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Post Info TOPIC: Type II Supernovae
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Title: Three-Dimensional Simulations of Core-Collapse Supernovae: From Shock Revival to Shock Breakout.
Author: Annop Wongwathanarat (1,2), Ewald Mueller (1), H.-Thomas Janka (1) ((1) MPI Astrophysics, (2) RIKEN)

We present 3D simulations of core-collapse supernovae from blast-wave initiation by the neutrino-driven mechanism to shock breakout from the stellar surface, considering two 15 Msun red supergiants (RSG) and two blue supergiants (BSG) of 15 Msun and 20 Msun. We demonstrate that the metal-rich ejecta in homologous expansion still carry fingerprints of asymmetries at the beginning of the explosion, but the final metal distribution is massively affected by the detailed progenitor structure. The most extended and fastest metal fingers and clumps are correlated with the biggest and fastest-rising plumes of neutrino-heated matter, because these plumes most effectively seed the growth of Rayleigh-Taylor (RT) instabilities at the C+O/He and He/H composition-shell interfaces after the passage of the SN shock. The extent of radial mixing, global asymmetry of the metal-rich ejecta, RT-induced fragmentation of initial plumes to smaller-scale fingers, and maximal Ni and minimal H velocities do not only depend on the initial asphericity and explosion energy (which determine the shock and initial Ni velocities) but also on the density profiles and widths of C+O core and He shell and on the density gradient at the He/H transition, which lead to unsteady shock propagation and the formation of reverse shocks. Both RSG explosions retain a great global metal asymmetry with pronounced clumpiness and substructure, deep penetration of Ni fingers into the H-envelope (with maximum velocities of 4000-5000 km/s for an explosion energy around 1.5 bethe) and efficient inward H-mixing. While the 15 Msun BSG shares these properties (maximum Ni speeds up to ~3500 km/s), the 20 Msun BSG develops a much more roundish geometry without pronounced metal fingers (maximum Ni velocities only ~2200 km/s) because of reverse-shock deceleration and insufficient time for strong RT growth and fragmentation at the He/H interface.

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Blobrana


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Title: First Simulations of Core-Collapse Supernovae to Supernova Remnants with SNSPH
Authors: Carola I. Ellinger, Gabriel Rockefeller, Christopher L. Fryer, Patrick A. Young, Sangwook Park

We present the first 3-dimensional simulations following the evolution of supernova shocks from their inception in the stellar core through the development of a supernova remnant into the Sedov phase. Our set of simulations use two different progenitors and two different conditions for the structure of the circumstellar environment. These calculations demonstrate the role that supernova instabilities (the instabilities that develop as the shock drive through the star) play in defining the structure and long-term development of instabilities in supernova remnants. We also present a first investigation of the mixing between stellar and interstellar matter as the supernova evolves into a young supernova remnant.

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Blobrana


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Title: Blue supergiant progenitor models of Type II supernovae
Authors: D. Vanbeveren, N. Mennekens, W. Van Rensbergen, C. De Loore

In the present paper we show that within all the uncertainties that govern the process of Roche lobe overflow in Case Br type massive binaries, it can not be excluded that a significant fraction of them merge and become single stars. We demonstrate that at least some of them will spend most of their core helium burning phase as hydrogen rich blue stars, populating the massive blue supergiant region and/or the massive Be type star population. The evolutionary simulations let us suspect that these mergers will explode as luminous hydrogen rich stars and it is tempting to link them to at least some super luminous supernovae.

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Blobrana


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Core-Collapse Supernovae
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Title: Core-Collapse Supernovae: Reflections and Directions
Authors: H.-Thomas Janka (1), Florian Hanke (1), Lorenz Huedepohl (1), Andreas Marek (1), Bernhard Mueller (1), Martin Obergaulinger (2) ((1) MPI for Astrophysics, Garching, (2) Universitat de Valencia)

Core-collapse supernovae are among the most fascinating phenomena in astrophysics and provide a formidable challenge for theoretical investigation. They mark the spectacular end of the lives of massive stars and, in an explosive eruption, release as much energy as the sun produces during its whole life. A better understanding of the astrophysical role of supernovae as birth sites of neutron stars, black holes, and heavy chemical elements, and more reliable predictions of the observable signals from stellar death events are tightly linked to the solution of the long-standing puzzle how collapsing stars achieve to explode. In this article our current knowledge of the processes that contribute to the success of the explosion mechanism are concisely reviewed. After a short overview of the sequence of stages of stellar core-collapse events, the general properties of the progenitor-dependent neutrino emission will be briefly described. Applying sophisticated neutrino transport in axisymmetric (2D) simulations with general relativity as well as in simulations with an approximate treatment of relativistic effects, we could find successful neutrino-driven explosions for a growing set of progenitor stars. First results of three-dimensional (3D) models have been obtained, and magnetohydrodynamic simulations demonstrate that strong initial magnetic fields in the pre-collapse core can foster the onset of neutrino-powered supernova explosions even in nonrotating stars. These results are discussed in the context of the present controversy about the value of 2D simulations for exploring the supernova mechanism in realistic 3D environments, and they are interpreted against the background of the current disagreement on the question whether the standing accretion shock instability (SASI) or neutrino-driven convection is the crucial agency that supports the onset of the explosion.

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Blobrana


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Physicists shed new light on supernova mystery

Physicists have a new theory on the mysterious mechanism that causes the explosion of massive, or core, stars. These Type II supernovae, the term given to exploding core stars, are huge and spectacular events; intriguing because for a short time they emit as much light as is normally produced by an entire galaxy. In fact, the enormous amount of energy they release is second only to the Big Bang itself. While there is general agreement on how the collapse of a core star begins, how the energy escapes from the star (the process that causes the explosion) is not fully understood. A paper published in Physics Letters B (3 November 2011) offers a new theoretical explanation.
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Blobrana


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Using supercomputers to understand the super stars of the cosmos

Is it a high-speed graphic animation of a yellow-golden cauliflower erupting in fast motion? No. Maybe it's some kind of time-lapse, computer-generated X-ray of a brain as it grows over years. No.
It's one of many images Princeton University astrophysicist Adam Burrows has conjured up, using supercomputers to simulate an explosion deep within a star called a supernova. It's not a run-of-the-mill thermonuclear explosion that fuels a healthy star. Instead, it's the kind of explosion that seals a star's fate.
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Blobrana


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Ultraviolet Spotlight on Plump Stars in Tiny Galaxies

Astronomers using NASA's Galaxy Evolution Explorer may be closer to knowing why some of the most massive stellar explosions ever observed occur in the tiniest of galaxies.
Over the past few years, astronomers using data from the Palomar Transient Factory, a sky survey based at the ground-based Palomar Observatory near San Diego, have discovered a surprising number of exceptionally bright stellar explosions in so-called dwarf galaxies up to 1,000 times smaller than our Milky Way galaxy. Stellar explosions, called supernovae, occur when massive stars -- some up to 100 times the mass of our sun -- end their lives.
The Palomar observations may explain a mystery first pointed out by Neil deGrasse Tyson and John Scalo when they were at the University of Austin Texas (Tyson is now the director of the Hayden Planetarium in New York, N.Y.). They noted that supernovae were occurring where there seemed to be no galaxies at all, and they even proposed that dwarf galaxies were the culprits, as the Palomar data now indicate.

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Blobrana


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Type II supernova
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Type II supernovae may join their Type Ia cousins as gauges of cosmic expansion.

A growing number of researchers are working on the idea that some Type II supernovae - which are caused by the gravitational collapse of giant stars with iron cores - may have a role as gauges of cosmic distance. The method could be put to use with next-generation sky surveys - including the Dark Energy Survey due to start at Cerro Tololo in Chile in late 2011, and the Large Synoptic Survey Telescope, still in the development phase, at Cerro Pachón, also in Chile. Both are expected to find tens of thousands of supernovae a year.
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Blobrana


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Type II Supernovae
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Title: Type II Supernovae as Probes of Cosmology
Authors: Dovi Poznanski, Eddie Baron, Stephane Blondin, Joshua S. Bloom, Christopher B. D'Andrea, Massimo Della Valle, Luc Dessart, Richard S. Ellis, Avishay Gal-Yam, Ariel Goobar, Mario Hamuy, Malcolm Hicken, Daniel N. Kasen, Kevin L. Krisciunas, Douglas C. Leonard, Weidong Li, Mario Livio, Howie Marion, Thomas Matheson, James D. Neill, Ken'ichi Nomoto, Peter E. Nugent, Robert Quimby, Masao Sako, Mark Sullivan, Rollin C. Thomas, Massimo Turatto, Schuyler D. Van Dyk, W. Michael Wood-Vasey

- Constraining the cosmological parameters and understanding Dark Energy have tremendous implications for the nature of the Universe and its physical laws.
- The pervasive limit of systematic uncertainties reached by cosmography based on Cepheids and Type Ia supernovae (SNe Ia) warrants a search for complementary approaches.
- Type II SNe have been shown to offer such a path. Their distances can be well constrained by luminosity-based or geometric methods. Competing, complementary, and concerted efforts are underway, to explore and exploit those objects that are extremely well matched to next generation facilities. Spectroscopic follow-up will be enabled by space- based and 20-40 meter class telescopes.
- Some systematic uncertainties of Type II SNe, such as reddening by dust and metallicity effects, are bound to be different from those of SNe Ia. Their stellar progenitors are known, promising better leverage on cosmic evolution. In addition, their rate - which closely tracks the ongoing star formation rate - is expected to rise significantly with look- back time, ensuring an adequate supply of distant examples.
- These data will competitively constrain the dark energy equation of state, allow the determination of the Hubble constant to 5%, and promote our understanding of the processes involved in the last dramatic phases of massive stellar evolution.

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