After twenty years of debate, scientists are getting nearer to determining precisely what the solar — and thus the entire universe — is made from.
The solar is generally composed of hydrogen and helium. There are additionally heavier parts resembling oxygen and carbon, however simply how a lot is controversial. New observations of ghostly subatomic particles referred to as neutrinos counsel that the solar has an ample provide of “metals,” the time period astronomers use for all parts heavier than hydrogen and helium, researchers report May 31 at arXiv.org.
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The outcomes “are fully compatible with [a] high metallicity” for the solar, says Livia Ludhova, a physicist at Research Center Jülich in Germany.
Elements heavier than hydrogen and helium are essential for creating rock-iron planets like Earth and sustaining life-forms like people. By far essentially the most ample of those parts within the universe is oxygen, adopted by carbon, neon and nitrogen.
But astronomers don’t know precisely how a lot of those parts exist relative to hydrogen, the most typical aspect within the cosmos. That’s as a result of astronomers sometimes use the solar as a reference level to gauge elemental abundances in different stars and galaxies, and two strategies suggest very completely different chemical compositions for our star.
One approach exploits vibrations contained in the solar to infer its inner construction and favors a excessive steel content material. The second approach determines the solar’s composition from how atoms on its floor take in sure wavelengths of sunshine. Two many years in the past, a use of this second approach recommended that oxygen, carbon, neon and nitrogen ranges within the solar have been 26 to 42 p.c decrease than an earlier dedication discovered, creating the present battle.
Another approach has now emerged that might determine the long-standing debate: utilizing photo voltaic neutrinos.
These particles come up from nuclear reactions within the solar’s core that flip hydrogen into helium. About 1 p.c of the solar’s vitality comes from reactions involving carbon, nitrogen and oxygen, which convert hydrogen into helium however don’t get used up within the course of. So the extra carbon, nitrogen and oxygen the solar really has, the extra neutrinos this CNO cycle ought to emit.
In 2020, scientists introduced that Borexino, an underground detector in Italy, had noticed these CNO neutrinos (SN: 6/24/20). Now Ludhova and her colleagues have recorded sufficient neutrinos to calculate that carbon and nitrogen atoms collectively are about 0.06 p.c as ample as hydrogen atoms within the solar — the primary use of neutrinos to find out the solar’s make-up.
And although that quantity sounds small, it’s even greater than the one favored by astronomers who assist a high-metal solar. And it’s 70 p.c higher than the quantity a low-metal solar ought to have.
“This is a great result,” says Marc Pinsonneault, an astronomer at Ohio State University in Columbus who has lengthy advocated for a high-metal solar. “They’ve been able to demonstrate robustly that the current low-metallicity solution is inconsistent with the data.”
Still, due to uncertainties in each the noticed and predicted neutrino numbers, Borexino can’t absolutely rule out a low-metal solar, Ludhova says.
The new work is “a significant improvement,” says Gaël Buldgen, an astrophysicist at Geneva University in Switzerland who favors a low-metal solar. But the expected numbers of CNO neutrinos come from fashions of the solar that he criticizes as too simplified. Those fashions neglect the solar’s spin, which may induce mixing of chemical parts over its life and alter the quantity of carbon, nitrogen and oxygen close to the solar’s middle, thereby altering the expected variety of CNO neutrinos, Buldgen says.
Additional neutrino observations are wanted for a closing verdict, Ludhova says. Borexino shut down in 2021, however future experiments may fill the void.
The stakes are excessive. “We’re arguing about what the universe is made of,” Pinsonneault says, as a result of “the sun is the benchmark for all of our studies.”
So if the solar has way more carbon, nitrogen and oxygen than presently thought, so does the entire universe. “That changes our understanding about how the chemical elements are made. It changes our understanding of how stars evolve and how they live and die,” Pinsonneault says. And, he provides, it’s a reminder that even the best-studied star — our solar — nonetheless has secrets and techniques.
