Astronomy Colloquium

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) aims to detect and characterize low-frequency gravitational waves by timing an array of millisecond pulsars. In 2023, together with international colleagues in the International Pulsar Timing Array (IPTA), we reported the first evidence for a stochastic gravitational-wave background. This signal is consistent with arising from a population of supermassive black hole binaries, but longer, more sensitive datasets are needed to determine its origin and use it to constrain the astrophysics of galaxy mergers and evolution. I will describe our next "20-yr" dataset, which contains multi-frequency observations of 80 millisecond pulsars with four radio telescopes. I will describe the properties of the dataset, the expected constraints it will provide on the stochastic gravitational-wave background, and the prospects for detecting an individual supermassive black-hole binary source. Finally, I will outline our strategy for future NANOGrav and IPTA data analyses, with particular attention to the transformational impact of the upcoming DSA radio telescope. By increasing both array sensitivity and the number of precisely timed pulsars, the DSA will accelerate progress toward robust detections of individual nanohertz gravitational-wave sources and enable detailed characterization of the gravitational-wave universe.

The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), the most comprehensive optical astronomical sky survey ever undertaken, will obtain panoramic images of the night sky every clear night for ten  years, starting this year. The resulting 60 petabytes of imaging data, essentially a digital color movie of the night sky, will include about 20 billion galaxies and a similar number of stars, and will be used for investigations ranging from cataloging potentially dangerous near-Earth asteroids to fundamental physics such as characterization of dark matter and dark energy. I will review scientific goals behind this project, showcase its early data, and discuss remaining fine tuning of the Observatory before we formally start LSST. 

TBD

In over 40 years at JPL and Caltech I have been fortunate to participate in two great scientific revolutions, the shift of IR astronomy into space and the discovery and characterization of exoplanets. The first of these owed much to Gerry's development of ground-based astronomy at Mt. Wilson and Palomar which set the stage for the dramatic leap to space with IRAS, followed by Spitzer, WISE and ultimately JWST. The second is the ongoing explosion in exoplanet science which happened mostly after Gerry retired, but as I pursue my own research, I continually hear him urging me to think about the key questions and to make sure I get the data right.

My scientific arc has been defined by increasing capabilities, from searching for massive protostars in giant molecular clouds with a 24" telescope on Mauna Kea, to identifying solar-type protostars with IRAS, to finding signposts of planet formation with IRAS and Spitzer, to detecting Jovian-mass brown dwarfs with 2MASS and WISE, and now searching for and characterizing planets from gas giants to super-Earths. Gerry shared a vision that interferometry would be important for finding other Earths using both astrometry and direct detection. But apart from getting a second Keck telescope built with NASA's partnership, that proved to be a road not taken—at least in the US. But many valuable capabilities came from those initial efforts which are enabling new instruments including single mode fiber spectrometers like Parvi and HISPEC and even the picometer control of optical structures for HWO.

I will describe some waypoints along this voyage of discovery and describe ways, direct and indirect, where I, along with the astronomical community, owe Gerry a great debt.