University of Washington

ASTRONOMY DEPARTMENT

I will describe the current status of modeling the formation of massive star clusters using hydrodynamic simulations of galaxy formation. Simulations can now reach a parsec-scale resolution and study the assembly of giant molecular clouds within the first galaxies. Not all of these clouds are capable of hosting star clusters with the properties as observed in the nearby galaxies. This allows us to place constraints on the duration of the epoch of globular cluster formation and their spatial distribution. A high fraction of the stellar population in the first galaxies is likely to be in the form of massive star clusters, whose radiative feedback could regulate the overall star formation rate. These models are strongly constrained by the observed metallicity distribution of the local globular cluster systems.

Neutron stars provide an exciting laboratory for the physics of matter at extreme densities. Recent neutron star observations are providing constraints on nuclear and many-body physics which go beyond what has been determined from terrestrial experiments. In particular, recent neutron star mass and radius observations are providing novel constraints on the equation of state of matter at high densities. Also, recent observations of the cooling of the neutron star in the Cassiopeia A supernova remnant generate novel constraints on the nature of superfluidity in the neutron star core. However, both of these connections are limited by important systematics which require both more observations and advances in the theoretical models. In this talk, I will review both of these classes of observations and explain how they are connected to nuclear physics.

Hey science faculty, are you making our society better? How would you know if you are? A large fraction of your students will never become science instructors or work in STEM fields. Yet, nearly all of them will become (or are) parents, taxpayers, and voters. You have 12-16 weeks per semester, and 3 hours per week, to make a difference in their worldviews. So, what should you do with them, and are you doing it now? Is your class preparing and encouraging our citizenry to engage in conversations about the importance of science in society? Is your time with your students transforming the knowledge, skills and beliefs of the future leaders and decision makers of our society to become the ambassadors of science we need for the US to stay prosperous and competitive in the world? A discussion of research on how we can teach to positively alter the worldviews of our citizenry regarding the role of science in society will be presented.

Binary and multiple stellar systems are common outcomes of the star formation process. More importantly, multiple systems contribute disproportionately to our understanding of topics ranging from stellar structure to cosmology. In this talk I will describe several theories for binary and multiple star formation, focusing on the role of protostellar accretion disks. I show that two modes of binary formation may account for the dependence of the observed binary fraction on stellar mass. These binaries can also host planets, just like their singleton counterparts. I will examine the architecture of these complex hierarchical systems, with a focus on the role of stellar evolution in long term stability.

The Long Wavelength Array (LWA) will be a new multi-purpose radio telescope operating in the frequency range 10-88 MHz. Scientific programs include pulsars, supernova remnants, general transient searches, radio recombination lines, solar and Jupiter bursts, investigations into the "dark ages" using redshifted hydrogen, and ionospheric phenomena. The first station of the LWA, called "LWA1", is located near the center of the VLA and has recently begun scientific operations as a stand-alone instrument with collecting area roughly equivalent to a 100m dish. The LWA1 images the sky in realtime using the "transient buffer - narrowband" (TBN) system which is operational with 256 dipoles, and a bandwidth of 70 kHz. The LWA1 can also form up to 4 beams on the sky simultaneously with 16 MHz bandwidth in each of two tunings and full polarization. Early results include observations of pulsars, the Sun, and Jupiter. The LWA1 is supported by NSF as a University Radio Observatory and as such is open for use by the community.

The better part of a century passed before more than a handful of serious scientists accepted Copernicus's theory (1543) that the Earth rotates while also orbiting the Sun. Galileo's telescopic as well as literary contributions together form the most famous early chapter in the story of the wider acceptance of heliocentrism. Nonetheless, without diminishing the enormous accomplishments of the first telescopic astronomer, I want to revisit Galileo to show how he "cheated"-and how he continues to skew our reading of the reception of Copernicanism. In fact, right through the seventeenth century, many of those resistant to heliocentrism founded their objections scientifically-not merely, like Galileo's character Simplicio, on dogmatic or traditionalist grounds.

The Kepler spacecraft launched on March 7, 2009, initiating NASA's first search for Earth-size planets orbiting Sun-like stars. Kepler has discovered 122+ exoplanets, including a system of five planets, Kepler-62, with two habitable zone planets (with radii of 1.4 and 1.6 Re). Kepler is proving to be a cornucopia of discoveries: it has identified 2,700+ candidate planets. An astounding 1171 of these candidates orbit 467 multiple systems. Never before has there been a photometer capable of reaching a precision near 20 ppm in 6.5 hours and capable of conducting nearly continuous and uninterrupted observations for years. In addition, Kepler is providing a wealth of astrophysics, revolutionizing the field of asteroseismology. Designing and building the Kepler photometer and the software systems that process and analyze the resulting data to make the discoveries presented a daunting set of challenges, including how to manage the large data volume as well how to detect miniscule transit signatures against stellar variability and instrumental effects. Reviewing the pipeline results is a huge, time consuming task for which machine learning techniques are helping to mitigate. The challenges continue into flight operations, as the photometer and spacecraft have experienced aging and changes in hardware performance over time.

The statement "75% of the Universe is made up of Dark Energy" assumes that General Relativity is an accurate description of how gravity behaves on cosmological scales. This assumption is not as well tested as we would like. In this talk, I will discuss the relationship between cosmology and our theory of gravity, introduce alternative theories of gravity that purport to allow cosmic acceleration without Dark Energy, and discuss how present and future data sets do and will constrain these theories.

Climate scientists have overwhelmingly agreed that global warming is unequivocal. I will present the latest evidence from observations detailing the warming and related climate change since pre-industrial times and compare it to proxy climatic records of the past few hundred thousand years.  The talk will include a description of the scientific basis for natural and anthropogenic mechanism of climate change. Finally, I will discuss the reliable of global climate models and their response to past climate forcing and future emissions scenarios.

Measurement of the spatial distribution of neutral hydrogen via the redshifted 21 cm line promises to transform our knowledge of the Epoch of Reionization (EoR). In my talk I will give an accessible introduction to this new field, discuss how we plan to observe the faint 21 cm fluctuations in the face of strong foregrounds, and show our latest results from prototype and early commissioning observations with the Murchison Widefield Array as we start to peer through the EoR window with the first generation of EoR observatories.