As the disk formed, star formation continues and the metal abundance in the gas increases. This region, in the direction of Sagittarius, is totally hidden by gas and dust. This would not be the result of one star, but of lots of old stars that drifted together in the dense nucleus. The evidence is the existence of an accretion disk of radius 100 pc viewed in other wavelengths. The velocity the gas is moving allows them to estimate the mass.
Some observations show jets coming from the core, and others show gamma rays.
The VLA shows material swirling inward.