People who devote themselves to studying the Sun inevitably encounter one problem. Their observations are carried out from afar. They rely on images and data from 140 million kilometers away. Whatever one may say, such data do not allow us to create an accurate picture of the magnetic fields that exist and, most importantly, are constantly changing, around the Sun.

But this problem cannot be left behind. On the contrary, scientists should pay maximum attention to it. Understanding the structure and dynamics of these fields will make it possible to understand how coronal ejections travel through space, including towards the Earth, where they can cause serious damage to satellites. A group of American specialists has developed an approach that combines old, well-tested mathematical methods with new theories and experimental techniques for observing the dynamics of coronal masses in order to create a new, fairly accurate model of the magnetic fields around the Sun. First of all, in the upper layers of its atmosphere, in the corona.

“The magnetic field is kind of the skeleton of the entire heliosphere, it determines how particles and coronal masses move towards Earth,” says solar specialist and Goddard Space Flight Center physicist Nat Gopalsuami. According to him, measuring magnetic fields near the surface of the Sun has become routine work for physicists, but they haven’t really learned how to go higher and take measurements in the atmosphere, especially in its upper layers. “Until recently, we could only measure the magnetic field at the top of the corona and under certain conditions. The new technique will allow for more general research.”

To use the new method, you only need to have good measurements of the coronal ejection. The method is based on the interaction between an object moving through the gas and the gas itself. In this case, a shock wave arises, and a region of compressed, nonequilibrium gas appears around the object, much like when a jet plane moves. This was discovered back in the 1960s. If an object moves through an electrified gas, plasma, its interaction with the gas is also determined by the magnetic field, especially its strength. Such a shock wave with a magnetic field is called a bow wave.

The problem is to detect the bow shock wave in the upper corona. In the upper part of the corona, scientists have not yet been able to notice those phenomena that usually distinguish a shock wave in areas that are closer to the surface of the Sun. However, on March 25, 2008, the Sun gave scientists a chance to gain insight into its secrets. A coronal ejection formed, moving at a speed of almost 5 million kilometers per hour. It has been spotted by many solar-observing spacecraft. Due to this, a three-dimensional image of the movement of coronal masses was obtained. It turned out that in the limb (in the extreme regions of the Sun) the movement of coronal masses is clearly visible. All phenomena observed in the limb are extremely convenient for observation and analysis. Scientists have obtained excellent data on the dynamics of a coronal ejection.

Gopalsuani suggested that the shock wave could be visible in standard images in white. She was indeed visible, but not in the way he expected. The trajectories of the shock waves were surprisingly imprecise, which is especially strange in the thin atmosphere of the Sun. Instead of being close to the coronal masses themselves, shock waves erupted from the boundaries of the moving mass.

During the March 25 ejection, scientists were able to notice the outlines of a kind of diffusion ring near the boundaries of the coronal ejection. Their structure made it possible to determine the strength of the magnetic field leading to the displacement of shock waves. The distance between the coronal masses and the shock wave front, as well as the radius of curvature of the ejection trajectory, provide comprehensive information for determining the magnetic properties of the medium through which they move. We can say that similarly, one can determine from waves whether they are moving in water or, for example, in oil.

The speed of shock wave propagation can be used to determine the so-called Alfvén velocity - the speed of propagation of the Alfvén wave. This speed determines how quickly a wave can travel through a magnetic medium. This is analogous to the speed of propagation of a sound wave in air. This speed can be used to determine to what extent the object's speed can reach before it creates a shock wave. Having determined this wave, one can then calculate the magnetic field strength in the medium.

The mathematical models used in these transformations were combined with more conventional models of shock wave propagation and allowed the creation of a new theory of the movement of coronal masses and their impact on the Earth. This is evidence of how mathematical methods applied in different fields of knowledge can be used together. In this case, a method originally developed for studying the geomagnetic field is used. It was then extended to analyze the motion of coronal masses in interplanetary space, then near the Sun, and finally to determine the magnetic field in the corona.

To verify the new method, scientists measured the magnetic field strength at different distances from the Sun. These data agreed well with the predictions of the new model, which gives hope that the new development will soon be actively used to measure the magnetic field strength in the corona. Together with other data currently measurable by humans, such as density, temperature and direction of magnetic field lines, measurements of magnetic field strength will provide a complete picture of the magnetic field in the solar corona.

Knowledge of the magnetic field is absolutely essential for predicting space weather.

Magnetic fields of the Sun and Stars

Magn. fields are present, apparently, on all stars. For the first time mag. the field was discovered on the closest star to us - the Sun - in 1908 by Amer. astronomer J. Hale, who measured the Zeeman splitting spectrum. lines in sunspots (see). According to modern measurements, max. magnetic tension spot fields 4000 E. The field in the spots is a manifestation of the general azimuthal magnetic field. fields of the Sun, the field lines of which have different directions in the Northern and Southern hemispheres of the Sun (Fig. 1). In 1953, Amer. astronomer X.W. Babcock discovered a much weaker dipole component of the solar magnet. fields (~1 Oe) with mag. moment oriented along the axis of rotation of the Sun (Fig. 2). In the 70s 20th century It was possible to detect approximately the same weak in intensity non-axisymmetric large-scale component of the solar magnet. fields. She found herself connected to an interplanetary magnet. a field having different directions of radial components in different spaces. sectors (see), which corresponds to a quadrupole on the Sun, the axis of which lies in the plane of the solar equator (Fig. 3). A two-sector structure corresponding to a dipole was also observed. In general, large-scale mag. The Sun's field looks quite complex. An even more complex field structure has been discovered on small scales. Observations indicate the existence of small-scale needle-like fields with strengths up to 2000 Oe. Small-scale mag. fields are also associated with convective cells (see), observed on the surface of the Sun. Magn. The field of the Sun does not remain unchanged. The axisymmetric large-scale field varies quasi-periodically with a period of approx. 22 (). In this case, every 11 years a reversal of the dipole component and a change in the direction of the azimuthal field occur. The non-axisymmetric sector component of the field varies by approx. with the period of revolution of the Sun around its axis. Small scale mag. fields change irregularly, chaotically.

Magn. the field is unimportant for the equilibrium of the Sun; the equilibrium state is determined by the balance of gravitational forces and pressure gradient. But all manifestations of solar activity are associated with magnetism. fields ( , ). Magn. The field plays a decisive role in the creation and heating (up to millions of degrees). Observations made in space. Skylab station (USA, 1973-1974), showed that illuminated in UV and X-ray. ranges, energy is released in numerous. localized areas identified with magnetic loops. fields. On the other hand, areas in which the radiation is significantly weakened () are identified with those open to the outside. space configurations magnetic. power lines. Fast flows are believed to originate in these areas.

All stars, except the Sun, are so distant from us that they are perceived as point objects. Therefore, directly. Observations of distant stars make it possible to determine the magnetic intensity. fields averaged over the surface of the star, and say little about the configuration (geometry) of the field. The relatively small amount of light received from distant stars allows only sufficiently strong magnetic fields to be detected using the Zeeman effect. fields. In this way, it was possible to discover a special group of stars with strong (up to E) fields - . The number of stars that have a magnetic field. the field recorded by the direct Zeeman method is small (several hundreds).

Existence of magnet. fields in other stars can be proven by indirect methods. Chromospheres have been discovered in main sequence stars. For more than ten such stars, it was possible to trace the stellar cycle (similar to the solar cycle) by observing changes in the intensity of the chromospheric Ca lines. Stars (such as BY Draconis) have been discovered and studied, the surface of which is covered with spots by 20-30%. The sun's spots cover no more than 2% of the surface. X-ray observations carried out from the NEAO-2 station (1980, USA) made it possible to detect hot coronas in a large number of stars of various spectral classes, from the hottest 0- and B-stars to cold dwarfs of classes K, M. Since everything on the Sun Similar phenomena are associated with the presence of magnetism. fields, these facts can be considered as evidence of the presence of magnetic fields. fields on other stars. The intensity and geometry of the fields, of course, can only be assessed indirectly. However, the star Boo (G 8) is known, for which, along with the indirect evidence listed above, the field (E) was also recorded directly from the Zeeman effect. This convinces us of the correctness of the general conclusion about the magnetism of stars.

Very strong magnets. A number of stars located in the enclosure have zeros. stages of evolution. For some, as observations of the circular polarization of their continuous radiation show, the field strength reaches 10 6 -10 8 Oe. Even stronger magnetic fields. fields are associated with rapidly rotating neutron stars -. The source of pulsar energy is the rotation of the neutron star. Magn. field of phenomena a transmission link that transforms the rotational energy of a star into the energy of particles and radiation. According to estimates, to explain the observed effects, the field strength on the surface of the star should reach ~ 10 12 Oe.

Very strong magnets. fields were also discovered in neutron stars that are part of binary star systems. An example is a neutron star, which appears as a binary system. Ionized gas from norm. star falls on a neutron star. Magn. The field of a neutron star slows down gas near the surface, which compares gas and magnetic field. pressure, and directs it to the magnetic field. the poles of the star, where the gas radiates. Models with a strong (10 10 -10 13 Oe) field satisfy the observations. Depending on the magnitude of the magnet. fields, gas flow and system parameters, outgoing X-ray. the radiation acquires a certain direction and polarization. A study of the directivity and polarization patterns will allow us to draw conclusions about the magnitude and geometry of the magnet. star fields. To directly study these fields, a spectrum is used. lines (gyrolines) caused by the emission of electrons in a magnetic field. field (see). The gyroline was detected, for example, in X-ray. spectrum of the pulsar Her X-1 [magn. field E]. The interpretation of the gyroline in the spectra of the sources made it possible to prove that the sources of bursts of phenomena. neutron stars with magnetic intensity. fields E.

As V.L. showed Ginzburg, uncharged should not have a mag. field. When a star collapses, its mag. the dipole moment and higher order moments disappear asymptotically. However, mag. fields apparently play a significant role in the processes occurring in the vicinity of black holes. In particular, according to existing theories, in binary stellar systems, one of the components of which phenomena. black hole, with the help of a magnet. field, the angular momentum of the gas falling onto the black hole can be transferred, and thereby the formation of a disk emitting X-rays. range.

Stars are formed from interstellar gas permeated with magnetic fields. field. The simplest solution to the problem (evolutionary approach), which consists in the fact that the observed fields of stars are a product of compression of the original field, turns out to be insufficient. Adiabatic. compression of the gas, not accompanied by a loss, would lead to too strong fields, since cf. The density of an ordinary solar-type star is greater than the density of the interstellar medium by ca. 10 24 times. Coeff. adiabatic The field gain in this case is equal to 10 16, i.e. an interstellar field of ~ 10 -6 Oe would turn into a field with a strength of 10 10 Oe, which contradicts observations. Evolution. approach to the origin of magnets. fields, apparently, is valid only for certain types of stars (magnetic stars, pulsars, possibly for white dwarfs). For most stars, the field disappears and is restored in times short compared to the characteristic times. Such rapid changes cannot be explained by ohmic dissipation (Joule damping, see) or evolution. changes. They occur as a result of magnetic transformation. fields under the influence of the movements of the highly conductive matter of stars. The field is most effectively changed by inhomogeneous rotation and convective movements (see.

Magnetic field of the sun

Magnetic fields are present, apparently, on all stars. The magnetic field was first discovered on the closest star to us - the Sun - in 1908 by the American astronomer J. Hale, who measured the Zeeman splitting of spectral lines in sunspots.

According to modern measurements, the maximum magnetic field strength of sunspots = 4000 Oe. The field in sunspots is a manifestation of the general azimuthal magnetic field of the Sun, the field lines of which have different directions in the Northern and Southern hemispheres of the Sun

Unlike nearby outer space, direct measurement of magnetic fields on the Sun with magnetometers is impossible not only because of the technical difficulties of sending a space probe to the Sun, but also because of the high temperature of its substance, which no instrument can withstand). Therefore, both on the Sun, and even more so on other more distant objects, magnetic fields can be measured only indirectly - by analyzing electromagnetic radiation.

On the Sun, the magnetic field is captured by hot matter or “frozen” into it. As it moves, solar matter carries with it as much of the magnetic field as it can. Since the rotation speed at the equator is faster than the rotation speed at the poles, the magnetic field lines are stretched, but the field lines do not break off during such winding; they are more like extremely elastic rubber. Like rubber, the more they stretch, the more energy they store.

The magnetic field of the spots suppresses convection in the upper layers of the convective zone, the energy transfer here sharply decreases, therefore the gas temperature in the spot area decreases by 1,500-2,000 K. In the close vicinity of the spot, where the field strength is relatively low, the magnetic field, on the contrary, enhances convective energy transfer. This is how bright formations arise - torches.

Estimates show that buoyancy is effective down to depths of about 15,000 km, while the thickness of the convective zone is about seven times greater. It follows that the magnetic fields of sunspots are formed in the upper part of the convective zone of the Sun.

In this regard, the following question arises: how is the inhomogeneous rotation of the Sun maintained? After all, the strengthening of magnetic fields and the formation of magnetic tubes occurs due to the inhibition of the rotational motion of the equatorial regions, and if this energy were not continuously supplied, then after several revolutions the Sun would begin to rotate as an absolutely rigid body, i.e. the angular velocity of rotation at the poles and at the equator would be the same.

The sun as a variable star

Variable stars are those luminaries whose luminosity changes over time as a result of physical processes occurring in its region.

It turns out that our Sun is such a star.

Information collected by the solar wind particle sensor Swoops probe Ulysses, allowed us to conclude that the solar wind has been continuously “weakening” since the mid-1990s. Moreover, this process apparently began much earlier. Currently, the speed of the solar wind has reached its absolute minimum for at least half a century - since direct research began using spacecraft. The decrease in solar wind speed over a decade is relatively small - about 3%, but it is a consequence of a decrease in the temperature and pressure of solar wind particles by 13% and 20%, respectively. It is impossible to say yet how long the process will take and how far it has gone. The cooling of the solar wind is also accompanied by a decrease in the strength of the Sun's magnetic field by a third over the same period.

Thus, the radiation situation in the Solar System and in near-Earth space has worsened - the flux density of especially dangerous high-energy protons coming from deep space has increased by about 20%.

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The anomalous decrease in solar wind activity complements the picture of difficult-to-explain anomalies in the behavior of the star itself. The unique activity of the star at the end of the last cycle was replaced by an abnormally long absence of spots - an indicator of activity - on the star.

A decrease in the number of sunspots, generally speaking, is characteristic of solar activity minima, but this time the process took too long. For almost a year now, there have been practically no spots on the Sun at all.

It is obvious that the scale of processes currently occurring on the Sun goes beyond the hypothesis of their 11-year cyclicity.

Heliospheric current layer

Heliospheric current sheet is a surface within the Solar System, upon crossing which the polarity of the Sun's magnetic field changes. This surface extends along the equatorial plane of the Sun and reaches the boundaries of the heliosphere. The shape of the current sheet is determined by the influence of the rotating magnetic field of the Sun on the plasma located in interplanetary space. The thickness of the current layer is about 10,000 km. A weak electric current is observed in the current layer (hence the name) - about 10 −10 A/m². The resulting current forms part of the heliospheric current circuit. Sometimes the heliospheric current sheet is called the interplanetary current sheet.

Characteristics

Form

As the Sun rotates, its magnetic field twists into a special spiral shape - the Parker spiral, which is a type of Archimedean spiral and named after its discoverer Eugene Parker. The spiral's magnetic field is divided into two parts by a current sheet, the mathematical model of which was first developed in the early 1970s. The spiraling magnetic field changes its polarity and takes on a complex form of wavy spiral folds, most reminiscent of a ballerina’s multi-layered skirt.

The reason for the formation of such a complex shape is sometimes called the “garden hose effect.” This is exactly the surface that a stream of water describes if you move the hose up and down and at the same time rotate around its axis. In the case of the Sun, the role of the water jet is played by the solar wind.

A magnetic field

The heliospheric current sheet rotates with the Sun, making one revolution every 27 days. During this period, the Earth, together with its magnetosphere, passes through the humps and troughs of the current sheet, interacting with it. Magnetic induction on the surface of the Sun is approximately 10 −4 tesla. If the magnetic field had a dipole shape, its strength would decrease in proportion to the cube of the distance and in the region of the Earth's orbit would be 10 −11 tesla. The existence of the heliospheric current sheet leads to the fact that the actual values ​​​​in the Earth's region are 100 times higher.

Electricity

In accordance with the laws of electrodynamics, the electric current in the current sheet is directed perpendicular to the magnetic field, that is, the current moves almost in a circle near the Sun and is directed almost radially at large distances. The “electrical circuit” is closed by a current directed from the Sun, which comes from the solar poles in directions perpendicular to the equator, and then descends along the heliopause to the equator, to the heliospheric current sheet. The total current in this circuit is about 3⋅10 9 amperes. For comparison, the currents that lead to the appearance of auroras on Earth are about a thousand times weaker and have a magnitude of about a million amperes. The maximum current density in the sheet is about 10−10 A/m² (10−4 A/km²).