MIT Astrophysics Colloquia

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 11 September :
Multi-Messenger EM-GW Astronomy: The View from the Radio End of the Electromagnetic Spectrum
Dale Frail
NRAO
Host: Salvo Vitale

Abstract: With the discovery of gravitational waves and electromagnetic radiation from the binary neutron star merger GW170817, the era of GW multi-messenger astronomy has begun with style. I will describe the discovery, show where progress has been made in several areas, and then move to describe a controversy regarding the origin of the afterglow emission. After explaining the importance of this issue, I will show how late-time radio observations have decisively resolved the issue. I will end with a discussion of the future, with an emphasis on the role of radio observations in finding and studying EM counterparts.

Tuesday 18 September :
NASA's Juno Mission to Jupiter: What's Inside the Giant Planet?
Fran Bagenal
CU Boulder/LASP
Host: John Belcher

Abstract: Juno's principal goal is to understand the origin and evolution of Jupiter. Underneath its dense cloud cover, Jupiter safeguards secrets to the fundamental processes and conditions that governed our solar system during its formation. As our primary example of a giant planet, Jupiter can also provide critical knowledge for understanding the planetary systems being discovered around other stars. With its suite of science instruments, Juno is investigating the interior structure, mapping Jupiter's intense magnetic field, measuring the distribution of water and ammonia in the deep atmosphere. JUNO is also the first spacecraft to fly over Jupiter's aurora and measuring both the energetic particles raining down on the planet and the bright northern & southern lights they excite. A huge bonus is the small public outreach camera that is taking fantastic images of Jupiters beautiful clouds. The images - some science, some art - are processed and shared by the public around the world. NASA's JUNO mission was launched in August 2011 and has been in orbit over Jupiter's poles since 4th July 2016.

Tuesday 25 September :
Isotopic Abundances of Low-Mass Stars
Ian Crossfield
MIT
Host:

Abstract: TBD

Tuesday 02 October :
In Search of Molecular Oxygen in Earth Analogs
Mercedes Lopez-Morales
CfA
Host: Diana Dragomir

Abstract: The discovery of the first transiting, potentially earth-like planets by projects like TESS, PLATO, SPECULOUS, MEarth, etc is just around the corner. Once discovered, those planets will immediately become the focus of observations in search for atmospheric biomarkers, such as H2O, CH4, O3, and O2. Given current and planned instrumentation, H2O, CH4, O3 will be best searched for from space. O2, on the other hand, will be best observed from the ground. Here I present ongoing work centered around optimizing the search for O2 in earth-like planets using high-resolution, doppler velocity techniques. I will show results of investigations of a series of technical and observational parameters, which will produce the most sensitive observations of O2 with instrumentation on the upcoming generation of extremely large telescopes (GMT, TMT, ELT).

Tuesday 09 October :
Cosmology in the era of multi-messenger astronomy with gravitational waves
Marcelle Soares-Santos
Brandeis U.
Host: Ian Crossfield

Abstract: Motivated by the exciting prospect of a new wealth of information arising from the first observations of gravitational and electromagnetic radiation from the same astrophysical phenomena, the Dark Energy Survey (DES) has established a search and discovery program for the optical transients associated with LIGO/Virgo events using the Dark Energy Camera (DECam). This talk presents the discovery of the optical transient associated with the neutron star merger GW170817 using DECam and discusses its implications for the emerging field of multi-messenger cosmology with gravitational waves and optical data.

Tuesday 16 October :
Kilonova Emission from a Binary Neutron Star Merger
Brian Metzger
Columbia
Host: Nevin Weinberg

Abstract: On August 17 the LIGO gravitational wave observatories detected the first binary neutron star merger event (GW170817), a discovery followed by the most ambitious electromagnetic (EM) follow-up campaign ever conducted. Within 2 seconds of the merger, a weak burst of gamma-rays was discovered by the Fermi and INTEGRAL satellites. Within 11 hours, a bright but rapidly-fading thermal optical counterpart was discovered in the galaxy NGC 4993 at a distance of only 130 Million light years. The properties of the optical transient match remarkably well predictions for “kilonova” emission powered by the radioactive decay of heavy nuclei synthesized in the expanding merger ejecta by rapid neutron capture nucleosynthesis (r-process). The rapid spectral evolution of the kilonova emission to near-infrared wavelengths demonstrates that a portion of the ejecta contains heavy lanthanide nuclei. Two weeks after the merger, rising non-thermal X-ray and radio emission were detected from the position of the optical transient, consistent with delayed synchrotron afterglow radiation from an initially off-axis relativistic jet (or a shock-heated "cocoon" produced as the jet interacts with the kilonova ejecta). I will describe efforts to create a unified scenario for the range of EM counterparts from GW170817 and their implications for the astrophysical origin of the r-process and the properties of neutron stars (particularly their radii and maximum mass, which are determined by the poorly understood equation of state of dense nuclear matter). Time permitting, I will preview the upcoming era of multi-messenger astronomy, once Advanced LIGO/Virgo reach design sensitivity and a neutron star merger is detected as frequently as every week.

Tuesday 23 October :
Star Formation Then and Now
Nia Imara
CfA
Host: Ian Crossfield

Abstract: Stars are of fundamental importance to astronomy, and how they form and shape their environments influence everything from exoplanet studies to cosmology. Stars form in heavily obscured molecular clouds, and understanding the initial conditions of star formation persists as one of the leading challenges of contemporary astrophysics. A major challenge is the wide range of physical scales involved: from the large-scale galactic environment, to molecular clouds, to the high-density filaments and cores most directly associated with the birth of stars, and all the way down to the physics of dust, atoms and molecules. I will discuss ways to overcome these challenges, focusing on the birth of molecular clouds from the atomic interstellar medium, the role of high-density substructure in the formation of stars, and the properties of molecular clouds in dwarf galaxies. I will also explore some cosmological implications of stardust, proposing theoretical models for dust in high-redshift galaxies and in the intergalactic medium.

Tuesday 30 October :
Circumgalactic Precipitation
Mark Voit
Michigan State
Host: Michael McDonald

Abstract: Galaxies are commonly thought to acquire much of the gas that fuels star formation through streams of cold gas that flow along filaments of larger-scale structure. However, the universe's largest galaxies appear to have a different gas supply: precipitation of cold clouds out of hot circumgalactic gas via radiative cooling and condensation. I will present both observational and theoretical support for the precipitation model in large galaxies and show how it may apply to galaxies of all masses. One of the attractive features of the precipitation model is that it makes observationally testable predictions about the state of the circumgalactic medium, if most star-forming galaxies are indeed in a precipitating state.

Tuesday 06 November :
The Milky Way Laboratory
Cara Battersby
U. Conn.
Host:

Abstract: Our home Galaxy, the Milky Way, is our closest laboratory for studying physical processes that occur throughout the Universe. Submillimeter observations of the cool, dense gas and dust in our Milky Way provide insights on universal processes including how stars form in both 'regular' and 'extreme' environments and how gas is organized on galactic scales. On a tour through our Milky Way Laboratory, I will discuss 1) how we can use dense, filamentary molecular clouds, potential "Bones of the Milky Way," to trace our Galaxy's spiral structure, and 2) how observing our extreme, turbulent Galactic Center (the Central Molecular Zone) can help us learn more about how gas is converted into stars during the peak epoch of cosmic star formation. I will also briefly discuss the Origins Space Telescope, a NASA mission concept study for the 2020 Decadal survey, opening up about 3 orders of magnitude of discovery space on science from first stars to life.

Tuesday 13 November :
Convection in Cool Stars, as Revealed through Stellar Brightness and Radial Velocity Variations
Fabienne Bastien
Penn State
Host:

Abstract: The breadth of stellar behavior unveiled in recent years, thanks in part to high precision Doppler surveys and space-based transiting exoplanet surveys, has given us new insights into and enabled novel studies of stellar variability, stellar structure and evolution. Here, we discuss how these variations enable us to more accurately measure the physical properties of Sun-like stars, to understand the nature of surface convection and its connection to magnetic activity, and to better determine the properties of planets around cool stars. We show how we may now measure stellar granulation from space-based light curves and use this to obtain a simple measurement of the stellar surface gravity with a precision of ~0.1 dex. We use this, together and solely with two other simple ways of characterizing the stellar photometric variations, to construct an evolutionary diagram for Sun-like stars from the Main Sequence on towards the red giant branch. We expand on this and show how we may use these light curves to measure other fundamental stellar properties and also predict which stars exhibit low levels of stellar radial velocity variability (“RV jitter”), enabling prioritization of transiting exoplanet candidates and facilitating target selection for RV surveys in general. Finally, we highlight previously under- appreciated but relevant astrophysics apparent at current benchmark levels of RV precision from our analysis of precise RVs obtained with Keck HIRES, astrophysics that may become increasingly important as the community pushes to ever higher levels of RV precision.

Tuesday 20 November :
Galaxies, AGN and their environments
Anna Sajina
Tufts U.
Host: Rob Simcoe

Abstract: A key direction in observational extragalactic astrophysics is the study of the evolution of galaxies and their black holes in the context of their local and large scale environments. This is now possible thanks to current and upcoming generations of large area photometric and spectroscopic surveys. Crucially, for a complete picture, such studies need to account for both unobscured and obscured star-formation and black hole growth. I will present current work in my group involving characterizing the environments of galaxies in 5sq.deg of the XMM-LSS field which has extensive photometric and spectroscopic coverage. This includes constraints on dust obscured galaxies and AGN thanks to Herschel and SCUBA2 surveys. We use the same methodology as used for the COSMOS field, but now with a combined area >3x the size of COSMOS alone, we can explore the role of environment in galaxy build-up and quenching as well as the role of AGN therein -- all with improved statistics and over a larger range of environments. Lastly I will discuss the future prospects for even better galaxy properties characterization and improved sampling of the cosmic web thanks to several planned large area photometric and spectroscopic surveys.

Tuesday 27 November :
Observations of quiescent and transient X-ray binaries in the central parsec
Chuck Hailey
Columbia
Host: Fred Baganoff

Abstract:

Tuesday 04 December :
Missing Baryons and Metals in Extended Halos of Galaxies
Joel Bregman
U. Michigan
Host: Paul Schechter

Abstract: Hot gas density distributions can be fitted to the X-ray emission and absorption observations of the Milky Way to determine the mass and metallicity, mainly within 50 kpc. We have now included optical depth effects in the critical O VII and O VIII lines and find the same result from three different data sets. An extended spherical hot halo is the main mass component, containing about 3-4E10 Msun within 250 kpc, significantly lower than the mass of missing baryons, about 1.7E11 Msun. The hot halo is rotating at 180 +/- 40 km/s within 50 kpc, the density declines as r^-3/2, and the metallicity is about half solar. Adding a disk component improves the fit but it is a minor contributor to the total mass. The missing baryons most likely lie beyond the virial radius, probably 2-3 R200. In nearby external galaxies, we detect a SZ signal when stacking the nearest dozen spiral galaxies with L ~ L*. This signal suggests a gas mass of about 5E10 Msun within R200, similar to that found around the Milky Way.

Tuesday 11 December :
Event Horizon Dynamics: Sgr A*'s Multi-wavelength Variability
Daryl Haggard
McGill
Host: Fred Baganoff

Abstract: Black holes represent one of General Relativity's most exotic predictions: objects so compact that they distort the fabric of spacetime. The last century has seen exciting tests of GR and the LIGO-Virgo Observatories have now definitively discovered black holes, and yet we are only beginning to approach the event horizon. Sagittarius A* is one of the most promising supermassive black holes targeted by the VLT's GRAVITY instrument and the Event Horizon Telescope. It also offers an exciting opportunity for coordinated, multi-wavelength campaigns, which are poised to identify the origin of observed X-ray and IR variability, connect it to horizon-scale structure in the submm, and distinguish between competing models: hot spots, inflow/outflow, reconnection regions, shocks, or even magnetosphere gaps. I will review recent highlights from observations of Sgr A* and prospects for future discovery.

This page is maintained by Ian Crossfield