A Celestial Snow Globe of Stars
Like a whirl of shiny flakes sparkling in a snow globe, Hubble catches an instantaneous
glimpse of many hundreds of thousands of stars moving about in the globular cluster M13,
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.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: C. Bailyn (Yale University), W. Lewin (Massachusetts Institute of
Technology), A. Sarajedini (University of Florida), and W. van Altena (Yale University)