Milky Way’s Heart
As the last blush of twilight drains from the evening sky this week, look low in the south for teapot-shaped Sagittarius. If you have dark skies, you can see some “steam” rising from the teapot’s spout: the subtle glow of millions of stars in the disk of our home galaxy, the Milky Way. And you might also notice a dark region beyond the steam. That, too, is part of the Milky Way: clouds of dust that block the light from the stars behind them.
Among other things, those clouds conceal the crowded heart of the Milky Way galaxy — a region of giant stars and giant star clusters, and of a black hole that’s four million times heavier than the Sun.
Astronomers know about these brilliant sights because they can view the center of the Milky Way at wavelengths of light that are invisible to the eye. These wavelengths penetrate the clouds, providing a clear look at the galaxy’s busy “downtown.”
But astronomers still debate just how far away that central district really is. Over the last decade or so, different teams have used several different techniques to measure the distance. But their results are all over the place. They range from as close as 23,500 to as far as 30,000 light-years. When you average them all together, you get about 27,000 light-years — a pretty good jaunt to reach the bright lights at the center of the galaxy.
We’ll talk about what you might see when you get there tomorrow.
Script by Damond Benningfield, Copyright 2011
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