Neutrinos Yield First Experimental Evidence of the CNO Energy-Production Mechanism of the Universe

Borexino Detector

View into the interior of the Borexino detector. Credit: Borexino Collaboration

Neutrinos Yield First Experimental Evidence of Catalyzed Fusion Dominant in Many Stars

An international team of about 100 scientists of the Borexino Collaboration, including particle physicist Andrea Pocar at the University of Massachusetts Amherst, report in Nature this week detection of neutrinos from the sun, directly revealing for the first time that the carbon-nitrogen-oxygen (CNO) fusion-cycle is at work in our sun.

The CNO cycle is the dominant energy source powering stars heavier than the sun, but it had so far never been directly detected in any star, Pocar explains.

For much of their life, stars get energy by fusing hydrogen into helium, he adds. In stars like our sun or lighter, this mostly happens through the ‘proton-proton’ chains. However, many stars are heavier and hotter than our sun, and include elements heavier than helium in their composition, a quality known as metallicity. The prediction since the 1930s is that the CNO-cycle will be dominant in heavy stars.

Neutrinos emitted as part of these processes provide a spectral signature allowing scientists to distinguish those from the ‘proton-proton chain’ from those from the ‘CNO-cycle.’ Pocar points out, “Confirmation of CNO burning in our sun, where it operates at only one percent, reinforces our confidence that we understand how stars work.”

Borexino Detector Under Apennine Mountains

The Borexino detector lies deep under the Apennine Mountains in central Italy at the INFN’s Laboratori Nazionali del Gran Sasso. It detects neutrinos as flashes of light produced when neutrinos collide with electrons in 300-tons of ultra-pure organic scintillator. Credit: Borexino Collaboration

Beyond this, CNO neutrinos can help resolve an important open question in stellar physics, he adds. That is, how the sun’s central metallicity, as can only be determined by the CNO neutrino rate from the core, is related to metallicity elsewhere in a star. Traditional models have run into a difficulty – surface metallicity measures by spectroscopy do not agree with the sub-surface metallicity measurements inferred from a different method, helioseismology observations.

Pocar says neutrinos are really the only direct probe science has for the core of stars, including the sun, but they are exceedingly difficult to measure. As many as 420 billion of them hit every square inch of the earth’s surface per second, yet virtually all pass through without interacting. Scientists can only detect them using very large detectors with exceptionally low background radiation levels.

The Borexino detector lies deep under the Apennine Mountains in central Italy at the INFN’s Laboratori Nazionali del Gran Sasso. It detects neutrinos as flashes of light produced when neutrinos collide with electrons in 300-tons of ultra-pure organic scintillator. Its great depth, size, and purity make Borexino a unique detector for this type of science, alone in its class for low-background radiation, Pocar says. The project was initiated in the early 1990s by a group of physicists led by Gianpaolo Bellini at the University of Milan, Frank Calaprice at Princeton, and the late Raju Raghavan at Bell Labs.

Until its latest detections, the Borexino collaboration had successfully measured components of the ‘proton-proton’ solar neutrino fluxes, helped refine neutrino flavor-oscillation parameters, and most impressively, even measured the first step in the cycle: the very low-energy ‘pp’ neutrinos, Pocar recalls.

Its researchers dreamed of expanding the science scope to also look for the CNO neutrinos – in a narrow spectral region with particularly low background – but that prize seemed out of reach. However, research groups at Princeton, Virginia Tech, and UMass Amherst believed CNO neutrinos might yet be revealed using the additional purification steps and methods they had developed to realize the exquisite detector stability required.

Over the years and thanks to a sequence of moves to identify and stabilize the backgrounds, the U.S. scientists and the entire collaboration were successful. “Beyond revealing the CNO neutrinos which is the subject of this week’s Nature article, there is now even a potential to help resolve the metallicity problem as well,” Pocar says.

Before the CNO neutrino discovery, the lab had scheduled Borexino to end operations at the close of 2020. But because the data used in the analysis for the Nature paper was frozen, scientists have continued collecting data, as the central purity has continued to improve, making a new result focused on the metallicity a real possibility, Pocar says. Data collection could extend into 2021 since the logistics and permitting required, while underway, are non-trivial and time-consuming. “Every extra day helps,” he remarks.

Pocar has been with the project since his graduate school days at Princeton in the group led by Frank Calaprice, where he worked on the design, construction of the nylon vessel, and the commissioning of the fluid handling system. He later worked with his students at UMass Amherst on data analysis and, most recently, on techniques to characterize the backgrounds for the CNO neutrino measurement.

Reference: “Experimental evidence of neutrinos produced in the CNO fusion cycle in the Sun” by The Borexino Collaboration, 25 November 2020, Nature.
DOI: 10.1038/s41586-020-2934-0

This work was supported in the U.S. by the National Science Foundation. Borexino is an international collaboration also funded by the Italian National Institute for Nuclear Physics (INFN), and funding agencies in Germany, Russia, and Poland.

13 Comments on "Neutrinos Yield First Experimental Evidence of the CNO Energy-Production Mechanism of the Universe"

  1. Is there more Protons than Neutrons in the Universe Forming matter …is The CNO cycle the reason why ? Isaac Asimov the famous Sci fi writer thought the reason that there is matter in the universe as opposed to it being ALL annihilated by anti matter and having nothing here ) (note… that this to be sounds like science fiction, ” Matter vs Anti matter and Annihilation ” but it is true we have a machine that uses this called a positron emission tomography or (PET) scan ). ” The CNO cycle is the dominant energy source powering stars heavier than the sun, but it had so far never been directly detected in any star, Pocar explains” another story said …….” Orebi Gann said an asymmetry between neutrinos and their antiparticles could also explain the apparent dearth of anti-matter in our universe and its dominance of normal matter – in other words, just why there is anything here at all, rather than absolutely nothing “

    • Torbjörn Larsson | November 26, 2020 at 5:11 pm | Reply

      You go into all sorts of sidetopics (“evil” is a notion from religious superstition by the way, you may mean “bad”). But let me try to respond to your lede:

      “Is there more Protons than Neutrons in the Universe Forming matter …is The CNO cycle the reason why ? Isaac Asimov the famous Sci fi writer thought the reason that there is matter in the universe as opposed to it being ALL annihilated by anti matter and having nothing here )”.

      These things are unrelated. During the hot big bang era energy was released to form thermal radiation and matter, with equal parts matter and antimatter, and as the universe expanded and cooled the matter and antimatter almost completely annihilated. We can see that from the cosmic background phtons outnumber protons by a factor 10^9.

      Protons and electrons are equal amounts since the universe is on average neutral. And as that matter formed atoms and later stars, fusion happened (big bang nucleosynthesis producing He and a smidgen B and Li; star fusion with pp. pep and the here researched CNO cycle). The number of protons and electrons change mildly when that happens.

      Gabbi show that your quote from Asimov must be misremembered. The conditions that allow matter-antimatter asymmetry are the Sakharov conditions [“Baryogenesis” @ Wikipedia] “The three necessary “Sakharov conditions” are:
      – Baryon number B violation.
      – C-symmetry and CP-symmetry violation.
      – Interactions out of thermal equilibrium.”

      An expanding universe is out of thermal equilibrium – no problem there.

      So CPT can’t be violated, because then relativity is violated (technically, the Lorentz condition). But C and CP asymmetries are observed, mildly in the known Standard Particle model for baryons but perhaps maximally for neutrinos due to neutrino masses. The 3 generations of standard particles means there are 3 diffferent neutrinos and that is exactly enough to allow CP violation to happen. And neutrino experiments imply – still att too low significance – that this may happen.

      Then it is essentially leptogenesis that happens first – it was electrons vs positrons that made the asymmetry – and a so called non-equilibrium “sphaleron process” could convert the lepton asymmetry into a baryon asymmetry [“Sphaleron” @ Wikipedia]. This is all very speculative, mind. Among other things the sphaleron conversion is a 1 in 100 likelihood result, so like in the case of vacuum energy – which observed range is a 1 in 10,000 result – you may have to apply to inflationary multiverses.

  2. More Protons than Electrons , not Neutrons,,may form matter Isaac Asimov 1966 ..
    the below post substituted Neutrons for Electrons
    in psychoanalysis people forget painful things,..oops my confession…I forgot sounds like electricity and electron both painful at time issues for i forgot them to survive.( notice when you misspell words it may have a painful connotation to you.. ) .In 1984 Dr A A Brill in the Basic Principles of Psychoanalysis writes about this , Dr Brill was a good friend of Dr Freud and America’s first Psychiatrist.

    source I think was NON FICTION

    Understanding physics: The electron, proton and neutron Hardcover – January 1, 1966
    by Isaac Asimov

  3. Correction, It was 1948 Dr A A Brill published his book : ” Basic Principles of Psychoanalysis. ” Dr Brill was America’s first Psychiatrist.

    Since this issue concerns issues of POWER, read the following:

    Psychoanalysis is mental analysis the science of the mind, why people do what they do:

    ” The 3 main motivations of every Human action concern one of 3 issues of:

    (1) Power

    (2) Sex Gratification and

    (3) Security from Death.

    (4) Because these issues hold survival value for people ”

    ( the root of all evil is the need for food )

    Providing your people with a real sense of a security from death with hope for a medical resurrection after being preserved in a cryonic ice cemetery is a good idea for civilization.

    I hope offering burial in an American ice cemetery helps maintain peace in our country.

    Whole body Cryonics for 35k ? see the Cryonics Institute near Detroit Michigan USA

  4. We speak of the noun “matter”
    And the verb “to matter”
    We also speak of antimatter as a noun (bequeathing some sense of coherency)
    What would the verb form be? Simply “to die?” To “not matter”?
    Is there coherency in antimatter? A relation between the two senses of Matter? Does antimatter matter?

    • Torbjörn Larsson | November 26, 2020 at 5:21 pm | Reply

      “Simply “to die?” To “not matter”?
      Is there coherency in antimatter? A relation between the two senses of Matter? Does antimatter matter?”

      As an aside, the process of biological lifeforms is evolution and it happens over populations. What individual organisms experience is … experience. So that stops when an individual “die”, and like the CNO cycle the C is recirculated into living populations.

      A but tongue in cheeckthen:

      – Antimatter is as coherent or incoherent as matter – you can make coherent Bose-Einstein condensates of both [“Bose–Einstein condensate” @ Wikipedia].

      – Matter and antimatter is – as the name implies – each others antiparticles (which may be the same type of particle in some cases, such as for photons) – they can annihilate each other to leave just energy radiation behind.

      – Antimatter matters a lot, such as in fusion processes. For a simpler example, neutron decay gives a proton, an electron and an antineutrino [“Free neutron decay” @ Wikipedia].

  5. Babu G. Ranganathan | November 26, 2020 at 11:53 am | Reply

    Babu G. Ranganathan*

    (B.A. Bible/Biology)

    JUST BECAUSE SCIENCE CAN EXPLAIN how an airplane works doesn’t mean that no one designed or made the airplane. And just because science can explain how life or the universe works doesn’t mean there was no Designer and Maker behind them.

    Natural laws may explain how the order in the universe works and operates, but mere undirected natural laws cannot explain the origin of that order. Once you have a complete and living cell then the genetic code and biological machinery exist to direct the formation of more cells from raw materials such as amino acids and other chemicals, but how could life or the cell have naturally originated when no directing code and mechanisms existed in nature? Read my Internet article: HOW FORENSIC SCIENCE REFUTES ATHEISM.

    WHAT IS SCIENCE? Science simply is knowledge based on observation. No human observed the universe coming by chance or by design, by creation or by evolution. These are positions of faith. The issue is which faith the scientific evidence best supports.

    SCIENCE SHOWS THAT THE UNIVERSE CANNOT BE ETERNAL because it could not have sustained itself eternally due to the law of entropy (increasing and irreversible net energy decay, even in an open system). Even a hypothetical oscillating universe could not continue to oscillate eternally! Einstein’s General Theory of Relativity shows that space, matter, and time all are physical and all had a beginning. Space even produces particles because it’s actually something, not nothing. What about the Higgs boson (the so-called “God Particle”)? The Higgs boson, even if it existed, would not have created mass from nothing, but rather it would have converted energy into mass. Einstein showed that all matter is some form of energy. Even time had a beginning! Time is not eternal.

    The law of entropy doesn’t allow the universe to be eternal. If the universe were eternal, everything, including time (which modern science has shown is as physical as mass and space), would have become totally entropied by now and the entire universe would have ended in a uniform heat death a long, long time ago. The fact that this hasn’t happened already is powerful evidence for a beginning to the universe.

    Popular atheistic scientist Stephen Hawking admits that the universe had a beginning and came from nothing but he believes that nothing became something by a natural process yet to be discovered. That’s not rational thinking at all, and it also would be making the effect greater than its cause to say that nothing created something. The beginning had to be of supernatural origin because science teaches us from the First Law of Thermodynamics that natural laws and processes do not have the ability to bring something into existence from nothing.

    The supernatural origin of the universe cannot be proved by science but science points to a supernatural intelligence and power for the origin and order of the universe. Where did God come from? Obviously, unlike the universe, God’s nature doesn’t require a beginning.

    The disorder in the universe can be explained because of chance and random processes, but the order can be explained only because of intelligence and design.

    Gravity may explain how the order found in the precise and orderly courses of thousands of billions of stars is maintained, but gravity cannot explain the origin of that order.

    Some evolutionary astronomers believe that trillions of stars crashed into each other leaving surviving stars to find precise orderly orbits in space. Not only is this irrational, but if there was such a mass collision of stars then there would be a super mass residue of gas clouds in space to support this hypothesis. The present level of residue of gas clouds in space doesn’t support the magnitude of star deaths required for such a hypothesis. And, as already stated, the origin of stars cannot be explained by the Big Bang because of the reasons mentioned above. It’s one thing to say that stars may decay and die into random gas clouds, but it is totally different to say that gas clouds form into stars.

    Even the father of Chaos theory admitted that the “mechanisms” existing in the non-living world allow for only very rudimentary levels of order to arise spontaneously (by chance), but not the kind or level of order we find in the structures of DNA, RNA, and proteins. Yes, individual amino acids have been shown to come into existence by chance but not protein molecules which require that the various amino acids be in a precise sequence just like the letters found in a sentence.

    Some things don’t need experiment or scientific proof. In law there is a dictum called prima facie evidence. It means “evidence that speaks for itself.”

    An example of a true prima facie would be if you discovered an elaborate sand castle on the beach. You don’t have to experiment to know that it came by design and not by the chance forces of wind and water.

    If you discovered a romantic letter or message written in the sand, you don’t have to experiment to know that it was by design and not because a stick randomly carried by wind put it there. You naturally assume that an intelligent and rational being was responsible.

    It’s interesting that Carl Sagan would have acknowledged sequential radio signals in space as evidence of intelligent life sending them, but he wouldn’t acknowledge the sequential structure of molecules in DNA (the genetic code) as evidence of an intelligent Cause. Read my popular Internet article, HOW DID MY DNA MAKE ME.

    I encourage all to read my popular Internet articles:


    Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION (This site answers many arguments, both old and new, that have been used by evolutionists to support their theory)


    *I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I’ve been privileged to be recognized in the 24th edition of Marquis “Who’s Who in The East” for my writings on religion and science.

    • Torbjörn Larsson | November 26, 2020 at 5:49 pm | Reply

      That is superstition, and has nothing to do with the CNO result.

      But FWIW, I consider religious superstition alongside other scams like astrology and homeopathy based on evidence, and myself simply as an observer – I don’t want to be labeled in superstitious terms like ‘atheist’ when I don’t rely on belief but facts.

      Specifically, the magic doesn’t work:
      – Intercessory prayers were shown as ineffective in comprehensive blind tests metaanalysis 2006. We live in a natural world.
      – Three sciences has all showed that there is no ‘soul’/’afterlife’ magic: in historical order medicin (anesthetics acts chemically), biology (evolution shows continuity) and physics (LHC 2012-2017 tested the standard model to leave no room for exotic processes – and that is watertight). We are enirely biochemical machines.
      – Flat space (Planck collaboration 2018, eBOSS collaboration 2020) puts a constraint on nature that we can test magic against: all energy and all work must each sum to zero. We live in an entirely natural world to 1:100,000 likelihood from cosmic background radiation noise.

      So seeing there are no “gods”, maybe pointing out that creationism has been rejected by science for almost 2 centuries now is superfluous. But in any case since you mention order, a cell works the same as a refrigerator – heat and disordering entropy is ezported to the exapnding universe space – and that is also 2 centuries old (Carnot cycle). And of course life evolved from geology – how else since Earth was born heat sterilized – and we have the phylogenies to prove that continuity since 2016 [“The physiology and habitat of the last universal common ancestor”, Weiss et al., Nature Microbiology].

      Science is the only known method to attain knowledge. So of course ad hoc scams like religion is erroneous at the core (and statistically they correlate with dysfunctional, unsafe societies, so who wants it anyway).

      Nitpick: Science shows nothing on the universe being eternal or not eternal, it is an open question in cosmology. The current inflationary hot big bang is naturally eternal. Unlikely constraints would prohibit the observed slow roll inflation [Planck collaboration 2018 ] from being in a frustrated ground state of attempting roll down but expanding faster so just resulting in an infinite number of local universes of volume meaure zero [in measure theory math, due to the exponential expansion] in the flat, zero energy and so likely eternal, zero temperature and zero entropy space. An introduction to modern inflationary hot big bang cosmology, and how it could be eternal, is the video “The Big Bang is Probably Not What You Think It Is” @ Youtube, with a script from a known astrophysicist.

      I could go on and nitpick creationist erroneous claims all day, but we all know you don’t heed the facts. This is for the science reading public, that unfortunately may read about your pseudoscience references. I wiosh you stop with that – science is published in peer review, not on creationist [!] scam sites.

  6. Torbjörn Larsson | November 26, 2020 at 4:47 pm | Reply

    The paper is interesting. The research is experimentally iffy with regular fusion pp and pep chain as well as contamination neutrinos covering the same spectral range. But they not only distinguished a certain neutrino signature among several such and other confounds, they managed it at 2 orders of magnitude higher sensitivity.

    The paper has a discussion on 1 % CNO ratio implying the figure is perhaps an older estimate and in that case the observation was a nice test of theory! “The CNO cycle is thought to contribute to the energy production in the Sun at the level of 1%, with a large uncertainty related to poorly known metallicity. Metallicity is relevant for two reasons: i) “metals” directly catalyse the CNO cycle, and ii) they affect the plasma opacity, indirectly changing the temperature of the core and modifying the evolution of the Sun and its density profile. We notice, in addition, that in the Sun the 16O lifetime at the core’s temperature is much longer than the solar age [4]. This makes the CNO sub-cycle II (see Fig. 1, upper plot) sub-dominant in the Sun.”

    The paper says on the ratio values: “The CNO solar neutrino interaction rate … corresponding to a flux of neutrinos on Earth of 7.0 +3.0 -2.0 ×10^8 cm^-2 s^-1.” “… number of solar neutrinos reaching the Earth (≈6× 10^10 ν cm^-2 s^-1) …”.

    Also, I can now see why the scientists wants to continue observations and try to resolve metallicity.

  7. Freya Holloway | March 17, 2022 at 9:05 am | Reply

    I read somewhere that the detection of CNO neutrinos not only helps confirm that it is the primary form of fusion in higher-mass stars, but that it also confirms that CNO fusion is the primary form of fusion in the Universe. Is this correct, and if so, how do we know this?

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