A Glorious Globular Cluster — Part 1

Summer is the best time to explore the southern Milky Way, the night’s most dazzling treasure chest.

[View I took of the summertime southern Milky Way many years ago. A juniper tree is in the foreground]

In late May, the last time I drove far enough from city lights to see the edge view of our galaxy, at sunset the Milky Way lay slanted, largely hidden by the horizon. In the morning it was at its best. But by July the sight will be beautiful soon after sunset and stunning at midnight. It shows off great star masses, streaks of dark nebulae, and the gauzy band of millions of stars so distant they are like a bright mist.

Sagittarius, the archer, is the constellation that dominates the region. I can’t make out an archer, just as I can’t really see a Great Bear near the North Star. Instead, I recognize the northern formations by way of the Big Dipper, a modern asterism that is part of the Great Bear, and I orient myself in the southern reaches by the Teapot, an asterism that’s part of Sagittarius.

A bright patch named Messier 22 is visible to the unaided eye as a starlike object a little to the left of the Teapot’s lid, no more impressive than many other lights and shapes in the Milky Way.

[Sagittarius with its Teapot asterism]

However, M22 is not a star; it’s a globular cluster of at least 186,000 stars clumped together, drifting 8,500 light-years from Earth. NASA’s Astronomy Picture of the Day site for June 27, 2005, notes, “Stars orbit the center of the cluster, and the cluster orbits the center of our Galaxy. So far, about 140 globular clusters are known to exist in a roughly spherical halo around the Galactic center.”

[Photo cropped to show a closer view of globular cluster M22]

M22 is 60 light-years across, not much room for nearly 200,000 ancient stars to ramble around in.

The most immense of the Milky Way globulars is Omega Centauri, which has 10 million stars and is 17,000 light-years away. It is far south, rarely visible from Utah. An intermediate-size black hole was tentatively identified at its core.

Astronomers have developed a straightforward method to determine the age of stars in globular clusters, says NASA. The age “nearly matches the 13.7 billion-year age of our entire universe.” Globular clusters, of which M22 is one of the brightest and nearest, are where we can view the oldest stars.

Dawn was breaking in the Millard County desert on May 28 when I took a few telescopic photos of the center of M22. I thought I wouldn’t see much because of the brightening atmosphere but the results were better than I had expected.

[Photo of center of M22, which I took on the morning of 5-28-2009]

Next: What’s lurking in M22?

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