• Unraveling formation time-scales of galactic bulges (iastro.pt)

The Instituto de Astrofisica e Ciencias de Espaco has announced that scientists using the Integral Field Spectroscopy have studied the central bulges of spiral galaxies to understand the factors that cause the bulges to grow.  Over several years, they computationally chewed through approximately 500,000 spectra that covered all possible variations on “non-interacting spiral galaxies.” By looking at every combination of disk, bulge, and arms, they hoped to identify what physical characteristics are linked together. With this data, the team was able to measure, among other things, how stellar ages vary across the galactic bulge as a function of kind of galaxy

Like many things now being determined with data, these results run counter to what we would have expected a few years ago. Specifically, they found that in low mass galaxies, stars go from young to old as you move out from the center, while in high mass galaxies, stars run from old to young as you move out. Yes folks, the distribution of stars by age varies with mass. This happens even though the galaxies themselves appear to form in the same manner, through aggregation of smaller systems. These differences may be related to past active galactic nuclei (AGN) in these bulges that blasted out radiation and cleared the core while pushing material to outer areas. 

Overall, they find the process of growing galaxy bulges is a slow and gradual process with bulges forming over 2 to 4 billion years, and an AGN defines a flipping point where the galactic core goes from densest in the core with star formation, to empty in the core due to light pressure.

This work should allow detailed models to be created that allow us to step through the process of bulge formation by looking at systems of every intermittent age and size. This is just cool and straight forward research that becomes complex in the computational power required to make this result possible. These results are reported in Astronomy and Astrophysics and was led by Iris Breda.