A radio perspective on the Gamma-Ray Burst/Supernova connection
Dr. Alicia Soderberg
Princeton University
Host: Rob Simcoe
February 19:
WHEN MAGNETIZED WINDS COLLIDE: PROBING THE INTERACTION
OF THE SOLAR SYSTEM WITH THE INTERSTELLAR MEDIUM
Prof. Merav Opher
George Mason University
Host: John Belcher
Abstract:
Magnetic effects are ubiquitous and known to be crucial in astrophysical
media; they affect shocks, accretion disks around T-Tauri, the
interstellar media, among other aspects. The twin spacecraft Voyagers are
providing us with an unexpected view of how stars interact with their
surrounding media. For the first time we are able to in-situ measure
particles and fields of the boundaries of the solar system. Voyager 1
crossed in Dec 2004, the
termination shock and is now in the heliosheath. Voyager 2 recently (Aug
2007) crossed the termination shock as well. This talk will explore the
different magnetic effects able to be sampled in the solar system using
state-of-the art computational models and observations. Recently, using
data from Voyager 1 and 2 streaming and radio data in conjunction with
state-of-the art 3D MHD modeling, we were able to constrain the
direction of the local interstellar magnetic field. As a result, the solar
system is asymmetric being pushed in the southern direction. I will also
review our previous work that showed that Kelvin-Helmholtz instabilities
and turbulence exist near the current sheets. These effects will be able
to be sampled b the Voyager observations in the heliosheath. I will
comment on these results and their implications as for example for the
local interstellar magnetic turbulence.
February 26:
ORIGIN OF GIANT PLANETS
Prof. Roman Rafikov
CITA & IAS
Host: Alar Toomre
Abstract:
Recent numerous discoveries of extrasolar giant planets have brough into
focus the question of their origin. At present there exist two competing
theories of the giant planet formation - core (nucleated) instability and
gravitational instability. I will critically review these two ideas,
emphasizing observational evidence of different kinds. In particular, it
will be demonstrated that giant planets can hardly form by the gravitational
instability at distances of less than about hundred AU from their parent
stars. This leaves core instability as a much better candidate for the giant
planet formation mechanism in the Solar System and the extrasolar systems
discovered through the radial velocity searches, and I will go over this
avenue of planet formation in detail. I will finally discuss the possibility
of directly observing young planets as they form in protoplanetary disks.
March 04:
AGN's: SEYFERTS, QUASARS, BLAZARS AND MORE
Dr. Martin Elvis
Harvard-Smithsonian Center for Astrophysics
Host: Walter Lewin
March 11:
THREE ASTROPHYSICAL LABORATORIES FOR PARTICLE PHYSICS
Prof. Avi Loeb
Harvard University
Host: Angelica de Oliveira-Costa
Abstract:
The Universe offers environments with extreme physical conditions that
cannot be realized in laboratories on Earth. These environments provide
unprecedented tests for extensions of the Standard Model. I will describe
three such "astrophysical laboratories", which are likely to represent new
frontiers in cosmology and astrophysics over the next decade. One provides
a novel probe of the initial conditions from inflation and the nature of
the dark matter, based on 3D mapping of the distribution of cosmic
hydrogen through its resonant 21cm line. The second allows to constrain
the metric around supermassive black holes based on direct imaging or the
detection of gravitational waves. The third involves the acceleration of
high-energy particles in cosmological shock waves. I will describe past
and future observations of these environments and some related theoretical
work.
March 18:
TWO TAILS OF A DISTRIBUTION FUNCTION: THE INITIAL MASS FUNCTIONS OF EXTREME STAR FORMATION
Prof. Michael Meyer
University of Arizona
Abstract:
``It was the best of times, it was the worst of times..." Considerable
progress has been made over the past decade in characterizing the shape of
the stellar and sub-stellar initial mass function in regions of nearby
star formation (e.g. Meyer et al. 2000; Luhman et al. 2006). However,
fundamental questions remain unanswered. Does the ratio of stars to
sub-stellar objects vary as a function of initial condition in molecular
clouds? Is there an "end" to the IMF set by the opacity-limit for
fragmentation? Does the ratio of high to low mass stars vary as a
function of metalicity, ambient gas pressure, and/or magnetic field
strength throughout the Milky Way, local group galaxies, and beyond? I
will summarize recent results from our group that offer answers to these
questions focusing on studies concerning: i) the sub-stellar IMF down to
30 Mjupiter in nearby star-forming regions; and ii) the promise of
constraining the ratio of high to low mass stars in unresolved super-star
clusters found in starburst galaxies using observations of their
integrated near-infrared spectra (Meyer and Greissl, 2005). Our goal is
to use observations of the shape of the IMF to reveal characteristic
physical scales (e.g. mean mass, variance, departures from the log-normal
form) and correlate any observed variations with initial conditions in
order to constrain predictive theories of star formation.
Host: Adam Burgasser
March 25: Spring break.
April 01:
BLACK HOLES, SCHRODINGER CATS, AND PARTICLE ACCELERATORS
Prof. Andrew Hamilton
University of Colorado
Abstract:
What really happens inside black holes?
As first pointed out by Poisson & Israel (1990), the classical empty
(Kerr-Newman) solutions for black holes, complete with their analytic
continuations through wormholes and white holes to new universe,
are subject to the mass inflation instability.
The instability has profound consequences for the interior structure
of black holes. If the instability is suppressed by large dissipation,
then the typical result is the creation of a huge amount of entropy
inside the black hole, orders of magnitude more than the Bekenstein-Hawking
entropy. If the second law of thermodyamics is to be saved, then
locality must break down inside black holes, so that entropy does
not accumulate inside black holes. In effect, what happens inside
the horizon of a black hole must constitute an alternate quantum reality
for each person that travels inside it. Alternatively, if dissipation
is more modest, then mass inflation will occur. Mass inflation is
caused by relativistic counter-streaming between ingoing and outgoing
streams. The result is a particle accelerator of extraordinary power:
the black hole accelerates ingoing and outgoing streams through each other
to center-of-mass energies that classically far surpass the Planck energy,
easily reaching conditions as extreme as those in the Big Bang.
Like the Big Bang, the conditions are not only energetic but of
low entropy.
What does Nature do with this remarkable beast?
Host: Max Tegmark
April 08:
MASS ESTIMATES AND MASS FUNCTIONS OF DISTANT SUPERMASSIVE BLACK HOLES
Dr. Marianne Vestergaard
University of Arizona
Host: Paul Schechter
April 15:
THE ASTROPARTICLE FRONTIER: RECENT RESULTS FROM THE PIERRE AUGER COSMIC RAY OBSERVATORY
Prof. Paul Sommers
Penn State
Abstract:
Arrival directions of the highest energy cosmic rays are correlated
with positions of nearby Active Galactic Nuclei. Potential
implications may include the following: (1) High energy cosmic rays
are accelerated in discrete extragalactic sources. (2) Pion
photoproduction causes the observed drop in the cosmic ray energy
spectrum near 10 Joules/particle. (3) Intergalactic magnetic fields
are not strong, nor are the fields in the halo of our Galaxy. (4) With
a bigger collecting area, the Auger Observatory will open a new window
of charged particle astronomy. (5) The primary particles are protons,
not larger nuclei. (6) Measured properties of the air showers
produced by these protons challenge the extrapolation of hadronic
interaction models to 300 TeV center-of-mass energy.
Host: Combined colloquium with LNS
April 22:
LIFE CYCLES OF STAR CLUSTERS:
FROM YOUNG SUPER STAR CLUSTERS IN THE ANTENNAE TO OLD GLOBULAR CLUSTERS IN THE MILKY WAY AND SOMBRERO
Prof. Michael Fall
Johns Hopkins University
Host: Ed Bertschinger
April 29:
COSMOLOGICAL NUCLEOSYNTHESIS
Prof. Gary Steigman
Ohio State University
Abstract:
Big Bang Nucleosynthesis (BBN) is a key pillar of modern cosmology,
providing a probe of the particle content and expansion rate of the
Universe a mere few minutes after the beginning. The observationally
inferred primordial abundances of Deuterium and Helium-4, when
compared to the BBN predictions, provide an excellent baryometer and
chronometer, respectively. Helium-4 is sensitive to the neutrino
content of the Universe and is a window onto any asymmetry between
neutrinos and antineutrinos and, a probe of the early Universe
expansion rate. On the other hand, the spectrum of temperature
fluctuations imprinted on the Cosmic Microwave Background radiation
(CMB), is sensitive to the baryon density and to the expansion rate
some 400 thousand years later in the evolution of the Universe. The
complementary constraints imposed by BBN and the CMB are reviewed,
revealing a consistent picture of the Universe at two very widely
separated epochs, leading to new, tighter constraints on the baryon
density at present and on possible new physics beyond the standard
models of particle physics and cosmology.
Host: Alan Guth
May 06:
TBA
Prof. Paul Butler
Carnegie Institution of Washington
Host: Josh Winn
May 13:
TBA
Prof. Eric Agol
University of Washington
Host: Josh Winn
This page is maintained by Angelica de Oliveira-Costa (angelica@space.mit.edu)