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Messier 107 (NGC 6171)
Christiaan Hazlett

Ghost of Jupiter

Messier 107 is a globular star cluster located in the large constellation Ophiuchus, which takes its name from the Greek word for “serpent-bearer” and is situated near the celestial equator.  It was discovered by Pierre Mechain in April of 1782, and is the last globular cluster in the Messier Catalogue—added in 1947 by Helen Sawyer Hogg.  At 20.9 thousand light-years from Earth and an estimated age of 13.95 ± ~0.5 billion years, M107 is a “very beautiful and extremely compressed cluster” in the words of Sir William Herschel, who independently rediscovered M107 on May 12, 1793.  One fact that sets M107 apart from many other globular clusters is that it contains 25 known variable stars.

A globular cluster is a tightly bound spherical pool of stars, which orbits around a galaxy, in the galaxy’s halo.  Globular clusters contain mostly old Population II stars, and must have been some of the first objects formed in the universe.  They are relatively common, and the Milky Way galaxy alone contains roughly 150 of them.  All stars in a globular cluster are constantly moving and interacting with one another, which gives the cluster its spherical shape.  In fact, the gravitational forces stars exert upon each other cause stars with relatively lower velocities to move toward the center of the cluster, resulting in globular clusters being the densest at the center, with the density tapering off toward the edges of the cluster.  In the image above, you can see that most of the stars have a somewhat light-yellow tint to them.  The visible light emitted by stars in the yellow spectrum indicates that most of them are somewhere in the F-K range along the main sequence, suggesting a generally older population of stars.

The above image of M107 was created by combining images taken in blue, red, and green wavelengths, as well as in the entire light spectrum, with a significant emphasis (more than half of the total observing time spent) on the blue wavelength to reduce the amount of noise received by the camera.

The graph above depicts the relationship between M107’s surface brightness and the size of the radius in which the surface brightness was measured.  The particular formula used to relate the data above is known as a King profile; it shows us exactly how the light emitted by the globular cluster tapers off toward the edges of the cluster, and is given by this equation:

From this profile, we can tell the central brightness of the cluster, the core radius, and the tidal radius.  The core radius is the point at which the apparent brightness of the galaxy has dropped by half, and for Messier 107 that value is 22.05 ± 3.01 light years.


"Messier 107." | Messier 107. AstroPixels. Web. 4 May 2015. <>.

Plotner, Tammy. "Messier 107." Universe Today. Universe Today, 9 Jan. 2010. Web. 4 May 2015. <>.

"Globular Cluster | Astronomy." Encyclopedia Britannica Online. Encyclopedia Britannica. Web. 4 May 2015. <>.

"The Different Components." The Different Components. Web. 4 May 2015. <>.

Forbes, Duncan A., and Terry Bridges. "Accreted versus in Situ Milky Way Globular Clusters." Monthly Notices of the Royal Astronomical Society(2010): n. pag. Web.

Wikipedia, "Messier 107".

Right Ascension (J2000) 16:32:31.86
Declination (J2000) -13:03:13.6
Filters used B (Blue), C (Clear), R (Red), V (Green)
Exposure time per filter B (300s x 15), V (300s x 4), and R (300s x 2); C (180s x 5)
Image dimension 1092x736 pixels; 23.8x16.1 arcminutes
Date/time observed March 29, 2015, 08:22 UT



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