Hey neighbor! Welcome our newest found stellar cousin

Contributed by
Mar 13, 2007

The European Southern Observatory has just announced they have discovered a previously unknown globular cluster orbiting the Milky Way.

Globular clusters are roughly globe-shaped (duh) collections of stars, usually containing a few hundred thousand to a few million stars. They orbit the centers of galaxies like bees buzzing around a hive, spending most of the time well outside their galaxies. We know of about 150 such clusters orbiting the Milky Way. Our Galaxy is a flattened disk, so globular clusters are usually easy to spot when they are well outside that plane. But sometimes, during their orbit, the pass right through that plane, and we see them against a crowded background of stars. Worse, the dust in the Galaxy obscures the clusters, making them very difficult to find.

This one, named FSR 1735, had been seen in previous surveys but it was unsure if it was a globular cluster or not. The image above, from the New Technology Telescope in Chile, appears to have removed that doubt. The cluster, containing something like 100,000 stars, is a bit difficult to see in the image, but it's the clot of stars in the center, somewhat denser than the distribution of background stars.

The cluster is fairly rich, but has remained hidden because it's located only about 10,000 light years from the center of the Milky Way, where the Galaxy is fairly thick with stars. To bring up that analogy again, it's a bit like trying to find a fly in a swarm of bees suspended in thick fog -- or in this case, dust. Infrared light can pass through the dust, so searches for new globular clusters are made in the IR: this image is in the near-infrared, with wavelengths just outside the range of the human eye. The colors in the image are therefore not real, but represent different wavelengths of IR light.

The cluster is about 30,000 light years away, and is only about 7 light years across. Imagine, 100,000 stars packed into a sphere that tiny! For comparison, the nearest known star system to the Sun, Alpha Centauri, is 4.3 light years away. What would the sky look like from a planet orbiting a star in such a cluster? It would be filled with stars, most yellowish,orange, or red, with hundreds of them blazing away brighter than Venus appears in our night sky.

The Universe is a beautiful place, and a surprising one. I'm always amazed at what delights are so close, yet lurk just beneath -- or for this case, just outside -- our notice.

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