The Gravitational Wave Signature of Core-Collapse Supernovae

We review the ensemble of anticipated gravitational-wave (GW) emission processes in stellar core collapse and postbounce core-collapse supernova evolution. We discuss recent progress in the modeling of these processes and summarize most recent GW signal estimates. In addition, we present new results on the GW emission from postbounce convective overturn and protoneutron star g-mode pulsations based on axisymmetric radiation-hydrodynamic calculations. Galactic core-collapse supernovae are very rare events, but within 3-5 Mpc from Earth, the rate jumps to 1 in ~2 years. Using the set of currently available theoretical gravitational waveforms, we compute upper-limit optimal signal-to-noise ratios based on current and advanced LIGO/GEO600/VIRGO noise curves for the recent SN 2008bk which exploded at ~3.9 Mpc. While initial LIGOs cannot detect GWs emitted by core-collapse events at such a distance, we find that advanced LIGO-class detectors could put significant upper limits on the GW emission strength for such events. We study the potential occurrence of the various GW emission processes in particular supernova explosion scenarios and argue that the GW signatures of neutrino-driven, magneto-rotational, and acoustically-driven core-collapse SNe may be mutually exclusive. We suggest that even initial LIGOs could distinguish these explosion mechanisms based on the detection (or non-detection) of GWs from a galactic core-collapse supernova.Comment: Topical Review, accepted for publication in CQG. 51 pages, 13 figures, a version of the article with high-resolution figures is available from http://stellarcollapse.org/papers/Ott_SN_GW_review2008.pdf. Update: Added section on core collapse simulations and the treatment of general relativit

Integration of vertical COM motion and angular momentum in an extended Capture Point tracking controller for bipedal walking

In this paper, we demonstrate methods for bipedal walking control based on the Capture Point (CP) methodology. In particular, we introduce a method to intuitively derive a CP reference trajectory from the next three steps and extend the linear inverted pendulum (LIP) based CP tracking controller introduced in [1], generalizing it to a model that contains vertical CoM motions and changes in angular momentum. Respecting the dynamics of general multibody systems, we propose a measurement-based compensation of multi-body effects, which leads to a stable closed-loop dynamics of bipedal walking robots. In addition we propose a ZMP projection method, which prevents the robots feet from tilting and ensures the best feasible CP tracking. The extended CP controller’s performance is validated in OpenHRP3 [2] simulations and compared to the controller proposed in [1]

The Progenitor Dependence of the Preexplosion Neutrino Emission in Core-Collapse Supernovae

We perform spherically-symmetric general-relativistic simulations of core collapse and the postbounce preexplosion phase in 32 presupernova stellar models of solar metallicity with zero-age-main-sequence masses of 12 M_{sun} to 120 M_{sun}. Using energy-dependent three-species neutrino transport in the two-moment approximation with an analytic closure, we show that the emitted neutrino luminosities and spectra follow very systematic trends that are correlated with the compactness (~M/R) of the progenitor star's inner regions via the accretion rate in the preexplosion phase. We find that these qualitative trends depend only weakly on the nuclear equation of state, but quantitative observational statements will require independent constraints on the equation of state and the rotation rate of the core as well as a more complete understanding of neutrino oscillations. We investigate the simulated response of water Cherenkov detectors to the electron antineutrino fluxes from our models and find that the large statistics of a galactic core collapse event may allow robust conclusions on the inner structure of the progenitor star.Comment: 16 emulateapj pages, 10 figures, 1 table. matches published versio

Convergence or mediation? Experts of vulnerability and the vulnerability of experts’ discourses on nanotechnologies – a case study.

Recent discussions about the evolvement of nanotechnologies criticize that the notion ‘risk’ is too abstract and an all-inclusive category. Moreover, the concept of risk is not precise enough to describe the potential issues related to the development of nanotechnologies. Instead, experts of technological development speak more about risk communication. Within the field of nanotechnologies, they even redefined this expression in February 2005 and related it to the question of the societal acceptance of nanotechnologies. Risk communication is about to gain stakeholder acceptance of policy decisions, whereas public and stakeholders are encouraged to participate actively in the communication process through public consultations, hearings, etc. Thus on the one hand, the category of risk has been pragmatically nuanced in order to better highlight the vulnerability of the communication on nanotechnologies. On the other hand, this vulnerable communication is not the result of a deficit of information. It is based on the idea of participation, where the vulnerability relies on the social groups specialized in the design, the application, and the diffusion of nanotechnologies within society. How is this participation possible, and what does it mean? We develop this question in the framework of a comparative survey on experts that are involved in the deployment of nanotechnologies in Grenoble (France) and Hamburg (Germany).nanotechnologies, society, risks, experts, collaboration.

Converging institutions. Shaping the relationships between nanotechnologies, economy and society

This paper develops the concept of converging institutions and applies it to nanotechnologies. Starting point are economic and socialogical perspectives. We focus on the entire innovation process of nanotechnologies beginning with research and development over diffusion via downstream sectors until implementation in final goods. The concept is applied to the nano-cluster in the metropolitan region of Grenoble and a possible converging institution is identified.converging institutions, converging technologies, nanotechnologies, systemic risks

The Role of Turbulence in Neutrino-Driven Core-Collapse Supernova Explosions

The neutrino-heated "gain layer" immediately behind the stalled shock in a core-collapse supernova is unstable to high-Reynolds-number turbulent convection. We carry out and analyze a new set of 19 high-resolution three-dimensional (3D) simulations with a three-species neutrino leakage/heating scheme and compare with spherically-symmetric (1D) and axisymmetric (2D) simulations carried out with the same methods. We study the postbounce supernova evolution in a $15$-$M_\odot$ progenitor star and vary the local neutrino heating rate, the magnitude and spatial dependence of asphericity from convective burning in the Si/O shell, and spatial resolution. Our simulations suggest that there is a direct correlation between the strength of turbulence in the gain layer and the susceptability to explosion. 2D and 3D simulations explode at much lower neutrino heating rates than 1D simulations. This is commonly explained by the fact that nonradial dynamics allows accreting material to stay longer in the gain layer. We show that this explanation is incomplete. Our results indicate that the effective turbulent ram pressure exerted on the shock plays a crucial role by allowing multi-D models to explode at a lower postshock thermal pressure and thus with less neutrino heating than 1D models. We connect the turbulent ram pressure with turbulent energy at large scales and in this way explain why 2D simulations are erroneously exploding more easily than 3D simulations.Comment: 13 pages, 8 figures, accepted by Ap

Supernova Fallback onto Magnetars and Propeller-powered Supernovae

We explore fallback accretion onto newly born magnetars during the supernova of massive stars. Strong magnetic fields (~10^(15) G) and short spin periods (~1-10 ms) have an important influence on how the magnetar interacts with the infalling material. At long spin periods, weak magnetic fields, and high accretion rates, sufficient material is accreted to form a black hole, as is commonly found for massive progenitor stars. When B ≾ 5 × 10^(14) G, accretion causes the magnetar to spin sufficiently rapidly to deform triaxially and produces gravitational waves, but only for ≈50-200 s until it collapses to a black hole. Conversely, at short spin periods, strong magnetic fields, and low accretion rates, the magnetar is in the "propeller regime" and avoids becoming a black hole by expelling incoming material. This process spins down the magnetar, so that gravitational waves are only expected if the initial protoneutron star is spinning rapidly. Even when the magnetar survives, it accretes at least ≈0.3 M_☉, so we expect magnetars born within these types of environments to be more massive than the 1.4 M_☉ typically associated with neutron stars. The propeller mechanism converts the ~10^(52)erg of spin energy in the magnetar into the kinetic energy of an outflow, which shock heats the outgoing supernova ejecta during the first ~10-30 s. For a small ~5 M_☉ hydrogen-poor envelope, this energy creates a brighter, faster evolving supernova with high ejecta velocities ~(1-3) × 10^4 km s^(–1) and may appear as a broad-lined Type Ib/c supernova. For a large ≳ 10 M_☉ hydrogen-rich envelope, the result is a bright Type IIP supernova with a plateau luminosity of ≳ 10^(43)erg s^(–1) lasting for a timescale of ~60-80 days

A method for rough terrain locomotion based on Divergent Component of Motion

Abstract—For humanoid robots to be used in real world scenarios, there is a need of robust and simple walking controllers. Limitation to flat terrain is a drawback of many walking controllers. We overcome this limitation by extending the concept of Divergent Component of Motion (DCM, also called ‘Capture Point’) to 3D. Therefor, we introduce the “Enhanced Centroidal Moment Pivot point” (eCMP) and the “Virtual Repellent Point” (VRP), which allow for a very intuitive understanding of the robot’s CoM dynamics. Based on eCMP, VRP and DCM, we present a method for real-time planning and control of DCM trajectories in 3D

Low-mass X-ray binaries from black-hole retaining globular clusters

Recent studies suggest that globular clusters (GCs) may retain a substantial population of stellar-mass black holes (BHs), in contrast to the long-held belief of a few to zero BHs. We model the population of BH low-mass X-ray binaries (BH-LMXBs), an ideal observable proxy for elusive single BHs, produced from a representative group of Milky Way GCs with variable BH populations. We simulate the formation of BH-binaries in GCs through exchange interactions between binary and single stars in the company of tens to hundreds of BHs. Additionally, we consider the impact of the BH population on the rate of compact binaries undergoing gravitational wave driven mergers. The characteristics of the BH-LMXB population and binary properties are sensitive to the GCs structural parameters as well as its unobservable BH population. We find that GCs retaining $\sim 1000$ BHs produce a galactic population of $\sim 150$ ejected BH-LMXBs whereas GCs retaining only $\sim20$ BHs produce zero ejected BH-LMXBs. Moreover, we explore the possibility that some of the presently known BH-LMXBs might have originated in GCs and identify five candidate systems.Comment: 27 pages, 18 figures, 7 tables, submitted to MNRA