The star cluster Messier 47
The bright star clusters Messier 47 and Messier 46 in the constellation of Puppis
Wide-field view of the bright star clusters Messier 47 and Messier 46
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This spectacular image of the star
cluster Messier 47 was taken using the Wide Field Imager camera,
installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla
Observatory in Chile. This young open cluster is dominated by a
sprinkling of brilliant blue stars but also contains a few contrasting
red giant stars.
Messier 47 is located approximately 1600 light-years from Earth, in the constellation of Puppis (the poop deck of the mythological ship Argo). It was first noticed some time before 1654 by Italian astronomer Giovanni Battista Hodierna and was later independently discovered by Charles Messier himself, who apparently had no knowledge of Hodierna’s earlier observation.
Although it is bright and easy to see, Messier 47 is one of the least
densely populated open clusters. Only around 50 stars are visible in a
region about 12 light-years across, compared to other similar objects
which can contain thousands of stars.
Messier 47 has not always been so easy to identify. In fact, for
years it was considered missing, as Messier had recorded the coordinates
incorrectly. The cluster was later rediscovered and given another
catalogue designation — NGC 2422. The nature of Messier’s mistake, and
the firm conclusion that Messier 47 and NGC 2422 are indeed the same
object, was only established in 1959 by Canadian astronomer T. F.
Morris.
The bright blue–white colours of these stars are an indication of their temperature, with hotter stars appearing bluer and cooler stars appearing redder. This relationship between colour, brightness and temperature can be visualised by use of the Planck curve. But the more detailed study of the colours of stars using spectroscopy also tells astronomers a lot more — including how fast the stars are spinning and their chemical compositions. There are also a few bright red stars in the picture — these are red giant stars that are further through their short life cycles than the less massive and longer-lived blue stars [1].
By chance Messier 47 appears close in the sky to another contrasting star cluster — Messier 46. Messier 47 is relatively close, at around 1600 light-years, but Messier 46 is located around 5500 light-years away and contains a lot more stars, with at least 500 stars present. Despite containing more stars, it appears significantly fainter due to its greater distance.
The bright blue–white colours of these stars are an indication of their temperature, with hotter stars appearing bluer and cooler stars appearing redder. This relationship between colour, brightness and temperature can be visualised by use of the Planck curve. But the more detailed study of the colours of stars using spectroscopy also tells astronomers a lot more — including how fast the stars are spinning and their chemical compositions. There are also a few bright red stars in the picture — these are red giant stars that are further through their short life cycles than the less massive and longer-lived blue stars [1].
By chance Messier 47 appears close in the sky to another contrasting star cluster — Messier 46. Messier 47 is relatively close, at around 1600 light-years, but Messier 46 is located around 5500 light-years away and contains a lot more stars, with at least 500 stars present. Despite containing more stars, it appears significantly fainter due to its greater distance.
Messier 46 could be considered to be the older sister of Messier 47,
with the former being approximately 300 million years old compared to
the latter’s 78 million years. Consequently, many of the most massive
and brilliant of the stars in Messier 46 have already run through their
short lives and are no longer visible, so most stars within this older
cluster appear redder and cooler.
This image of Messier 47 was produced as part of the ESO Cosmic Gems programme [2].
This image of Messier 47 was produced as part of the ESO Cosmic Gems programme [2].
Notes
[1] The lifetime of a star depends primarily on its mass. Massive
stars, containing many times as much material as the Sun, have short
lives measured in millions of years. On the other hand much less massive
stars can continue to shine for many billions of years. In a cluster,
the stars all have about the same age and same initial chemical
composition. So the brilliant massive stars evolve quickest, become red
giants sooner, and end their lives first, leaving the less massive and
cooler ones to long outlive them.
[2] The ESO Cosmic Gems programme is
an outreach initiative to produce images of interesting, intriguing or
visually attractive objects using ESO telescopes, for the purposes of
education and public outreach. The programme makes use of telescope time
that cannot be used for science observations. All data collected may
also be suitable for scientific purposes, and are made available to
astronomers through ESO’s science archive.
More Information
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Links
- Photos of the MPG/ESO 2.2-metre telescope
- Other photos taken with the MPG/ESO 2.2-metre telescope
- Photos of La Silla
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Tel: +49 89 3200 6655
Email: rhook@eso.org
Source: ESO
