Prof. Jason Steffen receives NASA grant

Jason Steffen, assistant professor in the Department of Physics and Astronomy, will be a co-investigator on a $380,000 grant with Jack Lissauer of NASA Ames Research Center entitled Architecture of Kepler's Multiple Planet Systems.

The project will study data from the NASA Kepler space mission to characterize the orbital properties of the thousands of planets discovered by that mission. The expected results will be key to understanding the important processes of planet formation and dynamical evolution across a variety of planetary systems.

Prof. Zhaohuan Zhu receives NASA astrophysics theory program grant

Zhaohuan Zhu, assistant professor in the Department of Physics and Astronomy, received a $444,188 grant from the NASA ATP (astrophysics theory program) for Predicting Observational Signatures of Planet Formation in Realistic Models of Protoplanetary Disks .

Recent high angular resolution observations (e.g. ALMA, VLT) of protoplanetary disks have begun to reveal complicated structure (e.g. spiral arms, gaps, rings etc.). In principle such observations can provide constraints on disk dynamics, and for the first time reveal the physical processes which control the planet formation process. However, this requires realistic theoretical models of disk dynamics, including a proper treatment of MHD effects, dust growth, settling, and feedback, as well as accurate radiative transfer calculations that can generate synthetic images for comparison to data. The goal of this project is to compute such models. We will calculate the most realistic global numerical models of protoplanetary disks and disk-planet interaction to date, compute synthetic images of the models based on a self-consistent treatment of the dust dynamics in the disk, and compare these models to interpret existing data and to predict future observations. In particular, we will compare our models with observations from existing NASA space missions (e.g. Spitzer, Herschel), and ground based telescopes (e.g. ALMA, EVLA, VLT, Subaru, Gemini), and we will make predictions for future observations. The proposed first-principle calculations (including MHD effects, dust-gas dynamics, and radiative transfer) will address fundamental questions on protoplanetary disks and allow us to study planet formation processes in detail. The predictions from these simulations will not only be compared with observations (e.g. ALMA) directly, but also serve as a foundation for understanding planet formation and exoplanet properties for future space missions (e.g. JWST, WFIRST, TESS).

Dr. Zhu will hire a postdoc to be included in the research. The postdoc will work with Zhu and Jim Stone from Princeton University. The UNLV's supercomputer "Cherry Creek" will be used as will, NASA Pleiades, and Stampede at Texas Advanced Computing Center.

Prof. Rebecca Martin receives NASA Grant

Rebecca Martin, assistant professor in the Department of Physics and Astronomy, has received a three-year, $297,116 grant from the NASA Exoplanets Research Program to study planet formation in binary star systems.

About half of observed exoplanets are estimated to be in binary star systems rather than around a single star like our Sun. Planet formation in binary star systems may be very different to planet formation around a single star since there are additional forces on the disc in which the planets form, and on the planets themselves. Martin will model the evolution of discs in binary systems and their interaction with planets that form. Their goal is to understand why many of the observed exoplanets have large eccentricities and large inclinations to the spin of their star. This is in contrast to the solar system in which the planets have low eccentricity and low orbital inclination.

With the money, Dr. Martin intends to hire a postdoc to be at UNLV and also have a graduate student work on the project.

Working with Dr. Martin is Steve Lubow from the Space Telescope Science Institute in Baltimore.

Fall 2017 Russell Frank Astronomy Lecture Held

This semester's Russell Frank Astronomy Lecture will take place 7:30PM, Thursday December 1 2016 in the Bigelow Physics Building room 102 at UNLV.

Professor Fiona Harrison of Caltech will give the talk entitled: From Spinning Black Holes to Exploding Stars: A New View of the High Energy Universe.

Space-based telescopes have greatly expanded our view of the cosmos, extending our ‘eyes’ into the X-ray band, where we can now observe some of the hottest and most energetic phenomena in the Universe. This talk centers on the remarkable discoveries made by NASA’s NuSTAR X-ray telescope, and the fascinating story of how a small space mission was able to make high energy X-ray images of our cosmos crisper and deeper than ever before.

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

Testing Einstein’s Weak Equivalence Principle with Gravitational Waves

Prof. Xuefeng Wu from Purple Mountain Observatory (former UNLV postdoc) and Prof. He Gao from Beijing Normal University (former UNLV PhD student) published one paper with Prof. Bing Zhang and other coauthors to suggest the use of gravitational waves to directly test Einstein’s Weak Equivalence Principle .

Prof. Bing Zhang recent work reported in AAS NOVA

Prof. Zhang recently published a paper in ApJ Letters suggesting that mergers of charged black holes can give rise to electromagnetic signals from gravitational wave events due to black hole - black hole mergers.

This work is reported in AAS NOVA .

First UNLV/Caltech Astrophysics Workshop Held

The first UNLV/Caltech astrophysics workshop was held in the Department of Physics and Astronomy on Apr. 11-12. The theme of this workshop is radio transients, specifically, a new type of cosmological transients named Fast Radio Bursts (FRBs). Sixteen external scientists from Caltech, National Radio Astronomical Observatory (NRAO), NASA Jet Propulsion Laboratory (JPL), Cornell Univ., Univ. West Virginia, Univ. Washington, Univ. McGill gathered at UNLV and discussed with Prof. Bing Zhang’s group and other faculty members, postdoc fellows and students in the department these mysterious cosmic transients. The workshop was opened with a welcome speech by the department chair Prof. Stephen Lepp, which is followed by more than 20 talks with a lot of discussion sessions in between. Prof. Zhang and graduate students Ye Li and Divya Palaswamy gave oral presentations at the workshop. During the workshop, UNLV astronomers also discussed with Caltech astronomers possible future collaborations in the direction of radio astronomy.

Prof. Rebecca Martin and Mario Livio featured in UNLV News

UNLV News reports on Rebecca Martin and Mario Livio's paper on a possible Super-Earth.

May 6, 2016 3:30PM BPB-217. Dipanjan Mitra. On the nature of coherent radio emission from pulsars.

Pulsars, are rotating and radiating neutron stars and are superb astrophysical laboratories of extreme physics. A typical neutron star has radius of ∼ 10 km, magnetic field of ∼ 10¹² Gauss, density of ∼ 10¹⁷ kg/m³, rotating at a frequency ∼ 1 Hz and has a surface gravity of ∼ 10¹²m/s². We observe pulsars as a sequence of periodic pulses mostly in the radio wavelength. What is mind-boggling is that the radio emission arises from a kilometer-sized emission patch which is at a distance of ∼ 10¹⁹ meter from us, and yet we see it!! The equivalent blackbody temperature of this radio emission is in the range 10²⁵--10³⁰ K, which exceeds the limit for any incoherent emission process. The physical mechanism of how this emission is generated is considered as one of the most challenging problems in astrophysics. In this talk I will discuss the wide spectrum of physical phenomena (like the QED phenomenon of magnetic pair creation, effect on the structure of neutron star surface, relativistic plasma dynamics etc) that takes place around the fast rotating, highly magnetized neutron star. These processes lead to generation of a highly relativistic flow of electron positron plasma in which we believe the radio emission is excited by a process called coherent curvature radiation, where charged ``bunches'' are accelerated in curved magnetic field. I will mention how evidence from high quality radio and X-ray observations of pulsars is putting stringent constraints to these ideas.

April 29, 2016 3:30PM BPB-217. Alexandre Lazarian. Turbulent reconnection and particle acceleration.

I shall explain how turbulence makes magnetic reconnection fast and will compare this approach with other ideas in the field, e.g. related to tearing instability. I shall discuss both non-relativistic and relativistic reconnection. I shall demonstrate that turbulent reconnection inevitably leads to the particle acceleration. Finally, I shall discuss the implications of the process for the famous ICMART model by Zhang & Yan.

April 27, 2016 12:00PM BPB-250. Rolf Kuiper. The Formation and Feedbak of the Most Massive Stars.

The formation of massive stars yields strong feedback effects onto its host core and stellar cluster environment via protostellar outflows, radiation heating, radiation pressure, ionization, stellar winds and mass loss, and supernova (in chronological order). From a theoretical point of view, the question arises, how a massive protostar is able to accrete its mass up to the observed upper mass limit despite its strong radiation pressure feedback. In this talk, I present results of several series of self-gravitating radiation-hydrodynamics simulations of core collapse towards high-mass star formation, including the effects of radiation heating, radiation pressure, protostellar outflows, and ionization. We propose a solution to the radiation pressure problem in the formation of massive stars via the so-called flashlight effect: due to the formation of an optically thick accretion disk, the thermal radiative flux becomes strongly anisotropic and preferentially escapes through the disk's atmosphere, i.e. perpendicular to the sustained accretion through the disk's mid-plane. Furthermore, including feedback of early protostellar outflows yields a large scale anisotropy, which extends the disk's flashlight effect from the few hundred AU scale of the circumstellar disk to a core's flashlight effect up to a 0.1-parsec scale. This core’s flashlight effect allows core gas to accrete on the disk for longer, in the same way that the disk’s flashlight effect allows disk gas to accrete on the star for longer. In summary, I will demonstrate straight-forward mechanisms, which allows the formation of the most massive stars known in the present-day universe despite of their strong feedback via outflows and radiation. The basic theory of star formation herein is just a scaled-up version of low-mass star formation, i.e. based on accretion from core to disk to protostellar scales.

April 22, 2016 3:30 BPB-217. Niel Brandt. A Good Hard Look at Growing Supermassive Black Holes in the Distant Universe.

Sensitive cosmic X-ray surveys with the Chandra, XMM-Newton, and NuSTAR observatories have revolutionized our ability to find and study distant active galactic nuclei (AGNs), the main sites of supermassive black hole growth in the Universe. I will describe some of the resulting discoveries about the demographics, physics, and ecology of AGNs. Topics covered will include the utility of deep X-ray plus multiwavelength surveys for investigating distant AGNs; evolution constraints for the typical AGNs of the distant Universe; the cosmic balance of power between supermassive black holes and stars; interactions between AGNs and their hosting galaxies; and the AGN content of newly forming galaxies. I will end by discussing some key outstanding questions and new observations and missions that aim to answer them.

April 15, 2016 3:30 BPB-217. Timothy Strobel. Beyond thermodynamic stability: synthetic pathways to new materials with exceptional properties.

Multiple allotropes and/or chemical compounds can be formed under various pressure / temperature conditions, and some of these could remain metastable under standard conditions for time scales as long as the age of the universe (in fact it is estimated that 50% of all known inorganic compounds are metastable ones!). But the number of known allotropes/compounds pales in comparison with the number of hypothetical ones with energetic feasibility. For any given thermodynamic state, thousands of energetically competitive structures are plausible, a subset of which will exhibit mechanical stability. Further subsets of these structures offer enticing physical properties that differ from those of thermodynamic ground states. Here we delineate thermodynamic and kinetic synthesis methods and discuss strategies and examples for accessing these states experimentally. In particular, we discuss successful experimental realization of new forms of silicon and carbon.

April 8, 2016 3:30 BPB-217. Richard de Grijs. Not-so-simple stellar populations in nearby, resolved massive star clusters.

Until about a decade ago, star clusters were considered "simple" stellar populations: all stars in a cluster were thought to have similar ages and the same metallicity. Only the individual stellar masses were thought to vary, in essence conforming to a "universal" initial mass function. Over the past decade, this situation has changed dramatically. Yet, at the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. I will discuss my group's recent progress in this context, with particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Local Group star clusters across the full age range. Our most recent results imply a reverse paradigm shift, back to the old simple stellar population picture for at least some intermediate- age (~2 Gyr-old) star clusters, which opens up exciting avenues for future research efforts.

March 18, 2016 3:30 BPB-217. Scott Tremaine. Statistical mechanics of self-gravitating N-body systems.

There have been many attempts to apply the powerful tools of statistical mechanics to self-gravitating N-body systems such as star clusters, galaxies, and planetary systems. I will describe why this is difficult, some notable failures and successes, and recent work on two arenas where these tools may offer new insight: the distribution of young stars in the central parsec of our Galaxy, and the distribution of orbits of exoplanets.

March 17, 2016 7:30 BPB-102. Russell Frank Astronomy Lecture: Scott Tremaine, Institute for Advanced Study. Is the Solar System Stable?

The planets in the solar system have completed a few billion orbits since they were born. The behavior of planetary orbits over such long times was not understood until recently despite three centuries of study. Computers now allow us to follow the motion of planets reliably for the lifetime of the solar system. We will see how the Earth's orbit has evolved throughout geological history, and learn of the Earth's ultimate fate. We will also discuss what determines the number and spacing of the planets and whether there are lost planets

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

Gravitational wave mystery discussed in Quanta Magazine highlights work by UNLV Astrophysicist Bing Zhang.

With LIGO's announcement last month that it discovered gravitational waves, astronomers are speculating on whether or not a nearly coincident detection of gamma rays could be an "electromagnetic counterpart" to the binary black hole merger event. It is still unclear if and how merging black holes can be accompanied by gamma ray emission. Quanta Magazine's article discusses this issue and of the three theories put forth, one is that of Professor Zhang.

February 29, 2016 3:30 BPB-217. Candidate: Zhaohuan Zhu. From Protoplanetary Disks to Exoplanets: Theory Confronts Observations.

We are entering a golden era of study in the field of planet formation. Recently commissioned telescopes and instruments (e.g., Subaru, GPI, VLA, ALMA, EVLA) are now finally able to resolve the protoplanetary disk down to the scale of a planet's immediate assembly zone, and a rich variety of disk features have been revealed: gaps, large scale disk asymmetry, and spiral arms. Despite this progress on the observational front, theoretical models have yet to be developed that can reveal what these observations are telling us about the physics of disk structure and planet formation. In this talk, I will present my work on numerical simulations of planet-disk interaction, with an emphasis on understanding current observations. My simulations have not only successfully reproduced observed spiral arms, gaps and asymmetric features, but also constrained protoplanetary disk properties and revealed potential planets in these disks. To directly find young planets, I will suggest that disks around these forming planets, so-called circumplanetary disks, could be the key and we may have already found some circumplanetary disk candidates. Finally, I will discuss how the new generation of numerical codes and simulations I am working on are important for not only interpreting upcoming observations but also revealing fundamental physical processes in protoplanetary disks. Combining the new generation of observations and simulations, we may finally unveil the mystery of planet formation in the next decade.

February 26, 2016 3:30 BPB-217. Anna Barnacka. Resolving the High Energy Universe with Strong Gravitational Lensing.

Gravitational lensing is a powerful tool for elucidating the origin of gamma-ray emission from distant sources. Cosmic lenses magnify the emission and produce time delays between mirage images. Gravitationally-induced time delays depend on the position of the emitting regions in the source plane. Temporal resolution at gamma-ray energies can be used to measure these time delays, which, in turn, can be used to resolve the origin of the gamma-ray flares spatially. As a prototypical example of the power of lensing combined with long, uniformly sampled light curves provided by the Fermi satellite, we investigated the spatial origin of gamma-ray flares from two known gravitationally lensed sources: PKS 1830-211 and B2 0218+35.

February 25, 2016 3:30 BPB-217. Candidate: Ivan Ramirez. High-precision spectroscopy: from exoplanets to Galactic chemical evolution.

Stellar spectra contain a wealth of information, but they can be difficult to interpret due to modeling limitations. Over the past few years, a new technique that circumvents these limitations and allows astronomers to determine atmospheric parameters and elemental abundances of stars with unprecedented precision (~1%) has been developed by me and my collaborators. Using this technique, we have discovered that the Sun has a peculiar chemical composition, one which can be interpreted as a signature of the formation of the solar system. We can use this technique to infer the presence and bulk composition of planets around other stars. Moreover, it allows us to peer into the formation histories of stars and how they could affect planet formation. In addition to being useful for exoplanet research, these data sets are also well-suited for studies of nucleosynthesis and the chemical evolution of our Milky Way galaxy. In this talk I will describe the methods and key results that we have obtained using high-precision stellar spectroscopy.

February 22, 2016 3:30 BPB-217. Candidate: Daniel Perley. The Environments of the Universe's Most Extreme Explosions Across Cosmic History.

Massive stars have been known to end their lives violently for almost a century, but the extremes of this process have become appreciated only recently: rare classes of "superluminous" supernovae are hundreds of times more luminous than other SNe, and long-duration gamma-ray bursts fleetingly outshine the brightest quasars by orders of magnitude. Their immense luminosities make these events easily detectable from great distance, from which they can serve as probes of the high-redshifts IGM, ISM, and rate and sites of cosmic star-formation. However, employing them as tools in this way requires a thorough understanding of how varying conditions such as metallicity may favor or disfavor their production in different environments. I will discuss two large surveys I am leading to study the connection between extreme transients and their galaxy environments: SHOALS, a multi-observatory effort to examine the impact of galaxy evolution on the GRB rate and host population across cosmic history, as well as the PTF superluminous-supernova host project at Keck and Palomar. Extreme transients will be discovered at a much wider range of distances and greater numbers in the coming era of all-sky synoptic surveys, and studies of these events and their environments with existing and upcoming facilities will prove invaluable for understanding the composition and evolution of dwarf galaxies, the history of the early universe, and theories of massive-stellar evolution and variations in the IMF.

February 11, 2016 3:30 BPB-217. Candidate: Norbert Werner. Sculpting 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 and evolution of galaxies is controlled by feedback processes, such as energy and momentum input from supernovae, and from the jets and winds of accreting supermassive black holes. I will start my talk by presenting observational results on the role of supermassive black holes in suppressing star formation in the most massive galaxies, keeping them 'red and dead'. Then, I will show how deep observations of extreme clusters of galaxies inform us about the microphysics of the intergalactic medium, which determines how the energy from accreting black holes couples with the diffuse gas. 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 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 the physics of galactic feedback.

Jared Rice wins NVSGC Graduate Research Fellowship

Jared Rice was awarded a prestigious Nevada NASA Space Grant Consortium Graduate Research Opportunity Fellowship in the amount of $21,000 for the 2015/2016 academic year. The NVSGC GROF supports Jared and his advisor Dr. Bing Zhang on their latest project on the characteristics of high-redshift tidal disruption events. Their proposal entitled "Tidal Disruption Events in the Early Universe" was selected by NVSGC as one of the top applications of the year across the state of Nevada. The fellowship is a 1:1 match from NVSGC and the UNLV Department of Physics and Astronomy. More details may be found on the NVSGC fellowship recipients page:

2015-2016 Fellowship Recipients

February 12, 2016 3:30PM BPB-207. Shanti Deemyad. Lithium under pressure.

Even at zero temperature lattice of lithium remains far from static. In periodic table lithium is the first element immediately after helium and the lightest metal. While fascinating quantum nature of condensed helium is suppressed at high densities, because of the presence of long range interactions in metallic systems, lithium is expected to adapt more quantum solid behavior under compression. Physics of dense lithium offers a rich playground to look for new emergent quantum phenomena in condensed matter. In this talk I will discuss the physics of ultra-light materials under extreme pressures and will present some of our studies on unraveling the physics of dense lithium.

February 5, 2016 3:30PM BPB-207. Rebekah Dawson. All Planets Great and Small.

Discoveries of exoplanets so different from those in our Solar System have called in question conventional theories for how planetary systems form and evolve. I will present recent progress in our understanding of the physical processes that drive the assembly of planetary systems and result in the surprising variety of orbital architectures we observe today. I will discuss orbital evolution in both the large and small planet regime and physical processes that link planetary orbits to their physical properties and properties of their host stars.

January 29, 2016 3:30PM BPB-207. Joseph M. Zaug. Ultrafast Shock Compression Experiments to Rapidly Test Extreme Condition Materials Predictions.

In this talk, we will discuss recent results from ultrafast tabletop laser compression experiments on fluids, polymers, and high energy density organic molecules including single crystals. Previous work on ultrafast shocked metals will be summarized and serve as an introduction to our technical approach. Extreme material theories benefit from this research through a growing understanding of how ultrahigh strain rate (10⁸ -10¹¹ s^-1) loading processes affect later-time high-strain rate (10⁴ -10⁶ s^-1) phenomena occurring on macroscale dimensions.

Larger scale gun-based compression platforms nominally generate 10⁶ s^-1 maximum equilibrated strain rate loads; however, initial rising transient strain rates —not measured— may actually reach ultrahigh values. At present, the ultrafast shock community currently utilizes diagnostics that measure hydrodynamic flow and UV/VIS absorption; however, these methods tell us nothing directly about structure or chemical states. (We can consider perspectives on the viability of potential solutions to this long-standing challenge.) Nonetheless, when we’ve matched —on identical temporal and spatial scales— hydrodynamic data with commensurate molecular dynamics or crystal mechanics simulation results, more comprehensive pictures materialize that further illuminate the progression of early-time shock induced phenomena, such as high-strain rate induced elastic to plastic wave transitions preceding chemical initiation. Definitive knowledge gaps are also discovered.

We will conclude this presentation with an example of how one may use ultrafast compression-quench experiments to freeze metastable intermediate products. Shockwave compression states normally release to high-temperature thermodynamic states governed by the heat capacity of the starting material; however, by stopping (at an early-stage) shock induced chemical decomposition, i.e., bond breaking, one can trap or even consider synthesizing previously inaccessible transient species. For example, diamond formation from shocked TATB (1,3,5-triamino-2,4,6-trinitrobenzene) had been predicted for decades and was finally proved correct using this novel experimental approach.

Dr. Joseph (Joe) Zaug - Founding member (1997) and leader of the High Pressure Chemistry Group within the Materials Sciences Division at Lawrence Livermore National Laboratory. (Ph.D. in Physical Chemistry, University of Washington, Seattle, 1994; B.S. in Chemistry, Illinois Institute of Technology, 1988) He has twenty-five years of experience developing tools that quasi-statically and/or dynamically compress materials and engineering new approaches to characterize extreme condition material response using primarily laser-based systems. Numerous grand-challenge science issues have been met by these innovations resulting in high-profile publications in disciplines such as geophysics, high-pressure physics and chemistry including chemical synthesis, and materials science. Joe and his group actively collaborate with international and U.S. collaborators. His current research focus is on measuring equations of state and physical or chemical phase transitions of single crystals, polymers, and composite materials subjected to quasi-static and ultrahigh strain rate loads. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

January 22, 2016 3:30PM BPB-207. David Radice. Turbulent Lives: Tales of Neutron Stars.

Neutron stars live interesting and mysterious lives: from the moment they are created in core-collapse supernovae, to the moment some of them eventually collapse to black-holes. In this talk, I will cover some aspects of their lives. I will discuss their birth in core-collapse supernovae, focusing on the key role of hydrodynamic turbulence in triggering the explosion, and their death in neutron star mergers. Finally, I will present recent results on the outcome of the dynamical ejection of neutron-star matter that might take place during mergers.

January 6, 2016. Jason Steffen on NPR's Marketplace.

Jason Steffen (Physics and Astronomy) was a guest on NPR's Marketplace, talking about how to more efficiently board an airplane. He began researching the issue as a graduate student after being frustrated by slow boarding processes and flight delays.

The press release from UNLV:

Jason Steffen News Center