Search for Magnetic Monopoles in Magnetic Reconnection Regions
aa r X i v : . [ a s t r o - ph . S R ] M a r Search for Magnetic Monopoles in Magnetic ReconnectionRegions
Jun Zhang, Ting Li
ABSTRACT
In order to satisfy the symmetry between electric and magnetic fields in thesource free Maxwell’s equations, electric charges might have magnetic counter-parts: magnetic monopoles. Many methods and techniques are proposed tosearch for the monopoles, but no confirmed results have been obtained. Basedon solar observations, we know that magnetic reconnections take place duringeruptive solar activities. The magnetic fields can be broken at first and thenrejoined, implying that the fields are source-relevant at the broken moment. It isspeculated that the magnetic lines undergo outward deflection movement duringthe broken moment, as the line tying effect disappears and the magnetic tensiontriggers the movement. The signal of the deflection is detected for the first timeby EUV and H α observations in reconnection processes. We propose that themonopoles appear in magnetic reconnection regions at first, and then the annihi-lation of opposite polarity monopoles releases energy and perhaps also producesparticles. To detect the predict monopoles, laboratory plasma experiments canbe used to provide some fundamental information. Subject headings:
Sun: activity — Sun: atmosphere — Sun: corona — magneticreconnection
1. Introduction
Following the predicted existence of monopoles from spontaneous symmetry breakingmechanisms (Dirac 1931), searches have been routinely made for monopoles produced ataccelerators, in cosmic rays, and bound in matter (Nakamura & Particle Data Group 2010).The main strategy to search for monopoles is that monopoles will interact with their pass
Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences,Beijing 100012; University of Chinese Academy of Sciences, Beijing 100049, China; [email protected]; [email protected]
2. Observations
The New Vacuum Solar Telescope (NVST; Liu et al. 2014) observe the Sun with hightemporal and spatial resolutions. We mainly use the H α line from the NVST to study thedynamic evolution of small-scale magnetic reconnection. Moreover, the Atmospheric Imaging 3 –Assembly (AIA; Lemen et al. 2012) multi-wavelength observations and the Helioseismic andMagnetic Imager (HMI; Scherrer et al. 2012; Schou et al. 2012) line-of-sight magnetogramsfrom the Solar Dynamics Observatory (SDO; Pesnell et al. 2012) are also used. SDO /AIAobserves the full disk of the Sun in 10 wavelengths with a pixel size of 0 ′′ .6 and a cadenceof 12 s. These data reveal the solar atmospheric temperatures from ∼ ∼
20 MK.The
SDO /HMI records the line-of-sight (LOS) magnetic field with a cadence of 45 s and aspatial sampling of 0 ′′ .5 pixel − .On 27 January 2012, two sets of EUV loops observed by AIA appeared above the westernsolar limb as seen from the Earth (Sun et al. 2015). AIA 171 ˚A and 94 ˚A images from ∼ ′′ × ′′ ,and the H α ′′
163 per pixel. The calibration, correctionand speckle masking (Weigelt 1977; Lohmann et al. 1983) reconstruction of these H α data,as well as the co-alignment between these H α data and SDO images are described by Yanget al. (2015).
3. Results
The concept of magnetic reconnection was proposed long time ago, and many obser-vations and theoretic models have been displayed and put forward. However, the mostimportant question (aspect) that whether magnetic field breaks or not during reconnec-tion has always been omitted. The advance of the solar observations help us to check thedetails of magnetic reconnection. This work tracks the following idea. If magnetic fieldbreaks during reconnection, the broken field will undergo a special outward movement, dueto the disappearance of the line tying effect and magnetic tension causes the movement ofthe broken field. Examining this movement will provide new clues about the essentials ofreconnection, such as the magnetic fields are source-relevant, and monopoles or equivalentmonopoles appear at the broken points.
Recently, both the ground-based and space-borne observations have provided a massof magnetic reconnection events in solar atmosphere. Two events are chosen to display theproperties of magnetic reconnection. The first event occurred on 27 January 2012. From ∼ ∼ ∼ − . At the later phase of thereconnection, the deflection (Fig. 2e and 2f) speed is 2.2 km s − , twice as large as that at thebeginning. An animation (movie1.mpeg) to display this deflection is available in the onlinejournal.The multi-wavelength observations from the AIA with the high spatial and temporalresolution successfully detect evidences for reconnection including plasma inflows, heatingclose to the reconnection site, and outward deflection relative to the broken fields. Toquantitatively analyze the inflows and deflection, we select three slices in the 171 and 94 ˚Acomposite images (“AB”, “CD” and “EF” in Fig. 1a). The stack plots (Fig. 3) clearly showthat the bilateral cool loops (cyan) keep moving towards the reconnection region. Once thevisible innermost loops come into contact at ∼ − (Fig. 3a and 3b). In addition, the average outwarddeflection speed of the loops at the upper side of the “Void” space is about 1.4 km s − .The second reconnection event is displayed in Fig. 4. Sequence of H α images show themagnetic reconnection between two sets of small-scale loops “L1” and “L2”, as shown inpanel (a). Prior to the initiation of rapid reconnection, the two sets of loops “L1” and “L2”were moving towards each other and then interacted. At 07:18:52 UT, both loops “L1” and“L2” were apparently broken (as denoted in panel (b)). Meanwhile, two broken loops (“B L ”and “B L ” in panel (b)) which were respectively related to “L1” and “L2” appeared, but thecurvatures of “B L ” and “B L ” were more different from that of “L1” and “L2”. Then “B L ”and “B L ” connected to form a loop “L4”, and loops “L1” and “L2” disappeared (panel(c)). To better exhibit this reconnection process, an animation (movie2.mpeg) is availablein the online journal. At the reconnection region and its proximity, the brightenings in theH α images (panels (b) and (c)) and the 171 and 94 ˚A composite images (panel (d)) can befound. As displayed in panel (e), all the three light curves in the reconnection region (blue 5 –window in panel (a)) reach the peak simultaneously, i.e., ∼ Traditional reconnection models presented that opposite magnetic fields form a currentsheet while the fields approach each other. Magnetic energy converts into heat and kineticenergy by Ohmic dissipation in the current sheet which locates in a tiny diffusion region.But the joint between the fields and the current sheet is always omitted, and nobody knowsthe physical properties of the joint. Although Dungey (1953) was the first to suggest that“lines of force can be broken and rejoined”, in the past decades and at present time, almostno researcher have considered that magnetic field lines must be broken firstly, if the linesare involved in reconnection. We suggest that while the field lines break, opposite polaritymonopoles at the two broken points appear. Figure 5 displays a series of schematic drawingswhich illustrate the magnetic reconnection process. The green arrows in panel (a) denotethe convergence of two sets of loops (“L1” and “L2”, “L3” and “L4”), and the verticalred structure (panels (b) and (c)) represents the current sheet (CS). At the joint (denotedby a blue point in panel (c)) between CS and L2, loop “L2” breaks. The correspondingmagnetic field −→ B −→ B Q − m appears at the joint. Similarly, “L3” and itscorresponding magnetic field −→ B Q m appear at this joint, as −→ B ∇·−→ B αQ − m (1) ∇·−→ B αQ m (2)Where α is a coefficient. We suggest that the monopoles are instable, they should beannihilated in a short time. It is possible that “L2” and “L3” (panel (c)) connects to form anew loop (panel (d)). The annihilation of opposite polarity monopoles releases energy ( En )and perhaps produces particle ( P ). This process can be expressed as Q − m + Q m −→ En + P (3) 6 –
4. Conclusions and Discussion
Based on both the ground-based and space-borne observations, we report two magneticreconnection events in solar atmosphere. Assuming that magnetic fields can be brokenat first and then rejoined during reconnection process, we suggest that the magnetic linesundergo outward deflection movement during the broken moment, as the line tying effectdoes not work and the magnetic tension triggers the movement. The signal of this movementis detected for the first time by EUV and H α observations in the two reconnection events. Tosatisfy the Gauss’s law for magnetism, we propose that the monopoles appear in magneticreconnection regions. The annihilation of opposite polarity monopoles releases energy andperhaps also produces particles, then new loop forms. It is speculated that the monopolescan be searched for in magnetic reconnection region, if the monopoles exist indeed in nature.The common features of most reconnection theories include the changes of magnetictopologies and the release of magnetic energy (Parker 1957; Sweet 1958; Petschek 1964; seethe review by Yamada et al. 2010). The topology changes are mainly the break of inflowinganti-parallel loops and the formation of new loops. When the loops reconnect in the diffusionregion, magnetic energy is released, thus heating the plasma. In addition, the reconnectedfield lines near the X-point are sharply bent and the magnetic tension force also impactsthe plasma to increase the kinetic energy. Therefore, the plasma is brightened and expelled.However, it is very few to take into account the break of magnetic field and the succedentmatter of the break. In this work, we forecast at first the deflection movement, and then wefind the signal of the movement in the reconnection events.Since the introduction of magnetic monopoles by Dirac (1931), they are compulsory inmany formulations of Grand Unified Theories (GUT, Polyakov 1974; ’t Hooft 1974). Al-though GUT-scale monopoles are commonly believed to be extremely heavy (10 GeV),there are other mechanisms resulting in production of much lighter monopoles after infla-tion. Kephart and Shafi (2001) proposed that monopoles with a magnetic charge of a fewDirac units and masses in the range 10 ∼ GeV could be occurred in symmetry-breakingevents. Furthermore, there is a speculation that these lighter monopoles are possible ultra-high energy cosmic rays, so monopoles can be searched for in cosmic radiation. Based onboth measurements and estimates of cosmic magnetic fields, it is suggested that they couldaccelerate monopoles lighter than 10 eV to relativistic velocities (Beck et al. 1996; Ryu etal. 1998). 7 –It is a fact that no traditional monopoles have been verifiably detected (Yao et al. 2006).Although there are some reports of magnetic monopole detections (Price et al. 1975; Cabrera1982; Caplin et al. 1986), these reports have often been challenged by the original authorsthemselves (Price et al. 1978; Huber et al. 1990). In this paper, we propose a new idea:search for magnetic monopoles in magnetic reconnection regions. Both remote observationsand local detections can be employed to search for monopoles in reconnection regions whichare in solar atmosphere and in laboratories, respectively.This work is supported by the National Natural Science Foundations of China (11533008,11221063, 11203037, 11303049 and 11303050) and the Strategic Priority Research Program − TheEmergence of Cosmological Structures of the Chinese Academy of Sciences, Grant No.XDB09000000. The data are used courtesy of NASA/
SDO and NVST science teams.
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This preprint was prepared with the AAS L A TEX macros v5.2.
11 – (a)
AIA 171 Å and 94 Å 02:00:13 UTA BC DE F (c)
800 1000 1200Solar X (arcsec)−600−500−400 S o l a r Y ( a rc s ec ) (b) (d) Fig. 1.— Composite images of the AIA 94 ˚A (red) and 171 ˚A (cyan) passbands showing thereconnection event on 27 January 2012. Lines “AB”, “CD” and “EF” in panel (a) denotethe positions that are used to obtain the stack plots displayed in Figure 3. 12 – (a)
AIA 171 Å and 94 Å 03:19:01 UT −600−500−400 S o l a r Y ( a rc s ec ) (d)
800 1000 1200Solar X (arcsec)−600−500−400 S o l a r Y ( a rc s ec ) (c) Y ( a rc s ec ) (b) Y ( a rc s ec ) (f) Y ( a rc s ec ) (e) Y ( a rc s ec ) Fig. 2.— Panels (a) and (d): two composite images of the AIA 94 ˚A (red) and 171 ˚A (cyan)passbands showing the approach (a) and reconnection (d) of two sets of coronal loops. Thewindow in panel (a) outlines the field-of-view of the 171 ˚A images in panels (b), (c), (e) and(f). Panels (b) and (c): outward deflection of the upper set of loops at the beginning ofthe reconnection. White (red) lines denote the inner boundary of the loops at 03:19:13 UT(03:42:13 UT). Panels (e) and (f): similar to panels (b) and (c), outward deflection of theupper set of loops at the later phase of the reconnection. Green (blue) lines denote the innerboundary of the loops at 04:11:13 UT (04:26:13 UT). An animation (movie1.mpeg) of thisfigure is available in the online journal. 13 –
AIA 171 Å and 94 Å (a) −1 −1 −1 S li ce A − B ( M m ) (b) −1 S li ce C − D ( M m ) (c) −1 Time (since 2012/01/27 02:00 UT) S li ce E − F ( M m ) Fig. 3.— Temporal evolution of plasma inflows (see the dotted lines in panels (a) and (b))and deflecting loops (denoted by the dotted line in panel (c)) during the reconnection. 14 – −30 −20 −10 −80−70−60 S o l a r Y ( a r cs e c ) L1 L2 (a) 07:16:27 UT B L1 B L2 (b) 07:18:52 UT L3L4 (c) 07:20:17 UT −30 −20 −10Solar X (arcsec)−80−70−60 S o l a r Y ( a r cs e c ) (d) 07:18:49 UT B r i gh t ne ss H α
171 Å94 Å (e)
Fig. 4.— Panels (a)-(c): time sequence of H α images showing the reconnection processbetween two sets of small-scale loops. Arrows “L1” and “L2” point to the loops beforereconnection, and arrows “L3” and “L4” denote the newly formed loops after reconnection.Two arrows in panel (b) denote two broken points, and the dashed curves B L and B L indicate two broken loops. Panel (d): composite image of the AIA 94 ˚A (red) and 171 ˚A(cyan) passbands showing the brightening at reconnection moment. Panel (e): light curvesin the H α , 171 ˚A, and 94 ˚A lines obtained from the area within the blue window in panel (a).An animation (movie2.mpeg) for this reconnection event is available in the online journal. 15 –Fig. 5.— Schematic drawings illustrating the magnetic reconnection process. The greenarrows in panel (a) denote the convergence of two sets of loops (“L1” and “L2”, “L3” and“L4”). The vertical red structure represents the current sheet (CS), and the blue dottedrectangle outlines the field-of-view of panels (c)-(d). The green curves in panel (c) representthe broken loops of “L2” and “L3”, −→ B −→ B m and Q − m are the positive and negative monopoles which appear near theends of the broken loops. The blue curve in panel (d) indicates the newly formed loop, afterthe monopoles annihilation (MA). 16 – T tT tΦ t| | t t t t t t t t t t t t (a)(b)(c) (d)(e)(f) Fig. 6.— Panels (a)-(c): schematic drawings illustrating the magnetic reconnection processwhich will be detected by laboratory plasma experiments. Red windows and red dots in thewindows represent probe array to measure magnetic flux | Φ | and ion temperature “T”.Panels (d)-(e): possible changes of magnetic flux | Φ | (d) and ion temperature “T” (e)during the reconnection process (t -t in panels (a)-(c)). Magnetic fields break and magneticmonopoles appear at t moment, then monopoles annihilation (t ) will transfer the magneticenergy to thermal energy and increase the ion temperature. Panel (f): magnetic energytransforming into the ion thermal energy by current sheet dissipation during the interval t and t3