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Trumpler 5, an old open cluster

Date created: 1992-03-18

Tags: dust, supernova, cluster

As they age, open clusters of stars begin to lose their identity. This is partly because the brighter members tend to self-destruct as supernovae, and, though the group members share a common motion through space, they are only loosely bound. Stars thus drift away from the cluster in a process that accelerates with time. However, some clusters are massive enough to retain their identity much longer than usual, and Trumpler 5 is one such. Its age is estimated to be about 3 billion years, which is very old for an open cluster and it must have been a spectacular sight in its youth.

The cluster is about 11,000 light years away and seems to be at the edge of the molecular cloud in Monoceros, where star formation is still producing new generations of young clusters. This location is probably the cause of significant interstellar dust absorption, which gives the cluster a slight reddish hue. The brightest star here is V493 Mon, a variable carbon star that appears yellow in this image. The image is about magnitude 13 on the red and green-light plates but almost invisible (at least six magnitudes fainter) on the plate taken in blue light, absorption of blue light that is taking place in the atmosphere of the star.

Photograph made from plates taken in January, 1992.
Top left is NE. Image width is about 15 arc min.

Credit: David Malin

© Australian Astronomical Observatory