MIT Astrophysics Colloquia - Fall 2016

Tuesdays at 4:00 PM in the Marlar Lounge, Room 37-252
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar Street, Cambridge, MA
(unless location otherwise noted)
Refreshments are served at 3:45 PM.

Sponsored by
the Astrophysics Division of the MIT Department of Physics and
the MIT Kavli Institute for Astrophysics and Space Research.

Tuesday Sep 13:
A New Era of Compact Objects
Feryal Ozel
University of Arizona
Host: D. Chakrabarty

Abstract: The discovery of many diverse populations of neutron stars and black holes is happening at an accelerating rate. The computational advances in calculating the properties of these compact objects, their multiwavelength observations, and the new avenues of studying them with gravitational waves have led to a new understanding of their formation, evolution, and of the fundamental physics that shapes their characteristics. In this talk, I will describe these parallel advances and show how this multi-faceted approach helps pin down our understanding of the evolution of massive stars, supernova explosions, and coalescing compact objects.

Tuesday Sep 20:
Dissecting the Multiphase Circumgalactic Gas
Hsiao-Wen Chen
University of Chicago
Host: R. Simcoe

Abstract: Tremendous progress has been made over the last decade in our empirical and theoretical understanding of how galaxies form and evolve across cosmic time. In particular, state-of-the-art cosmological simulations can not only match the large-scale statistical properties of galaxies, but they can also successfully reproduce the observed small-scale features. This success shows that the basic theoretical framework for modeling galaxy formation is on the right track. However, it appears that these models have fallen short in matching the empirical properties of diffuse gas, which constitutes 90% of all baryons in the universe, beyond visible galaxy disks and into circumgalactic space. An accurate characterization of the complex physical processes that govern the interactions between star-forming regions and this diffuse circumgalactic medium (CGM) is a critical next step toward a comphrehensive undersetanding of galaxy formation and evolution. I will highlight some of the observational efforts of my group at the University of Chicago to identify the dominant mechanisms which define the CGM properties.

Tuesday Sep 27:
Dark Energy and Cosmic Sound
Daniel Eisenstein
Harvard University
Host: P. Schechter

Abstract: I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature at a variety of redshifts. I will review our recent work on the theory and practice of the acoustic oscillation method, describe our latest cosmology results from SDSS-III on the expansion history of the Universe, and introduce the upcoming Dark Energy Spectroscopic Instrument (DESI) project.

Tuesday Oct 4:
Astrophysics and Exploration from the International Space Station with NASA's NICER Mission
Zaven Arzoumanian
NASA Goddard
Host: TBD

Abstract: Planned for launch in early 2017, NASA's Neutron star Interior Composition Explorer (NICER) is designed to study the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. Their exotic interiors, where density and pressure are higher than in atomic nuclei, harbor a form of ultra-dense matter that exists nowhere else in nature. NICER aims to reveal the fundamental physics of such matter -- a longstanding unsolved problem -- by inferring the masses and radii of neutron stars through high-precision timing and spectroscopy in the soft X-ray band, specifically targeting pulsars with millisecond spin periods. NICER will explore dynamic phenomena, such as thermonuclear explosions and starquakes, driven by accretion, strong gravity, and bulk quantum fluids. NICER will probe the extreme physics of pulsar magnetospheres, perhaps the most powerful cosmic particle accelerators anywhere. These objectives are enabled by an instrument that brings together established technologies in an innovative configuration, exploiting International Space Station infrastructure to offer a low-cost, low-risk, and highly capable instrument to the X-ray astrophysics community. This talk provides an overview of the NICER mission, its core science agenda, and its potential contributions across a range of X-ray astrophysics investigations made possible through a Guest Observer program. Finally, NICER's first-ever demonstration of spacecraft navigation using pulsars as beacons in a "Galactic Positioning System" -- the technology that may one day guide humankind through the Solar System and beyond -- is outlined.

Tuesday Oct 11:

Tuesday Oct 18:
How to Tell When You've Busted CDM
Cole Miller
University of Maryland
Host: S. Hughes

Abstract: Cold dark matter, along with dark energy, constitute 96% of the universe. Calculations using these components have successfully explained many aspects of structure formation, but as is appropriate for such a broad framework there have also been multiple challenges along the way. One recent challenge involves the existence of structure in the satellite galaxy distributions of the Galaxy and M31, such as thin planes with apparent kinematic coherence, which have been claimed to be inconsistent with the results from dark matter simulations. However, these are a posteriori claims: a pattern is seen in data, and then that particular pattern is analyzed for significance, which can easily lead to misleading assessments of improbability. I will discuss different statistical methods to determine more objectively whether observed patterns are consistent with data, and will also discuss planned future work to help compare different models of cold dark matter.

Tuesday Oct 25:
The Standard Model of Cosmology?
Chuck Bennett
Johns Hopkins University
Host: J. Hewitt

Abstract: As cosmological observations accumulated in the 1980s and 1990s a strange model emerged, a hot big bang universe dominated by nonbaryonic dark matter and an unexpected dark energy driving an accelerated expansion of the universe. Epic advances in measurement accuracy and precision in the decade of the 2000s put this model to an enormously rigorous test leaving us with a Standard Model of Cosmology: the LCDM model with 6 well-specified parameters. New measurements from just the past 3 years now raise the question, do we still have a standard model of cosmology: a LCDM model with 6 well-specified parameters? In this talk I will examine recent results of supernovae measurements of the Hubble Constant, measurements of baryon acoustic oscillations, and multiple measurements of the cosmic microwave background in the context of the LCDM model. I will also discuss some next experimental steps in observational cosmology.

Tuesday Nov 1:
Observations of Quasar Feedback
Nadia Zakamska
Johns Hopkins University
Host: P. Schechter

Abstract: Quasars are now thought to have made critical impact on galaxy formation. Feedback from accretion onto supermassive black holes is implicated in establishing the black hole mass vs galaxy bulge correlations and in limiting the maximal mass of galaxies. In this talk, I will review the indirect evidence for quasar feedback as required by galaxy formation models. I will then present recent multi-wavelength observations of powerful quasar-driven winds and outflows on galaxy-wide scales. These data may provide direct observational evidence for one of the long-standing paradigms in galaxy formation.

Tuesday Nov 8:
Hidden Monsters: The Cosmic Evolution of Supermassive Black Holes
Ryan Hickox
Dartmouth College
Host: M. McDonald

Abstract: In the past decade, extragalactic surveys and active galactic nucleus (AGN) synthesis models have made great progress in understanding the cosmic growth of supermassive black holes. However, our picture of black hole evolution has remained incomplete, due to the challenges of detecting AGN that are highly obscured or hidden beneath the light of their host galaxies. With the advent of new resources including hard X-ray observations from NuSTAR, mid-infrared data from WISE, and new insights from theoretical models, we can now identify millions of these “ hidden” AGN across much the sky, and characterize the nature of their obscuration and their role in the formation of galaxies. I will describe recent efforts to characterize the host galaxies, dark matter halos, and level of obscuration in these "hidden” AGN, and will present evidence that (at least some) powerful obscured quasars represent an evolutionary phase in the evolution of their host galaxies, as predicted by models of galaxy formation. Finally, I will point to the exciting potential for future of AGN population studies with the next generation of extragalactic surveys.

Tuesday Nov 15:
A Galactic Scale Gravitational Wave Observatory
Maura McLaughlin
West Virginia University
Host: S. Hughes

Abstract: Pulsars are rapidly rotating neutron stars with phenomenal rotational stability that can be used as celestial clocks in a variety of fundamental physics experiments. One of these experiments involves using an array of precisely timed millisecond pulsars to detect perturbations due to gravitational waves. The gravitational waves detectable through pulsar timing will most likely result from an ensemble of supermassive black hole binaries. I will describe the efforts of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration which monitors an array of over 50 millisecond pulsars with the Green Bank Telescope and Arecibo Observatory. The most recent limits on various types of gravitational wave sources will be presented, and I will show how these limits are already constraining models for galaxy formation and evolution. I will then describe the dramatic gains in sensitivity that are expected from discoveries of millisecond pulsars, more sensitive instrumentation, improved detection algorithms, and international collaboration and show that detection is possible before the end of the decade.

Tuesday Nov 22:
Frontiers in Massive Stellar Death
Sean Couch
Michigan State University
Host: McDonald

Abstract: Core-collapse supernovae are the luminous explosions that herald the death of massive stars. While core-collapse supernovae are observed on a daily basis in nature, the details of the mechanism that reverses stellar collapse and drives these explosions remain unclear. While the most recent high-fidelity simulations show promise at explaining the explosion mechanism, there remains tension between theory and observation. I will discuss the recent developments in the study of the supernova mechanism that could lead to a predictive theory of massive stellar death. In particular, I will describe our efforts to develop more realistic initial conditions for supernova simulations with fully 3D massive stellar evolution calculations. Such realistic 3D initial conditions turn out to be favorable for successful explosions, in large part because they result in stronger turbulence behind the stalled supernova shock. I will also discuss the important role turbulence is playing in the supernova mechanism and what might be required for accurately modeling the turbulence in our simulations. I will also mention recent work aimed at explaining the origin of pre-supernova outbursts from massive stars in the months and years prior to core collapse and explosion.

Tuesday Nov 29:
Turbulence in the Intracluster Medium
Irina Zhuravleva
Stanford University
Host: M. Bautz

Abstract: Intracluster medium (ICM) is filled with hot and dilute gas. Global thermodynamic properties of this gas are now routinely measured from Chandra and XMM-Newton data. However, our understanding of gas motions is very limited mainly due to insufficient spectral resolution of current X-ray observatories. This limits our ability to probe important physical process in the ICM such as, e.g., heating of the gas, biases in hydrostatic mass measurements, mechanisms of particle acceleration and the origin of radio halos. I will show how we can overcome the problem of limited spectral resolution and measure the velocities of gas motions through high-resolution X-ray images of galaxy clusters. I will discuss the effective equation of state of gas fluctuations in the ICM, the measurements of velocity power spectra on a broad range of spatial scales and the role of turbulent dissipation in mechanical radio-mode AGN feedback. Finally, I will overview first direct velocity measurements with the Hitomi observatory and discuss their consistency with other indirect velocity probes.

Tuesday Dec 6:
Joint MKI/EAPS Colloquium: The Fastest Road to Finding Life Beyond Earth
Jonathan Lunine
Cornell University
Co-Hosts: R. Binzel, J. Soderblom

Abstract: Four bodies beyond Earth have environments that might support or have supported life, and of these, the most dynamic, isolated and Earth-like is the ocean of Enceladus. The steps to detecting biological activity within Enceladus are rendered easier by the presence of a plume of ice and vapor emanating from its south pole. By exploring the plume with a modest, affordable payload, we might know within a generation whether our solar system supported the genesis of life twice.

Tuesday Dec 13:
The Evolution of Exoplanets Orbiting Low-mass Stars
Philip Muirhead
Boston University
Host: E. Newton

Abstract: Low-mass stars dominate stellar populations, and recent results from NASA's Kepler Mission suggest rocky planets are abundant around low-mass stars. With so many planets orbiting low-mass stars, exoplanet scientists can now turn to questions about their history and evolution. Unfortunately, measuring fundamental properties of low-mass stars is challenging for a variety of reasons. I will discuss the importance of near-infrared spectroscopy in this effort, presenting results from the TripleSpec spectrograph at Palomar Observatory and a new design for a high-resolution spectrograph on the Discovery Channel Telescope at Lowell Observatory. With near-infrared spectroscopy, we can measure detailed fundamental properties of low-mass stars, and with new techniques to measure stellar alpha and iron abundances, we can begin to measure the most challenging fundamental property: stellar age. These efforts are even more exciting in the coming years, when the TESS spacecraft is expected to discover five times as many planets orbiting low-mass stars as Kepler.

This page is maintained by Michael McDonald