March 27, 2015, 3:30 BPB-217. Kentaro Nagamine, Accelerated Structure Formation at High Redshift.

I will present two topics that suggest an accelerated growth of structures in high-density regions of the early universe. First is the birth of supermassive black hole (SMBH), and second is the formation of massive disk galaxies, both at redshifts z>6. Recent discoveries of billion solar mass SMBH at z=6-7 suggests that the gas accretion was quite rapid in the early universe with a super-Eddington rate. I will discuss a scenario called the 'Direct Collapse' of BH seed at high redshift, which has been attracting significant attention lately. I will also present our cosmological SPH simulation results of high-redshift galaxies at z=6-12, and discuss their observability with ALMA.

March 24, 2015 3:30 BPB-217. Kayhan Gultekin, Supermassive Black Holes

Supermassive black holes are some of the most fascinating energetic objects in the Universe, and they play a key role in what we can see across cosmic time and a large range of critical astrophysical phenomena. Despite their importance, much is unknown about their basic physics including how they were formed, how they grow, how they appear in different wavelengths, and what kind of galaxies they live in. The answers to many of these basic questions are within reach. I will review my recent, current, and future research plans to find their solutions.

March 19, 2015 3:30 BPB-217. Ashkan Salamat, A liquid-liquid phase transition to Metallic Hydrogen

Hydrogen is the simplest and most abundant element in the Universe. It is estimated that more than 70% of the planetary mass in our solar system is in the form of dense fluid hydrogen, with Jupiter and Saturn being the largest reservoirs. These planets contain extreme pressure and temperature conditions which are predicted to lead to the formation of metallic fluid hydrogen. The pressure-induced transition from insulator to metal in solid hydrogen was predicted as early as 1935 by Wigner and Huntington, but to date has not been experimentally confirmed. Metallic hydrogen is predicted to have spectacular properties such as room temperature superconductivity and metastability (i.e. it remains metallic when the pressure is released). If metallic hydrogen is found to be metastable, its application could revolutionize rocketry and fusion technology. There are two thermodynamic pathways to metallic hydrogen: direct pressurization at low or modest temperatures to a solid metallic phase, and in the megabar pressure region, heating into the liquid metallic phase. In this talk, I will present my recent work in which the insulator to metal transition in dense liquid hydrogen was observed experimentally for the first time.

March 18, 2015 10:45 BPB-217. Wei Bao, High-Pressure Single Crystal Neutron Scattering Study of the 245 Superconductor.

The iron vacancy order and the block antiferromagnetic order exist in the new iron 245 superconductors [1,2]. The appearance of the superconductivity crucially depends on the perfectness of the vacancy order [3]. The magnetic and vacancy orders in superconducting (Tl,Rb)2Fe4Se5 (245) single-crystals were investigated using high-pressure neutron diffraction technique [4]. Similar to the temperature effect, the block antiferromagnetic order gradually decreases upon increasing pressure while the Fe vacancy superstructural order remains intact before its precipitous drop at the critical pressure Pc =8.3 Gpa. Combining with previously determined Pc for superconductivity, our phase diagram under pressure reveals an intimate connection among the block antiferromagnetic order, the Fe vacancy order and superconductivity for the 245 superconductor. Similar connection between the perfectness of crystalline order and superconductivity has been previously demonstrated in our neutron scattering study on related Fe based superconductors [5,6].

March 17, 2015 3:30 BPB-217. Jake Simon, Probing the Nature of Accretion and Planet Formation in Protoplanetary disks: Connecting Theory with ALMA Observations.

Protoplanetary disks play a key role in star and planet formation processes. Turbulence in these disks, which arises from the magnetorotational instability (MRI), not only causes accretion of mass onto the central star, but also sets the conditions for processes such as dust settling, planetesimal formation, and planet migration. However, the exact nature of this turbulence is still not very well constrained in these systems. In this talk, I will first present recent numerical simulations of magnetohydrodynamic (MHD) turbulence in protoplanetary disks that point to the importance of large scale, vertical magnetic fields in driving disk accretion through both turbulent processes and magnetic winds. I will then describe new work, utilizing both state-of-the-art numerical simulations and powerful new radio observations, to directly link numerical predictions for the turbulent velocity structure of protoplanetary disks to observations by the Atacama Large Millimeter Array (ALMA). ALMA’s unprecedented resolution and sensitivity will allow us to generate a three-dimensional map of disk turbulence by measuring the turbulent broadening component of molecular lines at different disk heights (i.e., optical depths) and radii. A direct comparison between the observed turbulence values and those obtained from simulations will strongly constrain our theoretical understanding of these disks. I will conclude with an outlook for protoplanetary disk studies, and in particular how our current results may influence studies of planet formation processes and the construction of exoplanetary systems.

March 13, 2015 3:30 BPB-217. Florian Rodler, High-resolution spectroscopy of exoplanet atmospheres is cool!

High-resolution spectroscopy is a powerful tool to investigate the atmospheres of transiting exoplanets as well as of non-transiting ones. I will briefly review the basics underlying that technique and present the most important results up to now. In the light of the three upcoming Extremely Large Telescopes (ELTs), i.e. the GMT, TMT and E-ELT, I will further present feasibility studies dedicated on the detection of oxygen in the atmospheres of Earth-like planets orbiting M-dwarfs.

March 12, 2015 3:30 BPB-217. Norbert Werner, How supermassive black holes and star-formation sculpt the visible Universe

In the course of structure formation, only a small fraction of the baryons turned into stars - most remain in a diffuse intergalactic medium. The growth of galaxies is regulated by feedback processes, such as energy and momentum input from supernovae, and jets and winds of accreting supermassive black holes. These processes, collectively called galactic feedback, can limit or even inhibit star formation, and thus a detailed knowledge of how they work is essential for our understanding of galaxy formation and evolution. I will start my talk by presenting recent observational results on the role of supermassive black holes in keeping the most massive galaxies 'red and dead'. Then, I will 'zoom out' to the outskirts of galaxy clusters where we also find hints that supermassive black holes played an important role in the distant past. X-ray observations with the Suzaku satellite reveal a remarkably homogeneous distribution of iron out to the virial radius of the nearby Perseus Cluster, requiring that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity. Finally, I will talk about the upcoming ASTRO-H satellite which will revolutionize X-ray spectroscopy and our understanding of how feedback processes couple to the intergalactic medium.

March 10, 2015 3:30 BPB-217. Jason Steffen, Properties of exoplanets and systems with Kepler

NASA's Kepler mission has revolutionized the field of exoplanets and its discoveries give new insights into our theories of planet formation and dynamical evolution. With over 4000 planet candidates and 1000 confirmed planets, the variety of systems and planets shows the breadth of properties that planet formation models must encompass. I present some of the landmark results of the Kepler mission, especially relating to the planet masses and orbital architectures of the planetary systems. I discuss how these results affect our understanding of the solar system and of planets in general.

March 6, 2015 3:30PM BPB-217. Samaya Nissanke, Follow the chirp: seeing and listening to the transient Universe

The mergers of binary compact objects (black holes, neutron stars, white dwarfs) are amongst some of the most violent events in the Universe. The physics driving these events in strong field gravity are extremely complex, rich but still remain elusive. These cosmic laboratories present us now with both a challenge and an opportunity. The challenge is to explain the physics at play in strong-field gravity in Universe. The opportunity is to detect the accompanying radiation and panoply of multi-messenger particles (high energy neutrinos, cosmic rays and gravitational waves) for the first time with a suite of time-domain telescopes and experiments. In this pivotal new era of multi-messenger astronomy, the most compelling astrophysical sources are neutron star binary mergers, which should emit both in electromagnetic (EM) and gravitational waves (GW). I will first review the most recent advances in this blossoming field of EM+GW astronomy, which combines two active disciplines: time-domain astronomy and general relativity. I will discuss the promises of this new convergence by illustrating the wealth of astrophysical information that a combined EM+GW measurement would immediately bring. I will then outline the main challenge that lies ahead for this new field in pinpointing the sky location of neutron star mergers using GW detectors and EM wide-field synoptic surveys.

March 6, 2015 10:00AM BPB-217. Jean-Michel Desert, New Frontiers in Exoplanetary Science

The field of exoplanetology has recently transitioned from the investigation of individual objects to statistical studies. However, answers to key questions in exoplanetary science come not only from the statistics of discovery surveys, but also from the detailed characterisation of individual systems. I argue that the study of exoplanet atmospheres and their diversity is the next step in leveraging their detections. This is because a planet's atmosphere provides a fossil record of its primordial origins and controls its fate, size and appearance. The study of exoplanet atmospheres thus is crucial to answer fundamental questions in planetary formation and exoplanetary physics. In this context, I present new results from ongoing comparative exoplanetology programs that aim to characterise planetary systems transiting nearby stars through the observations of their atmospheres. This is achieved by combining ground- and space-based multi-wavelength observations secured over wide spectral regions. The results on the atmospheric composition and physical properties provide insights into the formation and evolution of planetary systems and enhance our understanding of our own Solar System's formation. Finally, I also present strategies for probing rocky exoplanet atmospheres orbiting in the habitable zone of their parent stars, and for searching for bio-signatures with future facilities.