indentions in the cloud's surface. The fingers inject the SLRI pollution. Less than .01 million years later, the cloud collapses and forms the core of the protostar that becomes the Sun and our solar system.

“The evidence leads us to believe that a supernova was indeed the culprit,” said Boss. However, more detective work needs to be done: Boss and Keiser still need to find the combination of cloud and shock wave parameters that will line up perfectly with observations of exploding supernovae.