Thursday, 15 February 2018

Berkeley 21: The edge of our galaxy

Loyal readers of my blog know that I'm obsessed with faint fuzzies... objects so difficult to see that you sometimes wonder whether what you see is real or whether you've entered the realm of science fiction. But perhaps the objects that fascinate me more than anything else are extremely remote (and therefore faint) open clusters. Last year already I took you to Berkeley 19, a cluster that lies even beyond the outermost spiral arm of our galaxy. Today, I'd like to take you just a little bit closer, to a distance of merely 16,000 light-years, right in the heart of this outermost spiral arm. There lies this old star cluster, denominated Berkeley 21, the light of which is nearly completely extinguished by the interstellar dust of the broad Perseus spiral arm which lies between the outer arm and our own. In other words, prepare for something very difficult to see. 

At 104x, I only got a hunch of a fuzzy patch... the suspicion that I had nailed it. It was not until I pushed telescope power to 285x that the cluster revealed itself and at 507x most of its stars could be resolved, albeit with great difficulty. For your information, the brighter stars you see on my sketch all lie a lot closer to us!

Star clusters in that extremely remote part of our galaxy are usually very old because the gravitational influence of the galaxy is a lot less and interstellar matter's not stirred up as much. So don't expect a lot of spectacular star formation there. And if eventually a star cluster does form, it stands a much better chance of remaining compact. Berkeley 21 therefore could be many billions of years old, perhaps even be as old as our galaxy itself.

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