Unlike the disk, the distribution of stars in the galactic bulge is not exponential. It was once thought to be spheroidal, with an effective radius - the radius which contains half the light - of a few kpc.

However, recent results indicate that the bulge is not spheroidal, but is more likely bar shaped. Infrared data show that if you look on one side of the galactic center or the other, on one side the bulge appears bigger in angular size, and on average the stars are closer to us than on the other side. This can't happen if the bulge is axisymmetric!



Instead live in a galaxy with a central bar, a few kpc in extent. Disentangling bar from bulge is tricky and perhaps not even correct -- some astronomers argue we may not have a classical central bulge at all.



Bulge or bar, the mass of the inner structure is about 1010 M sun , or about 1/6 that of the disk.