StarDate: November 27, 2009

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A spiral galaxy that's like a small version of our own soars high across the sky tonight. M33 is in the small, faint constellation Triangulum, which is high in the east at nightfall.

M33 is about half the diameter of our own galaxy, the Milky Way, and about one-tenth as massive. Pictures of the galaxy show spiral arms wrapping around a small, fairly faint core -- a structure that's similar to the Milky Way.

One of the galaxy's most prominent features is on the edge of one of the spiral arms -- a nursery that's given birth to hundreds or thousands of stars. A couple of hundred of them are many times brighter and more massive than the Sun, so they make the nursery stand out.

In one of those strange quirks of skywatching, though, some of those stars may no longer exist.

The galaxy is about three million light-years away. That makes it one of our closest galactic neighbors. But it also means that we see M33 as it looked three million years ago, because that's how long it takes light to cross that immense gulf.

The most massive stars live the shortest lifespans -- as little as a few million years. The stars in M33's nursery are a few million years old -- as we see them today. When you add in the travel time for their light, though, it's possible that the heaviest of these stars have already exploded, or collapsed to form black holes. If so, then we'll eventually see their demise -- sometime in the next three million years.

Script by Damond Benningfield, Copyright 2009

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