Let's visit the bar at the center of the Milky Way

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Unfortunately, you won't be able to order a drink there. It's actually a gigantic, bar-shaped formation of stars found right at the center of our home galaxy. And it rotates like nothing else in the Milky Way.

While we have known for about eighty years that the Milky Way is a spiral galaxy, figuring out the finer details of its structure has proven tricky. While we can easily observe other, far distant galaxies and determine how they are put together, we don't have that luxury for our own - that's the problem with being stuck inside the thing you want to observe.


We know that there are two basic types of spiral galaxies - ones that have elongated stellar structures, or bars, in their central bulges, and ones that don't. But it's only now that a team of astronomers led by Dr. R. Michael Rich of UCLA and Dr. Andrea Kunder of the Cerro Tololo Inter-American Observatory (CTIO) in Chile has been able to confirm just which of these categories our galaxy falls into.

The astronomers studied the motions of a large number of giant red stars over a four year period. They were able to build up data on the velocities of 10,000 M giant stars. They found that these stars formed a giant conglomeration, a bar-shaped structure that points nearly in the direction of our own solar system, only off by 20 degrees.


Intriguingly, while the rest of our spiral galaxy orbits the central point like a pinwheel, this bar orbits in a cylindrical fashion, like a toilet roll holder. A computer simulation suggests that the bar formed from a massive disk of stars, which was then reorganized into this bar structure by the intense force of gravity. We also know that the stars in the bar have a lower metal content than stars elsewhere in the galaxy, which means they are some of the oldest stars in the Milky Way.

Via NOAO. Image via NASA.