Globular clusters are amazing. The first one I saw in a telescope was M13, in Hercules. It was a rare clear night in the small village in England where I was living at the time, and I had taken delivery of a brand new 8″ reflecting telescope a few months before.
I was over the Moon, as I had just had some great evenings viewing Mars and was getting used to viewing deep sky objects when the Moon decided to appear. I mean I was literally over the Moon! As a new astronomer at the time I was developing a love/hate relationship with the Moon because it always seemed to dominate when the weather was good, and when I wanted to look at galaxies the weather seemed to always be rubbish. So I found that planets, open clusters and globular clusters were a great way to spend the time when the Moon was washing everything out.
Messier 13 Globular Cluster
M13 was the object I wanted to see, it is a well known object and was relatively easy to spot. I remember being enthused to get out under the moonlight and finally get a glimpse of a globular cluster. So M13 it was, the great globular cluster in Hercules, and what a sight it was, filling the eyepiece with a big ball of stars. It nearly looked three-dimensional and I could resolve stars well into the core – having recently perfected collimating my telescope certainly helped with that. I was amazed by the view and spent a lot of time glued to the eyepiece soaking up all of those photons. A few months after that amazing sight I had the addition of an equatorial mount and a DSLR camera and captured this image of M13, which really doesn’t do it justice but you get the idea.
So what are these big balls of stars? They are generally very old stars that probably formed at the same time that the galaxy did. They tend to be low in elements heavier than helium and there’s not much dust or gas floating around to kick off new waves of star formation. The clusters are also very densely packed with the distance between stars averaging about 1 light year at the most down to very close within the core, less the size of our Solar System in closeness! This makes them very hostile places for planets as the effect of passing stars can kick planets out of their solar systems. Because the stars are in all close proximity to each other and all orbiting around the centre, there’s a high chance that any planet in the cluster will be adversely effected just due to the number of stars wandering by. The globular clusters tend to hover around the central bulge of the galaxy, rather than in the galaxy, but they are an integral part as they all orbit the centre of the Milky Way. There are probably around 200 of these clusters hovering around our galaxy with some of them up to 130,000 light years away.
The image below is the M15 Globular Cluster in Pegasus – another very photogenic cluster! This cluster is about 33,000 light years away and estimated to be about 12 billion years old, so these are very old stars that have been chugging along burning hydrogen all of this time. M15 has about 100,000 stars and a very densely packed core, there’s even some suggestion that there may be a black hole at its centre.
in the Southern Hemisphere are two monster globular clusters, Tucanae 47 and Omega Centauri. The cover picture for this article is an image I took of Omega Centauri a few years ago. It is an amazing sight in the eyepiece as it fills the eye with millions of stars. Astronomers think that Omega Centauri is the centre of a galaxy captured by the Milky Way with its outer stars now assimilated into our own galaxy. The other Southern highlight is Tucanae 47 which is a beautiful object in the eyepiece, this is a very bright globular cluster and can be seen with the naked eye (though not in the middle of Wellington!).
The first globular cluster was discovered in 1665 by the German, Abraham Ihle and the first time individual stars could be seen in them was in 1764 when Charles Messier was looking for comets and making his famous list of fuzzy objects that weren’t comets. William Herschel was a prolific discoverer of globular clusters and starting in 1782, using his giant telescope, was able to find another 36.
The Milky Way isn’t the only galaxy with globular clusters, most galaxies seem to have a bunch of them. Next door in Andromeda there are around 500 so far observed and the huge galaxy M87 may have around 13,000 of them.
So when the moon is out and you can’t go galaxy hunting with your telescope, don’t forget that globular clusters make for fantastic viewing and can give you a really rewarding view of these objects that are orbiting our galaxy.