MIT Astrophysics Colloquia - Spring 2009
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.
Special Astrophysics Colloquium THURSDAY
January 29
Location: The Pappalardo Room, 4-349:
Directly Imaging the Horizons of Black Holes
Avery
Broderick
Canadian Institute for Theoretical Astrophysics
Abstract: For the first time it has become possible to
directly image the horizon of a black hole. This is being
accomplished for a handful of supermassive black holes via
the emerging millimeter and sub-millimeter VLBI capability.
Already, observations of the supermassive black hole at the
center of the Milky Way has placed an important constraint
upon fundamental gravitational physics: compact horizons
almost certainly exist, even if General Relativity fails to
describe black holes! Future measurements promise to test
whether or not the Kerr metric is an adequate description of
strong gravity in the vicinity of supermassive black holes.
In addition, such observations are being brought to bear upon
the many unresolved astrophysical questions regarding black
hole accretion and outflows, providing crucial empirical
insight into these processes at the smallest relevant scales.
I will discuss how these observations are being done, what we
expect to see (and have seen!), their implications for
fundamental questions in black hole science and how they
relate to existing and future gravitational wave experiments.
Tuesday February 3:
Accurate computing for precision
measurement: LIGO, LISA, and the future of gravitational-wave data
analysis
Michele Vallisneri
Jet Propulsion Laboratory
Abstract:Interferometric detectors such as LIGO are widely
expected to yield the first direct gravitational-wave detections in
the next decade; the space mission LISA will extend our reach to
thousands of gravitational-wave sources at lower frequencies and much
greater distances. For ground- and space-based detectors alike,
computation is integral to the measurement concept: no physical
conclusion is possible before filtering the raw data through complex
analysis workflows. In fact, LISA may be considered a software
interferometer, since its measurements become free of frequency noise
only after they are carefully recombined into the synthesized
observables of time-delay interferometry (TDI). In this talk, I
discuss how the beautiful mathematical formulation of TDI has led to
improvements and simplifications in LISA's architecture. Coming back
to Earth, I describe the plans to increase the sensitivity of LIGO
searches for spinning black-hole binary inspirals by adopting advanced
computation-intensive search techniques.
Tuesday February 10:
Relativistic Compact Objects and
their Environs
Jonathan McKinney
KIPAC/Stanford
Abstract: The violent birth of black holes and neutron stars
during core-collapse supernovae and merging events probes the
fundamental nature of gravity, neutrinos, high-density equations of
state, and beyond-QED-strength magnetic fields. Post-birth these
compact objects continue to be of significant interest by powering
pulsar wind nebulae, active galactic nuclei, x-ray binaries, and giant
flares from magnetars. Recent time-dependent numerical general
relativistic magnetohydrodynamic (GRMHD) simulations have broken new
ground in explaining these systems' birth and evolution, including how
magnetized accretion flows around rotating black holes launch
ultrarelativistic jets and how pulsars power their surroundings. I
discuss some of these recent successes, outstanding questions such as
how core-collapse supernovae occur, and how future time-dependent
simulations will play a vital role in progressing our understanding of
compact objects and their environments.
Tuesday February 17:
Quasars Probing Quasars:
Understanding the Physics of Massive Galaxy Formation
Joseph Hennawi
University of California, Berkeley
Abstract:
One of the most important problems in galaxy formation is
understanding the physics which governs the observed bimodality in the
galaxy population. Lower mass galaxies are gas rich and form a "blue
cloud" in the color magnitude diagram, whereas more massive
"red-and-dead" galaxies are gas poor and inhabit the red sequence. As
a result, all galaxy formation models include some variant of
feedback, which acts to "quench" star formation in massive
systems. Observing the formation epoch of red and dead galaxies will
shed light on the physics behind this quenching. The strong
clustering of luminous quasars at z ~ 2-3 indicates that they are
indeed the progenitors of galaxies on the red sequence today. I will
introduce a novel technique whereby a foreground quasar can be studied
in absorption against a background quasar, resolving scales as small
as 30kpc. This experiment reveals a rich absorption spectrum which
contains a wealth of information about the physical conditions of ISM
and halo gas in massive proto-galaxies. Absorption line modeling
techniques will be reviewed, and I'll discuss the implications of
these new observations for galaxy formation and feedback scenarios.
Special Astrophysics Colloquium MONDAY
February 23:
A Fresh Approach to Bridging Observations and Theory of Cosmic Explosions
Alicia Soderberg
Harvard-Smithsonian Center for Astrophysics
Abstract: Throughout history, observational supernova (SN)
studies have focused almost exclusively on their strong optical
emission that dominates the bolometric luminosity of all SN classes.
Yet many of the leading breakthroughs in our understanding of
supernovae and their progenitors have been enabled by observations at
other wavelengths. For example, through the combination of radio,
X-ray and gamma-ray observations, we now know that less than 1 percent
of all Type Ibc supernovae harbor ultra-relativistic gamma-ray burst
jets (GRBs, including those pointed away from us) that are visible to
the far reaches of the Universe and enable unique galaxy evolution
studies. The progenitors of GRBs must therefore share unusual
properties, the nature of which remain hotly debated, and are likely
to be revealed only through a detailed study of local SNe Ibc.
Similarly, as Type Ia SN studies are extended to higher redshifts and
trusted to constrain cosmological parameters, the favored
single-degenerate white dwarf model is increasingly called into
question by sensitive radio and X-ray observations of nearby SNe Ia
that have yet to reveal evidence for a donor star's wind. Theoretical
considerations suggest that progenitor mass, metallicity, angular
momentum and binary interaction all play a role in the production of
GRBs, SNe Ibc and SNe Ia. I will present a fresh approach to bridge
observations and theory of cosmic explosions that will ultimately shed
light on the nature of their progenitors.
Special Astrophysics Colloquium WEDNESDAY
February 25:
Dynamics Of Protoplanetary Disks
(and of Cosmological Haloes)
Yoram Lithwick
Canadian Institute for Theoretical Astrophysics
Abstract:
Protoplanetary disks are gaseous accretion disks around young
stars. I will show how vortices form and evolve within such disks.
Weak vortices live essentially forever. Strong vortices decay into
turbulence via a 3D instability. One implication is that dust can be
trapped within weak vortices, triggering planet formation. A second
implication is that strong vortices can be responsible for the
turbulence that makes these accretion disks accrete. I will also
briefly describe how cosmological dark matter haloes form. By
constructing the 3D self-similar solution for a collapsing halo, I
will show how the density profile within a halo may be understood.
Special Joint Astrophysics/Laboratory
for
Nuclear Science Colloquium Monday March 2:
Viewing the Universe at Very High
Energies
Rene Ong
University of California, Los Angeles
Location: 26-414 (NOT Marlar Lounge!)
Host: Gabriella Sciolla
Abstract:The field of very high energy (VHE) astrophysics has
developed rapidly during the last few years as a result of new
instruments and exciting discoveries. Ground-based telescopes, such
as VERITAS in southern Arizona, have detected numerous astrophysical
sources of TeV gamma rays, including supernova remnants and active
galaxies. These telescopes are also carrying out sensitive searches
for the annihilation of neutralino dark matter. We expect similar
exciting results from the newly-launched Fermi Gamma-ray Space
Telescope. This talk will review the status of the field and will
outline the scientific prospects over the next few years.
Note unusual location!!
Special Astrophysics Colloquium Wednesday
March 4:
Probing the early universe through
precision length measurement
Stefan Ballmer
California Institute of Technology
Location: Pappalardo Room, 4-349 (NOT Marlar Lounge!)
Host: Deepto Chakrabarty
Abstract:
Gravitational Radiation is the only known carrier of information that
has the potential of directly probing the "primordial dark age''
between the end of inflation and the start of Big Bang
Nucleosythesis. I present the limit on a stochastic gravitational wave
background derived from the LIGO S5 science run and look at the
cosmological implications. I will then discuss the currently thermal
noise limited design of AdvLIGO as the next experimental improvements
on these results will come from the next generation of GW
detectors. This also leads to some recent insight regarding the
cancellation of part of the thermal noise.
Note unusual location!!
Tuesday March 10:
What's going on at
Enceladus?
Francis Nimmo
University of California, Santa Cruz
Host: Peter Ford
Abstract:
The Cassini spacecraft revealed that Enceladus, a small icy moon of
Saturn, is unexpectedly interesting. In particular, it is one of only
four solar system bodies known to be geologically active: it has south
polar geysers spewing water vapour hundreds of km into space. In this
talk I will discuss recent theoretical work on Enceladus, focusing on
three particular issues: why is it active?; does it have an ocean?;
and how has it evolved? The answers are relevant to the
astrobiological potential of Enceladus, and may also influence the
design of future spacecraft missions.
Tuesday March 17:
The Large Synoptic Survey
Telescope: from Dark Energy to Killer Asteroids
Chris Stubbs
Harvard University
Host: Scott Hughes/Gabriella Sciolla (joint Astro-LNS colloquium)
Abstract: I will describe the motivation and status of the
Large Synoptic Survey Telescope (LSST), a project currently in the
design stage that promises to usher in the era of cosmic
cinematography by scanning the entire accessible sky every few days,
to 24th magnitude. The LSST is being engineered to minimize potential
sources of systematic error for precision photometry and weak
lensing. The LSST will allow for unprecedented parallel science from a
common image stream, for topics ranging from fundamental physics to a
census of the solar system.
Tuesday March 24:
Spring Break: No Colloquium
Tuesday March 31:
Extreme Astrophysics with Neutron
Stars
Marten van
Kerkwijk
University of Toronto
Host: Scott Hughes
Abstract: Neutron stars contain the densest matter and support
the strongest magnetic fields known. I will describe our attempts to
use the so-called Isolated Neutron Stars as laboratories for
dense-matter and strong-field physics, and discuss what we have
learned about the properties with which neutron stars are born.
Tuesday April 7:
Magnetic Dynamos in Low-Mass
Stars: Puzzles and Perspectives
Matthew
Browning
Canadian Institute for Theoretical Astrophysics
Host: Adam Burgasser
Abstract: Convection and magnetism are pervasive in
astrophysics. Magnetic fields play key roles in phenomena ranging
from accretion to stellar spindown; in many cases, those fields are
thought to arise dynamically, from the action of a magnetic dynamo.
Convection is likewise ubiquitous -- every main sequence star hosts
convection somewhere in its interior, for instance, as do many
planets. Observations and basic modeling both suggest that convection
and magnetism are intricately linked, with turbulent convective flows
likely playing an essential role in the generation of fields. But a
comprehensive theory of astrophysical dynamos has remained elusive. I
will talk about how observations and MHD simulations of stellar
magnetism are providing powerful new clues about the operation of such
dynamos.
Tuesday April 14:
Galactic Diversity: The Many Colors of Brown Dwarfs
Adam
Burgasser
Massachusetts Institute of Technology
Host: Scott Hughes
Abstract:
Fifteen years ago, astronomers detected the first unambiguous examples
of brown dwarfs---low-mass objects incapable of fusing hydrogen, that
bridge the gap between stars and giant gas planets. Since then,
hundreds of these intrinsically cold and dim sources have been
identified in the vicinity of the Sun, in young clusters and
associations, and as companions to nearby stars. With increasing
numbers has come the realization of substantial diversity in the brown
dwarf population, with a broad range of observational properties
associated with age, mass, metallicity, cloud characteristics and
multiplicity. In this talk I will review the distinct subclasses of
brown dwarfs that are now being recognized, what these subclasses
reveal about the physical character, thermal evolution and origins of
brown dwarfs, and what future steps must be undertaken to fully
exploit brown dwarfs as spatiotemporal probes of the Galaxy.
Tuesday April 21:
Celestial gamma-ray sources: First
data from the Fermi Observatory
Grzegorz
Madejski
SLAC National Accelerator Laboratory
Host: Mark Bautz
Abstract: Fermi Gamma-ray Space Telescope has been successfully
launched into orbit in June last year, and is providing excellent data
for many celestial gamma-ray sources. This presentation will
highlight the first results from Fermi's Large Area Telescope, and
will cover the early measurements of gamma-ray properties of rotating
neutron stars (pulsars), jet-dominated active galaxies, and gamma-ray
bursts.
Tuesday April 28:
AGN in Clusters of Galaxies:
Cooling Flows, Feedback, and High-z Systems
Elizabeth
Blanton
Boston University
Host: Scott Hughes
Abstract:
Observations over the last ten years with Chandra and XMM-Newton have
shed much light on cooling flows in the centers of clusters of
galaxies and the role of AGN heating. Cooling of the hot intracluster
medium in cluster centers can feed the supermassive black holes found
in the cores of the dominant cluster galaxies leading to AGN outbursts
which can reheat the gas, stopping cooling and large amounts of star
formation. AGN heating can come in the form of shocks, buoyantly
rising bubbles that have been inflated by radio lobes, and the
propogation of sound waves. I will present recent results of two
systems displaying AGN feedback, Abell 262 and Abell 2052. In
addition, I will discuss the use of radio sources as beacons for
clusters of galaxies at high redshifts, where the radio emission is
easier to detect than the optical or X-ray cluster emission.
Tuesday May 5:
Winds, Bubbles and
Supernovae
Vikram
Dwarkadas
University of Chicago
Host: Daniel Dewey
Abstract:
Mass loss from stars is a ubiquitous process. Massive stars
(> 8 solar masses) lose a substantial amount of their initial
mass, which can create complex structures such as wind-blown
bubbles surrounding the star. When these stars explode as
supernovae (SNe), the resultant shock wave interacts with
this surrounding medium, and not with the interstellar
medium, for a substantially long time. Evolution within the
ambient medium can significantly alter the SN evolution from
the conventional "textbook" phases that are usually studied.
In this talk we will explore, with the help of numerical
simulations, the formation of the ambient medium around
massive stars of various initial mass. Furthermore we will
investigate the interaction of the SN shock wave with this
medium. We will characterize the signatures of this
interaction, and its observational manifestations, with
several examples, including but not limited to the famous SN
1987A.
In recent times it is becoming apparent that some massive
stars undergo an episode of significant mass loss just prior
to their demise, perhaps within the last hundreds of years of
their existence. We will also explore SNe from such events
and what these observations reveal.
Tuesday May 12:
Flares and Flashes in the
Ultraviolet Universe
Suvi
Gezari
Johns Hopkins University
Host: Scott Hughes
Abstract:
We present two motivations for exploring the Ultraviolet Universe in
the time domain: 1) UV flares from the tidal disruption of stars by
supermassive black holes, and 2) UV flashes from shock breakout in
core-collapse supernovae. We describe our search for these events in
the GALEX Deep Imaging Survey, and report the discovery of 3 candidate
UV flares from tidal disruption events, and the discovery of UV
emission associated with shock breakout from 2 supernovae with red
supergiant progenitors. Tidal disruption events provide a unique
probe of dormant black holes in the nuclei of distant galaxies, while
shock breakout flashes clock the time of explosion in supernovae, and
are a sensitive probe of the structure of their progenitor stars.
Based on our studies with GALEX, we predict the detection capabilities
of the upcoming Pan-STARRS and GALEX time domain surveys.
This page is maintained by Scott Hughes