Spiral Galaxy - Origin of The Spiral Structure

Origin of The Spiral Structure

The pioneer of studies of the rotation of the Galaxy and the formation of the spiral arms was Bertil Lindblad in 1925. He realized that the idea of stars arranged permanently in a spiral shape was untenable. Since the angular speed of rotation of the galactic disk varies with distance from the centre of the galaxy (via a standard solar system type of gravitational model), a radial arm (like a spoke) would quickly become curved as the galaxy rotates. The arm would, after a few galactic rotations, become increasingly curved and wind around the galaxy ever tighter. This is called the winding problem. Measurements in the late 1960s showed that the orbital velocity of stars in spiral galaxies with respect to their distance from the galactic center is indeed higher than expected from Newtonian dynamics but still cannot explain the stability of the spiral structure.

Since the 1960s, there have been two leading hypotheses or models for the spiral structures of galaxies:

  • Star formation caused by density waves in the galactic disk of the galaxy.
  • The SSPSF model – star formation caused by shock waves in the interstellar medium.

These different hypotheses do not have to be mutually exclusive, as they may explain different types of spiral arms.

Read more about this topic:  Spiral Galaxy

Famous quotes containing the words origin of the, origin of, origin, spiral and/or structure:

    In the woods in a winter afternoon one will see as readily the origin of the stained glass window, with which Gothic cathedrals are adorned, in the colors of the western sky seen through the bare and crossing branches of the forest.
    Ralph Waldo Emerson (1803–1882)

    For, though the origin of most of our words is forgotten, each word was at first a stroke of genius, and obtained currency, because for the moment it symbolized the world to the first speaker and to the hearer. The etymologist finds the deadest word to have been once a brilliant picture.
    Ralph Waldo Emerson (1803–1882)

    Our theism is the purification of the human mind. Man can paint, or make, or think nothing but man. He believes that the great material elements had their origin from his thought.
    Ralph Waldo Emerson (1803–1882)

    What is art,
    But life upon the larger scale, the higher,
    When, graduating up in a spiral line
    Of still expanding and ascending gyres,
    It pushes toward the intense significance
    Of all things, hungry for the Infinite?
    Art’s life,—and where we live, we suffer and toil.
    Elizabeth Barrett Browning (1806–1861)

    Agnosticism is a perfectly respectable and tenable philosophical position; it is not dogmatic and makes no pronouncements about the ultimate truths of the universe. It remains open to evidence and persuasion; lacking faith, it nevertheless does not deride faith. Atheism, on the other hand, is as unyielding and dogmatic about religious belief as true believers are about heathens. It tries to use reason to demolish a structure that is not built upon reason.
    Sydney J. Harris (1917–1986)