3 research outputs found
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