Event Type: Astrophysics Colloquium

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

eROSITA was launched from Baikonur, Kazakhstan aboard the SRG spacecraft in July 2019. Following an extended commissioning phase, eROSITA entered full science operations in October of the same year, beginning with the calibration and performance verification (CalPV) phase. A variety of astrophysical targets were observed during this phase, demonstrating the high quality of the data.

The CHIME telescope, originally planned for Hydrogen intensity mapping, has two instruments sensitive to rapidly varying sources: a pulsar backend which processes tracking beams produced by the correlator, and a Fast Radio Burst (FRB) detector searching for these still-mysterious millisecond signals. I’ll present some of the early results from both instruments, including the many things

The Voyager spacecraft were launched in the fall of 1977. Forty-three years later, both spacecraft are in the interstellar medium, returning information about the fields and particle environment there. Up through the Uranus encounter in 1986, Herbert Bridge was Principal Investigator on the Plasma Science Experiment on the spacecraft.  John Belcher was then PI during the Neptune

Cosmic reionization is the last major phase transition undergone by our Universe. Although most studies agree on the general characteristics of H reionization (for example that it is driven by stars and it is mostly if not fully complete by z~6), its details are still largely unknown, among which the contribution from and role played

Claude-Andre Faucher-GiguereAbstract: Galaxies are remarkably diverse in their properties, ranging from irregular to disky to elliptical in morphology, and from blue to red in color. At the same time, when analyzed systematically, galaxy populations exhibit striking regularities, with clear trends with mass and redshift. How does this “regular complexity” emerge from the hot Big Bang?

Historically, our understanding of planet formation and the origins of planets’ compositions has been largely informed by our Solar System. However, we are just one system, and now with facilities like NASA’s Kepler and TESS telescopes, we are discovering a wide variety of planet types and architectures, many of which are unlike our own. In

One of the key objectives of modern astrophysics is to understand the formation and evolution of galaxies. In this regard, the Milky Way is a critical testing ground for our theories of galaxy formation. However, dissecting the assembly history of the galaxy requires a detailed mapping of the structural, dynamical  chemical, and age distributions of

I will discuss recent progress understanding how light particles thermalized in the early universe can be detected in the CMB ad large-scale structure surveys. We will focus in particular on the phase shift of the acoustic peaks caused by free streaming of these relics prior to recombination.  We will discuss the origin of this signal

The latest results from the LIGO-Virgo-KAGRA collaboration draw a spectacular fresco of binary black hole mergers, ranging from a few to more than hundred solar masses. In this talk, I will discuss the main astrophysical formation channels of binary black holes, highlighting their issues and open questions. On the one hand, models of stellar evolution

As transient surveys become wider and faster, and follow up facilities become more automated and global, we are able to discover and characterize new phase spaces of transients. Among these I will review new classes of supernovae which evolve either too rapidly or too slowly, or emit too much energy to be explained by conventional

Magnetic fields have long been thought to play key roles in driving accretion onto black holes and launching their relativistic jets. I will present spatially resolved long-baseline interferometry observations of linearly polarized synchrotron radiation from near the event horizons of two weakly accreting supermassive black holes, Sgr A* and M87. I will show how the

HectoMAP combines data from two of the world’s largest telescopes to map the universe at ages & 7.5 Gyr. Hectospec on the MMT provides redshifts and other spectroscopic measurements. Hyper Suprime-Cam on Subaru provides spectacular imaging over the entire 53 square degree strip. HectoMAP includes more than 2000 galaxy redshifts per square degree. The survey

The galaxy cluster A2146 is undergoing a major merger and hosts two huge, bright Mach 2 shock fronts, which provide a unique opportunity to measure the electron-ion equilibration timescale along with other key transport phenomena.  Collisionless shocks occur over a wide range of scales from accretion shocks to supernova remnants and heliospheric shocks.  However, only

STEM research and innovations have positively impacted many aspects of our society.  Today, the quality of the STEM enterprise must be elevated if the quality of innovation is to meet an increasing complexity of societal needs; and that elevation is inextricably linked to diversifying STEM disciplines. However, an ongoing challenge to STEM diversification continues to

NICER, the Neutron Star Interior Composition Explorer, is an X-ray telescope that installed on the International Space Station. Its mission is to study the nature of the densest matter in the Universe, found in the cores of neutron stars.  NICER uses Pulse Profile Modeling, where we use relativistic effects on X-rays emitted from the hot magnetic polar

The high-mass X-ray binary system Cygnus X-1 contains one of the first known and best-studied black holes. We recently refined the distance to this important source using astrometric very long baseline interferometry observations. The new distance implied that the masses of the two binary components both needed to be revised upwards, with our modelling showing

A modeler’s approach to visible (and, indeed, also dark) matter in the Universe is to think of it as a fluid, write some version of (magneto)hydrodynamical equations for its density, velocity and temperature, code them up and model away. By and large, this has given us a successful (at least visually) description of many astrophysical

Stellar activity is one of the main limiting factors for exoplanet surveys using the transit and radial velocity (RV) methods. It induces variations in the light and RV curves that can completely overwhelm planetary signals, particularly for young planets orbiting active stars, and for potentially habitable, Earth-like planets. My group use data-driven methods, particularly Gaussian

Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition; they provide the most stringent tests of general relativity, they make possible the study of faint and rare objects such as black holes and neutron stars, and they are the progenitors of gravitational wave sources. The components of binaries often interact,

The merger of a neutron star with a stellar mass black hole is one of the main sources of gravitational waves detectable by current ground-based observatories (LIGO, Virgo, KAGRA). The first two detections of these mergers were in fact just performed in 2020, with more events expected in future observational runs of LIGO/Virgo/KAGRA. If the

Type Ia supernovae involve the thermonuclear detonation of white dwarf stars, and are one tool allowing us to study the Universe on vast scales. However, violent explosions are not the only byproducts of the mergers of the endpoints of stellar binaries. I will discuss the growing number of observational signposts that can distinguish populations of

The study of compact objects such as black holes and neutron stars is an important component of modern astrophysics. Recent detections of astrophysical neutrinos, gamma-rays, ultrahigh-energy cosmic rays, and gravitational waves open up opportunities to study compact objects with multi-messengers. In this talk, we first review the latest progress in Astroparticle Physics, including some surprising

Supermassive black hole (SMBH) binaries are inevitably produced during galaxy formation, but observational evidence for them remains elusive. I will discuss the coupled dynamics of a SMBH binary with a circumbinary gas disk, and the expected characteristics of electromagnetic (EM) emission from such a system.  In particular, the emission is likely time-variable, and contain unique

The present-day population of supermassive black holes in low-mass galaxies offers a window into massive black hole formation in the early universe. While we cannot yet observe the formation of “black hole seeds” at high redshift, the fraction of small galaxies that host a supermassive black hole — and the properties of those black holes

The past 25 years have revealed a diversity of exoplanets far beyond what was imagined from the limited sample in the Solar System. With new and upcoming observing facilities and a rapidly growing number of nearby planets, we are poised to bring this diversity into focus, with detailed follow-up characterization of the planets’ atmospheres. In

The majority of the baryons in galaxies are inferred to comprise the circumgalactic medium (CGM) – gas that is mostly in either a cool (~10^4K) or a hot (10^5-10^6 K) phase. The former has been studied with QSO absorption line studies and the latter using X-ray observations. The observational picture, however, is unsatisfactory because of

Since the detection of the first gravitational wave transient in 2015 there has been a small revolution in our understanding of the mass distribution of black holes. But there are still many unknowns and theory is still struggling to understand how the observed distribution is determined. There are also other windows onto black holes that

Galaxy clusters are the most powerful gravitational lenses in the known Universe. Near the lensing caustics they host some of the most dramatically magnified extragalactic sources ever detected, including extremely magnified individual super-luminous stars, and compact super star clusters. These are systems where small-scale lens substructures strongly couple to the effects from the macroscopic lens

When the universe was merely three billion years old, about half of massive galaxies had already formed the bulk of their stars and new star formation plummeted. How these ‘red and dead’ (quiescent) galaxies quench at such early times remains a puzzle, as their dark matter halos contain large gas reservoirs. This gas should cool

Transmission spectroscopy of transiting exoplanets provides our best opportunity to identify the makeup of planetary atmospheres in the coming decade. However, stellar surface brightness inhomogeneities due to features such as star spots, can impact these measurements and contaminate the observed spectra. I will present the Pandora SmallSat mission that is designed to disentangle star and

In 2019 the Event Horizon Telescope (EHT) collaboration published the first direct image of a black hole shadow. This result signaled the arrival of event horizon scale observations that will allow us to test our knowledge of gravity and plasma physics around compact objects. Although the EHT uses unprecedented resolution, only two potential supermassive black

Tidal disruption events (TDEs) are currently discovered in ever increasing numbers by optical transient surveys. Similarly, the eROSITA and planned Einstein Probe X-ray satellites are expected to discover many TDEs in X-rays. TDEs are one of the most direct and promising routes to study otherwise quiescent supermassive black holes (SMBHs), but also stellar-mass BHs through

Machine learning is presenting new opportunities for astrophysics—and all the natural sciences. The standard machine-learning workflow represents a very different epistemology than that of other kinds of scientific methods. How does that impact our results and beliefs about those results? I’ll discuss the different roles for machine learning in astrophysics and discuss them in terms

Optical transit surveys have been extraordinarily fruitful in the detection and characterization of exoplanets orbiting main-sequence stars. While the bulk of a star’s lifetime is spent undergoing core hydrogen fusion, much can be learned about star-planet systems by turning our gaze away from the main sequence. In this talk, I discuss the observational properties of

The observed number of galaxy clusters provides a sensitive probe of the structure of the Universe by measuring the evolution of the halo mass function.  However, already current cluster surveys are systematically limited by uncertainties in the relation between cluster mass and observables (e.g. the number of galaxies, X-ray luminosity, or the imprint on the

From measurements of its remnant radiation (the cosmic microwave background or CMB), we comprehend more about the primordial universe than one might have guessed possible.  Data  from the Planck satellite have been compressed to a set of six parameters describing initial conditions for its evolution.  Meanwhile, measurements of the present-day universe reveal multiple aspects of

The Milky Way’s Galactic Center black hole Sagittarius A* is the closest to us supermassive black hole. It is an ideal candidate to explore near horizon effects, to test alternative theories of gravity, and to learn the mechanics of black hole feeding, accretion, and feedback — forces shaping galaxies and the Universe as a whole. 

Turbulence and magnetized disk winds are agents that can remove angular momentum and facilitate inflow through accretion disks. Initially considered as largely alternate hypotheses for why disks accrete, current theoretical work suggests that they are linked through the net flux – vertical magnetic field that threads the entire disk. Multiple numerical simulations, and more recently observations

We have recently seen a remarkable convergence in our overall understanding of how galaxies in the universe form, through the collapse of gas in dark matter halos, and growth through star formation and merging over cosmic time. However, many of the key physical processes, such as gas dynamics, feedback, and the growth and impact of

Contrary to what their name suggests, black holes are not empty space; they are the most extreme objects in the universe, so powerful that nothing can escape them, not even light. Filled with an exceptional amount of energy, they can easily destroy entire galaxies. The goal of my work is to understand the most massive black

Innovations in sensor technology, software, optical coatings, and mass production can be coupled to allow powerful wide-field imaging telescopes to be constructed unbelievably quickly and relatively inexpensively. The Dragonfly Telephoto Array (Dragonfly for short) is an example of this kind of thinking, and over the past few years it has ignited interest in the low