Like a
whirl of shiny flakes sparkling in a snow globe, many hundreds of thousands of
stars move about in the globular cluster M13, as Hubble catches an
instantaneous glimpse of one of the brightest and best-known globular clusters
in the northern sky. This glittering metropolis of stars is easily found in the
winter sky in the constellation Hercules, and can even be glimpsed with the
unaided eye under dark skies.
M13 is home
to over 100,000 stars and located at
a distance of 25,000 light-years. These stars are packed so closely together in
a ball approximately 150 light-years across that they will spend their entire
lives whirling around in the cluster.
Near the
core of this cluster, the density of stars is about a hundred times greater
than the density in the neighborhood of our sun. These stars are so crowded
that they can, at times, slam into each other and even form a new star, called
a "blue
straggler."
The
brightest reddish stars in the cluster are ancient red giants. These aging
stars have expanded to many times their original diameters and cooled. The
blue-white stars are the hottest in the cluster.
Globular
clusters can be found spread largely in a vast halo around our galaxy. M13 is
one of nearly 150 known globular clusters surrounding our Milky Way galaxy.
Globular
clusters have some of the oldest stars in the universe. They likely formed
before the disk of our Milky Way, so they are older than nearly all other stars
in our galaxy. Studying globular clusters therefore tells us about the history
of our galaxy.
This image
is a composite of archival Hubble
data taken with the Wide Field Planetary Camera 2 and the Advanced Camera for
Surveys. Observations from four separate science proposals taken in November 1999,
April 2000, August 2005 and April 2006 were used. The image includes broadband
filters that isolate light from the blue, visible and infrared portions of the
spectrum.
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