Spring 2003 Astronomy Colloquia - University of Texas at Austin
February 4, 2003
National Tsing Hua University
"Jets from Young Stellar Objects"
This talk reviews the modern view that the sun and planets both formed from an accretion disk that is built up by continuing infall from a surrounding molecular cloud core. A difficulty with this idea is that pre-main-sequence sunlike stars rotate much more slowly than naive expectations predict. A solution to the difficulty is possible if young stellar objects (YSOs) are strongly magnetized and truncate the inwardly drifting material of their accretion disks before the disks can reach the stellar surfaces. The resulting interactions drive powerful bipolar outflows that collimate slowly into protostellar jets. A prediction of the model is that the highly linear appearances of the outflows at their base, as imaged by the Hubble Space Telescope, are optical illusions. Using quantitative calculations of the collimation and heating and ionization processes, we compare the theoretical models with images and spectroscopic observations of YSO jets.
February 11, 2003
University of Chicago and Fermi Lab
"Search for Nearby Isolated Black Holes"
Using the Sloan Digital Sky Survey and the Rosat All-Sky Survey,
we searched for nearby, isolated, accreting, "stellar-mass" (3 to
100 solar mass) black holes. The colloquium will report on the search
strategy and resulting candidates.
February 18, 2003
"The End of the Dark Ages: The Formation of the First Stars and Quasars"
How and when did the cosmic dark ages end? I present simulations
of the formation of the first stars and quasars, discuss their feedback
on the IGM, and describe ways to probe their signature with NGST and MAP.
The first supernovae are responsible for the initial metal enrichment
of the IGM, and I address the impact of this initial enrichment event
on the subsequent history of structure formation. Finally, I describe
the properties and statistics of high redshift GRBs and SNe that result
from the first generation of stars.
February 20, 2003
"Formation of Globular Clusters: In and Out of Dwarf Galaxies"
Formation of Globular Clusters: In and Out of Dwarf Galaxies
Despite rapid observational progress in studying the structure and
distribution of young massive star clusters, the formation of globular
clusters remains poorly understood. I discuss a generic scenario for
their formation within the progenitor galaxies of the Milky Way,
supported by high-resolution hydrodynamical simulations. The oldest
clusters formed around redshift z = 9, but the process continued at
least until z = 4. The metallicity of 0.01-0.1 solar is provided by
the preceding generation of small star clusters. Depending on the
infall rate of fresh gas, the feedback from massive clusters may halt
the first episode of star formation in the dwarf halos. Because of
their high density, globular clusters survive when their progenitor
galaxies are disrupted by the Galactic tidal field.
February 25, 2003
University of Cambridge
"Radiative Feedback in the Early Universe: Clues to the Origin of Dwarf Spheroidals"
The theory of galaxy formation predicts that the creation process is
hierarchical: small objects form first, and large galaxies form later
from mergers of smaller subunits. The first galaxies are believed to
have formed 100 million years after the Big Bang, at redshift z ~ 30.
In these primordial galaxies, the first stars emitted light into a
previously dark universe. The radiation emitted at this time
influenced the subsequent evolution of the universe in a still-unknown
way. This process of self-regulation, in which the radiation emitted
by galaxies influenced the surrounding intergalactic medium and the
future formation of other galaxies, is termed "radiative feedback"
from galaxy formation. Using 3D cosmological simulations with
radiative transfer we find that the first galaxies are characterized
by a bursting star formation that is self-regulated by a feedback
process acting on cosmological scale. In contrast to massive galaxies,
which reionize voids first, small primordial galaxies partially ionize
only the dense filaments, while leaving the voids neutral.
Preliminary results indicate similarities between the properties of
simulated primordial galaxies and the bulk of dwarf spheroidal
galaxies (dSphs) in the Local Group and Andromeda. I briefly discuss
observational tests that could help in understanding the impact of a
population of small primordial galaxies on the cosmic evolution.
February 27, 2003
"The WMAP First Results: What Have We Learned About Cosmology?"
The First Year results of the Wilkinson Microwave Anisotropy Probe
(WMAP) satellite, which is currently mapping the entire microwave sky
to unprecedented accuracy and precision, are presented.
The primary goal of the mission is to produce high fidelity maps in
order to image the cosmic microwave background radiation (CMB).
We begin by describing the first-year maps and the power
spectra of the CMB temperature and polarization fluctuations,
and then focus on the implications of the results for our
understanding of cosmology, including precision determinations of
the cosmological parameters, and the evidence for early reionization
of the universe.
March 4, 2003
California Institute of Technology
"Beyond the CMB: Galaxy Formation as Cosmology"
The rapid progress in observational measurements of anisotropies
in the cosmic microwave background means that we now understand the global
structure and matter content of the Universe to good precision. One of the
main goals of cosmology now is to understand how those anisotropies grow
into the objects we see in the Universe today, namely galaxies. I will
describe how our understanding of galaxy formation as a cosmological
process is progressing, highlighting recent results in the areas of galaxy
clustering and the origins of dwarf galaxies and will examine the possible
existence of dark galaxies.
March 18, 2003
E. Sterl Phinney
California Institute of Technology
"Physics and Astronomy with LISA (Laser Interferometer Space Antenna)"
The NASA/ESA Laser Interferometer Space Antenna (LISA) mission,
planned for launch in 2010 (with a test mission scheduled for 2006)
will detect and measure gravitational radiation from astronomical
sources at frequencies 0.0001 Hz to 0.1 Hz (compared to 30-1000 Hz for
ground-based detectors like LIGO). LISA will detect continuous
signals from: thousands of exotic binary stars in the Milky Way,
merging supermassive black holes in the nuclei of merging galaxies at
redshifts from 0 to 100, and compact stars scattered into supermassive
black holes. The latter will provide precision tests of strong-field
predictions of relativity, such as the No-Hair Theorem and energy
extraction from rotating black holes. We will describe the principles
of operation of LISA, and the known and unknown physics, astrophysics,
and signal-processing which govern the sources it will detect and the
information we will gain.
March 25, 2003
California Institute of Technology
"Gamma-ray Bursts: The Brightest Explosions in the Universe"
A few times a day the sky is lit up by brilliant flashes of
gamma-rays. We now know that these bursts are located at cosmological distances and
perhaps even at the edge of the Universe. These bursts are then the most brilliant
astronomical objects. There are good reasons to suspect that the
bursts may well be responsible for the highest energy cosmic rays in
the Universe and are attractive targets for novel telescopes of the
future (gravitational wave interferometers, Terra Electron Volt
telescopes and neutrino telescopes). There is evidence that
GRBs result from the death of massive stars and perhaps may
signal the formation of rapidly spinning black holes.
March 31, 2003 -SPECIAL JOINT PHYSICS/ASTRONOMY COLLOQUIUM
Theoretische Physik, Ludwig-Maximilians Universitaet Muenchen
"Inflation: Conjectures vs. Facts"
The inflationary paradigm will be discussed. The robust model independent predictions of inflation will be stressed and elementary explanation of the physics behind them will be presented. The current and future observations testing these predictions will be discussed.
April 1, 2003
University of Texas at Austin, Dept. of Chemistry & Biochemistry
"The Difference Between Astronomy and Astrobiology: You Have A Better Time Machine, But At Least We Can Do Experiments"
In attempting to understand the origin of life, the
Universe, and everything, it would be marvelous if we could both have a complete record
of what has occurred in the past, and be able to carry out experiments in
which individual variables in the timeline could be altered to our
specifications. Of course, neither of these whims is even remotely a
possibility. However, astronomers have a wealth of data available to them
in the form of the cosmos, and much of this data is in effect a historical
record, since it has taken so very long to get here. In contrast,
astrobiologists have very little in the way of old data. There are blobs
in rocks that may be ancient microbial fossils, and some DNA evidence
ensconced in amber. By and large, though, astrobiologists must rely on
inferences derived from comparative biology to discern
origins. Fortunately, these inferences can in many instances be tested and
validated (or overturned) by laboratory experiments. Dr. Ellington will
present the intellectual underpinnings of the so-called 'RNA world,' the
period on Earth before the invention of protein catalysts, and will then
fall back on a discussion of relevant experiments in his lab.
April 8, 2003
John C. Mather
GSFC, NGST Project Scientist
"JWST Science and Technology Plans"
The James Webb Space Telescope (JWST) will extend the discoveries of the Hubble Space Telescope by deploying a large cooled infrared telescope at the Sun-Earth Lagrange point L2. With a 6 m aperture and three instruments covering the wavelength range from 0.6 to 28 Ám, it will provide sensitivities orders of magnitude better than any other facilities. It is intended to observe the light from the first galaxies and the first supernovae, the assembly of galaxies, and the formation and evolution of stars and planetary systems. In this talk I will review the scientific objectives, the hardware concepts and technology, and the predicted system performance.
April 15, 2003
"Type I X-ray Bursts in Neutron Stars and Black Holes"
Type I X-ray bursts are very common in accreting neutron stars. They
occur when the accreting material undergoes thermonuclear explosions
on the surface of the neutron star. Type I bursts exhibit a variety
of interesting phenomena, including quasi-periodic oscillations
associated with the spin of the star.
Not all accreting neutron stars have bursts. The talk will describe a
theoretical formalism that enables us to understand why only some
neutron stars burst while others do not. The formalism will then be
applied to accreting black hole candidates, which are known from
observations never to burst. It will be argued that the only
plausible reason for the lack of bursts is that these objects lack
surfaces. Thus, the absence of bursts provides strong evidence that
black hole candidates truly are black holes, with event horizons.
April 22, 2003
University of Washington
"SuperMacho and Supernovae, Astrophysics in the Time Domain"
A number of forefront problems can be addressed with time-domain
observations. I will describe two projects in this vein; 1) a
next-generation LMC microlensing survey and 2) a project that is
attempting to determine the equation of state of the Dark Energy
using type Ia supernovae. Both of these are being used as precursor
projects to face up to the software challenges of the Large
Synoptic Survey Telescope (LSST), which is presently under development.
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