March 8, 2018. 7:30PM. Bigelow Physics Building 102. Mitchell C. Begelman. What Can Black Holes Do for You?

The Russell Frank Astronomy Lecture Series
UNLV Department of Physics & Astronomy

What Can Black Holes Do for You?

Professor Mitchell C. Begelman
Department of Astrophysics and Planetary Sciences
University of Colorado

Black holes are often regarded as cosmic vacuum cleaners, but it is actually rather hard to get them to eat. And when they do feed, they make a mess, disturbing their surroundings out to thousands or even millions of light years. I will explain why black holes are “fussy eaters”, and why the messes they make are important for the evolution of the Universe.

This talk is intended for a general audience including enthusiasts of all backgrounds and ages.

Dr. Dean Smith and members of Salamat Lab published in Phys. Rev. Materials

The Salamat lab has successfully demonstrated that the mineral CaCO3, under high pressure and temperature conditions, is capable of undergoing sp² -sp³ hybridization change purely in a P 2₁ /c structure—forgoing the accepted postaragonite Pmmn structure. Their newly reported work in Phys. rev. Materials has significant relevance for the storage of carbon within the Earth’s deep mantle.

Postaragonite phases of CaCO3 at lower mantle pressures
Dean Smith, Keith V. Lawler, Miguel Martinez-Canales, Austin W. Daykin, Zachary Fussell, G. Alexander Smith, Christian Childs, Jesse S. Smith, Chris J. Pickard, and Ashkan Salamat
Phys. Rev. Materials 2, 013605 (2018) – Published 31 January 2018

Prof. Bing Zhang and former UNLV students/postdocs published in Nature Publishing Group journals

Prof. Bing Zhang from Department of Physics and Astronomy published two papers in Nature Publishing Group journals recently: one in the 2018 January issue of Nature Astronomy (DOI:10.1038/s41550-017-0309-8) and the other in the upcoming issue of Nature Communications (DOI: 10.1038/s41467-018-02847-3). Both papers are led by former UNLV Ph.D. student Dr. Bin-Bin Zhang, who just finished a postdoctoral fellowship at Instituto de Astrofísica de Andalucía (IAA-CSIC), Spain (where the research reported in both papers was carried out) and joined the faculty of Nanjing University, China, as an associate professor. Prof. Zhang is the second and co-corresponding author of both papers.

In the Nature Astronomy paper, the team discovered for the first time a change of the composition of the gamma-ray burst (GRB) jet in one source, dubbed GRB 160625B. GRBs are the most luminous explosions in the universe, marking the birth of a black hole when a massive star collapses or two compact stars merge. A collimated “jet”, whose composition is poorly known, is launched from the system and travels towards earth with a speed greater than 0.99995 speed of light, which is observed as a burst of gamma-rays. In the past, there has been a debate within the community regarding whether the jet is mostly made of matter we are familiar with (which is called a “fireball”) or strong alternating magnetic and electric magnetic fields (which is called a Poynting-flux-dominated flow). The Nature Astronomy paper, which is co-authored by 54 people from 39 institutions, reported a detailed observation of a bright burst GRB 160625B, which has three clearly-separated emission episodes. A detailed analysis by the team suggests that the jet composition of the burst clearly transitions from a fireball in the first episode to a Poynting outflow in the second episode. The results shed light on the poorly known explosion mechanism of these mysterious events.

The most important discovery in astronomy in 2017 was the groundbreaking discovery of a gravitational wave event GW170817 due to the merger of two neutron stars as well as its associated short GRB 170817A and other electromagnetic counterpart emissions in multi-wavelength. The Nature Communications paper reports an independent analysis of the emission properties of GRB 170817A as well as the physical implications. This paper has 18 authors, including 4 former UNLV Ph.D. students (Drs. He Gao, Ye Li, Hou-Jun Lü besides Bin-Bin Zhang) and 3 former UNLV postdoc fellows (Drs. Wei-Hua Lei, Xue-Feng Wu, and En-Wei Liang) as the key authors. This paper nicely complements the official papers by the LIGO/Virgo gravitational wave detector team and the NASA’s Fermi Gamma-Ray Telescope team by studying the luminosity function of short GRBs as well as the possible physical mechanism that powers this unique event.

December 8, 2017. 3:30PM. Bigelow Physics Building 102. Ho-kwang Mao. Solids, Liquids, and Gases Under High Pressure.

Pressure has long been recognized as a fundamental thermodynamic variable, but its application was previously limited by the available pressure vessels and probes. The development of multi-megabar pressure vessels and a battery of associated in-laboratory and synchrotron techniques at the turn of the century have opened a vast new window of opportunities. With the addition of the pressure dimension, we are facing a new world with an order of magnitude more materials to be discovered than all that have been explored at ambient pressure. Pressure drastically and categorically alters all elastic, electronic, magnetic, structural, and chemical properties, and pushes materials across conventional barriers between insulators and superconductors, amorphous and crystalline solids, ionic and covalent compounds, vigorously reactive and inert chemicals, etc. In the process, it reveals surprising high-pressure physics and chemistry and creates novel materials. I will describe the principles and methodology used to reach ultrahigh static pressure, the in situ probes, the physical phenomena to be investigated, the long-pursued goals, the surprising discoveries, and the vast potential opportunities. Examples include the recent advances and surprising findings in high-pressure research of hydrogen, oxygen, iron, and carbon. Overall, this review demonstrates that high-pressure research is a new dimension in physics, chemistry, Earth and materials sciences.

November 30, 2017. 7:30PM. Bigelow Physics Building 102. Shane L. Larson. Whispers from the Cosmos: The Dawn of Gravitational Wave Astronomy.

The Russell Frank Astronomy Lecture Series
UNLV Department of Physics & Astronomy

Whispers from the Cosmos:
The Dawn of Gravitational Wave Astronomy

Professor Shane L. Larson
Northwestern University

We tell the story of the discovery of gravitational waves (awarded the Physics Nobel Prize this year). These waves reveal what happens when two black holes collide, how the inner core of a star destroys itself during a supernova explosion, and how the graveyard of the galaxy is filled with the whisper of binary white dwarf stars that spiral together as they fade into oblivion. We will also look ahead to the future of this new branch of astronomy.

This talk is intended for a general audience including enthusiasts of all backgrounds and ages.

November 14, 2017. 2:00PM. BPB-217. Anna Childs. Exterior Giant Planet Effects on Terrestrial Architecture.

Masters defense

Terrestrial planet formation is a chaotic and violent process which is not fully understood. Prior to Kepler, Solar System observations were the basis for planet formation models. However, Kepler observations have shown that exoplanet systems are very different from our solar system, thus requiring a more complete planet formation model. With advancements in computational ability, N-body integrators, and collision models, we can explore planet formation by experimenting with simulations in different parameter space. Our Solar System has shown us that exterior giant planets can play a vital role in the shaping of the final terrestrial planet system. Our recent N-body simulations have explored the relationship between exterior giant planets of varying mass and size, and final terrestrial planet architecture. Understanding the relationship between the presence of giant planets and terrestrial system structure will help us interpret observation, and aid in the formulation of a general terrestrial planet formation model.

November 13, 2017. 3:00PM. BPB-217. Champika Sandamali Weerasooriya. Probing Broad Line Regions of Active Galactic Nuclei.

Ph.D. Defense

The broad line regions (BLR) of Type I Active galactic nuclei are too small to be spatially resolved even with the most powerful telescopes available. Observations suggest that the BLR gas is moving under the influence of the gravitational potential of a central super massive black-hole and responds to the variations in the ionizing continuum flux of the accretion disk. The continuum flux variations cause broad emission line variations with a time delay. Reverberation mapping campaigns seek to use this time variability to resolve the BLRs in the time domain instead of spatial domain, providing a way to infer geometry and kinematics of the BLR and calculate the mass of the central black hole. Numerous BLR models have been proposed over the years but only few of them are physically motivated. In this work, we examine the feasibility of constraining the parameters of such a physically motivated model; a disk-wind model of the BLR. We employ a Bayesian inference framework to compare predicted line light curves to an observed line light curve, using simulated data. A shortcoming of reverberation mapped data is that they may contain large gaps between consecutive observations. We have implemented a method and developed a code to evenly sample observed continuum light curves. One can then carry out, using observational data, an analysis similar to the one discussed above.