The Observational Signatures of Primordial Pair-Instability Supernovae

Massive Population III stars from 140 - 260 solar masses ended their lives as pair-instability supernovae (PISNe), the most energetic thermonuclear explosions in the universe. Detection of these explosions could directly constrain the primordial IMF for the first time, which is key to the formation of the first galaxies, early cosmological reionization, and the chemical enrichment of the primeval IGM. We present radiation hydrodynamical calculations of Pop III PISN light curves and spectra performed with the RAGE code. We find that the initial radiation pulse due to shock breakout from the surface of the star, although attenuated by the Lyman-alpha forest, will still be visible by JWST at z ~ 10 - 15, and possibly out to z ~ 20 with strong gravitational lensing. We have also studied metal mixing at early stages of the explosion prior to breakout from the surface of the star with the CASTRO AMR code and find vigorous mixing in primordial core-collapse explosions but very little in PISNe. This implies that the key to determining progenitor masses of the first cosmic explosions is early spectroscopy just after shock breakout, and that multidimensional mixing is crucial to accurate low-mass Pop III SNe light curves and spectra.Comment: 4 pages, 3 figures, proceedings of Deciphering the Ancient Universe with Gamma-Ray Bursts, Kyoto, Japan, April 19 - 23, 201

Race, Reform, & Progressive Prosecution

The progressive prosecution movement is one of the most recent efforts to reform the United States criminal justice system. In this Article, I analyze two assumptions that appear to be guiding this movement. The first is that prosecutors have unilateral power to change the system. The second is that those who bear the biggest burden of our current system—black Americans—would be the primary beneficiaries of the decarceration proposals advanced by progressive prosecutors. I argue that each of these assumptions is misguided. A successful criminal justice reform movement must recognize the contingent power of prosecutors and actively seek to advance racial justice on top of its decarceration efforts. To avoid exacerbating the problems they intend to correct, reformists must reexamine the principles underlying the movement and the aims they expect to achieve

Which America?: Judge Roger L. Gregory and the Tradition of African-American Political Thought

In this Article, written in connection with a symposium honoring Chief Judge Roger L. Gregory’s twenty years on the bench, I place Judge Gregory’s jurisprudence within the tradition of African-American political thought. I suggest that, at bottom, Judge Gregory has a leveling-up jurisprudence that seeks to interpret the Constitution in a way that ensures the least well-off in society are granted the same rights as the most privileged. This brand of democratic theorizing approximates a mainstream position by Black political theorists optimistically seeking to have the least well-off integrated into a fully equal society. By comparing and contrasting his work with other legal and political thinkers in this tradition, I sketch an example of how Judge Gregory uses his role in the judiciary to help shape an America that lives up to the ideals expressed in its founding documents

Modeling Emission from the First Explosions: Pitfalls and Problems

Observations of the explosions of Population III (Pop III) stars have the potential to teach us much about the formation and evolution of these zero-metallicity objects. To realize this potential, we must tie observed emission to an explosion model, which requires accurate light curve and spectra calculations. Here, we discuss many of the pitfalls and problems involved in such models, presenting some preliminary results from radiation-hydrodynamics simulations.Comment: 6 pages, 3 figures, proceedings of 'The First Stars and Galaxies: Challenges for the Next Decade", Austin, TX, March 8-11, 201

Compact Remnant Mass Function: Dependence on the Explosion Mechanism and Metallicity

The mass distribution of neutron stars and stellar-mass black holes provides vital clues into the nature of stellar core collapse and the physical engine responsible for supernova explosions. Using recent advances in our understanding of supernova engines, we derive mass distributions of stellar compact remnants. We provide analytical prescriptions for compact object masses for major population synthesis codes. In an accompanying paper, Belczynski et al., we demonstrate that these qualitatively new results for compact objects can explain the observed gap in the remnant mass distribution between ~2-5 solar masses and that they place strong constraints on the nature of the supernova engine. Here, we show that advanced gravitational radiation detectors (like LIGO/VIRGO or the Einstein Telescope) will be able to further test the supernova explosion engine models once double black hole inspirals are detected.Comment: 37 pages with 16 figures, submitted to Ap

#AllCatsAreBeautiful: Ambient affiliation and the visual-verbal representation and appreciation of cats in online subversive discourses

This paper investigates the topics and affiliations associated with the hashtag #AllCatsAreBeautiful on the social media platform Twitter. Drawing on concepts from social semiotics (systemic functional theory) and critical animal studies, the paper identifies a number of potentially overlapping topics or fields, including anti-policing, the commodification of nonhuman animals, gender and sexism, and body image or body-shaming, as well as a more general positive appreciation or admiration of cats. The paper discusses how people position themselves in relation to those topics, through patterns of ideational and attitudinal meanings, and how cats are represented and appreciated visually, verbally and intersemiotically. Cats, in this context, play an important role in struggles for social justice, symbolizing freedom and resistance as well as love and solidarity. #AllCatsAreBeautiful highlights topics or spaces around which bonds can be made and communities of shared values or interests can be co-constructed.publishedVersio

The Los Alamos Supernova Light Curve Project: Computational Methods

We have entered the era of explosive transient astronomy, in which upcoming real-time surveys like the Large Synoptic Survey Telescope (LSST), the Palomar Transient Factory (PTF) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) will detect supernovae in unprecedented numbers. Future telescopes such as the James Webb Space Telescope may discover supernovae from the earliest stars in the universe and reveal their masses. The observational signatures of these astrophysical transients are the key to unveiling their central engines, the environments in which they occur, and to what precision they will pinpoint cosmic acceleration and the nature of dark energy. We present a new method for modeling supernova light curves and spectra with the radiation hydrodynamics code RAGE coupled with detailed monochromatic opacities in the SPECTRUM code. We include a suite of tests that demonstrate how the improved physics is indispensable to modeling shock breakout and light curves.Comment: 18 pages, 19 figures, published in ApJ Supplement

Missing Black Holes Unveil The Supernova Explosion Mechanism

It is firmly established that the stellar mass distribution is smooth, covering the range 0.1-100 Msun. It is to be expected that the masses of the ensuing compact remnants correlate with the masses of their progenitor stars, and thus it is generally thought that the remnant masses should be smoothly distributed from the lightest white dwarfs to the heaviest black holes. However, this intuitive prediction is not borne out by observed data. In the rapidly growing population of remnants with observationally determined masses, a striking mass gap has emerged at the boundary between neutron stars and black holes. The heaviest neutron stars reach a maximum of two solar masses, while the lightest black holes are at least five solar masses. Over a decade after the discovery, the gap has become a significant challenge to our understanding of compact object formation. We offer new insights into the physical processes that bifurcate the formation of remnants into lower mass neutron stars and heavier black holes. Combining the results of stellar modeling with hydrodynamic simulations of supernovae, we both explain the existence of the gap, and also put stringent constraints on the inner workings of the supernova explosion mechanism. In particular, we show that core-collapse supernovae are launched within 100-200 milliseconds of the initial stellar collapse, implying that the explosions are driven by instabilities with a rapid (10-20 ms) growth time. Alternatively, if future observations fill in the gap, this will be an indication that these instabilities develop over a longer (>200 milliseconds) timescale.Comment: ApJ, accepted: comments added on recent Ugliano et al. and Kreidberg et al. studie