Luis Ho
Luis Ho and colleagues have discovered most of the known black holes in nearby galaxies using the Hubble Space Telescope. Their work established that black holes, once thought to be rare, are in fact an integral component of galactic structure. Indeed, black-hole formation appears to be an inevitable consequence of galaxy formation. Understanding why and how this phenomenon occurs is one of the dominant themes of observational and theoretical research. Ho’s particular focus is to understand the energetic events and physical processes associated with matter accreting onto these objects, and the broader connection between black hole formation and galaxy evolution.
Material accreting onto a black hole heats up and emits radiation characteristically across the electromagnetic spectrum. The spectra hold important clues about the physics of the accretion disk—how matter is accreted, how energy is generated, and how relativistic jets are launched. Ho uses ground-based and space-based telescopes to measure the signal from the nucleus at different wavelengths (radio to X-rays). Initial results indicate that most massive black holes in nearby galaxies are on a starvation diet. When the universe was only a billion years old, well-fed black holes shined as brilliant quasars. Today many are but feeble remnants. However, a minority of nuclei are burning on overdrive. Ho is quantifying the factors that control how black holes turn "on" and "off," and how this activity governs their cosmic evolution.
In other research, Ho studies a class of massive star clusters recently found to be important constituents of galaxies experiencing vigorous star formation. How these "super star clusters" form and how they will survive are open issues. Closely related to these objects are dense stellar systems such as ultramassive globular clusters and central nuclei in disk galaxies. Ho has been systematically quantifying the internal kinematics, masses, and stellar populations of these unique entities using both the Magellan and Hubble telescopes. He has also begun to investigate the internal structure and kinematics of nearby galaxies, with the ultimate aim of explaining the origin of the Hubble sequence. In addition, Ho uses the Las Campanas facilities for his long-term, comprehensive imaging and spectroscopic survey of bright galaxies in the Southern Hemisphere.
