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Neutrinos from Stellar Collapse Chris Fryer (LANL/UNM) “Normal” Core Collapse: Collapse and Bounce, Fallback and Cooling More massive Stars Low Mass Stars.

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Presentation on theme: "Neutrinos from Stellar Collapse Chris Fryer (LANL/UNM) “Normal” Core Collapse: Collapse and Bounce, Fallback and Cooling More massive Stars Low Mass Stars."— Presentation transcript:

1 Neutrinos from Stellar Collapse Chris Fryer (LANL/UNM) “Normal” Core Collapse: Collapse and Bounce, Fallback and Cooling More massive Stars Low Mass Stars Plans for Topical Center

2 Neutrinos from Collapse/Bounce Phase Herant et al. 1994 Buras et al. 2003 The electron neutrino raises during the collapse until the core is sufficiently dense to trap the neutrinos. After bounce, the shock moves out until the neutrinos are no longer trapped, releasing a burst of neutrinos. The electron anti- neutrinos and mu/tau neutrinos rise later (this depends somewhat on simulations).

3 Standing Accretion Shock Instability (SASI) Blondin et al. 2003 SASI occurs in an extended convective phase with large oscillations that are potentially detectable. Lund et al. 2010

4 Neutrinos from Convective Phase The evolution of the neutrino signal after bounce depends upon the evolution of the convective phase. The general trend is that neutrino energies converge. In this model, the convective phase lasts for over 0.5s after bounce. Fryer & Young 2007

5 Post Explosion Evolution - Fallback With the launch of the explosion, a shock is launched. The inner material drives out the rest of the star, but at a price – it decelerates. Some of this decelerated material falls back, accreting onto the newly formed neutron star. This fallback can lead to further explosions and enhanced neutrino emission

6 Neutrinos post-explosion Neutrinos from cooling neutron stars emit below 1 foe/s at 10s with energies around 10MeV - Burrows 1988 Neutrinos from fallback are generally above 1 foe/s 5-10s after explosion with energies around 20 MeV – Fryer 2009

7 Nakazato et al. 2010 For a 40 solar mass star, the energies and luminosities may be even higher!

8 Metallicity effects Total mass from stellar models: Heger Solar – 12.9 Heger Zero – 24.9 Limongi Zero – 24.7

9 Progenitor Effects on Neutrinos: Collapse/Bounce+ Despite differences in progenitor, the neutrino signal from collapse and bounce are very similar. Ultimately, the subsequent convective evolution and the amount of fallback will cause differences (~20% level).

10 Supermassive Stars Formation scenarios for galactic black holes (10 6 -10 9 solar masses) require either the initial collapse of million solar mass stars or the formation of 1000 solar mass seed black holes. Although these black holes may have formed only at high redshift, observations of ultra-luminous X-ray sources suggest that ~1000 solar mass black holes at low redshifts (and in the nearby universe). Strohmayer XMM conference

11 Vanbeveren etal 2009 Glebbeek etal 2009 Formation scenarios: First Stars or collisions: all seem to have trouble at higher metallicities. But they seem to exist at metallicities above 0.1 solar. Winds incorrect?

12 Supermassive Stars The higher the stellar mass, the higher the entropy at collapse. Higher entropies alter pressure support (electron degeneracy less important) Higher entropies alter nature of neutrino cooling Fryer & Heger 2010

13 Supermassive Stars For normal core collapse, the loss of electron degeneracy pressure leads to a dramatic collapse of the inner core. The collapse halts only when the core reaches nuclear densities. For supermassive collapse, the entire star compresses, forming a proto-black hole. Fryer & Heger 2010

14 Massive Stars Initial studies of a 300 solar mass star showed the development of a massive proto-black hole. The entire core eventually fell within the event horizon. Fryer, Woosley & Heger 2001 Nakazato et al. 2010 seem to not see this.

15 Supermassive Stars Large core masses make large energy resevoir. Low densities mean that neutrinos escape easily. Both mean that the neutrino luminosities can be very high! Fryer & Heger 2010

16 Supermassive Stars Pair annihilation dominates – electron and anti-electron energies nearly Unfortunately, the low densities mean low temperatures (despite high entropy). Neutrino energies low! Fryer & Heger 2010

17 Low Mass Stars Low mass collapses come in a variety of forms: WD/WD merger, ONe collapse, iron collapse But the collapse of these systems all behave very similarly (due to low envelope mass). Smartt 2009

18 Low-Mass Stars and a Clean Neutrino Diagnostic Convection believed to play a minor role (explosions occur quickly) Fallback minimal (low binding energy) Clean cooling neutron star signal. Other diagnostics also available: GWs, photons, nucleosynthesis Fryer et al. 1999, Dessart et al. 2007, Abdikamalov et al. 2010

19 From yesterday’s talk: Temperature increases in first second in Keil et al. (1996). This is not inconsistent with the new Hudepohl (2010) result.

20 Neutrinos with the Topical Collaboration In multi-dimensional calculations, neutrino transport effects become much more noticeable. Currently, no collapse simulations use “higher- order” transport in multi- dimensional calculations. However, some approaches have allowed scientists to add more detailed microphysics (at the cost of doing transport)

21 The LANL Approach Monte-Carlo is ideally suited for heterogeneous architectures. It is easy to add detailed microphysics in a Monte Carlo scheme. LANL’s multi-step plan:  Post-process code including detailed microphysics – calculated in-situ.  Monte Carlo in 1-dimension (Compare with S n schemes)  Monte Carlo in 3D SNSPH calculations.

22 Errors in Transport - Implicit Monte Carlo Represent radiation as a set of packets. Implicit nature includes re- emission by treating a fraction of the absorption as a scattering term. Problems - expensive, especially if one wants to eliminate Monte-Carlo noise.

23 Flux-Limited Diffusion We have thrown out angular information. Radiation flows down the path of least resistance. In the transport regime, this means FLD corners better than nature.

24 S N and P N Discretizing the angular information: Problems: These methods have stability issues and SN has ray effects in multi- dimensions.

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