arXiv subjects

Chris L. Fryer

Publications and source records attributed to Chris L. Fryer.

At least 91 records · Page 5Linked to original sources

arXiv2013

Supermassive Population III Supernovae and the Birth of the First Quasars

The existence of supermassive black holes as early as z ~ 7 is one of the great unsolved problems in cosmological structure formation. One leading theory argues that they are born during catastrophic baryon collapse in z ~ 15 protogalaxies in strong Lyman-Werner UV backgrounds. Atomic line cooling in such galaxies fragments baryons into massive clumps that are thought to directly collapse to 10^4 - 10^5 solar-mass black holes. We have now discovered that some of these fragments can instead become supermassive stars that eventually explode as pair-instability supernovae with energies of ~ 10^55 erg, the most energetic explosions in the universe. We have calculated light curves and spectra for supermassive Pop III PI SNe with the Los Alamos RAGE and SPECTRUM codes. We find that they will be visible in NIR all-sky surveys by Euclid out to z ~ 10 - 15 and by WFIRST and WISH out to z ~ 15 - 20, perhaps revealing the birthplaces of the first quasars.

astro-ph.CO↗

arXiv2013

The Biggest Explosions in the Universe. II

One of the leading contenders for the origin of supermassive black holes at $z \gtrsim$ 7 is catastrophic baryon collapse in atomically-cooled halos at $z \sim$ 15. In this scenario, a few protogalaxies form in the presence of strong Lyman-Werner UV backgrounds that quench H$_2$ formation in their constituent halos, preventing them from forming stars or blowing heavy elements into the intergalactic medium prior to formation. At masses of 10$^ 8$ \Ms\ and virial temperatures of 10$^4$ K, gas in these halos rapidly cools by H lines, in some cases forming 10$^4$ - 10$^6$ \Ms\ Pop III stars and, a short time later, the seeds of supermassive black holes. Instead of collapsing directly to black holes some of these stars died in the most energetic thermonuclear explosions in the universe. We have modeled the explosions of such stars in the dense cores of line-cooled protogalaxies in the presence of cosmological flows. In stark contrast to the explosions in diffuse regions in previous simulations, these SNe briefly engulf the protogalaxy but then collapse back into its dark matter potential. Fallback drives turbulence that efficiently distributes metals throughout the interior of the halo and fuels the rapid growth of nascent black holes at its center. The accompanying starburst and x-ray emission from these line-cooled galaxies easily distinguish them from more slowly evolving neighbors and might reveal the birthplaces of supermassive black holes on the sky.

astro-ph.CO↗

arXiv2013

Finding the First Cosmic Explosions I: Pair-Instability Supernovae

The first stars are the key to the formation of primitive galaxies, early cosmological reionization and chemical enrichment, and the origin of supermassive black holes. Unfortunately, in spite of their extreme luminosities, individual Population III stars will likely remain beyond the reach of direct observation for decades to come. However, their properties could be revealed by their supernova explosions, which may soon be detected by a new generation of NIR observatories such as JWST and WFIRST. We present light curves and spectra for Pop III pair-instability supernovae calculated with the Los Alamos radiation hydrodynamics code RAGE. Our numerical simulations account for the interaction of the blast with realistic circumstellar envelopes, the opacity of the envelope, and Lyman absorption by the neutral IGM at high redshift, all of which are crucial to computing the NIR signatures of the first cosmic explosions. We find that JWST will detect pair-instability supernovae out to z > 30, WFIRST will detect them in all-sky surveys out to z ~ 15 - 20 and LSST and Pan-STARRS will find them at z ~ 7 - 8. The discovery of these ancient explosions will probe the first stellar populations and reveal the existence of primitive galaxies that might not otherwise have been detected.

astro-ph.CO↗

arXiv2013

The Biggest Explosions in the Universe

Supermassive primordial stars are expected to form in a small fraction of massive protogalaxies in the early universe, and are generally conceived of as the progenitors of the seeds of supermassive black holes (BHs). Supermassive stars with masses of ~55,000 M_Sun, however, have been found to explode and completely disrupt in a supernova (SN) with an energy of up to ~10^55 erg instead of collapsing to a BH. Such events, ~10,000 times more energetic than typical SNe today, would be among the biggest explosions in the history of the universe. Here we present a simulation of such a SN in two stages. Using the RAGE radiation hydrodynamics code we first evolve the explosion from an early stage through the breakout of the shock from the surface of the star until the blast wave has propagated out to several parsecs from the explosion site, which lies deep within an atomic cooling dark matter (DM) halo at z ~ 15. Then, using the GADGET cosmological hydrodynamics code we evolve the explosion out to several kiloparsecs from the explosion site, far into the low-density intergalactic medium. The host DM halo, with a total mass of 4 x 10^7 M_Sun, much more massive than typical primordial star-forming halos, is completely evacuated of high density gas after < 10 Myr, although dense metal-enriched gas recollapses into the halo, where it will likely form second-generation stars with metallicities of ~ 0.05 Z_Sun after > 70 Myr. The chemical signature of supermassive star explosions may be found in such long-lived second-generation stars today.

astro-ph.CO↗

arXiv2013

Can Stellar Mixing Explain the Lack of Type Ib Supernovae in Long-Duration GRBs?

The discovery of supernovae associated with long-duration gamma ray burst observations is primary evidence that the progenitors of these outbursts are massive stars. One of the principle mysteries in understanding these progenitors has been the fact that all of these gamma-ray burst associated supernovae are type Ic supernovae, with no evidence of helium in the stellar atmosphere. Many studies have focused on whether or not this helium is simply hidden from spectral analyses. In this paper, we show results from recent stellar models using new convection algorithms based on our current understanding of stellar mixing. We demonstrate that enhanced convection may lead to severe depletion of stellar helium layers, suggesting that the helium is not observed simply because it is not in the star. We also present light-curves and spectra of these compact helium-depleted stars, compared to models with more conventional helium layers.

astro-ph.HE↗

arXiv2013

The Supernova that Destroyed a Protogalaxy: Prompt Chemical Enrichment and Supermassive Black Hole Growth

The first primitive galaxies formed from accretion and mergers by z ~ 15, and were primarily responsible for cosmological reionization and the chemical enrichment of the early cosmos. But a few of these galaxies may have formed in the presence of strong Lyman-Werner UV fluxes that sterilized them of H_2, preventing them from forming stars or expelling heavy elements into the IGM prior to assembly. At masses of 10^8 Ms and virial temperatures of 10^4 K, these halos began to rapidly cool by atomic lines, perhaps forming 10^4 - 10^6 Ms Pop III stars and, later, the seeds of supermassive black holes. We have modeled the explosion of a supermassive Pop III star in the dense core of a line-cooled protogalaxy with the ZEUS-MP code. We find that the supernova (SN) expands to a radius of ~ 1 kpc, briefly engulfing the entire galaxy, but then collapses back into the potential well of the dark matter. Fallback fully mixes the interior of the protogalaxy with metals, igniting a violent starburst and fueling the rapid growth of a massive black hole at its center. The starburst would populate the protogalaxy with stars in greater numbers and at higher metallicities than in more slowly-evolving, nearby halos. The SN remnant becomes a strong synchrotron source that can be observed with eVLA and eMERLIN and has a unique signature that easily distinguishes it from less energetic SN remnants. Such explosions, and their attendant starbursts, may well have marked the birthplaces of supermassive black holes on the sky.

astro-ph.CO↗

arXiv2013

Illuminating the Primeval Universe with Type IIn Supernovae

The detection of Pop III supernovae could directly probe the primordial IMF for the first time, unveiling the properties of the first galaxies, early chemical enrichment and reionization, and the seeds of supermassive black holes. Growing evidence that some Pop III stars were less massive than 100 solar masses may complicate prospects for their detection, because even though they would have been more plentiful they would have died as core-collapse supernovae, with far less luminosity than pair-instability explosions. This picture greatly improves if the SN shock collides with a dense circumstellar shell ejected during a prior violent LBV type eruption. Such collisions can turn even dim SNe into extremely bright ones whose luminosities can rival those of pair-instability SNe. We present simulations of Pop III Type IIn SN light curves and spectra performed with the Los Alamos RAGE and SPECTRUM codes. Taking into account Lyman-alpha absorption in the early universe and cosmological redshifting, we find that 40 solar mass Pop III Type IIn SNe will be visible out to z ~ 20 with JWST and out to z ~ 7 with WFIRST. Thus, even low mass Pop III SNe can be used to probe the primeval universe.

astro-ph.CO↗

arXiv2013

Finding the First Cosmic Explosions II: Core-Collapse Supernovae

Understanding the properties of Pop III stars is prerequisite to elucidating the nature of primeval galaxies, the chemical enrichment and reionization of the early IGM, and the origin of supermassive black holes. While the primordial IMF remains unknown, recent evidence from numerical simulations and stellar archaeology suggests that some Pop III stars may have had lower masses than previously thought, 15 - 50 \Ms in addition to 50 - 500 \Ms. The detection of Pop III supernovae by JWST, WFIRST or the TMT could directly probe the primordial IMF for the first time. We present numerical simulations of 15 - 40 \Ms Pop III core-collapse SNe done with the Los Alamos radiation hydrodynamics code RAGE. We find that they will be visible in the earliest galaxies out to z ~ 10 - 15, tracing their star formation rates and in some cases revealing their positions on the sky. Since the central engines of Pop III and solar-metallicity core-collapse SNe are quite similar, future detection of any Type II supernovae by next-generation NIR instruments will in general be limited to this epoch.

astro-ph.CO↗

arXiv2013

When can gravitational-wave observations distinguish between black holes and neutron stars?

Gravitational-wave observations of compact binaries have the potential to uncover the distribution of masses and angular momenta of black holes and neutron stars in the universe. The binary components' physical parameters can be inferred from their effect on the phasing of the gravitational-wave signal, but a partial degeneracy between the components' mass ratio and their angular momenta limits our ability to measure the individual component masses. At the typical signal amplitudes expected by the Advanced Laser Interferometer Gravitational-wave Observatory (signal-to-noise ratios between 10 and 20), we show that it will in many cases be difficult to distinguish whether the components are neutron stars or black holes. We identify when the masses of the binary components could be unambiguously measured outside the range of current observations: a system with a chirp mass $\mathcal{M} \le 0.871 $ M$_\odot$ would unambiguously contain the smallest-mass neutron star observed, and a system with $\mathcal{M} \ge 2.786 \Msun$ must contain a black hole. However, additional information would be needed to distinguish between a binary containing two 1.35 M$_\odot$ neutron stars and an exotic neutron-star--black-hole binary. We also identify those configurations that could be unambiguously identified as black-hole binaries, and show how the observation of an electromagnetic counterpart to a neutron-star--black-hole binary could be used to constrain the black-hole spin.

gr-qc↗

arXiv2013

The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission

The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 13 June 2012, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 -- 79 keV, extending the sensitivity of focusing far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low-background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than one-hundred-fold improvement in sensitivity over the collimated or coded-mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity, spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives, and will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6degree inclination orbit, the Observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of ten years, we anticipate proposing a guest investigator program, to begin in Fall 2014.

astro-ph.IM↗

arXiv2013

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.

astro-ph.HE↗

arXiv2013

The Long-Lived UV "Plateau" of SN 2012aw

Observations with the Swift UVOT have unambiguously uncovered for the first time a long-lived, UV "plateau" in a Type II-P supernova (SN). Although this flattening in slope is hinted at in a few other SNe, due to its proximity and minimal line-of-sight extinction, SN 2012aw has afforded the first opportunity to clearly observe this UV plateau. The observations of SN 2012aw revealed all Swift UV and u-band lightcurves initially declined rapidly, but 27 days after explosion the light curves flattened. Some possible sources of the UV plateau are: the same thermal process that cause the optical plateau, heating from radioactive decay, or a combination of both processes.

astro-ph.HE↗

arXiv2012

Seeing the First Supernovae at the Edge of the Universe with JWST

The first stars ended the cosmic Dark Ages and created the first heavy elements necessary for the formation of planets and life. The properties of these stars remain uncertain, and it may be decades before individual Pop III stars are directly observed. Their masses, however, can be inferred from their supernova explosions, which may soon be found in both deep-field surveys by JWST and in all-sky surveys by WFIRST. We have performed radiation hydrodynamical simulations of the near infrared signals of Pop III pair-instability supernovae in realistic circumstellar environments with Lyman absorption by the neutral intergalactic medium. We find that JWST and WFIRST will detect these explosions out to z ~ 30 and 20, respectively, unveiling the first generation of stars in the universe.

astro-ph.CO↗

arXiv2012

Gamma-Ray Bursts in Circumstellar Shells: A Possible Explanation for Flares

It is now generally accepted that long-duration gamma ray bursts (GRBs) are due to the collapse of massive rotating stars. The precise collapse process itself, however, is not yet fully understood. Strong winds, outbursts, and intense ionizing UV radiation from single stars or strongly interacting binaries are expected to destroy the molecular cloud cores that give birth to them and create highly complex circumburst environments for the explosion. Such environments might imprint features on GRB light curves that uniquely identify the nature of the progenitor and its collapse. We have performed numerical simulations of realistic environments for a variety of long-duration GRB progenitors with ZEUS-MP, and have developed an analytical method for calculating GRB light curves in these profiles. Though a full, three-dimensional, relativistic magnetohydrodynamical computational model is required to precisely describe the light curve from a GRB in complex environments, our method can provide a qualitative understanding of these phenomena. We find that, in the context of the standard afterglow model, massive shells around GRBs produce strong signatures in their light curves, and that this can distinguish them from those occurring in uniform media or steady winds. These features can constrain the mass of the shell and the properties of the wind before and after the ejection. Moreover, the interaction of the GRB with the circumburst shell is seen to produce features that are consistent with observed X-ray flares that are often attributed to delayed energy injection by the central engine. Our algorithm for computing light curves is also applicable to GRBs in a variety of environments such as those in high-redshift cosmological halos or protogalaxies, both of which will soon be targets of future surveys such as JANUS or Lobster.

astro-ph.HE↗

arXiv2012

High Mass X-ray Binaries: Future Evolution and Fate

BH-NS and BH-BH systems are among the most promising gravitational wave sources detectable by advanced LIGO/VIRGO and the Einstein Telescope. Although the rates of these systems may be above those of NS-NS mergers, BH-NS and BH-BH systems are difficult to detect, and thusfar none have been observed. But the progenitors of BH-NS and BH-BH binary systems may have been observed, in the form of High-Mass X-ray Binaries (HMXBs). In this paper, we continue work studying these potential progenitors of these important gravitational wave sources. In the first two papers of the series, we have demonstrated that IC10 X-1 and NGC300 X-1 are direct progenitors of BH-BH systems and that Cyg X-1 may form, alas with a very low probability, a BH-NS system. Here, we analyze the Galactic binaries GX 301-2, Vela X-1, XTEJ1855-026, 4U1907+09, Cir X-1 and extra-galactic LMC X-1, LMC X-3, M33 X-1. In each case, we find that the future evolution will not allow the formation of a BH-NS nor a BH-BH system. Most of these binaries will soon merge in the common envelope phase, with a compact object sinking into a helium-rich core of a stellar companion. This "helium-merger" may be a progenitor for long duration gamma-ray bursts (GRBs). Based on the observed HMXB population, the rate of helium-mergers may make up a sizable fraction of long-duration GRBs. Due to this high number of potential GRB progenitors, a chance that a Galactic HMXB has caused one of the recent major mass extinction events is significant (10-20%).

astro-ph.HE↗

arXiv2012

Do R Coronae Borealis Stars Form from Double White Dwarf Mergers?

A leading formation scenario for R Coronae Borealis (RCB) stars invokes the merger of degenerate He and CO white dwarfs (WD) in a binary. The observed ratio of 16O/18O for RCB stars is in the range of 0.3-20 much smaller than the solar value of ~500. In this paper, we investigate whether such a low ratio can be obtained in simulations of the merger of a CO and a He white dwarf. We present the results of five 3-dimensional hydrodynamic simulations of the merger of a double white dwarf system where the total mass is 0.9 Mdot and the initial mass ratio (q) varies between 0.5 and 0.99. We identify in simulations with $q\lesssim0.7$ a feature around the merged stars where the temperatures and densities are suitable for forming 18O. However, more 16O is being dredged-up from the C- and O-rich accretor during the merger than the amount of 18O that is produced. Therefore, on a dynamical time scale over which our hydrodynamics simulation runs, a 16O/18O ratio of ~2000 in the "best" case is found. If the conditions found in the hydrodynamic simulations persist for 10^6 seconds the oxygen ratio drops to 16 in one case studied, while in a hundred years it drops to ~4 in another case studied, consistent with the observed values in RCB stars. Therefore, the merger of two white dwarfs remains a strong candidate for the formation of these enigmatic stars.

astro-ph.SR↗

arXiv2012

The Formation of Supermassive Black Holes from Low-Mass Pop III Seeds

The existence of 10$^9$ M$_{\odot}$ black holes (BH) in massive galaxies by $z \ sim$ 7 is one of the great unsolved mysteries in cosmological structure formation. One theory argues that they originate from the black holes of Pop III stars at $z \sim$ 20 and then accrete at the Eddington limit down to the epoch of reionization, which requires that they have constant access to rich supplies of fuel. Because early numerical simulations suggested that Pop III stars were $\gtrsim$ 100 M$_{\odot}$, the supermassive black hole seeds considered up to now were 100 - 300 M$_{\odot}$. However, there is a growing numerical and observational consensus that some Pop III stars were tens of solar masses, not hundreds, and that 20 - 40 M$_{\odot}$ black holes may have been much more plentiful at high redshift. However, we find that natal kicks imparted to 20 - 40 M$_{\odot}$ Pop III BHs during formation eject them from their halos and hence their fuel supply, precluding them from Eddington-limit growth. Consequently, supermassive black holes are far less likely to form from low-mass Pop III stars than from very massive ones.

astro-ph.CO↗

arXiv2011

Simulating the Common Envelope Phase of a Red Giant Using SPH and Uniform Grid Codes

We use three-dimensional hydrodynamical simulations to study the rapid infall phase of the common envelope interaction of a red giant branch star of mass equal to 0.88 \msun and a companion star of mass ranging from 0.9 down to 0.1 \msun. We first compare the results obtained using two different numerical techniques with different resolutions, and find overall very good agreement. We then compare the outcomes of those simulations with observed systems thought to have gone through a common envelope. The simulations fail to reproduce those systems in the sense that most of the envelope of the donor remains bound at the end of the simulations and the final orbital separations between the donor's remnant and the companion, ranging from 26.8 down to 5.9 \rsun, are larger than the ones observed. We suggest that this discrepancy vouches for recombination playing an essential role in the ejection of the envelope and/or significant shrinkage of the orbit happening in the subsequent phase.

astro-ph.SR↗