Jump to: navigation, search

Astrophysics Seminars From 2017 - 2018


Fall 2017

September 19, 2017

NOTE: Special Talk
on Sexual Harassment
Tuesday @ 1:00 in the Qualcomm Room, Jacobs Hall - 1st floor (EBU1)
Joan Schmelz

Arecibo Observatory Deputy Director
Universities Space Research Association (USRA)
Host: Coil

 Abstract: With the issue of sexual harassment repeatedly in the news, one hopes that student groups, academic departments, and university admini- strators are discussing what can be done to eliminate this plague from our community. There are fundamental flaws in the current system where the pressure for righting these wrongs is often placed on the shoulders of young women who can be in the most vulnerable stages of their careers, and where such harassing behavior can remain an “open secret” for years. We have to change the system – to train those with privilege to become not only allies but advocates who will add their voices and prestige to fight for right, to create a “safe space” where anyone facing sexual harassment can get help and advice, and to shine a light on the harassers who still operate in the shadows. Universities and their senior staff can do more to deter, detect, and effectively address inappropriate behavior. This talk gives advice and suggestions on how to change the system and is intended for students, faculty, and administrators.

This event is sponsored by the Division of Physical Sciences and the Office of the Vice Chancellor for Equity, Diversity, and Inclusion at UCSD.''

September 20, 2017

 "History, Science & Discovery at the Arecibo Observatory"
Joan Schmelz

Arecibo Observatory Deputy Director
Universities Space Research Association (USRA)
Host: Coil

 Abstract: The Arecibo Observatory celebrated its 50th anniversary in 2013 and continues to do cutting-edge research in radio astronomy, planetary radar, and atmospheric science. Early discoveries include the 33-ms period of the pulsar in the Crab Nebula supernova remnant and the 59-day rotation rate of the planet Mercury. Later discoveries include the first binary pulsar, the first radar maps of Venus, the first megamaser galaxy, the first millisecond pulsar, and the first extrasolar planet. Arecibo’s legacy of great discoveries continues unbroken to the this day with the new detection of the first repeating Fast Radio Burst, which rules out an entire class of models requiring catastrophic explosions. Arecibo’s planetary radar observations provides information on the orbit and physical properties of the Near-Earth Asteroid, Bennu, paving the way for NASA’s OSIRIS-REx mission, which will travel Bennu and return a sample to Earth in 2023. The atmospheric radar has recently discovered the unexpected large amount of helium in the upper reaches of the ionosphere, forcing us to revise our understanding of the coupling between the ionosphere and the plasmasphere. High priority science investigations now include using pulsars to search for gravitational waves, characterizing near-Earth objects that threaten civilization, and heating the ionosphere to perform controlled plasma experiments. This talk will discuss 50 years of science at the Arecibo Observatory, from the early construction to the latest discoveries.

Bio: Joan Schmelz works for Universities Space Research Association (USRA) and currently serves as the deputy director of the Arecibo Observatory in Puerto Rico. She was honored in 2015 as one of Nature’s top ten people who made a difference in science for her work fighting sexual harassment. She is a former program officer for the National Science Foundation's Division of Astronomical Sciences and the former chair of the American Astronomical Society's Committee on the Status of Women in Astronomy. She was a professor at University of Memphis for over 20 years where she recently resigned her tenured position. During that time, she was a regular visitor to the Harvard-Smithsonian Center for Astrophysics, where she worked with multiple colleagues developing observational constraints to test models of solar coronal heating. Schmelz has published papers on a variety of astronomical topics including stars, galaxies, interstellar matter, the cosmic microwave background, and the Sun using data from ground- and space-based telescopes at every band of the electromagnetic spectrum (except gamma rays). She also writes regular posts for the Women in Astronomy BlogSpot on topics such as unconscious bias, stereotype threat, and the gender gap.

September 27, 2017

 "Formation of Close-in Super-Earths, Super-puffs and Ultra-Short Period Planets"
Eve Lee

Sherman Fairchild Postdoctoral Scholar in Theoretical Physics
Host: Konopacky

 Abstract: The riddle posed by super-Earths is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. In this talk, I will demonstrate that this puzzle is solved if super-Earths formed late, in environments akin to the inner cavities of transitional disks. Super-puffs present the inverse problem of being too voluminous for their small masses. I will show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside 1 AU, and then migrate in just after super-Earths appear. Super-Earths and Earth-sized planets around FGKM dwarfs are evenly distributed in log orbital period down to ~10 days, but dwindle in number at shorter periods. I will demonstrate that both the break at ~10 days and the slope of the occurrence rate down to ~1 day can be reproduced if planets form in disks that are truncated by their host star magnetospheres at co-rotation. Planets can be brought from disk edges to ultra-short (<1 day) periods by asynchronous equilibrium tides raised on their stars.

October 4, 2017

 "Secondary astrophysical production of anti-deuteron and anti-Helium3
cosmic ray"
Ryosuke Sato

Postdoctoral Fellow
Weizmann Institute
Host: Flauger

 Abstract: Cosmic-ray anti-deuterium and anti-helium have long been suggested as probes of dark matter, as their secondary astrophysical production was thought extremely scarce.

But how does one actually predict the secondary flux? Anti-nuclei are dominantly produced in pp collisions, where laboratory cross section data is lacking.

We make a new attempt at tackling this problem by appealing to a scaling law of nuclear coalescence with the physical volume of the hadronic emission region. The same volume is probed by Hanbury Brown-Twiss (HBT) two-particle correlations.

We demonstrate the consistency of the scaling law with systems ranging from central and off-axis AA collisions to pA collisions, spanning 3 orders of magnitude in coalescence yield. Extending the volume scaling to the pp system, HBT data allows us to make a new estimate of coalescence, that we test against preliminary ALICE pp data.

For anti-helium the resulting cross section is 1-2 orders of magnitude higher than earlier estimates. The astrophysical secondary flux of anti-helium could be within reach of a five-year exposure of AMS02.

October 11, 2017

 "Dwarf galaxy formation and the nature of dark matter"
Anna Nierenberg

UC Chancellor Postdoc
UC Irvine
Host: Wright

 Abstract: The abundance of low mass dark matter halos (M_vir <10^9 M_sun) provides key insight into the nature of dark matter, as this abundance depends on the free-streaming length of dark matter at early times and thus its particle properties. Measuring the abundance of low mass halos is difficult as stars become increasingly poor tracers of structure on these scales owing to the complex and not yet well understood physics of star formation in these systems. I will present two complementary approaches to resolving these issues. First I will present measurements of the properties of faint satellite galaxies at a range of redshifts and around a variety of host types and demonstrate how these place strong new constraints on theoretical models of star formation in low mass halos. Secondly, I will present a novel approach to gravitational lensing which makes it possible directly measure the subhalo mass function to masses well below the mass scale of the missing satellite problem in a much larger sample of systems than previously possible. I will conclude by discussing future prospects for these programs given the next generation of ground and space based facilities.

October 18, 2017

 "Outflows in active galactic nuclei"
Sibasish Laha

Postdoctoral Scholar
Host: Rothschild

 Abstract: The last couple of decades have seen the most crucial developments in the understanding of AGN winds. This can be attributed mostly to the advent of great observatories like ALMA (Molecular outflows), Hubble space Telescope (UV outflows), XMM-Newton and Chandra (X-ray outflows). Coupled with advancement in theories, our understanding about AGN outflows in different wavelength bands (Radio, Infra-red, Optical, UV and X-rays) has never been better, yet there are many outstanding questions which we still need to answer. We present here the results from a comprehensive study of the warm absorbers (WA) in X-ray in a flux limited complete sample of Seyfert galaxies (WAX-I, Laha et. al. 2014, MNRAS 441, 2613), using high resolution XMM-Newton data. We found that the WA clouds are present in around 65% of the sources. We also found a gap in the ionization parameter distribution of the WA, pointing to thermal instability. We have found evidences of WA being radiatively driven and they originate from the dusty torus (WAX-II, Laha et al. 2016, MNRAS 457, 3896L). The dust opacity can also play a leading role in driving these clouds. These WA clouds can sometimes give “effective feedback” to the host galaxies. In another extensive sample study of AGN exhibiting molecular outflows (to be submitted), we find that the AGN plays the most important role in driving these large kpc scale outflows. However, we are still uncertain how the AGN interacts with these large scale molecular clouds.

October 25, 2017

 "What matter(s) around galaxies? Shining a bright light on the cold phase of the
Circum Galactic Medium"
Sebastiano Cantalupo

Assistant Professor
Institute for Astronomy, ETH Zurich
Host: Keres

 Abstract: I will present the results of a new program to directly detect and study high-redshift cosmic gas in emission using bright quasars and galaxies as external "sources of illumination’. By looking in emission rather than in absorption, this program provides new and unique information on the morphology and physical properties of the cold phase of the Circum Galactic Medium (CGM) on both large and small scales. In particular, I will show results from ultra-deep narrow-band imaging and recent integral-field-spectroscopy as a part of the MUSE Guaranteed Time of Observation program that revealed numerous giant Lyman-alpha emitting filaments extending up to several hundred kpc around quasars and bright galaxies. I will discuss how the unexpectedly high luminosities of these systems, together with the constraints from Helium and metal extended emission, represent a challenge for our current understanding of cosmological structure formation. In particular, I will show that current observations suggest that a large amount of “cold" and dense gaseous “clumps" should be present around high-redshift galaxies and I will present our first attempts to understand the origin and nature of these structures in the Early Universe. At the same time, current galaxy formation models lack an efficient mechanism to prevent too much cooling of the CGM onto galaxies at later epochs and rely on very strong “ejective" feedback. In the second part of the talk, I will show how the interaction between high-energy radiation from star-forming galaxies and the CGM - still ignored by almost all galaxy formation models - provides a natural way to prevent excessive CGM cooling onto galaxies (“preventive” feedback). Finally, I will mention recent COS observations that provide support for the importance of this “preventive” feedback mechanism and, at the same time, can give vital constraints on the SED of star-forming galaxies in the FUV range.

November 1, 2017

 "The Development of the Next Generation Instrumentation for the Compton
Spectrometer and Imager"
Jarred Roberts

Postdoctoral Scholar
Host: Boggs/Fuller

 Abstract: The Compton Spectrometer and Imager (COSI) is a balloon-borne, soft-gamma ray imager, spectrometer, and polarimeter with sensitivity from 0.2 to 5 MeV. Utilizing a compact Compton telescope design with twelve cross-strip, high-purity germanium detectors, COSI has three main science goals: to study the 511 keV positron annihilation line from the Galactic plane, to image diffuse emission from stellar nuclear lines, and to perform polarization studies of gamma-ray bursts and other extreme astrophysical environments. The COSI experiment is currently undergoing a significant instrumentation development that aims to improve the energy and angular resolution of the instrument. This talk will focus on the current status of these developments and the scientific motivation for making these improvements to the instrument.

November 8, 2017

 "Revolutionizing our Understanding of Galaxy Evolution using the Circumgalactic
Cameron Hummels

NSF Postdoctoral Fellow, Department of Astronomy
Host: Sandstrom

 Abstract: Cosmological hydrodynamics simulations are increasingly able to reproduce galaxies like those we observe in nature. However, the detailed structure of the circumgalactic medium (CGM), the tenuous gas around galaxies, remains an unresolved challenge. As the interface between star formation, feedback, galactic gas accretion, and acting as a reservoir hosting half the baryons in a galaxy, the CGM is the key to understanding what drives galactic evolution. I will discuss my recent work at modeling the circumgalactic medium with a focus on the absorber sizes and phase structure of the halo gas as probed through the FIRE and the Tempest simulations, the two highest resolution zoom hydro simulations of the CGM produced to date. Lastly, I will present Trident, an open-source code for generating synthetic spectra to compare simulations with observations.

November 15, 2017

 "Clouds in the Galactic Sky - The Gaseous Halos of Galaxies from the synergy of Observation and Theory"
Cameron Liang

Graduate Student, Department of Astronomy and Astrophysics
University of Chicago
Host: Coil

 Abstract: Undoubtedly, the Earth's atmosphere is an integral part of its ecosystem. Everyday weather and long-term climate of the atmosphere are directly linked to activities on the surface of the Earth and vice versa. Gaseous halos, known as the circumgalactic medium (CGM), are the equivalent atmosphere of galaxies. The galactic climate arises from infalling gas from intergalactic space, enriched materials launched from the interstellar medium and more. The CGM is one of the largest gas reservoirs with complex baryonic cycles. It is paramount to improve our understanding of the CGM to achieve a complete picture of galaxy formation and evolution.

In this talk, I will first focus on the observational efforts to place empirical constraints on the spatial extent and the metallicity of the CGM. I will then present some theoretical work on the baryonic cycles in cosmological zoom-in simulations and show that the CGM provides orthogonal constraints to star formation and feedback processes. Finally, I will present a new high-resolution (< 1pc) simulation study to model the CGM more systematically with radiative cooling, thermal conduction, and magnetic fields.

November 29, 2017

 "Cosmology Results from the Dark Energy Survey Year 1"
Elisabeth Krause

Research Scientist
Host: Galitzki/Flauger

 Abstract: This talk presents cosmology constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive with those from Planck cosmic microwave background measurements.

I will describe the validation of measurements and modeling from catalogs to cosmology, and highlight cosmology constraints from the combination of DES Y1 with external data sets.

Based on DES Collaboration 2017 (1708.01530) and supporting papers.

December 1, 2017

NOTE: Special Plasma-Astro Seminar @ 3:00 in SERF 329
 "Using properties of MHD turbulence to study B-fields and remove B-mode
Alex Lazarian

Professor of Astronomy
University of Wisconsin-Madison
Host: Diamond

 Abstract: I shall discuss a new technique of tracing magnetic fields in the galaxy that uses the properties of MHD turbulence and show the advantages of this new technique compared to the traditional ways of magnetic field study. I shall also show that the observed properties of galactic CMB foreground, in particular the E/B mode ratio measured for the foreground polarized emission, is consistent with the expectations of the MHD theory.

December 5, 2017

NOTE: Joint Physics-CASS-CER Seminar @ 4:00 in SERF 383
 "Ultra-strong laser fields: from linear to nonlinear QED"
Felix Mackenroth

Distinguished Postdoctoral Fellow
Max-Planck-Institute for the Physics of Complex Systems, Dresden, Germany
Host: Fuller/Beg/Diamond

 Abstract: In the interaction of ultra-intense laser fields with matter the ever increasing peak laser intensities render relativistic quantum effects ever more prominent. Such effects are properly described in the framework of quantum electrodynamics and range from manifestations of the photons' particle nature to the famous production of matter from light. Furthermore, the unprecedentedly high photon densities reached at state-of-the-art laser facilities lead to nonlinearities in the interaction with the laser photons, requiring nonperturbative field theoretical methods. Nonlinear or strong-field QED, the proper framework to describe such phenomena, is still an area of intense research. In this talk we are going to discuss a recent proposal how the linear QED effect of producing matter from a two-photon collision could be observed for the first time. Then, we turn to the underlying principles of strong-field QED and how to compute nonperturbative scattering amplitudes. We present quantitative examples for typical nonlinear QED processes. The full result is then benchmarked against common approximations employed in large-scale numerical plasma simulations and it is demonstrated that these approximations have certain limitations. These limits are then discussed in light of upcoming experimental tests.

Author information:

The author received his undergraduate education in physics in Konstanz and Heidelberg, Germany, and did his PhD on quantum radiation in ultra-intense laser pulses under the supervision of PD Antonino Di Piazza in the quantum dynamics group of Prof. Keitel at the Max-Planck-Institute for Nuclear Physics in Heidelberg. For his PhD thesis he was awarded the Otto-Hahn medal of the Max-Planck-Society in 2013 and the thesis was selected to be published under the distinguished Springer Theses program. He then did a post-doc on relativistic plasma physics and laser-based ion acceleration at Chalmers Technical University in Gothenburg, Sweden, from 2014 to 2016. In late 2016 he moved back to Germany to join the Max-Planck-Institute for the Physics of Complex Systems in Dresden where he currently holds a position as Distinguished Postdoctoral Fellow.

December 6, 2017

 "The Breakthrough Listen Search for Advanced Life Beyond Earth”
Andrew Siemion

Director, Berkeley SETI Research Center
UC Berkeley
Host: Wright

 Abstract: The Breakthrough Listen Initiative is an ambitious effort to conduct the most comprehensive and sensitive search for advanced extraterrestrial life in humanity’s history. Breakthrough Listen has secured approximately 20% of the time on two of the largest radio telescopes in the world, the 64m Parkes Telescope in NSW, Australia and the 100m Green Bank Telescope at Green Bank Observatory in West Virginia, along with 36 nights per year on the 2.4m Automated Planet Finder at Lick Observatory. Breakthrough Listen has also entered into an agreement with the National Astronomical Observatory of China to collaborate on the development of search techniques, software and observing procedures for the 500m FAST Telescope, and the Jodrell Bank Observatory / University of Manchester to work together in a similar fashion toward developing SETI capabilities on the 76m Lovell Telescope and the MERLIN network.

Breakthrough Listen observations at the APF employ the Levy Spectrometer to conduct ``spectroscopic optical SETI’’ observations, searching for artificially narrow spectral lines that are known only to arise from technological sources (lasers). At the GBT and Parkes, Breakthrough Listen is deploying state-of-the-art digital backends capable of searching for a wide variety of signals indicative of a technological source, across many GHz of instantaneous bandwidth. As of this writing, Breakthrough Listen has deployed a 6 GHz system at the Green Bank Telescope and a 5 GHz system at the Parkes Telescope.

The current Breakthrough Listen target list includes a spectral-type complete sample of nearby stars, 100 nearby galaxies spread over all morphological types, a complete survey of the galactic plane and exotic objects and targets of opportunity (e.g. KIC 8462852, FRB121102). The Breakthrough Listen team is currently exploring opportunities to engage in commensal SETI programs with the SKA and its precursors. These potential extensions to the Breakthrough Listen program would allow significant expansion of the Breakthrough Listen target list and would lay the groundwork for extremely high sensitivity observations with the full SKA. These latter observations would be the first SETI ever conducted that would be sensitive to Earth-level leakage radiation from nearby stars.

Here I will review the Breakthrough Listen program, current observational capabilities and latest results.

Winter 2018

January 10, 2018

NOTE: Seminar will be held in SERF 329
 "Cosmology Through the Dust: Mitigating Galactic Foregrounds with HI"
Brandon Hensley

Postdoctoral Fellow
Host: Keating

 Abstract: Whether galaxy surveys in the optical or polarized CMB measurements in the microwave, cosmological observations are sensitive to contamination from Galactic dust. I will first present new, large scale maps of interstellar reddening constructed from the fully-sky, spectroscopic HI observations of the HI4PI Survey. Using atomic hydrogen as a tracer of Galactic dust eliminates the need for dust temperature corrections and allows easy removal of extragalactic contamination, producing reddening maps of higher fidelity than those based on far-infrared dust emission, such as that of Schlegel, Finkbeiner, and Davis 1998 ("SFD"). Given the ability of HI to serve as a template for the dust column, I will describe a novel method for using HI to make Cosmic Infrared Background (CIB) maps with high fidelity on large angular scales. Finally, I will discuss some possibilities for using HI and other ancillary data to constrain dust physics and ISM structure, enabling more effective component separation in CMB experiments.

January 17, 2018

 "Analysis of dust emission in nearby galaxies - Implications of the modeling
Jérémy Chastenet

Postdoctoral Scholar
Host: Sandstrom

 Abstract: My work focused on the implications of dust emission modelisation choices on its derived properties in nearby galaxies. A first approach showed that all models do not fit observations of two nearby galaxies adequately and similarly, although they all managed to fit the Milky Way infrared emission. It also highlighted that the dust composition is not the same between those two galaxies, and also with that of the Milky Way. The choice of the dust grains environment, through the incident radiation field, can significantly impact results like the total dust masses. A second project investigated the systematics errors due to the empirical laws used to describe theradiation field that heats the dust grains. I showed that some parameters can be over- or underestimated, while showing good fits to the observations. By getting rid of uncertainties due to dust composition, my results show that the current approach leads to discrepancies in the dust content in spite of a correct dust description.

January 19, 2018

NOTE: Special Lecture from 3:00-5:00PM in Liebow Auditorium
 "Dark Matter Decay According to Conformal Cyclic Cosmology: Does it Provide
Detectable Gravitational Signals?"
Sir Roger Penrose

Oxford/Penrose Institute
Host: Keating

 Abstract: In the cosmological scheme of conformal cyclic cosmology (CCC), the equations governing the crossover form each aeon to the next demand the creation of a dominant new scalar material, postulated to be dark matter. In order that this material does not build up from aeon to aeon, it is taken to decay away completely over the history of each aeon. The dark matter particles (erebons) may be expected to behave almost as classical particles, though with bosonic properties, being probably of about a Planck mass, and interacting only gravitationally. Their decay would be to gravitational signals, and responsible for the (~scale invariant) temperature fluctuations in the CMB of the succeeding aeon. In our own aeon, erebon decay might well show up in signals discernable by gravitational wave detectors.

January 24, 2018

 "Unraveling the nature of dark matter via galaxy evolution at low and high-redshift"
Victor Robles

Postdoctoral Researcher
UC Irvine
Host: Keres

 Abstract: Recently there have been major improvements in the numerical implementations that model astrophysical processes, partly motivated to solve some discrepancies in the CDM paradigm, where the main study deals with modifying the dark matter distribution by stellar feedback. On the other hand, there is an increasing interest in detecting dark matter (DM) in either indirect and direct detection experiments. In this talk I will discuss a different approach that could help to unravel the DM nature. While hydrodynamics simulations show that CDM can react in a non linear way to astrophysics, the opposite implication is rarely addressed in a general context. I perform hydrodynamics simulations to show how the baryons react to a different DM nature and explore the consequences in dwarf galaxies. By restricting to the FIRE implementation for the astrophysics, I study the self-interacting dark matter(SIDM) as well as the ultra light scalar field (Bose-Einstein condensate or BEC) dark matter models. I find that different dark matter models provide clear predictions in the inner regions of dwarf galaxies, making them ideal targets for deeper observation, especially with the upcoming surveys mapping the near and far universe. Regarding the far universe, I discuss some implications at high redshift for the BECDM model which can change how the first galaxies form and when reionisation happened, leading to a different picture from the standard CDM paradigm. I point to future research at high-redshift that will help to confirm or discard some dark matter fundamental properties.

January 31, 2018

 "Breaking the Habit - The peculiar 2016 eruption of the remarkable recurrent nova
in M31"
Martin Henze

San Diego State University
Host: Rubin

 Abstract: Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and a high accretion rate, which is the most promising candidate for the progenitor of a type-Ia supernova known to date. The previous three eruptions of M31N 2008-12a have displayed remarkably homogeneous multi-wavelength properties. In contrast, the delayed 2016 eruption (in December last year) showed significant deviations from this pattern. In this talk, I will discuss the 2016 observing campaign and its results, together with possible interpretations on the physics and evolution of this unique system in the context of extragalactic nova science.

February 7, 2018

NOTE: Joint Astro-Plasma Physics Seminar
 "The Basis for Cosmic Ray Feedback: Microscales to Macroscales"
Ellen Zweibel

W. L. Kraushaar Professor of Astronomy & Physics, Department of Astronomy
University of Wisconsin-Madison
Host: Diamond

 Abstract: Cosmic rays, mostly relativistic protons, represent less than a billionth of interstellar particles, but comprise roughly the same energy density as the thermal gas. Their interaction with the thermal gas is primarily collisionless, mediated by the ambient magnetic field. I will discuss the plasma physics that underlies this interaction, and how it allows cosmic rays to sculpt, or feed back on, their environments.

February 14, 2018

 "Challenges in Measuring the Polarization of the Cosmic Microwave Background: Next-generation Experiments"
Joy Didier

Host: Keating

 Abstract: In the last decades, increasingly sensitive measurements of the temperature of the Cosmic Microwave Background (CMB) have provided us with a wealth of information such as the age, composition and geometry of the universe. A widespread experimental effort is currently underway to map the polarization of the CMB to probe for primordial gravitational waves and understand the high energy physics of the early universe. CMB polarization also encodes information about the distribution of ordinary and dark matter, dark energy and the sum of the mass of neutrinos. To probe this science, the CMB polarized signals to be measured are extremely faint and experiments have to achieve exquisite sensitivity and controls of systematics, as well as measure precisely the Galactic foregrounds. In my talk I will review those challenges and ways to address them through future experiments like the ground based Simons Observatory telescope, the balloon-borne BLAST-TNG polarimeter, and the NASA PICO probe.

February 28, 2018

 "Closing in on Black Hole Spins"
John Tomsick

Researcher, Space Sciences Lab
UC Berkeley
Host: Rothschild

 Abstract: Determining how rapidly black holes (BHs) spin has been a key goal of astrophysics for decades. Knowing the spin rates of BHs is relevant to probing regions of strong gravity, understanding how relativistic jets are powered, and determining how BHs form and evolve. In this talk, I will discuss methods that have been developed for measuring the spins of accreting BHs with X-ray spectral and timing observations. This includes past X-ray timing and spectral measurements with RXTE, recent X-ray reflection measurements with the Nuclear Spectroscopic Telescope Array (NuSTAR), and future X-ray and soft gamma-ray polarization measurements with IXPE, XIPE, and COSI-X. Comparisons between spins of accreting stellar mass BHs and the constraints found by gravitational wave measurements for BH/BH merger events will also be presented.

March 7, 2018

 "Fine-Tuning Constraints on Stellar Operations"
Fred Adams

Ta-You Wu Collegiate Professor of Physics
University of Michigan
Host: Fuller

 Abstract: Motivated by the possible existence of other universes, with different values for the fundamental constants, this talk considers stars and stellar structure with different values for the fundamental constants of nature. Focusing on the fine structure and gravitational constants, we first enforce the following constraints: [A] long-lived stable nuclear burning stars exist, [B] planetary surfaces are hot enough to support chemistry, [C] stellar lifetimes are long enough to allow biological evolution, [D] planets are massive enough to maintain atmospheres, [E] planets are small enough to remain non-degenerate, [F] planets are massive enough to support complex biospheres, [G] planets are less massive than stars, and [H] stars are less massive than galaxies. The parameter space that satisfies these constraints is relatively large: viable universes can exist when the structure constants vary by several orders of magnitude. Next we consider a number of other fine-tuning issues, including the triple alpha fine-tuning problem for carbon production, nucleosynthesis in universes without stable deuterium, and structure formation in universes with varying amplitudes for the primordial density fluctuations. In all of these scenarios, the basic parameters of physics and cosmology can vary over wide ranges and still allow the universe to operate.

March 13, 2018

NOTE: Special Astro Seminar @ 9:30AM - SERF 383
 "Gravitational wave astrophysics: a new era of discovery"
Jessica McIver

Postdoctoral Scholar
Host: Tytler

 Abstract: Large-scale interferometric detectors including LIGO and Virgo sense gravitational waves; minuscule fluctuations in space-time from the most extreme phenomena in the Universe. The recent detection of gravitational waves by LIGO and Virgo in concert with an associated electromagnetic counterpart was a breakthrough in multi-messenger astronomy that confirmed the association between neutron star collisions and short gamma-ray bursts (sGRBs) and yielded new insight into the physical engine driving sGRBs. Future gravitational wave observations have the potential to provide critical insight into key open questions in astrophysics, including the distribution of compact objects in the Universe, the evolution of compact binary systems, galaxy formation, and the explosion mechanism of core-collapse supernovae.

March 14, 2018

 "Insights on the diffuse magnetized ISM through starlight polarimetry"
Gina Panopoulou

Staff Scientist, Radio Astronomy
Host: Keating

 Abstract: The magnetized nature of the ISM presents challenges for studies of the origins of stars as well as for searches for an inflationary signature in the CMB. Part of the challenge arises from the difficulty in measuring the magnetic field. No single technique can provide complete information on this 3D vector. The most recent advances in our knowledge of the field's properties have come from measurements of the plane-of-sky component of the magnetic field, through the polarization of thermal dust emission observed with Planck. However, information is still lacking at scales below Planck's resolution and at regions with extremely low dust content. Starlight polarimetry is ideally suited to provide this complementary information. I will present what we have learned about the magnetic field in a translucent molecular cloud, where sub-Planck resolution is necessary for identifying the slender filamentary gas morphology. I will also discuss the properties of ISM polarization in parts of the sky with minimum dust content.

March 19, 2018

NOTE: Special Astro Seminar @ 9:30AM - SERF 383
 "Probing strong-field gravity: Black holes and mergers in general relativity
and beyond"
Leo Stein

Postdoctoral Researcher
Host: Tytler

 Abstract: General relativity—Einstein's theory of gravitation—has been studied for more than 100 years. Over the past century, we have learned that the theory agrees with all available experimental and observational tests. At the same time we know that the theory is incomplete, as it leads to inconsistencies when coupled with quantum mechanics.

The strong-field regime is our best hope to study GR, both observationally and theoretically, and thus understand how to correct its shortcoming. In this talk, I will discuss investigations in the strong field, including black holes and neutron stars, in GR and theories beyond GR. The main focus will be predicting gravitational waves from merging black holes beyond GR. These predictions will allow for the most rigorous testing of general relativity, using LIGO, in the dynamical strong-field regime.

March 22, 2018

NOTE: Special Astro Seminar @ 11:00AM - SERF 383
 “Numerical relativity in the era of gravitational-wave observations”
Geoffrey Lovelace

Assistant Professor, Department of Physics
CSU Fullerton
Host: Tytler

 Abstract: With their first observations of merging black holes and merging neutron stars, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo have inaugurated a new era of gravitational-wave astronomy. In this talk, I will discuss the latest discoveries from LIGO and Virgo and how numerical relativity is playing a key role in interpreting gravitational-wave observations. I will highlight some of the ways my students and I are contributing to these discoveries as well as our future plans.

March 26, 2018

NOTE: Special Astro Seminar @ 10:00AM - SERF 383
 "Black holes, alone and in pairs"
Aaron Zimmerman

Senior Research Associate
Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto
Host: Tytler

 Abstract: The recent detections of gravitational waves have revealed an invisible side of the universe: black holes in binaries. These observations test our understanding of black holes, their violent mergers, and the theory of general relativity. A combination of analytic approximations and full numerical simulations is required to understand black hole binaries and predict the gravitational waves they emit. I will take us on a tour of these systems, discuss the "ringdown" of the final merged black hole, and present the most recent results from the Advanced LIGO and Virgo detectors.

Spring 2018

April 2, 2018

NOTE: Special Astro Seminar @ 9:30AM - SERF 383
 "The Dawn of Precision Gravity: From LIGO to LISA"
Rafael Porto

International Centre for Theoretical Physics, South American Institute for Fundamental Research (ICTP-SAIFR), Brazil
Host: McGreevy

 Abstract: The nascent field of gravitational wave (GW) science will be an interdisciplinary subject — enriching different branches of physics — yet the associated computational challenges are enormous. Faithful theoretical templates are a compulsory ingredient for successful data analysis and reliable physical interpretation of the signals. This is critical, for instance, to study the equation of state of neutron stars, the nature of black holes, and binary formation channels. However, while current templates for compact binary sources may be sufficient for detection and crude parameter estimation, they are still too coarse for precision physics with GW data. We then find ourselves in a situation in which, for key processes within empirical reach, theoretical uncertainties may dominate. To move forward, and profit the most from GW observations, more accurate waveforms will be needed. The ‘effective field theory approach’ to the binary inspiral problem in general relativity — which my collaborators and I have developed — has been instrumental for the construction of the state-of-the-art GW template bank. I will review how these novel techniques will provide key results that will enable foundational investigations in physics through GW precision data: from probes of dynamical spacetime and strongly interacting matter, to the potential to discover exotic compact objects and ultra-light particles in nature.

April 4, 2018

 "Is Anyone Out There?
The Search for ET with Help from Eight Million Volunteers"
Dan Werthimer

Chief Scientist, SETI, Department of Astronomy
UC Berkeley
Host: Wright

 Abstract: When will Earthlings discover intelligent life in the universe? Can we detect radio, infrared, or visible wavelength signals from alien civilizations? Current and future projects searching for such signals may provide an answer. Dan Werthimer will describe plans for future searches and show how new technologies are revolutionizing the search for extra-terrestrial intelligence (SETI). Dan will also describe Berkeley's SETI@home project, which analyzes data from the world's largest radio telescopes using desktop computers and cell phones from millions of volunteers, forming one of Earth's most powerful supercomputers.


Dan Werthimer was in the “Homebrew Computer Club” with Steve Jobs and Steve Wozniak; everyone in that club became filthy rich, except Dan, because Dan fancied utilizing his signal processing and electronics skills in astrophysics. Dan holds the Marilyn and Watson Alberts SETI Chair and is Chief Scientist of the Berkeley SETI Research Center, where he oversees SETI@home, the $100 million Breakthrough Listen project, and several other SETI programs. Dan also directs the Center for Astronomy Signal Processing and Electronics Research (CASPER) and is associate director of the Berkeley Wireless Research Center (BWRC). He has been associate professor in the engineering and physics departments of San Francisco State University and a visiting professor at Beijing Normal University, the University of St. Charles in Marseille, and Eotvos University in Budapest. Dan has also taught at universities in Peru, Egypt, Ghana, Ethiopia, Zimbabwe, Uganda and Kenya.

April 11, 2018

 "Cosmochemical perspectives on the delivery and retention of volatile elements on the terrestrial planets"
Emily Pringle

Scripps Postdoctoral Fellow
Host: Day

 Abstract: Volatile element abundances are variable among inner Solar System bodies, with differing degrees of depletion compared to primitive materials such as carbonaceous chondrites. These variations are a consequence of the processes of planetary formation, but their exact origin is debated. The conditions and the mechanisms of planetary accretion and differentiation can be investigated by analyzing the stable isotope compositions of terrestrial and extraterrestrial samples. The moderately volatile lithophile (rock-loving) elements are particularly useful to distinguish between the effects of accretion and those of core formation, while siderophile (metal-loving) elements give clues to understanding the timing of volatile delivery. For example, recent work has shown that isotopes of the moderately volatile elements Zn, K, and Rb exhibit variations in inner Solar System bodies that may be a signature of volatile loss during planetary accretion. I will discuss the current evidence for understanding the delivery and retention of volatiles in in inner Solar System, with the goal of linking cosmochemical observations to models of planetary accretion.

April 25, 2018

 "Characterizing the Life Cycle of the Interstellar Medium and Star Formation in Galaxies with the [CII] 158μm line"
Jorge Pineda

Research Scientist
Host: Sandstrom

 Abstract: The [CII] 158μm line is a powerful tool to understand the evolution of the interstellar medium and star formation in galaxies. The [CII] line traces different phases of the interstellar medium (ISM), including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions (PDRs). In particular, the [CII] line is a tracer of the CO-dark H2 gas, in which hydrogen is molecular but carbon is ionized and thus is not traced by CO. This CO-dark H2 gas is the likely precursor of dense molecular clouds that will eventually form stars. The [CII] 158μm line is also the brightest far–infrared cooling line in galaxies and reprocesses UV starlight from newly formed stars. Thus it is also a potentially powerful tracer of star formation activity. In this talk I will review recent work on using velocity resolved observations of the [CII] line taken with Herschel/HIFI and SOFIA/GREAT to characterize the evolution of the interstellar medium and star formation in the Milky Way, the Magellanic Clouds, and the M51 grand design spiral galaxy.

May 2, 2018

 "Very High Energy Astronomy with the Cherenkov Telescope Array"
Rene Ong

Professor, Department of Physics and Astronomy
Host: Fuller

 Abstract: The field of very high energy (VHE) astronomy had been revolutionized by the results from ground-based gamma-ray telescopes, including the current atmospheric Cherenkov telescopes: HESS, MAGIC and VERITAS. The Cherenkov Telescope Array (CTA) will capitalize on the power of the Cherenkov technique to achieve a better angular resolution, a wider energy range and field of view, and much greater collection area compared to existing instruments. This will allow CTA to carry out much deeper surveys of the VHE universe to explore key science topics such as cosmic particle acceleration on all scales and understanding extreme environments close to neutron stars and black holes. Exploring physics frontiers is another important component of CTA science, including the search for WIMP dark matter and axion-like particles. CTA will consist of two large arrays, one in each hemisphere, each containing telescopes of different sizes to provide a balance between cost and overall performance over a wide energy range. This talk will review the current status of VHE astronomy, provide the scientific motivation for CTA (with emphasis on a planned survey of the Galactic plane and on the foreseen dark matter program), and summarize the current status of the technical design and plan for construction.

May 9, 2018

 "Why Circumgalactic Matter Matters for Galaxy Evolution"
Jessica Werk

Assistant Professor
University of Washington
Host: Rubin

 Abstract: The circumgalactic medium (CGM; non-ISM gas within a galaxy virial radius) regulates the gas flows that shape the assembly and evolution of galaxies. It most likely contains enough material to harbor most of the metals lost in galaxy winds and to sustain star-formation for billions of years. Owing to the vastly improved capabilities in space-based UV spectroscopy with the installation of HST/COS, observations and simulations of the CGM have emerged as the new frontier of galaxy evolution studies. In this talk, I will describe observational constraints we have placed on the origin and fate of this material by studying the gas kinematics, metallicity and ionization state of gas 10 - 200 kpc from galaxies’ stars. I will conclude by introducing several exciting new techniques for resolving the gaseous structures in the CGM, and by posing unanswered questions about the CGM that will be addressed with future survey data and hydrodynamic simulations in a cosmological context.

May 16, 2018

 "The MASSIVE Survey of Early-Type Galaxies and Supermassive Black Holes in the Local Universe"
Chung-Pei Ma

Professor of Astronomy and Physics
UC Berkeley
Host: Wright

 Abstract: Massive galaxies in the local universe offer a unique perspective on galaxy evolution, having the oldest stellar populations, the most massive black holes, and the longest history of major and minor merger events.

I will describe the ongoing MASSIVE Survey, a volume-limited, multi-wavelength, spectroscopic and photometric survey of the structure and dynamics of the 100 most massive early-type galaxies within 100 Mpc.

A combination of integral-field spectroscopy on sub-arcsecond and large scales enables us to perform simultaneous dynamical mass modeling of the supermassive black holes, stars, and dark matter. I will also highlight properties of other mass components — cold, warm, and hot gas — from our multi-wavelength datasets and discuss the implications of our black hole findings for the Pulsar Timing Array searches for gravitational waves.

May 23, 2018

 "Cooler than Gaia: Parallaxes of Ultracool Objects with WISE"
Christopher Theissen

Postdoctoral Scholar
Host: Wright/Konopacky

 Abstract: Trigonometric parallaxes are one of the most fundamental measurements astronomers can make, providing a wealth of information about our Galaxy and its constituents. These measurements are also crucial for calibrating the distance ladder and our ability to measure distances to extragalactic sources. The imminent release of over one billion parallaxes from the Gaia satellite will revolutionize our understanding of the Milky Way. That being said, Gaia will be limited in its ability to observe the lowest mass, coolest stars and brown dwarfs in our Galaxy. I will discuss the potential to use the Wide-field Infrared Survey Explorer (WISE) to measure relatively precise parallaxes of nearby, very low-mass stars and brown dwarfs, exceeding the limits of Gaia. I will show recent results using this method, and illustrate the importance in precise distances for measuring the fundamental parameters of stars and brown dwarfs. I will also discuss future directions on improving this method for even cooler (and fainter) objects.

May 30, 2018

 "Disks, Planet Formation, and the Structure of Planetary Systems"
Ruth Murray-Clay

UC Santa Cruz
Host: Sandstrom/Konopacky

 Abstract: What sets the extent of giant planet formation, and what does this tell us about the structures of planetary systems in general? I will provide evidence that observed protoplanetary disks may be more massive than previously thought, show that gas turbulence coupled with pebble accretion may set the largest distances at which giant planets form, and discuss ways that we can use observations of wide-separation planets in concert with Kepler and radial velocity samples to constrain planet formation theories. Finally, I will comment on why Uranus and Neptune are not giants and discuss implications for the diversity of planetary systems.

May 31, 2018

NOTE: Special Astro Seminar @ 1:00PM - SERF 383
 "Kinetic inductance detectors for millimeter-wave polarimetry"
Heather McCarrick

PhD Candidate, Department of Physics
Columbia University
Host: Arnold

 Abstract: Future cosmic microwave background (CMB) experiments will require advances in detectors technologies. In the first part of the talk, I will present the design and measured performance of dual-polarization, lumped-element kinetic inductance detectors (LEKIDs) for next-generation experiments. We have designed, fabricated, and tested arrays of these devices. They are horn-coupled and sensitive to a single spectral band centered on 150 GHz. I will show the measured performance of the detectors including the response, noise-equivalent temperature, and polarization properties. In the second part, I will present initial results from our multi-chroic kinetic inductance detectors (KIDs), which are based on the Advanced ACTPol orthomode transducer design and sensitive to two polarizations in two spectral bands. Along the way, I will present some interesting device physics experiments we have been conducting lately, like investigating quasiparticle relaxation times.