The ratios of carbon-12 to carbon-13 isotopes in these grains were a flawless match to what astronomers have observed in the clouds of dust and gas around ageing stars like the Egg Nebula and the Ring Nebula.
Stardust forms in the material ejected from stars and carried by stellar winds, getting blown into interstellar space.
They discovered that the grains are the oldest solid material ever found on Earth.
"This is one of the most exciting studies I've worked on, "said cosmochemist Philipp Heck of the Field Museum of Natural History and the University of Chicago". But they offer astronomers insight into how stars formed in the early stages of our galaxy.
And one of the grains analyzed in a study published today in the Proceedings of the National Academy of Sciences is estimated to be roughly 7 billion years old, making it the oldest known material on Earth. Over time, the freed stardust particles condense to form new stars and planets, or - in the case of these particular grains - meteorites.
They're rare, found only in about five percent of meteorites that have fallen to Earth, and they're tiny-a hundred of the biggest ones would fit on the period at the end of this sentence.
It was extracted from the Murchison meteorite, which fell to Earth in the Victorian country town of Murchison in 1969. The age range of the grains also intrigued the scientists: the majority were from 4.6bn to 4.9bn years ago, suggesting that a bumper crop of new stars formed in the Milky Way about 7bn years ago - the lifetime of a star typically being a few billion years.
To separate the ancient grains from the relatively younger ones, scientists crushed fragments of the meteorite into a powder.
"It's the next best thing to being able to take a sample directly from a star", added Jennika Greer, a co-author of the study and graduate student at the Field Museum and the University of Chicago, in a statement.
"I always compare it to burning down the haystack to find the needle", Heck said.
Presolar grains can be dated by how long they've been exposed to cosmic rays.
They used scanning electron microscopy, secondary ion mass spectrometry and noble gas mass spectrometry, looking for the effects of exposure to cosmic radiation, which can penetrate solid material such as meteorites and leave its mark on the silicon carbide grains. These high-energy particles flit around space and can pass through solid matter, creating new elements inside the existing minerals as they interact with them. By measuring how many of these new cosmic ray-produced elements are present in a presolar grain, we can tell how long it was exposed to cosmic rays, which tells us how old it is.
About 30 years ago it was found that the rocks housed "presolar grains" - tiny grains of silicon carbide older than the Sun. They are from silicon carbide, the first mineral formed when a star cools.
In doing so, the team found that most of the grains were between 4.6 and 4.9 billion years old.
His team discovered that about 60% of the grains are between 4.6 and 4.9 billion years old, while some other grains are even older: 5.5 billion years or more. During the solar system's birth, this dust was incorporated into everything that formed including the planets and the sun but survived intact until now only in asteroids and comets.
This finding is ammo in a debate between scientists about whether or not new stars form at a steady rate, or if there are highs and lows in the number of new stars over time. "Some people think that the star formation rate of the galaxy is constant", says Heck. "This is one of the key findings of our study".
Of the 40 grains the researchers examined, the most ancient, at 7 billion years old, are 2.5 billion years older than Earth. "No one thought this was possible at that scale", Philipp Heck explained.
The team looks forward to all of these discoveries furthering our knowledge of our Galaxy.
"These hits are pretty constant over time, so we can just count the products from those hits and determine how long they were flying in space", Heck said. "We hope this will be picked up and studied so that people can use this as input for models of the whole galactic life cycle", Dr. "It contains some of the oldest condensates in the solar system and also presolar materials".