Simons Society of Fellows Alumni Symposium 2019

Yacin Ali-Haïmoud

It is now well established that a large part of the matter in the Universe is some substance which appears to be oblivious to any force but gravity. The nature of this “dark matter” remains a mystery. Could it be a new particle, as light as an electron, or might it be made of black holes as massive as many Suns? In this talk, I will first describe how one can hope to tease out some of the properties of dark matter from the Cosmic Microwave Background (CMB), the relic radiation from the very early Universe. I will review the basic physics underlying the CMB, in particular why it has a nearly perfect blackbody spectrum, and what the tiny changes of temperature across the sky tell us about the history and contents of the Universe. I will then illustrate how precise measurements of the CMB properties may inform us about the nature of dark matter. Last but not least, I will explain how gravitational waves, recently directly detected by LIGO, may provide an entirely new window into the mystery of dark matter.

Gurtina Besla

Our understanding of the motions of stars within our Milky Way and of the many small galaxies that orbit around it has changed dramatically over the past few years owing to new observational surveys and significant advancements in our understanding of galaxy structure. Specifically, new surveys now enable us to precisely measure the motions of objects that orbit our Galaxy, like clusters of stars, satellite galaxies and stellar streams. The motions of these objects trace the so-called “dark matter” distribution, the unseen material that is expected to exist within and around our Galaxy, making up the bulk of its mass. I will provide an overview of this evolving picture and how we can use such data to test the cold dark matter paradigm in the near future using next-generation instruments and models.

Jo Dunkley

There is currently a tension between various measurements of the expansion rate of the universe. I will give a recap of this issue, and talk about how we use the Cosmic Microwave Background, our most distant observation, to infer the local expansion rate of space. I will explain what assumptions we make about the cosmological model in doing so, and how we might modify this model to bring different measurements of the expansion rate better in line. I will talk about new measurements we are making in Chile to improve estimates of the Hubble constant derived from the CMB, using the Atacama Cosmology Telescope, and the upcoming Simons Observatory.

Jennifer Johnson

The Universe makes elements in many ways:  collapsing stars, merging stars, burping stars, exploding stars, and the Big Bang itself. Each of these processes has special characteristics, which imprint themselves on the composition of the Universe. The important physics leading to the formation of the elements will be highlighted, as well as the evidence we have of the contributions of different events to give us the elements from helium to uranium.

Johanna Teske

Exoplanet science was kick-started in the 1990’s by the first radial velocity (RV) or “Doppler wobble” measurements of a extrasolar planet’s gravitational effect on its host star. Since then, the most productive means of finding new exoplanets has moved from the radial velocity method to the transit method, in which a planet passes in front of its host star and we measure from Earth the small decrease in the star’s brightness. However, going beyond “butterfly collecting” to better understand exoplanet demographics necessitates RV observations to measure the bulk compositions of transiting exoplanets, as well as explore parameter spaces that are not typically covered by the transit method. In this talk I will describe what we are learning today from RV studies of exoplanets, the current limitations to these studies and how we (think we) can overcome them, and how future RV studies will help us understand whether our Solar System is rare in the Galaxy or not.

Brendan Bowler

Finding and characterizing extrasolar planets has become one of the fastest-paced and most rapidly evolving fields in astronomy. Direct imaging—spatially resolving exoplanets from their host stars—is especially challenging but provides unique insight into the architectures, atmospheres, and formation of planets. By exploring planetary systems from the outside-in and directly detecting photons originating in their atmospheres, imaging complements other planet-finding techniques sensitive to smaller orbital separations and enables detailed studies of atmospheric structure and composition. In this talk I will review the field of high-contrast adaptive optics imaging with an emphasis on discoveries and statistical patterns that have emerged over the past several years. I will also outline the long-term future of the field with the next generation of telescopes like JWST, WFIRST, and ground-based facilities with thirty meter apertures which are now under construction. Eventually these will pave the way for a dedicated space-based mission to image and characterize Earth analogs, one of the most formidable but consequential goals in modern astronomy.

Courtney Dressing

One of the most successful techniques used to identify planetary systems is the transit method, in which astronomers monitor the brightness of a star and look for periodic dimming events caused by the passage (or “transit”) of a planet across the stellar surface. Since the discovery of the first transiting planet 20 years ago, astronomers have detected thousands of transiting planets orbiting stars with a diverse range of temperatures, radii, and masses. The majority of the currently known transiting planets were detected by the NASA Kepler mission, which revealed that our Galaxy is teeming with planetary systems and that Earth-sized planets are common. Most of the planets detected by Kepler orbit stars that are too faint to permit detailed study, but NASA’s Transiting Exoplanet Survey Satellite (TESS) launched in April 2018 and is finding hundreds of small planets orbiting stars that are much closer and brighter. I will describe key discoveries from ground- and space-based searches for transiting planets and explain how follow-up spectroscopic analyses of transiting planets can be used to probe planetary atmospheres and investigate the formation and habitability of planetary systems.

Aditi Sheshadri