Dust Formation By Failed Supernovae

We consider dust formation during the ejection of the hydrogen envelope of a red supergiant during a failed supernova (SN) creating a black hole. While the dense, slow moving ejecta are very efficient at forming dust, only the very last phases of the predicted visual transient will be obscured. The net grain production consists of ~0.01 solar masses of very large grains (10 to 1000 microns). This means that failed SNe could be the source of the very large extrasolar dust grains identified by Ulysses, Galileo and radar studies of meteoroid re-entry trails rather than their coming from an ejection process associated with protoplanetary or other disks.Comment: submitted to MNRA

Dust Formation in the Presence of Photons I: Evaporation Rates for Small Dust Grains

The temperature of newly forming dust is controlled by the radiation field. As dust forms around stars, stellar transients, quasars or supernovae, the grains must grow through a regime where they are stochastically heated by individual photons. Since evaporation rates increase exponentially with temperature while cooling times decrease only as a power law, the evaporation rates for these small grains are dominated by the temperature spikes. We calculate effective evaporation temperatures for a broad range of input spectra that are encapsulated in a series of simple interpolation formulae for both graphitic and silicate grains. These can be easily used to first determine if dust formation is possible and then to estimate the radius or time at which it commences for a broad range of radiation environments. With these additional physical effects, very small grains may form earlier than in standard models of AGB winds. Even for very high mass loss rates, the hottest stars that can form dust are G and F stars particularly in the case of silicate dusts. For hotter stars, the higher fluxes of ultraviolet photons prevent dust formation. Thus, episodic dust formation by OH/IR stars and LBVs is primarily driven by fluctuations in their apparent temperatures rather than changes in luminosity or mass loss rates.Comment: 13 pages, 10 figures, submitted to MNRA

Failed Supernovae Explain the Compact Remnant Mass Function

One explanation for the absence of higher mass red supergiants (16.5 Msun < M < 25Msun) as the progenitors of Type IIP supernovae (SNe) is that they die in failed SNe creating black holes. Simulations show that such failed SNe still eject their hydrogen envelopes in a weak transient, leaving a black hole with the mass of the star's helium core (5-8Msun). Here we show that this naturally explains the typical masses of observed black holes and the gap between neutron star and black hole masses without any fine-tuning of the SN mechanism beyond having it fail in a mass range where many progenitor models have density structures that make the explosions more likely to fail. There is no difficulty including this ~20% population of failed SNe in any accounting of SN types over the progenitor mass function. And, other than patience, there is no observational barrier to either detecting these black hole formation events or limiting their rates to be well below this prediction.Comment: Submitted to Ap

The Evolution and Structure of Early-type Field Galaxies: A Combined Statistical Analysis of Gravitational Lenses

We introduce a framework for simultaneously investigating the structure and luminosity evolution of early-type gravitational lens galaxies. The method is based on the fundamental plane, which we interpret using the aperture mass-radius relations derived from lensed image geometries. We apply this method to our previous sample of 22 lens galaxies with measured redshifts and excellent photometry. Modeling the population with a single mass profile and evolutionary history, we find that early-type galaxies are nearly isothermal (logarithmic density slope n = 2.06 +/- 0.17, 68% C.L.), and that their stars evolve at a rate of dlog(M/L)_B/dz = -0.50 +/- 0.19 (68% C.L.) in the rest frame B band. For a Salpeter IMF and a concordance cosmology, this implies a mean star formation redshift of > 1.5 at 95% confidence. While this model can neatly describe the mean properties of early-type galaxies, it is clear that the scatter of the lens sample is too large to be explained by observational uncertainties alone. We therefore consider statistical models in which the galaxy population is described by a distribution of star formation redshifts. We find that stars must form over a significant range of redshifts (Delta z_f > 1.7, 68% C.L.), which can extend as low as z_f = 1 for some acceptable models. However, the typical galaxy will still have an old stellar population ( > 1.5). The lens sample therefore favors early star formation in field ellipticals -- even if we make no a priori assumption regarding the shape of the mass distribution in lenses, and include the range of possible deviations from homology in the uncertainties. Our evolution results call into question several recent claims that early-type galaxies in low-density environments have much younger stars than those in rich clusters.Comment: 36 pages including 6 figures, (re-)submitted to Ap