Stardust Found In A Meteorite Illuminates The Sun’s Birth Story

The Orion Nebula, seen here below Orion’s Belt (center), is part of an enormous complex of gas and dust called the Orion Molecular Cloud complex. Rogelio Bernal Andreo / CC BY-SA 3.0

Wonder where all the stuff that made the solar system came from? Trees, rocks, clouds, air … even your dog. They all started as gases formed shortly after the Big Bang, combined with dust blown into space by later generations of stars. The solar system coalesced 4.6 billion years ago from within a denser clot of gas and dust inside a molecular cloud about 65 light years across.

How stars form inside molecular clouds — from cold gas to young stars (protostars) embedded in their birth dust. The Milky Way Galaxy contains between 1000 and 2000 giant molecular clouds. James Schombert / University of Oregon

Molecular clouds are just what they sound like — enormous clouds of gas and dust where low temperatures encourage the formation and preservation of many types of molecules. Denser regions inside the cloud are called “cores.” Here, gravity’s grip crushes and heats the material to form newborn suns. The Orion Nebula and surroundings are a good example of a current molecular cloud where tens of thousands of stellar newborns are blooming like dandelions in May.

Clouds contain mostly hydrogen and helium, the most common gases in the universe. They formed 380,000 years after the Big Bang, an event that occurred 13.7 billion years ago. 10 percent of the atoms in your body are hydrogen. Each connects every one of us to nearly the beginning of time.

But we’re also made of more complex elements like oxygen, carbon and nitrogen. Where did these come from? They’re the gifts of dying stars, manufactured through nuclear fusion within the star’s core and released into space when the star is near the end of its life. In fusion, simpler elements like hydrogen and helium fuse under the heat and pressure in a star’s core to become more complex elements like carbon and oxygen.

Artist’s impression of a red giant star blowing out gas and dust as bubbles of hot gas rise from its core. These seed space with fresh matter that can gather to form a new generation of stars. JAXA/ISAS/LIRA

Stars like the sun expand and cool to become red giants. Molecules form in their atmospheres, and gusty stellar winds waft them into space. Other stars explode as supernovae and blast their all manner of elements into space which combine to produce huge quantities of dust. The material gathers with red giant dust into molecular clouds, where new stars are forged, and the entire process begins again. In this way the universe recreates itself, fashioning new from old and forever surprising us with novelty.

These are highly magnified views of several grains of silicon carbide star dust found in the Murchison meteorite. Heck et al, doi: 10.1073/pnas.1904573117

Most of the material in the solar system dates back to about 4.6 billion years ago, but Prof. Philipp Heck, a curator at the Field Museum and lead author of a new study, found star dust dating back more than 5.5 billion years in the Murchison meteorite. Fragments of the carbon-rich meteorite that fell in Australia in 1969 were dissolved into a paste that smelled “like rotten peanut butter” according to the scientists. Heck and his team then extracted 40 grains of silicon carbide (also known as carborundum, an abrasive) from this goo and dated them by examining how cosmic ray bombardment had altered their composition. Cosmic rays are atomic nuclei — usually protons — whipping around the galaxy at incredible speeds, up to 99.6 percent that of light.

Based on their ages, which range from 4.6 to older than 5.5 billion years, the granules were here long before the sun and planets were born. In fact, these microscopic bits are now the oldest material that’s ever been dated. Their composition points to an origin in powerful winds blowing from a long-ago generation of red giant stars.

“They’re solid samples of stars, real stardust,” said Heck.

And they seeded that long-ago cloud that grew into the sun and planets. Heck found more grains than expected which leads him to believe they formed during a time of vigorous star formation about 7 billion years ago. Ancient as the solar system is, it blows the mind to think what preceded it.

Every thing and everybody has a story. While all the specialized equipment and physics may feel intimidating at times, storytelling is at the heart of astronomy. This new discovery extends the story of the sun and planets further back in time, and in effect, the story of you and me.