Log10 of the density distribution for model 40-200-0.1 after 2:00 x 104 yrs of evolution, plotted in the z = 0 plane. Contours show the color field plotted at 0.01, 0.025, 0.05, 0.075, and 0.1. The x axis is horizontal and the y axis is vertical. The downward propagating shock wave has compressed the target cloud core and is injecting shock front material through multiple Rayleigh-Taylor (RT) fingers.

For
decades it has been thought that a shock wave from a supernova
explosion triggered the formation of our Solar System. According to this
theory, the shock wave also injected material from the exploding star
into a cloud of dust and gas, and the newly polluted cloud collapsed to
form the Sun and its surrounding planets. New work from Carnegie’s Alan
Boss and Sandra Keiser provides the first fully 3D
models for how this process could have happened. Their work will be
published by The Astrophysical Journal Letters.

Traces
of the supernova’s pollution can be found in meteorites in the form of
short-lived radioactive isotopes, or SLRIs. SLRIs—versions 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 and turn into different, so-called daughter, elements. A
million years may sound like a long time, but it is actually considered
short when compared to other radioactive isotopes studied by geochemists
and cosmochemists, which have half-lives measured in billions of years.

When
scientists find the daughter elements distributed in telltale patterns
in primitive meteorites, this means that the parent SLRIs had to be
created just before the meteorites themselves were formed. This presents
a timing problem, as the SLRIs must be formed in a supernova, injected
into the presolar cloud, and trapped inside the meteoritic precursors,
all in less than a million years.

The
telltale patterns prove that the relevant daughter elements were not
the ones that were injected. This is because the abundances of these
daughters in different mineral phases in the meteorite are correlated
with the abundances of a stable isotope of the parent element. 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 that those daughters had to be derived
from the decay of unstable parent elements after those solids were
crystallized.

One
of these SLRIs, iron-60, is only created in significant amounts by
nuclear reactions in massive stars. The iron-60 must have come from a
supernova, or from a giant star called an AGB star. Boss and Keiser’s
previous modeling showed that it was likely that a supernova triggered
our Solar System’s formation, as AGB star shocks are too thick to inject
the iron-60 into the cloud. Supernova shocks are hundreds of times
thinner, leading to more efficient injection.

Now
Boss and Keiser have extended those models to 3-D, so they can see the
shock wave striking the gas cloud, compressing it and forming a
parabolic shock front that envelopes the cloud, creating finger-like
indentations in the cloud’s surface. The fingers inject the SLRI
pollution from the supernova. Less than 0.1 million years later, the
cloud collapses and forms the core of the protostar that became the Sun
and its surrounding planets. The 3-D models show that only one or two
fingers are likely to have caused the SLRI pollution found in primitive
meteorites.

 

“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.

For a video of this, click here.

Source: Carnegie Institution