The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. Dynamo can refer to more than one item. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... To meet Wikipedias quality standards, this article may require cleanup. ...

Formal Definition

Dynamo theory describes the process through which motion of a conductive body in the presence of a magnetic field acts to regenerate that magnetic field. This theory is used to explain the presence of anomalously long-lived magnetic fields in astrophysical bodies. In such bodies, dynamo action depends on the presence of highly conducting fluids such as the Earth's liquid iron, outer core or the ionized gas of the sun. Dynamo theory of astrophysical bodies uses magnetohydrodynamic equations to investigate how the flow of the conducting materials in the interior of an object can continuously regenerate the magnetic fields of planetary and stellar bodies. It was actually once believed that the dipole, which comprises the Earth's magnetic field and is misaligned along the rotation axis by 11.3 degrees, was caused by permanent magnetization of the materials in the earth. This means that dynamo theory was originally used to explain the sun's magnetic field in its relationship with that of the Earth. However, this theory, which was initially proposed by Joseph Larmor in 1919, has been modified due to extensive studies of magnetic secular variation, paleomagnetism (including polarity reversals), seismology, and the solar system's abundance of elements.

In the case of the Earth, the magnetic field is believed to be caused by the convection of melting iron and nickel, within the outer planetary core, along with Coriolis effect caused by the overall planetary rotation. When conducting fluid flows across an existing magnetic field, electric currents are electromagnetic induction, creating another magnetic field. When this magnetic field reinforces the original magnetic field, a dynamo is created which sustains itself. Similar magnetic fields are present in many celestial bodies including most stars such as the Sun (which contains conducting plasma physics) and active galactic nuclei. In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. ...

Kinematic Dynamo Theory

Dynamo theory is a very complex concept to study. Often, college courses and research focuses mainly of kinematic dynamo theory, which is a more simplistic version of the former. It involves the vector velocity field, V, which is prescribed. To examine this sector of the theory, an assumption that must be made is that the magnetic field has to be sufficiently small so that it cannot affect the velocity field. Because of this, the approach cannot divulge anything about the long-term behavior of a dynamo system. This analysis begins with the magnetohydrodynamic theory version of Ohm’s law once it has been modified to include resistivity (resistivity is the reciprocal of conductivy σ, J is the current density), which is assumed to be a constant in order to further simplify the investigation. Vector field given by vectors of the form (-y, x) In mathematics a vector field is a construction in vector calculus which associates a vector to every point in a Euclidean space. ... The velocity of an object is simply its speed in a particular direction. ... MHD Simulation of Solar Wind Magnetohydrodynamics (MHD), or magnetofluiddynamics, is the academic discipline which studies the dynamics of electrically-conducting fluids. ... Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of electric current. ...

Using Maxwell’s Equations simultaneously with the curl of the aforementioned equation, one can derive what is basically the linear eigenvalue equation for magnetic fields (B) which can be done when assuming that the magnetic field is independent from the velocity field: In electromagnetics, Maxwells equations are a set of four equations, developed by James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter. ...

The most functional feature of kinematic dynamo theory is that it can be used to determine what fields or systems are or are not dynamos. By applying a certain velocity field’s flow to a small magnetic field, it can be determined through observation whether the magnetic field tends to grow or not in reaction to the applied flow. If the magnetic field does grow, then the system is either capable of dynamo action or is a dynamo, but if the magnetic field does not grow, then it is simply referred to as non-dynamo.

The membrane paradigm is a way of looking at black holes that allows for the material near their surfaces to be expressed in the language of dynamo theory. In black hole theory, the black hole membrane paradigm is a useful toy model method or engineering approach for visualising and calculating the effects predicted by quantum mechanics for the exterior physics of black holes, without using quantum-mechanical principles or calculations. ... A black hole is an object predicted by general relativity[1] with a gravitational field so strong that nothing can escape it — not even light. ...