|I had the pleasure of joining the Astronomy & Space Exploration Society for their 12th Annual Symposium at the University of Toronto on January 23, 2015. ASX is an undergraduate-run organization that organizes regular seminars on topics related to astronomy and space and they put together their yearly symposium that is always under a special theme. This year's symposium had the theme "Stellar Graveyard" -- of course that's a topic I have something to say about. I gave a lecture on The Theory of Stellar Death and Explosion. The symposium was a lot of fun! A broad and diverse audience of about 450 people attended and most stayed until the end of my talk (at 10:15 pm!).|
What drives hypernovae, extreme supernova explosions that have many times the explosion energy of a garden-variety supernova from a massive star?
Detailed simulations show that the standard mechanism for core-collapse supernovae -- the neutrino mechanism -- seems to lack the efficiency to drive such powerful explosions.
A possibly more powerful alternative could be the magnetorotational mechanism. In this scenario, rapid rotation (a proto-neutron star with a millisecond spin period) in combination with a very strong toroidal magnetic field (1015-1016 G) are expected to push out energetic bipolar outflows along the axis of rotation.
Our team has just completed the first set of full 3D, dynamical-spacetime GR-magnetohydrodynamic simulations of magnetorotational core-collapse supernovae. This work was led by postdoc Philipp Mösta and grad student Sherwood Richers (DOE Computational Science Graduate Fellow) made important contributions.
In collaboration with other team members, Philipp and Sherwood showed that the configuration that leads to strong jets in axisymmetry is unstable in 3D to an MHD kink instability, leading to a spiral deformation of the outflow. The volume rendering the left shows the entropy distribution at some 160 milliseconds after core bounce. Red indicates high entropy (about >10 kB/baryon), blue low entropy (a few kB/baryon). The vertical axis is the vertical and the scale is 1600 km. Instead of a clean jet, two huge lobes develop that move out secularly as the proto-neutron star pushes spiral streams of out hot, highly magnetized plasma into polar regions.
CGWAS 2013 is a summer school for senior undergraduates and graduate students interested in the astrophysics of gravitational wave sources, gravitational wave astronomy, and multi-messenger follow-up observations of gravitational wave detections in the Advanced LIGO/Virgo era.
CGWAS will take place July 22-26, 2013 on the Caltech campus. Attendance is free, but limited. Support for accomodation in Caltech campus housing is available. Apply at http://www.cgwas.org.
CGWAS is supported by my NSF CAREER award and is part of my CAREER education/outreach program.
We ran four full 3D full GR (time-evolving Einstein's field equations)
simulations of a 27-solar-mass progenitor star that was shown by Müller
et al. to be especially susceptible to the Standing Accretion
Shock Instability (SASI) in axisymmetry. |
Our goal was to see (1) if the SASI develops in a similar way even in 3D (where the dynamics is not forced to be symmetric about one of the axes) and (2) how the behavior of the SASI changes when the strength of neutrino heating is varied.
We found that the SASI, while present in 3D, never reaches the strength seen in the 2D simulations of Müller et al. In our simulations, neutrino-driven convection was seeded early on and grew to become the dominant instability. We also found that as the explosion developed, the shock front became strongly distorted, showing large scale asymmetry and many small-scale protrusions, as can be seen in the volume rendering of the specific entropy distribution shown on the right.
|E. O'Connor & C. D. Ott|
|A new open-source code for spherically symmetric stellar collapse to neutron stars and black holes.|
Published as part of the Classical and Quantum Gravity Special Issue
for MICRA 2009|
(guest editors C. D. Ott, C. Pethick, and L. Rezzolla).
CQG 27, 114103 (2010)
The article is available from ->here<- free of charge for 30 days!
|E. Abdikamalov, C. D. Ott, L. Rezzolla, L. Dessart, H. Dimmelmeier, A. Marek, and H.-T. Janka|
|Axisymmetric General Relativistic Simulations of the Accretion-Induced Collapse of White Dwarfs|
|Submitted to Phys. Rev. D. (ads/arXiv)|
|This paper has been published now: PRD 81, 044012, 2010 (ads)|
|CQG has just (2009/10/06) published my new article "Probing the Core-Collapse Supernova Mechanism with Gravitational Waves," (CQG) in which I lay out how gravitational waves may be used to constrain the core-collapse supernova mechanism. It turns out that even the non-detection of gravitational waves from a galactic core collapse event would give us important clues on what is driving core-collapse supernovae! The article is available for free for 30 days! Hurry up and get your copy!|
Today (Feb 23, 2009), Classical and Quantum Gravity published
my review article on the gravitational-wave signature of core-collapse
supernova. It is a comprehensive summary of what has been
happening in the field in the past couple of years as more and more
people are becoming aware that some great supernova science can be
done with gravitational-wave astronomy. I hope you enjoy reading it.|
(The electronic version of the article is available for free for 30 days after Feb 23!)
|I have won the Postdamer Nachwuchs-Wissenschaftspreis (Young Scientist Prize of the City of Potsdam). I received the prize at the Einsteintag of the Berlin-Brandenburg Academy of Sciences (the former Prussian Academy) on December 14, 2007. Read the entire story in German on the City of Potsdam Website.|
We present a new theory for the gravitational-wave signatures of core-collapse supernovae. Previous studies identified axisymmetric rotating core collapse, core bounce, postbounce convection, and anisotropic neutrino emission as the primary processes and phases for the radiation of gravitational waves. Our results, which are based on axisymmetric Newtonian supernova simulations, indicate that the dominant emission process of gravitational waves in core-collapse supernovae may be the oscillations of the protoneutron star core. The oscillations are predominantly of g mode character, are excited hundreds of milliseconds after bounce, and typically last for several hundred milliseconds. Our results suggest that even nonrotating core-collapse supernovae should be visible to current LIGO-class detectors throughout the Galaxy, and depending on progenitor structure, possibly out to megaparsec distances.