M81 Internal Motions, van Maanen

The photo on the right was made with Mt. Wilson's 100 inch reflector. (Source NASA). This photo was digitally quantized into six brightness levels to form the background for the van Maanen information on the left.

Both photographs above are misleading to a degree because over-exposure in the central region of M81 makes it look as though that region is comprised of thousands or millions of stars (which may or may not be true). To see a clearer picture of the central region, go to the Space.com article
http://www.space.com/scienceastronomy/astronomy/newton_galaxy_010625.html Stunning View of Galaxy M81 Released. [Article no longer available.] The authors of that article said that the strangely active center of M81 might represent a maturing black hole or a starburst. If it turns out that M81 is about where van Maanen suggested, i.e., nearby to the Milky Way, then some other interpretation of the small nucleus might be in order.

For further evidence of a small (star like?) core for M81 see NRAO's page Radio Images of Galaxies. [Added 05 Sep 2003.]

See the related articles M33 Internal Motions and On Spiral Nebulae, van Maanen et al.

"Hubble's preference for a recessional or expanding model is further revealed in a 1936 paper communicated to the National Academy of Sciences. In this paper he reviewed previous counts of nebulae and reported the results of two new surveys. The data, enlarged from that of the previous year, still pointed to the same conclusion: the observations more nearly fit the non-expanding model." [Emphasis added.]

It is fitting to quote van Maanen's tribute to James Jeans in the final two paragraphs of his 1921 paper (MA21) on Messier 81.

    The close agreement of the displacements in direction with the spiral arms suggests that we have here a realization of the motions described by Jeans in Problems of Cosmonogy and Stellar Dynamics, from which I quote freely.

    "If so, we must then suppose that before the formation of the spiral arms the nebular masses were rotating and had reached a lenticular shape. The formation of Laplace's ring requires perfect symmetry of mass about the axis of rotation. The distances of adjacent masses in space are in general so great that their gravitational influence will be extremely small, but even the slightest external gravitational field will be sufficient to preclude the formation of a ring; instead of this, the matter will will be thrown off at two antipodal points. The masses first thrown off at the antipodal points form in themselves a tide-generating system which concentrates the region of ejection more and more at two points. The result is an extension farther and farther into the equatorial plane as the evolution of the nebula proceeds. The determination of the shape of the arms seems at present to be beyond the reach of mathematical analysis, but the long streams of gaseous matter must become longitudinaly unstable and will tend to break up into condensations or nuclei." [Adams Prize Essay, University of Cambridge, 1917.]

Jeans' other publications on spiral nebulae (JJ17), (JJ23), and (JJ25) should be of interest to students of the History of Astronomy.

Readers are encouraged to see the Hubble Site 07 Feb 2002 release, Hubble Reveals 'Backwards' Spiral Galaxy". Future findings may invalidate the picture but, at present, astronomers suggest that "the galaxy called NGC 4622 appears to be rotating in the opposite direction to what they expected." The apparent direction of rotation is similar to that for van Maanen's measured internal motions for M81 shown above.
[Added 06 August 2003.]

See Jay Bitterman's Astronomy Bio... "Adriaan van Maanen" at http://www.bpccs.com/lcas/Articles/maanen.htm . [Added 27 August 2003. Article no longer online, 28 Aug 2013.]

Adriaan van Maanen (left), Bertil Lindblad (center), Unidentified man (right),
on the platform for observation at the Newton focus of the 1 meter reflector of
the Stockholm Observatory in Saltsjöbaden Sweden. August 1938.*
(Lindblad was Director of the Stockholm Observatory from 1927 to 1965.)

Photograph by Dorothy Davis Locanthi,
courtesy AIP Emilio Segrè Visual Archives,
Dorothy Davis Locanthi Collection

* Thanks to Per Olof Lindblad for the location and date of the photograph.

References

HB92 - Hetherington, N., Brashear, R., Journal for the History of Astronomy 23, 53-56 (1992).

JJ17 - Jeans, J., Internal Motion in Spiral Nebulae, The Observatory 40 60-61(1917) - NADS [No article or abstract]

JJ23 - Jeans, J., Internal Motions in Spiral Nebulae, MNRAS 84, 60-76 (1923) - NADS

JJ25 - Jeans J., Note on the Distances and Structure of the Spiral Nebulae, MNRAS 85, 531-534 (1925) - NADS

MA21 - van Maanen, Adriaan, Investigations on Proper Motion - Fifth Paper: The Internal Motion in the Spiral Nebula Messier 81, Astrophysical Journal 54, 347-356 (1921) - NADS

See: On Spiral Nebulae, van Maanen et al.
        Messier 33 Internal Motions.