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

Neutrinos from Collapse/Bounce Phase

Herant et al. 1994Bu

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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).

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

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

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

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

Nakazato et al. 2010

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Metallicity effects

• Total mass from stellar models:

• Heger Solar – 12.9• Heger Zero – 24.9• Limongi Zero – 24.7

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).

Supermassive Stars• Formation scenarios for galactic black holes (106-109 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

Vanbeveren etal 2009Glebbeek 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?

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

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

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, W

oosley & H

eger 2001Nakazato et al. 2010 seem to not see this.

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

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

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

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

From yesterday’s talk: Temperature increases in first second in Keil et al.

(1996). This is not inconsistent with the new Hudepohl (2010) result.

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)

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 Sn schemes)

Monte Carlo in 3D SNSPH calculations.

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.

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.

SN and PN

• Discretizing the angular information:

• Problems: These methods have stability issues and SN has ray effects in multi-dimensions.