M14

What is truly interesting about M14 is that this jumble of stars actually helped astronomers put the pieces of a puzzle together. The star indicated in the cropped center of M14 (taken from the same data, just not brightened as much) is a special star. It is called a "CH star" because its atmophere has carbon-hydrogen molecules. Everything heavier than hydrogen, helium, and lithium is basically created in the centers of stars through nuclear fusion or as a by-product of supernovae explosions- the ultimate stellar crucible. Generally small stars do not reveal what heavy elements are contained in their cores until they dredge up this materials from thier cores near the ends of their lives (and later expell them in the form of a planetary nebula). However this star shown below is not old enough to have done this! Thus astronomers wondered why should CH stars have carbon in their atmospheres?

An answer was soon found when astronomers discovered that all CH stars are part of a binary system. One of the stars, near the end of its life, dredges up its stellar ashes of nuclear fusion and proceeds to expell it into space. Much of this material is dumped onto the other companion. So, although too young to have carbon this companion gets a good helping from its dying friend.

What is so special about finding a CH (binary) star in M14 (or any globular cluster) is that these stars are first generation stars of our universe. There are very few planetary nebulae to be found in globular clusters; so studying the nuclear products of these stars has been difficult. But here, using this CH star astronomers can directly examine the make up of one of these stars by examing the atmosphere of the other!