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Spiral Galaxy M81
Daniel Van Noord

Spiral Galaxy M81

M81 is a spiral galaxy located more then twelve million light years away. Like all galaxies it is a massive collection of stars, dust and dark matter bound together by gravity. Similarly to the Milky Way, our home galaxy, M81 is about 30 kilo parsecs across. This means that a photon of light will take more then one hundred thousand years to cross this galaxy! Unlike elliptical galaxies spiral galaxies have massive spiral arms wrapping around the galactic core, leading to truly spectacular images. Despite the majestic spiral arms, when the galaxy was discovered in the late 1700’s by Johann Bode it was called a nebula. Thus to this day it retains the name “Bode’s Nebula”. In addition to its beauty at optical wavelengths this galaxy is very interesting as it contains an active, supper massive black hole at its center.

The optical image that I created contain many interesting and often subtle points. As one’s eyes move from the bright white core outwards, look for dark bands. These are thick areas of dust. These dust bands block light from the stars behind them. Then the spiral arms become visible. If you look carefully you can see bands of hot, young, blue stars on the arms. These are areas of new star formation. The galaxy is a SA(s) ab type galaxy. These means that it is a spiral without a bar in the middle an has moderately tight spiral arms. All of these specifics should be visible in the optical image.

M81 in UVFigure 1: M81 from ASTRO-1 in Ultra violet light. UV light is mostly produced by young and extremely hot stars. Thus UV images of other galaxies show areas of new star formation. If you look closely these bright regions coincide with the blue regions in the optical image.





M81 at 21cmFigure 2: M81 from the VLA in 21 CM light. This is a radio image of M81. 21 CM light show HI regions. The light is emitted when the spins of electrons in neutral HI flip. If you look carefully at the image you can see that the brightest areas trace out the spiral arm. The dense distorted region on the left is likely from an interaction with another galaxy in the distant past.




Image courtesy of NRAO/AUI



Adler, D. S. "Atomic hydrogen in M81." National Optical Astronomy Observatory. Accessed 11 Apr. 2013. <>.

Kutner, Marc L. Astronomy: A Physical Perspective, 2nd ed. Cambridge: Cambridge University Press, 2003.

Frommert, Hartmut, and Christine Kronberg. "Ultraviolet image from the ASTRO-1 mission (UIT)". Students for the Exploration and Development of Space. Accessed 11 Apr 2013. <>.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Right Ascension (J2000) 09:55:33
Declination (J2000) +69:03:55
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 5x60 seconds in C, 10x60 seconds in BVR
Date observed

March 26, 2013 (CBVR)

This image was a mosaic of two fields. The data was calibrated in MaxIM for thermal noise, dark current and flat fielding. It was then combined into a single image using Registar and Maxim. Finally the image had Gamma stretch applied.



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