Event Type: Astrophysics Colloquium

Observing atmospheric evolution in extrasolar planets Atmospheric escape has driven the long-term evolution of most known planetary atmospheres, including terrestrial planet atmospheres in our Solar System. In this talk, I will discuss the wealth of information we can learn from studying atmospheric escape in extrasolar planets, focusing on three main observational efforts. I will first

The Zwicky Transient Facility: concept to results The Zwicky Transient Facility (ZTF) is at present undertaking an ambitious survey of the dynamic optical night sky. It searches systematically for exploding stars, burping quasars, variable stars and moving objects.  ZTF is considered to be the pre-cursor of the Rubin Observatory’s Legacy Survey of Space & Time

Microlensing is uniquely capable of studying planets across a wide range of masses at a few AU from their host stars, At the lower masses, these planets are difficult to impossible to find with other techniques. I will discuss recent results in microlensing suggesting a turnover in the planet mass ratio function around 10^-4, i.e.

space, permanently transforming the Universe. Determining exactly when and how reionization occurred is therefore central to our efforts to understand these early sources, as well as the physics that governs the interaction between galaxies and their environments. I will describe what we know about reionization from the study of quasar absorption lines and other probes

The solar cycle causes the Sun to change on timescales that can affect life. The maxima of cycles are marked by an increased occurrence of sunspots that cause solar flares and coronal mass ejections that can cause potentially harmful geomagnetic storms. Despite the fact that the existence of the solar cycle has been known for

The CMB presents a unique probe of dark matter physics. Ultra-light axions of mass around 1e-22 eV are a promising dark matter candidate well motivated by high energy physics. The Simons Observatory (SO) is a new cosmic microwave background (CMB) experiment being built on Cerro Toco in Chile, due to begin observations in the early

Although thermonuclear (Type Ia) supernovae and neutron star mergers are some of the most important astrophysical events, our understanding of these explosions is vague.  I will present abundance measurements of elements across the periodic table (Mg, Fe, Ni, Ba, and others) that address the nature of both types of explosions.  The measurements are based on

Women and people of color are severely underrepresented in many STEM departments, especially in physical sciences and engineering. Professional societies and universities have issued reports full of recommendations. Which ones have worked? This talk will identify departments that are most successful in diversifying bachelor’s and doctoral degrees in STEM. Using data on student and faculty

With increasing cadence and areal coverage, optical transient surveys can probe fast and rare regions of transient parameter space. In particular, ~100 transients have been discovered whose properties (a fast rise to peak, and high peak luminosity) challenge our understanding of how energy is deposited and transported in stellar explosions. Here we present ZTF18abukavn (SN2018gep),

The Event Horizon Telescope recently revealed the first picture of the black-hole shadow in the center of the M87 galaxy. I will discuss the technological and theoretical advances during the last decade that led to this result. I will then focus on how this picture allows us to accurately measure the mass of the black

In the upcoming era of JWST and 30-meter class ground-based telescopes we will be forced to reckon with the full 3-D nature of extrasolar planets. Today, many current models treat exoplanet atmospheres in one dimension, as a vertically stratified global average — similar to 1-D models of stars and many solar system planets. Yet we

Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. New surveys now enable us to map the 3D structure of our Milky Way and the dynamics of tracers of its dark matter

Exoplanet collection identified in the last 25 years ranges from massive and big planets like Jupiter to smaller denser and more compact objects similarly to Earth. Most of these planets are assembled in system orbiting close to their star. In that rich and stimulating landscape, this talk will describe two specific programs aiming to fill-in

Are we drowning in exoplanets, or have we barely begun to discover them?  What do we currently understand about the broad exoplanet population? With hundreds to thousands of new transit candidates coming from the TESS and Gaia missions, and major new populations to be discovered by WFIRST and direct imaging surveys, things are starting to

Nearly all galaxies appear to harbor a supermassive black hole. The origin and properties of initial black hole seeds that grow to produce the detected supermassive black hole population are unconstrained at present, as actively growing seeds are not directly observable near their birth epochs. Nevertheless, some unique signatures of seeding do survive and still

Testing the predictions of general relativity in the dynamical strong-field regime, in particular black holes and their dynamics, has only recently become possible with LIGO/Virgo observations of black hole mergers. I will review some of the tests that have been performed to date. However, one obstacle to extracting the most stringent constraints possible is the

Quadruply lensed quasars (“quads”) are used to study several important astronomical problems, one of which, the abundance of LIGO-mass primordial black holes, we discuss at some length. But quads are rare, with only one out of every 3000 quasars lensed into a quad. The alternative schemes used to identify them all have serious shortcomings of

Blueshifted ionized absorption features at near-relativistic velocities (v~0.1c or higher). known as ultra-fast outflows (UFOs), seem to be ubiquitously present in x-ray spectra of many AGN populations of different luminosity. Canonical AGN UFOs, typically detected in Fe K band, exhibit massive column (NH > 1e23 cm^-2), highly ionized ions (log \xi ~ 4 – 6)

The ever-increasing need for accurate prediction for complex non-linear processes leads to large scale dynamical systems whose simulations and analysis make overwhelming and unmanageable demands on computational resources. The evolution of the Universe is one of these complex processes that the computational cost of the traditional full-order numerical simulations is extremely prohibitive. In this talk, we

Measurements of the Cosmic Microwave Background and the large-scale structure of the universe have made it possible to determine with great precision the universe’s inventory, as well as properties of its initial conditions. However, there are profound questions that remain unanswered. Cosmological observations and galaxy dynamics seem to imply that 84% of all matter in

Globular clusters are the relics of extreme star formation in high-redshift galaxies. Their enormous potential as tracers of high-redshift galaxy formation is broadly recognised, but concrete applications of this link have remained out of reach. The key missing ingredient has been to construct an end-to-end model for star cluster formation and evolution in a cosmological

The oldest, most metal-poor stars found in the Galactic halo and satellite dwarf galaxies retain in their atmospheres the chemical footprints of the high redshift Universe. Employing “stellar archaeology” – the diverse use of the chemical and dynamical properties of metal-poor stars – outstanding questions about the early Universe can be answered. Using high resolution optical and UV spectroscopic observations

Strong gravitational lenses with measured time delays between the multiple images can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe.  An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the tension in current H0 measurements.

Supermassive black hole binaries (SMBHBs) are a product of galaxy mergers and progenitors of coalescing binaries, considered to be the prime sources for future gravitational wave (GW) detectors. Expectations for detection of gravitational radiation from SMBHBs have recently been raised by the success of the Laser Interferometer Gravitational-Wave Observatory, by the increasing sensitivity of the

The current standard cosmological paradigm is remarkably  successful at describing the distribution and motion of galaxies  on large scales (>10 Mpc). The talk will discuss part of the strong evidence for the standard paradigm,  but also argue that minor modifications might be inevitable. In particular, it will focus on constraints and implications of models with

The Chandra X-ray Observatory was launched over 20 years ago, but the development of its instruments began more than 20 years before that. This talk will describe the little-known saga of the High Energy Transmission Grating Spectrometer (HETGS) on Chandra, including technical challenges, political wrangling, Congressional hurdles and near-death experiences. Spoiler-alert: It all came out

Linking observable properties of galaxies to the assembly history of their host haloes is one of the great challenges in cosmology. In this colloquium, I will address this challenge from  the view-point of the “tree entropy”, an interesting mathematical way to characterize the structure merger trees. The tree entropy puts every halo merger tree on a scale between a “minimal

From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles of “haze”.  With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed

Pure dark matter structure formation simulations in LCDM predict that dwarf galaxies should inhabit dark matter halos that have steeply rising central density “cusps”. However, observations of nearby dwarf irregulars favour instead constant density dark matter “cores”. Many solutions to this cusp-core problem have been proposed, from modifications to the nature of dark matter to

Within the last few years, gravitational wave astronomy has progressed from notable single detections to a steady stream of events that provide a continually deeper view into the population of merging compact binaries in the universe. These detections are only possible due to sophisticated analyses of noisy interferometer strain data that were historically conducted within

The recent gravitational wave detections by LIGO/Virgo revolutionized the way we sense our universe. These detections have resurfaced a long-standing question about the formation channels of merging black holes and raised new challenges about forming gravitational sources in general. Motivated by these challenges, I will suggest how few-body gravitational interactions in a dense environment can

Astronomical transients are signposts of catastrophic events in space, including the most extreme stellar deaths, stellar tidal disruptions by supermassive black holes, and mergers of compact objects. Thanks to new and improved observational facilities we can now sample the night sky with unprecedented temporal cadence and sensitivity across the electromagnetic spectrum and beyond. This effort

For over two decades, the Hubble Space Telescope has been heavily used to locate supernovae in high redshift environments, with the primary goal of improving constraints on the nature of dark energy. Along the way we have made surprising observations on the nature of supernovae themselves, and clues to their elusive progenitor mechanisms, some of which are difficult