Physics Photo of the Week
Globular Cluster Messier 3
There are two kinds of star clusters: globular clusters and open
clusters. The globular cluster featured here is the third object
in Messier's 18th century catalog of nebulous objects. Globular
clusters such as this contain about 500,000 stars, they are
gravitationally bound, and are believed to harbor a black hole in the
center. Open stellar clusters, on the other hand, feature items
such as the Pleiades
(PPOW December 1, 2006), and several other Messier
objects featured on PPOW May 6, 2005. Open clusters contain
at most a few hundred stars - many fewer than a globular cluster.
(Watch for future PPOW's featuring open clusters). This image was
made with with the assistance of astronomy students Kat Coker, Suzanne Lutsky, and Baldwin Saer on April 16,
2008. The students worked the controls to line-up the
telescope. On the previous night (April 15, 2008) several other
students (Karel Teifer, Phil Waidner, and Sam Wells) performed similar
alignment and observed the cluster, but had run out of time before
images could be procured.
Globular clusters are fascinating astronomical objects in a number of
ways: the sheer number of stars located within each globular is
overwhelming; the gravitational stability of these clusters leads
to very long life such that the more massive stars have become highly
evolved, hence the clusters are very old; globular clusters are very
(over 30,000 light years for M3) located on the perimeter of the Milky
galaxy; each star of the cluster is in orbit about the center of mass
of the cluster in a random direction somewhat like the windings on a
ball of yarn.
Globular clusters also contain many variable stars - especially Messier
3. In spring of 2007 I photographed M3 over an extended period of
time in one night. At right we see two images that were taken 95
minutes apart. The two images have been aligned and
adjusted such that all stars show about the same brightness, and played
back in rapid succession. This is called "blinking". The
arrow indicates a rapidly varying star. See if you can see any
more stars that change in brightness as the blinking image switches
between the two. The preliminary processing and alignment of the
images was performed by Jessica Harris
in May 2007.
Photo of the
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
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the world around us. Students, faculty, and others are invited to
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