The Spherical Component
The Spherical Component
Goals: Explore the spherical component of the Galaxy, including the Galactic bulge and its halo.
Before starting, turn on: galaxy
You will be using: bulge, halo
As you've just seen, the disk component of the Galaxy is the lifeblood of the system. This is where stars are forming and where they explode into clouds of glowing hydrogen. The spherical component is from an era when the Galaxy was forming. The stars in this part of the Galaxy are older, cooler stars that formed long ago and have long lifetimes. Let's explore the structural elements that make up this component of the Galaxy.
The Galactic Bulge
The innermost component is the Galactic bulge. The bulge is the brightest part of the Galaxy and contains the Galactic bar and nucleus. While it contains many older stars, it also contains the active Galactic center, where stars form and orbit in the disk component. Overall, the stars in the bulge are more metal-rich and younger than those found in the halo, the region surrounding the bulge.
The Galactic Halo
The Galactic halo is a large, roughly spherical volume that encompasses the entire Galactic disk. The halo is filled with old, faint stars and globular clusters. Recall that the globulars are densely packed clusters of 100,000 to 1 million stars. The stars in the halo and inside globular clusters are metal-poor, older stars that formed close to the era of Galaxy formation.
The shape is thought to be slightly flattened like the bulge but is spherical to first order. The size of the halo remains under study. In the Milky Way Atlas, we set the radius to 41,000 pc (about 130,000 light-years). If you have the globular clusters on, you'll see that most of the clusters lie within the halo but that a handful do not. Do these clusters belong to our Galaxy? Is the halo significantly larger, as some astronomers suggest? The answers to these questions will be found in two areas: in the nature of globular clusters versus small dwarf galaxies, and with our increased knowledge of our Galactic neighbors.
Our last tutorial of the Milky Way Atlas addresses the latter topic: our Galactic neighbors.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott