Globular Clusters are some of the oldest structures in the Universe. They are typically a collection of several hundred thousand stars that are bound together by gravity. They orbit their host galaxy in the outer region of the galaxy called the halo, occasionally passing through the main plane of the galaxy along the way. M12 is no exception to this rule, and is presently 15,000 light years away from us. There are currently about 200,000 stars in the M12 globular cluster. What is curious however, is the absence of lower mass stars.
Typically, when you have a collection of stars, they tend to follow a particular pattern. The brightest stars tend to be stars with the most mass, as well as stars that are more fully evolved. They are relatively few in number. As you go to progressively lower masses and cooler temperatures, we see more and more stars, all the way down to the lowest-mass stars: the M-class red dwarfs. These red dwarfs are the most numerous and make up roughly 3 out of every 4 stars.
So when we look at the core of M12 with a high power telescope, we see something surprising…there are hardly any Red Dwarfs! Practically no M-class stars at all, compared to what would be expected. Close to one million stars are missing and 600,000 of the million are red dwarfs. Where are they?
The leading idea is that like many globulars, M12 passes through the galactic plane periodically. However, unlike most globulars, its orbit takes it very close to the galactic center. During that journey, we believe that the lowest mass stars were preferentially kicked out. Kind of like if you were to kick a pebble and a boulder with the same force, the pebble would tend to go further. The strong gravitational forces that surround our galactic center have sling-shot into space the red dwarfs of M12 during its close encounters with the galactic core.
And now you know the reason for the missing million stars!
(Or at least, sciences best guess!)
Image Acquisition info:
Date: July 2014
Location: Starlodge Observatory, Ione, CA
Camera: SBIG STL 11000
Telescope: Planewave 12.5