New research, published in ‘Proceedings of the National Academy of Sciences’, conducted on a meteorite that struck Australia has found evidence of stardust that formed over five billion years ago, before our solar system formed. It is believed to be the oldest known material found on our planet.
At the beginning of the universe only the elements hydrogen and helium existed. Stars started to form from clouds of dust and gas, that collapsed under the force of gravity. Stars act like a nuclear reactor, converting hydrogen into helium, and helium into carbon, and eventually everything we are made of.
When stars get to the end of their lives, they swell up and fall together, throwing off their outer layers. If a star is heavy enough, it will explode in a Supernova. It is mainly these large and ancient stars that release tiny granules of stardust as they die and explode. When studied, these granules can reveal clues about how stars were formed in the Milky Way.
The Australian meteorite accumulated the stardust during the billions of years it spent soaring through space before it crashed down to Earth near the town of Murchison, Victoria in 1969. Results showed that the granules had absorbed many cosmic rays over the eons. The oldest grains were dated to about 7 billion years ago, with the majority dating to between 4.6 billion and 4.9 billion years ago, and a small handful dating to 5.6 billion years ago. So, all the interstellar particles found in the Murchison meteorite originated before the formation of our Sun and solar system!
Scientists can infer from these results that star formation was not a constant in our galaxy. The relatively high number of particles dating to 4.6 billion – 4.9 billion years ago, suggests these grains originated during a time of intense stellar formation. This was labelled as the key finding of the study.
So, what does all this mean in terms of you and me? Effectively, all the material that we’re made of comes out of dying stars. We even contain a small amount of stardust from the estimated beginning of the universe 13.8 billion years ago!
In fact, a study in 2017 proved this. The Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic Evolution Experiment (APOGEE) in New Mexico, analysed the composition of 150,000 stars using a method called spectroscopy. Humans and the milky way share 97% of the same atoms, and the elements of life appear to be more prevalent toward the galaxy’s centre, the research found.
Jennifer Johnson, professor at The Ohio State University states that, “this allows us to place constraints on when and where in our galaxy life had the required elements to evolve, a sort of temporal galactic habitable zone.”
Although the new research helps answer some more questions on the stellar formation of the Milky Way, there is still much to be discovered. Scientists believe even older granules could be present in the Murchison meteorite, as well as others. It is hoped that additional research might help further map the changes in rates of stellar formation in our Galaxy.