Spiral Arms

Discussion in 'Astronomy, Exobiology, & Cosmology' started by wet1, Jan 28, 2002.

  1. wet1 Wanderer Registered Senior Member

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    The Spiral Arms of NGC 4622
    Credit: G. Byrd, R. Buta, (Univ.Alabama, Tuscaloosa), T. Freeman (Bevill State College), NASA
    While stirring a morning cup of coffee and thinking cosmic thoughts many astronomers would glance at this Hubble Space Telescope image of spiral galaxy NGC 4622 and assume that the galaxy was rotating counterclockwise in the picture. Two hundred million light-years away in the constellation Centaurus, NGC 4622's gorgeous outer spiral arms, traced by bright bluish star clusters and dark dust lanes, should be winding up like ... well, like swirls in a cup of coffee. But a closer look at this galaxy reveals that a pronounced inner spiral arm winds in the opposite direction. So which way is this galaxy rotating? Recent evidence combining ground-based spectroscopy and the sharp Hubble image data surprisingly indicates that the galaxy is likely rotating clockwise in the picture, its outer spiral arms opening outward in the direction of rotation. There are further indications that a past collision with a smaller companion galaxy has contributed to this bizarre rotational arrangement of spiral arms, essentially unique among known large spiral galaxies, in NGC 4622.
     
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  3. harpdude Registered Member

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    Well...

    The spiral arms of galaxies are a kind of optical illusion. The individual stars rotate around the center of the galaxy independently of the spiral arms.

    The spiral arms are merely places where stars bunch up as they travel around the galactic center; but these arms do exert a peculiar effect a stars velocity and trajectory as it rotates around the core.

    As a star approaches a galactic arm it speeds up due to the increase in the gravitational influence of the bunched up stars. Because it speeds up, the star also moves farther away from the center of the galaxy.

    Conversely, as a star leaves a galactic arm it slows down a bit and drops its orbit a tad towards the galactic core. These perturbations cause the spiral arms to become more pronounced over time.

    A star in a spiral galaxy acts like a roller coaster as it travels around the galaxy.
     
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