Galactic Bar

Group Name	`bar`
Reference	Merrifield, M. & Binney, J. 1998, Galactic Astronomy (Princeton: Princeton University Press)
Prepared by	Carter Emmart & Brian Abbott (AMNH/Hayden)
Labels	No
Files	`bar.speck`
Dependencies	`halo.sgi`

The Milky Way has two main structural elements: the disk and the spherical components. The disk is a thin layer of stars, gas, and dust that contains the Galaxy's spiral arms. The spherical component includes the Galactic bulge and the halo. The bulge, at the center of the Galaxy, contains both old and young stars with some gas and dust.

Most of the mass and luminosity of the Galaxy are contained in the Galactic bar, an oblate spheroid located at the center of the Galaxy. The bar is shaped like an American football, with axes (a_x, a_y, a_z) = (5500, 2050, 1370) light-years. Because we are located on the outskirts of the Galactic disk, we cannot see directly to the center of the Galaxy with all the gas and dust in our way. How do we know there is a bar if we cannot see it in the visible spectrum?

The main evidence for the existence of a bar is the infrared luminosity differences around the Galactic center. Because dust obscures our view of the Galaxy, we must turn to the near infrared (around 2 to 4 microns) to peer through it. In these wavelengths, the intensity on one side of the Galactic center is higher than it is on the opposite side. Astronomers deduced that there must be a triaxial bar present, with the bright side of Galaxy center corresponding to the end of the bar that is closest to us. Currently, the long axis of the bar (which is parallel to the Galactic plane) is believed to be inclined 14^o to the line connecting the Sun and the center of the Galaxy.

We represent the bar as a yellow ellipsoid with a glow texture at its center. The glow is composed of three polygons that lie in the x, y, and z planes, respectively. The glow can be turned off with the Polygon Toggle Button.

Digital Universe Atlas

Digital Universe Guide

Galactic Bar

Galactic Bar