Past Seminars

MSI Faculty Jamboree

MSI Faculty

McGill Space Institute
Sep 12, 2017

MSI Seminar
Bell Room

Learn about the diversity of research that goes on at the McGill Space Institute.

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Observing the Dynamics of Accretion Disks Around Supermassive Black Holes in Quasars

Mike Eracleous

The Pennsylvania State University
Sep 20, 2017

Astrophysics Seminar
Board Room (ERP 105)

The broad emission lines found in the spectra of quasars are a hallmark and defining characteristic of this class of astronomical object. They are thought to originate in dense (by astrophysical standards) gas that is in close proximity to the central supermassive black hole. The profiles of these lines and their time variability are now used as tools for a variety of applications. Examples include estimating black holes masses, probing the dynamics of the accretion flow, and searching for binary supermassive black holes. The utility of the broad lines as tools depends on our understanding of the structure of the gaseous medium that emits them, the "broad-line region." In this talk I will begin by summarizing what we know about the broad-line region and introduce some of the physical models that have been devised to describe it. I will then talk about projects that my collaborators and I have been carrying out in which we make use of the long-term variability of the broad emission lines. In one of these projects we exploit the variability of the line profiles on time scales of several years to probe the dynamics of the accretion disk that feeds the supermassive black hole. Through these studies we are arriving at a picture in which the accretion disk is massive and self-gravitating.

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Fade to Black: The Origin and Utility of Changing-Look Quasars

John Ruan

McGill Space Institute
Sep 26, 2017

MSI Seminar
MSI Conference Room

The proliferation of wide-field multi-epoch imaging surveys has now opened a new window to the time-domain for discovery of new and rare time-variable phenomena. From these surveys, the recent discovery of ‘changing-look’ quasars poses potential challenges to our understanding of accretion onto supermassive black holes. In this phenomenon, luminous quasars suddenly fade into quiescent galaxies over timescales of just a few years, a factor of 10000 faster than expected. I will examine different explanations for the origin of changing-look quasars, and discuss their incredible usefulness in probing accretion physics, supermassive black hole feedback, and galaxy evolution over cosmic time.

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MSI and Trottier Fellows Research Showcase

MSI and Trottier Fellows Research Showcase

McGill
Sep 28, 2017

MSI Seminar
Bell Room

Short presentations by students & postdoctoral fellows doing space-related research, supported by the Trottier Family Foundation

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Using High-Mass X-ray Binaries to Probe Massive Binary Evolution

Kristen Garofali

University of Washington
Oct 3, 2017

Astrophysics Seminar
Bell Room

High-mass X-ray binaries (HMXBs) provide an exciting window into the underlying processes of both binary as well as massive star evolution. Because HMXBs are systems containing a compact object accreting from a high-mass star at close orbital separations they are also likely progenitors of gamma-ray bursts and gravitational wave sources. I will present work on the classification and age measurements of HMXBs in M33 using a combination of deep Chandra X-ray imaging, and archival Hubble Space Telescope data. I am able to constrain the ages of the HMXB candidates by fitting the color-magnitude diagrams of the surrounding stars, which yield the star formation histories of the surrounding region. Unlike the age distributions measured for HMXB populations in the Magellenic Clouds, the age distribution for the HMXB population in M33 contains a number of extremely young (<5 Myr) sources, including M33 X-7, an eclipsing binary composed of a ~15 Msun black hole accreting from a 70 Msun O star companion. I will discuss these new results for M33 in the context of the effect of host galaxy properties on the observed HMXB population.

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Pushing Down and Out: Characterizing hot Jupiters in detail and expanding into new regimes

Emily Rauscher

University of Michigan
Oct 10, 2017

MSI Seminar
MSI Conference Room

We can characterize exoplanets by measuring their global, orbital, and atmospheric properties, through a variety of different observational methods. The first exoplanet discovery, the first detection of an exoplanet's atmosphere, and the vast majority of characterization measurements have all been of hot Jupiters, gas giants that orbit with about 0.1 AU of their host star. These planets are the biggest and brightest of the transiting exoplanets, making them the best targets for characterization measurements, although much work is being done to push to smaller and farther out planets. I will show that, even though we have been studying them the longest, hot Jupiters still show us mysterious properties, such as the presence of some kind of aerosol(s) in the atmospheres of some planets (but not all). I will present three-dimensional models that include a treatment for clouds or hazes, as part of our work toward understanding aerosols in this extreme regime. I will demonstrate that we can make progress in better characterizing these worlds through cutting-edge methods such as high-resolution spectroscopy, which contains detailed information about a planet's multi-dimensional temperature and wind structure, and enables us to constrain wind speeds, rotation rates, and temperature gradients. Finally, I will also demonstrate that in the upcoming JWST era we will be able to make exquisite observations beyond the hot Jupiter population, for example using secondary eclipse mapping to resolve two-dimensional images of planets on longer orbital periods, and I will discuss some of the scientific implications of these future results.

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MULTI-MESSENGER MONSTERS!

Sarah Burke-Spolaor

West Virginia University
Oct 17, 2017

Astrophysics Seminar
Bell Room

We are seeking both light and gravitational waves from binary supermassive black holes, the biggest, meanest discrete binary systems in the Universe. When two supermassive binary black holes pair up as a binary at the center of a merger remnant, they may ignite as active nuclei and send off unique electromagnetic signatures as they consume the ambient matter from the remnant's core. During their inspiral and coalescence phases, they will produce intense gravitational radiation, which we expect to detect with Pulsar Timing Arrays in the coming ~decade. If the inspiral of black holes is isolated and smooth, we should by now have already detected nanohertz-frequency gravitational waves with pulsar timing arrays... or so we thought. This talk will discuss what our latest, most stringent limits on gravitational waves mean for galaxy evolution and supermassive binary black holes. It will also show a few results from several ongoing searches for binary supermassive black holes, and will consider the prospects of Pulsar Timing Arrays to detect or place physically interesting gravitational wave limits on these targets.

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High-energy X-rays from the Galactic Center: "zombie stars" and particle physics

Kerstin Perez

Massachusetts Institute of Technology
Oct 24, 2017

Astrophysics Seminar
Bell Room

The inner parsecs of the Galaxy contain one of the highest concentrations of both high-energy sources and dark matter in the Milky Way. The supermassive black hole, pulsar wind nebulae, supernova remnants, X-ray binaries, and hot interstellar gas are copious emitters of X-rays and gamma-rays. In addition, this region contains a large density of dark matter, making it an important source of both dark matter interaction signatures and backgrounds to dark matter searches. NuSTAR provides a view of the hard X-ray (3-79 keV) band, a critical bridge between the soft X-ray and gamma-ray emission, with unprecedented angular resolution. I will present the first sub-parsec scale images of the Galactic Center in hard X-rays, obtained with NuSTAR, which offer leading constraints on the radiative decay of dark matter, in particular from sterile neutrinos, as well as new insight into the “zombie star” population that underlies this emission.

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Strong field tests of gravity with PSR J1141-6545

Vivek V. Krishnan

Swinburne University
Oct 25, 2017

Special Astrophysics Seminar
MSI Conference Room

Pulsars in relativistic binary systems provide the most stringent tests of gravity to date in the strong field regime. While pulsars such as the double neutron star system (B1913+16) and the double pulsar (J0737-3039A/B) provide significant tests for the predictions of the General Theory of Relativity (GR), their gravitational symmetry makes them less sensitive to testing the predictions of alternative theories of gravity such as scalar-tensor theories. Such theories are natural extensions of GR that deviate strongly from GR in the strong-field regime, especially in the predictions of multipolar contributions to the gravitational radiation losses in the system. Pulsars in gravitationally asymmetric binaries, such as pulsars with white dwarf or black hole companions, are better-suited systems for testing such theories. PSR J1141-6545 is one such pulsar in a 4.8-hour relativistic orbit around a white dwarf companion. In this talk, I will talk about the 17-year timing campaign of this pulsar and the test of GR and scalar-tensor theories with this pulsar.

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Autonomous and robotic observations of the Arctic sea ice and the associated ecosystem

Christian Katlein

Alfred Wegener Institute
Oct 31, 2017

MSI Seminar
MSI Conference Room

To better observe the ongoing changes in the polar climate- and ice-associated ecosystem, the Alfred-Wegener-Institute is developing new technologies for ice-tethered observations in the framework of the Helmholtz initiative “FRontiers in Arctic marine Monitoring (FRAM)”. This includes the development and regular deployment of a new versatile remotely operated vehicle (ROV) for interdisciplinary observations under sea ice as well as the development of autonomous drifting observatories enabling the continuous monitoring of various physical and biogeochemical parameters in the sea ice and upper ocean. These platforms allow us to assess current changes, such as increasing light transmission through sea-ice, changing primary production and the polar carbon pump.

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Doors left ajar in storms: Insights into atmospheric planetary science

John Moores

York University
Nov 7, 2017

MSI Seminar
MSI Conference Room

Our spacecraft have taken us to visit and explore many stark and ancient landscapes in the solar system. At first glance, very little appears to have changed for billions of years, but if we look to the atmosphere we see a dynamism that belies active processes in the present era and that hints at changes at and below the surface. In this talk, we will proceed through these open doors to explore the movement of dust, ice and methane in the hauntingly familiar environment of Mars. We will then travel further to more exotic planetary destinations including Titan, Pluto and Venus. Past results will be discussed along with future developments to explore the atmospheres of our solar system and beyond.

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Our Crowded X-ray Galactic Center

Mel Nynka

McGill Space Institute
Nov 14, 2017

Astrophysics Seminar
Bell Room

The era of X-ray astronomy issued a new understanding of astrophysical processes by observing the high-energy universe. Focusing X-ray telescopes in particular allowed an unprecedented view into previously obscured or undetected objects. The Galactic Center in particular is a complex, crowded region with many interconnected and overlapping astrophysical objects. I will discuss how we can use X-ray observatories, along with complementary multi-wavelength data, to study GC sources such as Sgr A*, nearby supernovae, and X-ray transients, and in turn shed light on the structure and evolution of the Galactic Center.

Gravitational-Wave Discoveries Driving the Promise of Multi-Messenger Astronomy

Vassiliki Kalogera

Northwestern University
Nov 21, 2017

MSI Seminar
Bell Room

The LIGO detectors have opened for us a new way of studying compact objects in the time domain with direct detections of gravitational-wave bursts from binary mergers of compact objects. I will highlight what current results imply and what we can look forward to in terms of advancing our understanding of the densest objects in nature, their origins and the explosive phenomena they cause.

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Setting Stellar Chronometers: The PTF(+) Open Cluster Survey

Marcel Agueros

Columbia University
Nov 28, 2017

Astrophysics Seminar
Bell Room

While we have known for 40 years of the existence of a relation between a solar-mass star's age, rotation, and magnetic activity, observational limitations have hampered the assembly of uniform samples of rotation and activity measurements for stars spanning a wide range of ages and masses. We are still far from being able to describe fully the evolution of either rotation or activity for low-mass stars, or from being able to use rotation or activity measurements to estimate accurately the ages of isolated field stars. I will describe results from our efforts to assemble a complete sample of rotation and activity measurements for low-mass stars in six nearby open clusters ranging in age from ~100 Myr to ~3 Gyr. I will focus on our recent results for the benchmark clusters Praesepe and the Hyades, on new results for NGC 752, and on tests of models of rotational evolution that these data have enabled.

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Astromaterials in Accreting Neutron Stars

Matthew Caplan

McGill Space Institute
Jan 9, 2018

MSI Seminar
MSI Conference Room

Stars freeze. As they age and cool white dwarfs and neutron stars crystallize, with remarkable materials forming in their interiors. These 'astromaterials' have structures similar to terrestrial crystalline solids and liquid crystals, though they are over a trillion times denser. Notably, because their material properties affect the observable properties of the star, astromaterials must be understood to interpret observations of neutron stars. Thus, astromaterial science can be thought of as an interdisciplinary field, using techniques from material science to study nuclear physics systems with astrophysical relevance. In this talk, I will discuss recent results from simulations of astromaterials and how we use these results to interpret observations of neutron stars in X-ray binaries.

Observational Properties of Simulated Galaxies: Computational Cosmology as Seen through a Telescope

Connor Bottrell

Connor Bottrell
Jan 17, 2018

Special Astrophysics Seminar
MSI Conference Room

The most recent generations of large-volume cosmological hydrodynamical simulations are valuable instruments for understanding the formation and evolution of galaxies. However, the crux of the interpretive power for such simulations is fundamentally in whether they can reproduce the observed properties of galaxies. Furthermore, it is crucial that any comparison between simulated and real galaxies is fair. To facilitate a valid comparison, simulated galaxies must adopt the observational biases that affect galaxies seen in the real Universe. I put galaxies from the Illustris simulation directly in the context of observational galaxy astronomy using an unprecedentedly rigorous suite of observational realism in the Sloan Digital Sky Survey (SDSS). Parametric photometry and structural analysis of simulated galaxies with observational realism are performed using the same pipeline that was used in the analysis of 1.12 million real galaxies in the SDSS — which collectively forms the comparison sample. In this talk, I will discuss promising similarities along with intriguing contrasts between real and simulated galaxy populations. With major Intregral Field Spectroscopic surveys such as SAMI and MaNGA defining new frontiers in observational galaxy astronomy, the completeness with which simulated galaxies may be benchmarked against observations has never been better.

Cosmology Large Angular Scale Surveyor (CLASS)

Katie Harrington

John Hopkins
Jan 18, 2018

Special Astrophysics Seminar
MSI conference room

The Cosmology Large Angular Scale Surveyor (CLASS) is a four telescope array designed to detect and characterize relic primordial gravitational waves from inflation and the optical depth to reionization through a measurement of the polarized cosmic microwave background (CMB) on large angular scales. The frequency bands of the CLASS telescopes, one at 40 GHz, two at 90 GHz, and one dichroic system at 150/220 GHz, are chosen to avoid regions of high atmospheric emission and span the minimum of the polarized galactic foregrounds: synchrotron emission at lower frequencies and polarized dust emission and higher frequencies. Low noise transition edge sensor detectors and a rapid front-end polarization modulator provide a unique level of high sensitivity, stability, and control of systematics. The CLASS site, at high altitude in the Chilean Atacama desert, allows for daily mapping of up to 70% of the sky and enables the observation of the largest angular scales. Using this combination of a broad frequency range, large sky coverage, control over systematics, and high sensitivity, CLASS will observe the reionization and recombination peaks of the CMB E- and B-mode power spectra. CLASS will make a cosmic variance limited measurement of the optical depth to reionization and will measure or place upper limits on the tensor-to-scalar ratio, r, down to a level of 0.01 (95% C.L.).

Juno’s first year at Jupiter

Yohai Kaspi

Weizmann Institute of Science
Jan 23, 2018

MSI Seminar
MSI Conference Room

The Juno spacecraft has been in orbit around Jupiter since July 2016. In this talk we will review the mission and the preliminary results from its first year. Particularly we will focus on the Juno gravity experiment, which has revealed the depth and vertical structure of Jupiter’s atmospheric dynamics and interior flows.

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Cancelled : Meteorites: time capsules of the formation of the Solar System and planets

Audrey Bouvier

University of Western Ontario
Jan 23, 2018

MSI Seminar
MSI Conference Room

Note that this talk has been cancelled since the speaker is unavailable. It will be rescheduled. Planetary formation and evolution during the first 500 millions years of the Solar System’s history can be deciphered through the study of meteorites and samples returned from space missions as well as from remote observations. By studying meteorites, we have found evidence that several short-lived radiogenic isotopes were present initially in the early Solar System and are now extinct. Some of them like 26-Al contributed to the internal heating of planetesimals and hence their ability to melt as well as setting their budgets in volatile elements delivered to planets. Other refractory elements can be used as tracers for the building blocks, late accretion, and constraining the timing of volatile element delivery within the terrestrial planets. I will talk about our current knowledge of the nucleosynthetic heritage of the Solar System, how we can use isotopes as tracers and chronometers of planetary formation, and how major planetary impact events have influenced the evolution of our planet and set the geological conditions for life to develop.

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Status Report on Observational 21cm Cosmology

Lincoln Greenhill

Harvard/SAO/CfA
Jan 30, 2018

Astrophysics Seminar
Bell Room

Characterization of baryonic and dark matter structure in the intergalactic medium during the Epoch of Reionization (z~10) and the "pre-galactic" medium during Cosmic Dawn (z=20-30) is a frontier cosmological challenge. There is little data that directly constrains theory. I will review several early milestones in attempts to detect HI emission and absorption at these redshifts, focusing on the LEDA and EDGES projects that target the zero-mode at z~20, and the proposed EOS Array project that would be dedicated to detection of high-order modes during Cosmic Dawn.

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The Molecular Origins of Life

Maikel Rheinstädter

McMaster University
Feb 6, 2018

MSI Seminar
MSI Conference Room

A fundamental question of science is how nucleic acids first assembled and then were incorporated into the earliest forms of cellular life 3.5 – 4 billion years ago. However, in the absence of enzymes and metabolism there has been no obvious way for RNA-like molecules to be produced and then encapsulated in cellular compartments, an essential first step in the origin of cellular life. The question of life’s origin has also recently become of critical practical importance in light of the intense scientific effort that is being invested in the search for life elsewhere in our Solar System and beyond, and with NASA’s recent ground-breaking discovery of 3 habitable Earth like planets. The new, CFI funded Origins of Life Laboratory at McMaster University will test and challenge the hypothesis of how RNA could have formed under prebiotic conditions similar to the early Earth, Mars and other newly discovered Earth-like planets. The lab enables a comprehensive research program, from the preparation and advanced characterization of nucleic acid samples to the quantitative determination of RNA products and molecular structure determination and computer simulations. At the heart of the laboratory is a planetary simulation chamber to model early planetary environments (atmospheric gases, planetary materials, temperatures, pressures, humidity, irradiation) and enable fast and controlled cycling of these parameters. I will talk about the design and capabilities of this new facility and present first results how nucleotides organize in different environments and form RNA-like polymers.

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Obscured and reddened quasars at the peak of galaxy formation: searching for multi-scale quasar winds

Rachael Alexandroff

Dunlap/CITA
Feb 13, 2018

Astrophysics Seminar
Bell Room

Black holes of masses one million to one billion times that of the sun are now believed to reside at the centers of almost all massive galaxies in the universe including our own Milky Way. Though small on the scale of a galaxy and negligible for the overall galaxy dynamics, these supermassive black holes are now thought to play a crucial role in the evolution of their host galaxy. Feedback from the actively accreting supermassive black hole or ‘quasar’, in the form of galaxy-scale winds, is necessary to shut-off star formation and thus inhibit the growth of very massive galaxies and to drive correlations between black hole and galaxy properties. Nevertheless, such a mechanism is not yet well supported by observational evidence, especially at the peak of galaxy formation (z~2.5). I will present new multi-wavelength results from a sample of quasars at the peak of galaxy formation and black hole growth that may represent the “blowout phase” of AGN evolution where we see quasar feedback in action. The combination of various observational techniques allows us to probe, if indirectly, scales from the broad-line region all the way to the entire host galaxy and to understand the nature of the multi-component outflow (both ionized and molecular components). In particular, Keck spectropolarimetry results argue for the presence of dusty outflows on scales of the emission line region while near-infrared spectroscopy reveals some of the most extreme ionized gas velocities observed (> 5000 km/s), indicating wind speeds too large to be contained by the galaxy potential. Finally, a dearth of CO (1-0) emission as traced by the Very Large Array indicates the molecular gas necessary for star formation may have been removed from the host galaxy. Taken together, these results provide a robust observational window into important mechanisms of galaxy growth and quenching via quasar feedback.

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What are the thousands of X-ray emitting point sources in the center of the Milky Way?

Kaya Mori

Columbia University
Feb 20, 2018

MSI Seminar
MSI Conference Room

The Nuclear Spectroscopic Telescope Array (NuSTAR), carrying the first focusing telescopes capable of making sub-arcminute resolution images above 10 keV, conducted a deep survey of the Galactic Center region. One of our primary goals was to identify the origin of the ~9,000 unidentified X-ray sources detected by Chandra in the central ~100 pc of our Galaxy. As a result, NuSTAR discovered the diffuse, central hard X-ray emission (CHXE) over a ~10 pc region centered on the supermassive black hole Sgr A* and detected 70 hard X-ray sources above 10 keV. The CHXE and most of the NuSTAR point sources were attributed to a class of highly magnetized white dwarf binaries called intermediate polars. Their hard X-ray emission (kT ~ 30 keV), in contrast to the softer X-ray emission (kT ~ 15 keV) in the Galactic Ridge detected by Suzaku and INTEGRAL, suggests distinct X-ray source populations between the Galactic Center and Ridge. In the central parsec, NuSTAR detected four X-ray transients including a new magnetar SGR J1745-2900. Our NuSTAR spectral and timing analysis of two new Swift-discovered X-ray transients in 2016 suggests they were outbursting black hole binaries. In addition to an overabundance of transient X-ray binaries observed by Swift and NuSTAR, I present a remarkable cluster of quiescent X-ray binaries in the central parsec, identified with Chandra, and whose properties, numbers and distribution indicate the presence of the long-sought black hole cusp. Throughout my talk, I will present our current understanding of the X-ray source populations in the Galactic Center based on the recent results from NuSTAR, Chandra and other X-ray telescopes.

Winds of Change Around Black Holes

Greg Sivakoff

University of Alberta
Feb 27, 2018

Astrophysics Seminar
Bell Room

Accretion disks, where matter with angular momentum spirals down through a disk, occur around objects ranging from the youngest stars to supermassive black holes. But not all of this material reaches the center of the disk. Instead, some material is accelerated away from the disk. These outflows can be ejected in a narrow opening angle (what astronomers call "jets") or can be relatively unfocused (what astronomers call “winds”). While we do not know the precise processes that accelerate and collimate winds and jets, magnetic fields almost certainly play a key role. My team and I study black hole X-ray binaries, stellar-mass black holes accreting from a nearby star. We combine observations across the electromagnetic spectrum to learn about the physics of accretion and jets. In this talk, I will discuss how we have revealed two new windows onto the physics of inflows and outflows in X-ray binaries: fast variability measured across the electromagnetic spectrum (which provides the potential to accurately identify the accretion physics that launch relativistic jets) and the modelling of changes in the X-ray brightness of black hole X-ray binaries (which implies that strong winds from the accretion disk are universal). With the advent of new and upcoming facilities, we have a huge potential to take advantage of these winds of change in the next decade.

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Robots Under the Ice, and One Day, In Space?

Britney Schmidt

Georgia Tech
Mar 13, 2018

MSI Seminar
MSI Conference Room

Europa is one of the most enticing targets in the search for life beyond Earth. With an icy outer shell hiding a global ocean, Europa exists in a dynamic environment where immense tides from Jupiter potentially power an active deeper interior and intense radiation and impacts bathe the top of the ice, providing sources of energy that could sustain a biosphere. Europa’s icy plate tectonics, and evidence for shallow water within the ice, implies that rapid ice shell recycling could create a conveyor belt between the ice and ocean, allowing ocean material to one day be detected by spacecraft. Beneath ice shelves on Earth, processes such as accretion, melt and circulation mediate the ice as an important element of the climate system. Here, ice-ocean exchange may be similar to that on Europa, but is difficult to observe given the harsh environment and thickness of the ice. Thus exploring the cryosphere can form the foundation of our understanding of other ocean worlds and a test bed for their exploration. In this presentation, we will explore environments on Europa and their analogs here on Earth.  NASA will launch the Europa Clipper Mission in 2021, but while we wait to get there, we are looking to our own cosmic backyard to help us to better understand this enigmatic moon.  I will describe our work on the McMurdo and Ross Ice Shelves under our 2017-2020 field program, RISE UP, using the Georgia Tech built under ice AUV/ROV Icefin. Using this new robotic capability, we are working to gather unique new data relevant to climate and planetary science, and develop techniques for exploring Europa, an ice covered world not so unlike our own.

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Modelling Superfluid Neutron Stars

Vanessa Graber

McGill Space Institute
Mar 20, 2018

Astrophysics Seminar
Bell Room

Neutron stars unite many extremes of physics and can serve as astrophysical laboratories that allow us to probe states of matter at densities which cannot be reached on Earth. One exciting example is the presence of superfluid and superconducting components in mature neutron stars. When developing mathematical models to describe these large-scale quantum condensates, physicists tend to focus on the interface between astrophysics and nuclear physics. Connections with low-temperature experiments are generally ignored, although there has been significant progress in understanding laboratory condensates. In this talk, I will highlight the connection between laboratory superfluids and neutron stars, suggesting several novel ways that we could make progress in understanding astrophysics using low-temperature laboratory experiments. I will specifically focus on the concept of mutual friction and present new results on how it influences the neutron star dynamics, in particular the initial response following a glitch.

Hazes and Clouds in Cold and Hot Planetary Atmospheres

Xi Zhang

UC Santa Cruz
Mar 27, 2018

MSI Seminar
MSI Conference Room

Hazes and clouds are ubiquitous in all substantial atmospheres in the outer solar system. Abundant condensed particles are also inferred from the transmission observations in the warm and hot (500-2200 K) atmospheres of exoplanets which are hundreds to thousands of degrees warmer than the solar system planets. These exotic clouds could result from condensation of salts, silicates and metals, and/or hydrocarbons produced by atmospheric chemistry upon UV radiation. In this presentation, I will first talk about the thin, cold and hazy atmospheres in the outer solar system such as on Saturn’s moon Titan, Neptune’s moon Triton, and Pluto. I will present how these atmospheres regulate themselves such that the chemical-produced hydrocarbon haze particles significantly dominate the radiative energy balance over the gas volatiles. In particular, the haze particles could explain the colder-than-expected temperature on Pluto observed by the New Horizons mission. Then I will talk about the thick, hot and cloudy atmospheres of hot Jupiters and brown dwarfs. I will show how to form clouds of salts, silicates and metals in this regime, highlighting the important physical processes such as seed formation, nucleation, condensation, gravitational settling as well as atmospheric particle transport. I will also emphasize the importance of particle size distribution on interpreting the transmission spectra of exoplanets and how to predict it from first principles in a self-consistent microphysical cloud formation model.

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Direct Imaging of Extrasolar Planets

Bruce Macintosh

Stanford University
Apr 3, 2018

Astrophysics Seminar
Bell Room

Thousands of extrasolar planets and candidates have now been detected, but almost all through indirect methods, such as transit photometry or radial velocity. Though statistically powerful, these techniques provide in most cases just a basic measurement of an object’s size and orbital parameters, and are biased towards small separations. Direct imaging, by contrast, is most sensitive to planets in wide orbits (>5 AU); and if a planet’s light can be seen, it can be characterized spectroscopically. Currently this is only practical for young (below a few hundred million years) self-luminous massive (>1 Jupiter mass) planets. Although this has been done for only a dozen systems, each provides insights into the atmospheric structure and evolutionary history of such systems. This sample is expanding with new facilities such as the Gemini Planet Imager (GPI), a dedicated high-contrast adaptive optics instrument on the Gemini South telescope. Reaching contrast levels of 10-6 , GPI has reported its first planet discovery, 51 Eridani b, in 2015. This planet is sufficiently young, low-mass, and cool that it displays strong atmospheric methane features, and its luminosity likely retains the memory of its formation. I will discuss GPI, the discovery of 51 Eri b, its properties, and the emerging statistical picture of the frequency of wide-orbit planets. I will also briefly discuss future prospects for facilities such as WFIRST, HABEX, LUVOIR, and TMT, and the ultimate path to direct imaging of Earthlike planets.

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Formation of the lunar fossil bulges and its implication for the early Earth and Moon

Shijie Zhong

University of Colorado Boulder
Apr 10, 2018

MSI Seminar
MSI Conference Room

First recognized by Laplace over two centuries ago, the Moon’s present tidal-rotational bulges are significantly larger than hydrostatic predictions. They are likely relics of a former hydrostatic state when the Moon was closer to the Earth and had larger bulges, and they were established when stresses in a thickening lunar lithosphere could maintain the bulges against hydrostatic adjustment. We formulate the first dynamically self-consistent model of this process and show that bulge formation is controlled by the relative timing of lithosphere thickening and lunar orbit recession. Viable solutions indicate that lunar bulge formation was a geologically slow process lasting several hundred million years, that the process was complete about 4 Ga when the Moon-Earth distance was less than ~32 Earth radii, and that the Earth in Hadean was significantly less dissipative to lunar tides than during the last 4 Gyr, possibly implying a frozen hydrosphere due to the fainter young Sun.

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