November 6, 2015 3:30PM BPB-207. Duncan Lorimer. Fast Radio Bursts: The Story So Far.

I will describe a brief history of discovery and some exciting recent developments in the world of pulsars and fast radio bursts. Pulsars, rapidly rotating highly magnetized neutron stars, were discovered in 1967 and continue to surprise and delight astronomers as powerful probes of fundamental physics and astrophysics. Fast radio bursts are millisecond-duration pulses of currently unknown origin that were discovered in 2007. Both pulsars and fast radio bursts have great promise at probing the universe on large scales and in fundamental ways. I will describe the science opportunities these phenomena present, and discuss the challenges and opportunities presented in their discovery.

October 26, 2015 12:00PM BPB-207. Yan-Fei Jiang. Iron Opacity Bump Changes the Structure and Stability of Black Hole Accretion Disks in AGNs.

In the standard thin accretion disk model, electron scattering is usually thought to be the dominant opacity in the radiation pressure dominated inner region of black hole accretion disks. I will show that this is not the case for most AGNs, where the density and temperature ranges in the accretion disks are similar as in the envelopes of massive stars and opacity bump caused by Irons are much more important. Through a series of self-consistent radiation MHD simulations, I will show that the iron opacity bump can significant decrease the growth rate of thermal instability in the standard thin accretion disk model compared to case with dominated electron scattering opacity. It can even stabilize the disk. Viscous instability also does not exist for AGN disks with iron opacity bump. I will also discuss implications of the iron opacity bump on resolving various puzzles between standard thin disk models and observations.

October 16, 2015 3:30PM BPB-207. Jason Steffen. Laser Probes of the Dark Sector.

The majority of the universe is composed of exotic matter and energy of which we know very little. This "dark sector" comprising dark matter, dark energy, and gravity, is likely to be one of the primary scientific challenges of the 21st century. I report on a series of three laboratory experiments at Fermilab to probe this dark sector. These experiments include searches for dark matter axions, dark energy chameleons, and tests of the very nature of space time.

Jason Steffen featured in online UNLV news "New Faces".

New faces introduces new faculty to the university community. The article on Jason is here.

Michael Pravica receives 2015 Stewardship Science Academic Alliances Award.

Michael Pravica recently received a 2015 Stewardship Science Academic Alliances award through the U.S. Department of Energy's National Nuclear Security Administration. The three-year, $780,000 grant is to develop a novel field of science Pravica has been developing, called "useful hard X-ray photochemistry." He takes advantage of the highly focused, highly penetrating, and highly ionizing properties of hard X-rays (>7keV) to initiate novel decomposition and synthetic chemistry under isolated or extreme conditions.

October 9, 2015 3:30PM BPB-207. Kazumi Kashiyama. Searching for Newborn Black Holes and Magnetars

Stellar-mass black holes and magentars have been identified by their bright non-thermal emissions. It is highly uncertain how these objects are formed, which is a missing link of massive stellar evolution. Newborn black holes and magnetars in collapsing massive stars have been considered as the central engine of e.g., gamma-ray bursts and superluminous supernovae. However, the event rates of such luminous transients are extremely small, say ~ 0.01 % of core-collapse supernovae. On the other hand, the formation rates of black holes and magnetars has been estimated to be possibly as high as ~10% of core-collapse supernovae. Thus, a large fraction of black-hole and magnetar formation would occur with ordinary supernovae or less prominent new transients. The key questions are "What are possible smoking guns of black-hole and mangetar formation?", "Whether they can be detectable by multi-messenger time-domain astronomy in the coming years?", and "What is the optimal observational strategy?". I will present some theoretical modeling of multi-messenger signals from newborn black holes and magnetars in collapsing massive stars and discussing the detectability by using current and future observational facilities.

October 2, 2015 3:30PM BPB-207. Drew Clausen. Using Tidal Disruption Events to Study Massive Black Holes and Their Environments.

When a black hole tidally disrupts a star, accretion of the debris will produce a luminous flare and reveal the presence of a dormant black hole. Emission lines produced when the stellar debris and/or other gas in the black hole's vicinity are photoionized by the accretion flare have considerable diagnostic power. I will discuss models of the emission line spectrum produced in the debris released when evolved stars are tidally disrupted by an intermediate-mass black hole (100-10000 solar masses), and discuss the possibility of using the emission lines to identify such events and constrain the properties of the black hole. While there is some agreement between these models and observations of white dwarf tidal disruption candidates in globular clusters associated with NGC 4472 and NGC 1399, there are also drawbacks to interpreting these sources as tidally disrupted white dwarfs. I will also present results from time-dependent photoionization calculations that model the emission line spectrum produced when ambient, circumnuclear gas is illuminated by a tidal disruption flare. The emission line light curves are consistent with the transient extreme coronal line emitters recently identified in SDSS. These tidal disruption event light echoes can be used to probe the circumnuclear environments of quiescent galaxies and to constrain the extreme UV component of tidal disruption flares.

UNLV Physics & Astronomy Forum Schedule