Luis Ho is a world-renowned black hole expert. Using the Hubble Space Telescope, Ho and colleagues have discovered most of the known black holes in nearby galaxies. Once thought rare, Ho and team instead established that black holes are so common they are integral galactic components. 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 across the electromagnetic spectrum. These spectra hold important clues about the physics of the accretion disk—how matter grows, how energy is generated, and how relativistic jets are launched. Ho uses ground-based and space-based telescopes to measure the signals 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 evolution.
Ho also studies a class of massive star clusters recently found to be important constituents of galaxies with vigorous star formation. Closely related to these objects are dense stellar systems such as ultramassive globular clusters—spheroidal groups of stars that are gravitationally bound—and central nuclei in disk galaxies. He also investigates the internal structure and motions of nearby galaxies. Ho uses Carnegie’s Las Campanas facilities for his long-term, comprehensive imaging and spectroscopic survey of bright galaxies in the Southern Hemisphere.
Ho received his B.A. in astronomy and physics from Harvard University and his M.A. and Ph. D. from UC-Berkeley. Before becoming a staff astronomer in 2000, he was a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics and then an associate staff astronomer at Carnegie. For more information see http://users.obs.carnegiescience.edu/lho/