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Credit & Copyright: Tolga Gumusayak,
Robert Vanderbei
Explanation:
M13 is modestly
recognized as the Great Globular Star Cluster in Hercules.
A ball of stars numbering in
the hundreds of thousands
crowded into a region 150 light years across, it lies some 25,000
light-years away.
The sharp, color
picture of M13 at upper left is familiar to many
telescopic imagers.
Still, M13's Color vs Magnitude Diagram in the panel below and right,
made from the same image data, can offer
a more
telling view.
Also known as a
Hertzsprung Russell (HR) diagram
it plots the
apparent brightness of individual cluster stars against color index.
The color index is determined for each star by subtracting its brightness
(in
magnitudes) measured through a red
filter from its brightness measured with a blue filter (B-R).
Blue stars are hot and red stars are cool so that
astronomical color index ranging from bluer to redder
follows the relative stellar temperature scale from
left (hot) to right (cool).
In M13's HR diagram, the stars clearly fall into distinct groups.
The broad swath extending diagonally from the bottom right is
the cluster's main sequence.
A sharp turn toward the upper right hand corner follows the
red giant branch while the
blue giants are found grouped in the upper left.
Formed at the same time, at first M13's stars
were all located along the main sequence by mass,
lower mass stars at the lower right.
Over time higher mass stars have
evolved off the main sequence
into red, then blue giants and beyond.
In fact, the position of the turn-off from the
main sequence to the red giant branch
indicates the cluster's age at about
12 billion years.
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NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture
Of the Day
Publications with keywords: M 13 - globular cluster
Publications with words: M 13 - globular cluster
See also: