What are the most actively researched areas in astronomy today?

According to the 1994 issue of Astronomy and Astrophysics Abstracts there are 2496 topics under which some 16,000 research papers could be filed. The largest categories are as follows:

Active Galactic Nuclei
Black Holes
Comets
Cosmology
Galactic Structure and Evolution
Gamma-ray Astronomy
Infrared Astronomy
Interstellar Gas and Dust
Magnetic Fields
Molecular Clouds
Planetary Astronomy
Pulsars
Quasars
Radio Sources
Solar Physics
Star Formation
Stellar Evolution
Supernova
X-Ray Astronomy