M101- A Different View
Description:
M101 is
a well-known spiral galaxy in Ursa Major. From Earth, we see this
galaxy face-on, but through the magic of 3D processing in Photoshop CS4
Extended, I have portrayed M101 as it might look if viewed at an
angle. The conventional,
face-on image of M101 was graciously provided to me for this
project by Rob Gendler,
and the background starfield was obtained from my own image of M103. The
processing technique that I used is fairly straightforward and is
nicely explained in this video
tutorial by Russell Brown. Although this is not a completely
realistic
portrayal of the galaxy's rotation (because the outer arms would not
rotate in synch with the inner arms), it provides an interesting
perspective of this familiar
object. The above image is accelerated for visual effect- the
period of revolution for a typical galaxy like the Milky Way is
approximately 225 million years!
Vera Rubin was
the first astronomer to note that the rotation speed of the outer
arms of galaxies was faster than predicted by Newtonian
dynamics. In particular, Newtonian dynamics predicts that orbital
velocity should be inversely proportional to the square root of the
distance from the center of gravity, which is how planets in our solar
system behave.
And yet, when Rubin determined the speed of rotation in galaxies by
studying Doppler shifts in the radio
emission line of hydrogen, she found that the outer portions of
galaxies were spinning more rapidly than expected, suggesting the
presence of additional, unseen matter ("dark matter"). It is now
generally accepted that the visible portion of galaxies like M101 and
others comprises only a small fraction of the total galactic mass, with
the remainder of the mass consisting of dark matter, which forms a dark matter "halo"
that extends well beyond the conventional visible light boundary of the
outer galactic arms.
Please
note: Graphics on this website
may not be reproduced without author permission.
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