Supernova Sand Grains: Cosmic Dust from Exploding Star Discovered in Meteorites

Long before our solar system formed, stars burned brightly in our Universe before becoming explosive supernovas and slowly winking out of existence. Now scientists are finding out a little bit more about these ancient stars by examining the specks of cosmic dust carried to Earth in meteorites.

Although you may think examining dust couldn't tell you all that much about stars, the technique has more benefits than you might expect. It can allow researchers to better understand the composition of ancient stars.

Scientists examined a primitive meteorite that had been picked up in Antarctica by a U.S. team. Using a NanoSIMS 50 ion microprobe, they looked for presolar grains in the meteorite. Eventually, they discovered a silica grain, the most common constituent of sand, which was too small to be seen by the naked eye. This, in particular, is surprising since silica isn't one of the minerals expected to condense in stellar atmospheres.

After further examining the grain, the researchers discovered that it was enriched in oxygen-18, which meant it came from a core-collapse supernova. This massive star would have exploded at the end of its life. They found a similar grain in another meteorite picked up in Antarctica.

The two grains that were discovered join five other silica grains that were found earlier. The earlier discoveries were actually thought to originate from AGB stars, the red giants that puff up to enormous sizes at the end of their lives.

The researchers decided to tackle the difficult problem of calculating exactly how a supernova might have produced silica grains. Right before a star explodes, the supernova looks like a giant onion; it's made up of concentric layers that are dominated by different elements. Since some theoretical models have predicted that silica might be produced in massive, oxygen-rich layers near the core of the supernova, the researchers decided to examine the possibility that this is what occurred.

They found that they could actually reproduce the oxygen-18 observed in the particles by mixing small amounts of material from the oxygen-rich inner zones and the oxygen-18-rich helium/carbon zone with large amount of material from the hydrogen envelope of the supernova. Yet this mixing would have been unique to each star. Because the two grains have similar isotopic compositions, it's very possible that they could have come from a single supernova--perhaps even the one that triggered the formation of the solar system.

The findings could allow researchers to better understand ancient stars and their deaths. In addition, it may give them a bit more insight into how our own solar system formed.

The findings are published in The Astrophysical Journal.