# Stars/Sun/Neutrinos/Lecture

< Stars‎ | Sun‎ | Neutrinos
This "neutrino image" of the Sun is produced by using the Super-Kamiokande to detect the neutrinos from nuclear fusion coming from the Sun. Credit: R. Svoboda and K. Gordan (LSU), and NASA.

Neutrinos are being produced by processes above the photosphere and probably within 2-4 solar radii as most solar flares give off energy close to and into the chromosphere.

## Neutrons

Data from the Climax, Colorado, surface neutron monitor is an indicator of primary cosmic rays in the GeV range. Credit: John N. Bahcall and William H. Press.

The data on the right "from the Climax, Colorado, surface neutron monitor [...] is an indicator of primary cosmic rays in the GeV range."[1]

"Variation with the solar cycle [dotted curve of sunspot data] is evident."[1]

"The tendency of the cosmic-ray modulation to lag sunspots (at least at times of sunspot decline) is visible, as is the somewhat more sawtooth form of the cosmic rays."[1]

"The surface neutron flux [...] is largest at solar minimum and smallest at solar maximum, and [...] has the same sense as the 37Ar production variations."[1]

"Primary cosmic rays below ~1 GeV are shielded by heliospheric currents which build up during solar maximum; see, e.g., Simpson 1989 and references there in."[1]

## Neutrinos

All of the data from the Homestake solar neutrino experiment are shown versus dates. Credit: John N. Bahcall and William H. Press.

The first piece of information that seems to be needed are the reactions that produce the higher energy neutrinos: νµ and ντ.

For antiproton-proton annihilation at rest, a meson result is, for example,

${\displaystyle p^{+}+{\bar {p}}^{-}\rightarrow \pi ^{+}+\pi ^{-},}$[2]
${\displaystyle {\pi }^{+}\rightarrow {\mu }^{+}+{\nu }_{\mu }\rightarrow e^{+}+{\nu }_{e}+{\bar {\nu }}_{\mu }+{\nu }_{\mu },}$[3] and
${\displaystyle D_{S}\rightarrow \tau +{\bar {\nu }}_{\tau }\rightarrow \nu _{\tau }+{\bar {\nu }}_{\tau }.}$[4]

"All other sources of ντ are estimated to have contributed an additional 15%."[4]

${\displaystyle \tau \rightarrow e+\nu _{\tau }+\nu _{e},}$[4]

for two neutrinos.[4]

${\displaystyle \tau \rightarrow h+\nu _{\tau }+X,}$[4]

where ${\displaystyle h}$ is a hadron, for two neutrinos.[4]

The "data set [on the right from the Homestake solar neutrino experiment] now spans almost two complete solar cycles."[1]

## Electrons

Beam of electrons are moving in a circle in a magnetic field (cyclotron motion). Lighting is caused by excitation of atoms of gas in a bulb. Credit: Marcin Białek.

“Free electrons in vacuum can be influenced by electric and magnetic fields [so] as to form a fine beam. At the spot of collision of the beam with the particles of the solid-state matter, most portion of the kinetic energy of electrons is transferred into heat. The main advantage of this method is the possibility of very fast local heating, which can be precisely electronically (computer) controlled. The high concentration of power in a small volume of matter, which can be reached in this way results in very fast increase of temperature in the spot of impact causing the melting or even evaporation of any material, depending on working conditions. This makes the electron beam an excellent tool in many applications.”[5]

## Sun

Main sources: Stars/Sun and Sun (star)

"The highest flux of solar neutrinos come directly from the proton-proton interaction, and have a low energy, up to 400 keV. There are also several other significant production mechanisms, with energies up to 18 MeV.[6]"[7]

## Sunspot cycles

This figure shows a detected 94 % correlation between scaled sunspot numbers and neutrino detections. Credit: John N. Bahcall.
37Ar production data are shown above inverted sunspot data. Credit: John N. Bahcall and William H. Press.

"Neutrinos can be produced by energetic protons accelerated in solar magnetic fields. Such protons produce pions, and therefore muons, hence also neutrinos as a decay product, in the solar atmosphere."[8]

"Energetic protons in the solar corona could explain Figure 2 [at right] only if (1) they tap a substantial fraction of the entire energy generated in the corona, (2) the energy generated in the corona is at least 3 times what has been deduced from the observations, (3) the vast majority of energetic protons do not escape the Sun, (4) the proton energy spectrum is unusually hard (p0 = 300 MeV c-1, and (5) the sign of the variation is opposite to what one would predict. As the likelihood of all of these conditions being fulfilled seems extremely small, we do not believe that neutrinos produced by energetic protons in the solar atmosphere contribute significantly to the neutrino capture in the 37Cl experiment."[8]

"The 37Ar production rate [at second right] in the Homestake solar neutrino experiment is anticorrelated (significance level of parts in 105) with solar activity (as measured by sunspot number) in the second two-thirds of the data, approximately 1977-1989; no significant correlation is substantiated in the first third of the data, 1970-1977."[1]

## Chromospheres

"The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere.[9]"[10]

## Transition regions

[Transition Region and Coronal Explorer] (TRACE) produced a 19.5 nm wavelength image of the transition region as a low, bright fog over the surface of the Sun and as a thin bright nimbus around the prominence itself. Credit: TRACE Data Center.

"The solar transition region is a region of the Sun's atmosphere, between the chromosphere and corona.[11] It is visible from space using telescopes that can sense ultraviolet. It is important because it is the site of several unrelated but important transitions in the physics of the solar atmosphere:"[12]

• "Below, most of the helium is not fully ionized, so that it radiates energy very effectively; above, it is fully ionized."[12]
• "Below, gas pressure and fluid dynamics dominate the motion and shape of structures; above, magnetic forces dominate the motion and shape of structures, giving rise to different simplifications of magnetohydrodynamics."[12]

"The thin region of temperature increase from the chromosphere to the corona is known as the transition region and can range from tens to hundreds of kilometers thick. An analogy of this would be a light bulb heating the air surrounding it hotter than its glass surface. The second law of thermodynamics would be broken."[13]

## Coronal clouds

Def. a cloud, or cloud-like, natural astronomical entity, composed of plasmas at least hot enough to emit X-rays is called a coronal cloud.

As of December 5, 2011, "Voyager 1 is about ... 18 billion kilometers ... from the [S]un [but] the direction of the magnetic field lines has not changed, indicating Voyager is still within the heliosphere ... the outward speed of the solar wind had diminished to zero in April 2010 ... inward pressure from interstellar space is compacting [the magnetic field] ... Voyager has detected a 100-fold increase in the intensity of high-energy electrons from elsewhere in the galaxy diffusing into our solar system from outside ... [while] the [solar] wind even blows back at us."[14]

The source of heat that brings the coronal cloud near the Sun hot enough to emit X-rays may be an electron beam heating effect due to "high-energy electrons from elsewhere in the galaxy diffusing into our solar system from outside".[14]

## Solar flares

"One of [...] the outstanding problems of the outer atmosphere of the Sun is the identification of the physical mechanisms that give rise to the eruption of solar flares."[15]

There is a "hydrodynamic response of the solar atmosphere to the injection of an intense beam of electrons [as described] in a numerical simulation of a solar flare."[15]

"The hydrodynamics is predicted [...] and the geometric form is of a semi-circular loop having its ends in the photosphere. [...] the loop is filled at supersonic speed with plasma at temperatures characteristic of flares. At the same time a compression wave is predicted to propagate down towards the photosphere. After the heating pulse stops, the plasma that has risen into the loop, starts to decay and return to the condition it was in before the pulse started."[15]

The "impulsive phase of a flare [may be] initiated by an electron beam (having a power-law energy spectrum down to some minimum energy) depositing its energy in a model atmosphere representing the pre-flare condition."[15]

There may be "a magnetic field parallel to the electron beam, and sufficiently strong that the electrons and subsequent flare plasma are contained within the beam dimensions, and transport negligible thermal energy in transverse directions."[15]

The "pre-flare atmosphere is [...] for the chromosphere with a suitable extension into the corona."[15]

An "input beam pulse of 1011 erg cm-2 s-1 for 10 s is capable of filling a loop structure with plasma at a peak temperature of over 30 million degrees K, with associated flare velocities of over a thousand kilometers per second. Associated with this upward flaring material, is a compression wave moving towards the photosphere, and attaining particle densities of up to 1014 cm-3."[15]

"[N]eutrino flux increases noted in Homestake results [coincide] with major solar flares [14]."[16]

"The correlation between a great solar flare and Homestake neutrino enhancement was tested in 1991. Six major flares occurred from May 25 to June 15 including the great June 4 flare associated with a coronal mass ejection and production of the strongest interplanetary shock wave ever recorded (later detected from spacecraft at 34, 35, 48, and 53 AU) [15]. It also caused the largest and most persistent (several months) signal ever detected by terrestrial cosmic ray neutron monitors in 30 years of operation [16]. The Homestake exposure (June 1–7) measured a mean 37Ar production rate of 3.2 ± 1.5 atoms/day (≈19 37Ar atoms produced in 6 days) [13]; about 5 times the rate of ≈ 0.65 day −1 for the preceding and following runs, > 6 times the long term mean of ≈ 0.5 day−1 and > 2 1/2 times the highest rates recorded in ∼ 25 operating years."[16]

## Coronal loops

The image shows solar coronal loops observed by the Transition Region And Coronal Explorer (TRACE), 171 Å filter. Credit: TRACE/NASA.
The image shows the cooling post-flare arcade (rotated by -90 degrees so that north is to the right) 6h after the flare (at 00:11 UT on September 8. Credit: TRACE/NASA.

"Almost as soon as Active Region 10808 rotated onto the solar disk, it spawned a major X17 flare. TRACE was pointed at the other edge of the Sun at the time, but was repointed 6 hours after the flare started. The image on the left shows the cooling post-flare arcade (rotated by -90 degrees so that north is to the right) 6h after the flare (at 00:11 UT on September 8); the loop tops still glow so brightly that the diffraction pattern repeats them on diagonals away from the brightest spots. Some 18h after the flare, the arcade is still glowing, as seen in the image on the right (at 11:42 UT on September 8). In such big flares, magnetic loops generally light up successively higher in the corona, as can be seen here too: the second image shows loops that are significantly higher than those seen in the first. Note also that the image on the right also contains a much smaller version of the cooling arcade in a small, very bright loop low over the polarity inversion line of the region."[17]

Nearly all of the TRACE images of coronal loops and the transition region indicate that material in these loops and loop-like structures returns to the chromosphere.

"Normally, solar energetic particle (SEP) events associated with disturbances in the eastern hemisphere are characterized by slow onset and lack of high-energy particles. The SEP event associated with the first major flare (X17) [...] is among very few such events over several decades in that although the source region was on the east limb, the particle flux started to rise only a few hours from the flare onset, while the flux of protons with energies in excess of 100 MeV went up by more than a factor of one hundred. We do not understand how these energetic particles can reach the Earth from that side of the Sun, because there should be no magnetic connectivity."[17]

## Surface fusions

Based on the 3He-flare flux from the Sun's surface and Surveyor 3 samples (implanted 15N and 14C in lunar material) from the surface of the Moon, the level of nuclear fusion occurring in the solar atmosphere is approximately at least two to three orders of magnitude greater than that estimated from solar flares such as those of August 1972.[18]

Although 7Be is usually assumed to have been produced by the Big Bang nuclear fusion, excesses (100x) of the isotope on the leading edge[19] of the Long Duration Exposure Facility (LDEF) relative to the trailing edge suggest that fusion near the surface of the Sun is the most likely source.[16] The particular reaction 3He(α,γ)7Be and the associated reaction chains 7Be(e-e)7Li(p,α)α and 7Be(p,γ)8B => 2α + e+ + νe generate 14% and 0.1% of the α-particles, respectively, and 10.7% of the present-epoch luminosity of the Sun.[20] Usually, the 7Be produced is assumed to be deep within the core of the Sun; however, such 7Be would not escape to reach the leading edge of the LDEF.

## Earth

Main source: Earth

Here on the Earth's surface the νe flux is about 1011 νe cm-2 s-1 in the direction of the Sun.[21]

"The total number of neutrinos of all types agrees with the number predicted by the computer model of the Sun. Electron neutrinos constitute about a third of the total number of neutrinos. [...] The missing neutrinos were actually present, but in the form of the more difficult to detect muon and tau neutrinos."[21]

"[L]ow-altitude regions of downward electric current on auroral magnetic field lines are sites of dramatic upward magnetic field-aligned electron acceleration that generates intense magnetic field-aligned electron beams within Earth’s equatorial middle magnetosphere."[22]

## Jupiter

Main sources: Wanderers/Jupiter and Jupiter

"Field-aligned equatorial electron beams [have been] observed within Jupiter’s middle magnetosphere. ... the Jupiter equatorial electron beams are spatially and/or temporally structured (down to <20 km at auroral altitudes, or less than several minutes), with regions of intense beams intermixed with regions absent of such beams."[22]

## Hypotheses

Main source: Hypotheses
1. All or a portion of the photosphere is being heated by electron bombardment; i.e., electron beam heating.

## References

1. John N. Bahcall and William H. Press (1 April 1991). "Solar-cycle modulation of event rates in the chlorine solar neutrino experiment". The Astrophysical Journal 370 (04): 730-742. doi:10.1086/169856. Retrieved 2016-11-22.
2. Eberhard Klempt, Chris Batty, Jean-Marc Richard (July 2005). "The antinucleon-nucleon interaction at low energy: annihilation dynamics". Physics Reports 413 (4-5): 197-317. doi:10.1016/j.physrep.2005.03.002. Retrieved 2014-03-09.
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16. Maurice Dubin and Robert K. Soberman (April 1996). "Resolution of the Solar Neutrino Anomaly". arXiv: 1-8. Retrieved 2012-11-11.
17. Fred Espenak (September 8, 2005). "Images of the Sun taken by the Transition Region and Coronal Explorer". Palo Alto, California USA: Stanford-Lockheed Institute for Space Research and NASA Small Explorer program. Retrieved 2014-03-11.
18. Fireman EL, Damico J, Defelice J (March 1975). Solar-wind tritium limit and nuclear processes in the solar atmosphere, In: Lunar Science Conference Proceedings 6th Houston TX. 2. New York: Pergamon Press, Inc.. pp. 1811–21. Retrieved 2014-03-11.
19. Fishman GJ, Harmon BA, Gregory JC, Pamell TA, Peters P, Phillips GW, King SE, August RA, Ritter J, Cuichin JH, Haskins PS, McKisson JE, Ely D, Weisenberger AG, Piercey RB, Dybler T (February 19991). "Observation of 7Be on the surface of LDEF spacecraft". Nature 349 (6311): 678-80. doi:10.1038/349678a0.
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