Magnetic Field of the Milky Way

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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Halliday, Resnick & Walker. Fundamentals of Physics.New York: Wiley, 2001. "Some Approximate Magnetic Fields … In interstellar space 10-10 T" 0.1 nT
 Illingworth, Valerie. Facts on File Dictionary of Astronomy. New York: Facts on File. 1985. "The magnetic flux density lies in the range 10-10 to 10-9 tesla, with 3.0–6.0 × 10-10 tesla being the best estimate at present." 0.3–0.6 nT
Components of the Galaxy. Online Journey Through Astronomy. "The disk of the galaxy is permeated by a magnetic field. This field is weak, being only about 1/50,000 of the strength of the Earth's magnetic field at the surface, but it influences the motion of charged particles in the galaxy. One important consequence of the magnetic field is that it can bend the path of and even trap the high-energy charged particles that we call cosmic rays." 0.1 nT
"Galactic Magnetic Field." American Institute of Physics Handbook. 3rd Edition. New York: McGraw-Hill, 1972. "A comparison of the observed cosmic-ray electron spectrum with the non-thermal radio spectrum arising from galactic synchrotron radiation indicates that the magnetic field is 10 to 20 microgauss near the galactic center, 5 to 10 microgauss near the solar system and approximately 2.5 microgauss for the halo." 0.5–2 nT
Milky Way Galaxy. Encyclopædia Britannica. "The strength of the galactic field is only about 0.000001 times the strength of the Earth's field at its surface, a value that is much too low to have dynamical effects on the interstellar gas that could account for the order represented by the spiral-arm structure." 0.05 nT

There is strong evidence that the Milky Way galaxy contains an ordered, large-scale magnetic field of the value 10-10 tesla (0.1 nT). This field configuration has been explored in the past through various methods which include analysis of starlight polarization, modeling pulsar or Faraday rotation, and Zeeman splitting of hydroxyl masers in regions of star formations. This Zeeman splitting of atomic or molecular lines indicated the direction and magnitude of a component of the magnetic field in a cloud of gas.

A spiral galaxy like the Milky Way has three basic components to its visible matter which include the disk (containing the spiral arms), the halo, and the nucleus or central bulge. Each contains different degrees of interstellar medium which include gases (mostly composed of Hydrogen and Helium) and dust grains. Because of the varying density in the galaxy's components, the magnetic field has a range of values from 0.5 to 2 nT which are ideally represented in a schematic diagram showing the field's direction along the spiral arms.

The magnetic field of a galaxy -- although not strong in comparison to that of the Earth, which is approximately 5.0 × 10-5 T (50 µT) -- can gradually act on the dust particles and cause their rotational axes to line up so that their short axes are parallel to the direction of the field which is in turn aligned with the Milky Way band and the galactic plane. This pattern is confirmed by polarization measurements.

Rebecca Rudberg -- 2001

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
The Magnetic Field - A Crop Circle Under Scrutiny for Meaning. Dreams of the Great Earth Changes. 22 July 2000. "Gradually astronomers have deduced that the Milky Way has a magnetic field of roughly five microgauss, generally directed along the galaxy's spiral arms. (By comparison, the earth's north-pointing magnetic field is about 500,000 microgauss.)" 0.5 nT
Schewe, Phillip F. & Ben Stein. Magnetic Fields are Everywhere. Physics News Update The American Institute of Physics Bulletin of Physics News. Number 482 (Story #2), 3 May 2000. [alternate location] "Basically, Philipp Kronberg (416-978-4971) of the University of Toronto finds magnetic fields every place he has looked in the cosmos: within the Milky Way (where the fields are typically about 5 microgauss), in intergalactic areas within galaxy clusters (1-2 microgauss for the Coma cluster, 350 million light years away), and even outside clusters." 0.10.5 nT
Science and The Citizen: Magnetic Anomalies. Scientific American. August 2000. "Gradually astronomers have deduced that the Milky Way has a magnetic field of roughly five microgauss, generally directed along the galaxy's spiral arms. (By comparison, the earth's north-pointing magnetic field is about 500,000 microgauss.)" 0.5 nT
Intergalactic magnetism runs deep and wide.(Brief Article) Author/s: P. Weiss Issue: May 6, 2000 "He finds on an average even higher field strengths, about 5[micro]G, than he did a decade ago" 0.5 nT

A Magnetic field is a region in a magnet, electric current, or changing electric field, in which magnetic forces are observable. Magnetic fields such as that of the Earth cause magnetic compass needles and other permanent magnets to line up in the direction of the field. Magnetic fields force that are moving are electrically charged particles in a circular or helical path.

Magnetic fields may be represented by continuous lines of force or magnetic flux that emerge from north-seeking magnetic poles and enter south-seeking magnetic poles. The density of the lines indicates the magnitude of the magnetic field. Equally spaced parallel straight lines represent a uniform magnetic field. The direction of the flux is the direction in which the north-seeking pole of a small magnet points. The lines of flux are continuous, forming closed loops.

Magnetic fields may be represented mathematically by quantities called vectors that have direction as well as magnitude. Two different vectors are in use to represent a magnetic field: one called magnetic flux density, or magnetic induction, is symbolized by B; the other, called the magnetic field strength, or magnetic field intensity, is symbolized by H.

Svetlana Lozover -- 2001


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