Star Formation in Galaxies Along the Hubble Sequence

Observations of star formation rates (SFRs) in galaxies provide vital clues to the physical nature of the Hubble sequence, and are key probes of the evolutionary properties of galaxies. The focus of this review is on the broad patterns in the star formation properties of galaxies along the Hubble sequence, and their implications for understanding galaxy evolution and the physical processes that drive the evolution. Star formation in the disks and nuclear regions of galaxies are reviewed separately, then discussed within a common interpretive framework. The diagnostic methods used to measure SFRs are also reviewed, and a self-consistent set of SFR calibrations is presented as an aid to workers in the field.Comment: 41 pages, with 9 figures. To appear in Volume 36 of the Annual Review of Astronomy and Astrophysic

An unusually massive stellar black hole in the Galaxy

Here we report a measurement of the orbital period and mass function of GRS 1915+105 which allow us to deduce a mass of 14 +- 4 solar masses for its black hole. This large mass provides a challenge for black hole formation scenarios in binaries, since black holes with masses above 5-7 solar masses are hard to explain. Also, the mass estimate allows us to understand the unique X-ray variability of GRS 1915+105 as being due to instabilities of a radiation-pressure dominated disk radiating near the Eddington limit. Finally, several models are constrained which relate observable X-ray properties to the spin of black holes in microquasars. Once further calibrated, these relations may soon turn into a valuable tool to study relativistic effects in strong gravitational fields.Comment: appeared in Nature 414, p. 522 (Nov. 29, 2001