What do the ashes of a dying star tell us about the birth of our solar system

A speck of dust forged in the throes of the death of a missing star was discovered by a team of researchers led by the University of Arizona.

The discovery challenges some of the current theories about how dying stars seed the universe with raw materials for planet formation and, ultimately, the precursor molecules of life.

Nestled in a chondritic meteorite collected in Antarctica, this tiny dot represents star dust, probably projected into space by a star that explodes before our own sun exists. Although it is thought that these grains provide important raw materials contributing to the mixture from which the sun and our planets have formed, they rarely survive the turmoil that accompanies the birth of a system. solar.

"As real dust from stars, these presolar grains allow us to better understand the building blocks of our solar system," said Pierre Haenecour, lead author of the article, whose online publication is planned in advance on Nature Astronomy April 29 website. "They also provide us with a direct snapshot of the conditions of a star at the time of formation of that grain."

Dubbed LAP-149, the grain of dust is the only known assembly of graphite and silicate grains that can be attributed to a specific type of stellar explosion called nova. Remarkably, he survived the journey through interstellar space and traveled to the region that would become our solar system some 4.5 billion years ago, maybe earlier, where he is become anchored in a primitive meteorite.

The Novae are binary star systems in which the core of a star, called a white dwarf, is about to gradually disappear from the universe, while its companion is a main sequence star of low mass or a red giant. The white dwarf begins to whistle the material of his swollen companion. Once it has added enough new star material, the white dwarf reignites in sufficiently violent periodic explosions to create new chemical elements from the stellar fuel and toss them back into space, where they can travel to new star systems and integrate with their raw materials. .

Shortly after the Big Bang, while the universe contained only hydrogen, helium and traces of lithium, star explosions contributed to the explosion. chemical enrichment of the cosmos, giving rise to the plethora of elements that we see today.

Taking advantage of the sophisticated ion and electron microscopy facilities at the AU Lunar and Planetary Laboratory, a research team led by Haenecour analyzed the microbe-sized dust particle to the atomic level. The tiny messenger of space turned out to be truly an extraterrestrial highly enriched in a 13C carbon isotope.

"The isotopic composition of carbon in everything we have ever sampled and coming from any planet or body in our solar system usually varies by a factor of about 50," he said. Haenecour, who will join the Lunar and Planetary Laboratory as an Assistant Professor. the fall. "The 13C we found in LAP-149 is enriched more than 50,000 times, and these results provide further evidence in the laboratory that carbon-rich and oxygen-rich novae grains have contributed to the building blocks of our solar system."

Although their parent stars no longer exist, the isotopic and chemical composition as well as the microstructure of the starburst grains identified in meteorites are unique constraints in terms of dust formation and thermodynamic conditions in the stream of stars, wrote the authors.

A detailed analysis revealed even more unexpected secrets: unlike similar dust grains believed to have been forged in dying stars, LAP-149 is the first known graphite grain containing an inclusion of oxygen-rich silicate.

"Our discovery gives us insight into a process we could never see on Earth," Haenecour added. "He explains to us how the dust grains form and move inside when expelled by the nova.We now know that carbonaceous and silicate dust grains can form in the same nova ejecta and that 39 they are transported through chemically distinct dust piles ejecta, something that has been predicted by novae models but never found in a specimen. "

Unfortunately, the LAP – 149 does not contain enough atoms to determine its exact age, so researchers hope to find other larger and similar specimens in the future.

"If we could date these objects one day, we could have a better idea of ​​what our galaxy looked like in our region and what triggered the formation of the solar system," said Tom Zega, scientific director of the center of the solar system. 39, Kuiper Materials imaging and characterization of the AU. and Associate Professor at the Lunar and Planetary Laboratory and the Department of Materials Science and Engineering of the AU. "Maybe we owe our existence to a nearby supernova explosion, squeezing the clouds of gas and dust with its shockwave, lighting up the stars and creating stellar nurseries, similar to what we see in the Hubble's famous "Pillars of Creation" painting.

The meteorite containing the dust particle star is one of the most pristine meteorites in the collection of the Lunar and Planetary Laboratory. Classified as a carbonaceous chondrite, it would be similar to that of Bennu, the target asteroid of the OSIRIS-REx mission led by the AU. By taking a sample of Bennu and bringing it back to Earth, the OSIRIS-REx mission hopes to provide scientists with material that has hardly been tampered with since the formation of our solar system.

Until then, researchers depend on rare discoveries such as LAP-149, which survived after being ejected by an exploding star, caught in a collapsed cloud of gas and dust that would become our solar system and cooked in a pre-asteroid to fall to the ground.

"It's remarkable when we think of all the paths that should have killed this grain," Zega said.