Star Formation

The conditions at the Galactic Center produced by the presence of a supermassive black hole, large magnetic field, a large internal cloud velocity and a curious distribution of gas and dust, have resulted in a number of theories as to how stars could possibly form in such an extreme environment.

The strong tidal forces created by the supermassive black hole require material to have a larger than normal density in order for it to collapse from its own gravity. The rate of the cloud collapse is further restricted by the larger than normal magnetic fields which permeate throughout the galactic center. Finally, the material at the galactic center contains a larger amount of metals (all atoms besides hydrogen or helium) than the rest of the galactic disk. This increase in metallicity impedes the collapse of the star since the material has an large opacity which prevents energy from escaping the collapsing cloud. Both the larger density of material required for collapse and the decrease in the speed of the collapse allow for more massive stars to be formed.

While the central parsec region of the galactic center is surrounded by the CND, the central parsec itself is relatively devoid of material in which to produce stars. So the question remains as to how and when the diverse collection of stars we observe there were created. Since the harsh conditions inhibit star formation due to the collapse of a cloud from to its own self-gravity, other methods for triggering star formation must be considered. The surrounding CND provides for the possibility of cloud collisions which would result in an external compression of material and loss of angular momentum causing an eventual infall toward Sgr A*. External compressions could also occur from neighboring supernova events which would cause shock fronts throughout the interstellar medium.

The two distinct ages of the stellar populations seen at the galactic center give us a clue about the different epochs of star formation necessary to produce the observed types of stars. The population of M and K supergiants and HeI/HI emission line stars suggests that there was a burst of star formation 10^7 years ago while the population of intermediate asymptotic giants branch stars (AGB) were formed 10^8 years ago. This has prompted us to believe that there have been multiple epochs of star formation at the galactic center possibly triggered by the sporadic infall of material toward the supermassive black hole.

Finally, there is a unique collection of objects both within the central parsec and Quintuplet cluster which have featureless near-infrared spectra which means we are unable to determine their evolutionary state.