9 research outputs found
Atypical Thermonuclear Supernovae from Tidally Crushed White Dwarfs
Suggestive evidence has accumulated that intermediate mass black holes (IMBH)
exist in some globular clusters. As stars diffuse in the cluster, some will
inevitable wander sufficiently close to the hole that they suffer tidal
disruption. An attractive feature of the IMBH hypothesis is its potential to
disrupt not only solar-type stars but also compact white dwarf stars. Attention
is given to the fate of white dwarfs that approach the hole close enough to be
disrupted and compressed to such extent that explosive nuclear burning may be
triggered. Precise modeling of the dynamics of the encounter coupled with a
nuclear network allow for a realistic determination of the explosive energy
release, and it is argued that ignition is a natural outcome for white dwarfs
of all varieties passing well within the tidal radius. Although event rates are
estimated to be significantly less than the rate of normal Type Ia supernovae,
such encounters may be frequent enough in globular clusters harboring an IMBH
to warrant a search for this new class of supernova.Comment: 13 pages, 4 figures, ApJ, accepte
Tidal disruption and ignition of white dwarfs by moderately massive black holes
We present a numerical investigation of the tidal disruption of white dwarfs
by moderately massive black holes, with particular reference to the centers of
dwarf galaxies and globular clusters. Special attention is given to the fate of
white dwarfs of all masses that approach the black hole close enough to be
disrupted and severely compressed to such extent that explosive nuclear burning
can be triggered. Consistent modeling of the gas dynamics together with the
nuclear reactions allows for a realistic determination of the explosive energy
release. In the most favorable cases, the nuclear energy release may be
comparable to that of typical type Ia supernovae. Although the explosion will
increase the mass fraction escaping on hyperbolic orbits, a good fraction of
the debris remains to be swallowed by the hole, causing a bright soft X-ray
flare lasting for about a year. Such transient signatures, if detected, would
be a compelling testimony for the presence of a moderately mass black hole
(below ).Comment: 38 pages, 19 figures, further simulations adde
Tidally-induced thermonuclear Supernovae
We discuss the results of 3D simulations of tidal disruptions of white dwarfs
by moderate-mass black holes as they may exist in the cores of globular
clusters or dwarf galaxies. Our simulations follow self-consistently the
hydrodynamic and nuclear evolution from the initial parabolic orbit over the
disruption to the build-up of an accretion disk around the black hole. For
strong enough encounters (pericentre distances smaller than about 1/3 of the
tidal radius) the tidal compression is reversed by a shock and finally results
in a thermonuclear explosion. These explosions are not restricted to progenitor
masses close to the Chandrasekhar limit, we find exploding examples throughout
the whole white dwarf mass range. There is, however, a restriction on the
masses of the involved black holes: black holes more massive than M swallow a typical 0.6 M dwarf before their tidal forces
can overwhelm the star's self-gravity. Therefore, this mechanism is
characteristic for black holes of moderate masses. The material that remains
bound to the black hole settles into an accretion disk and produces an X-ray
flare close to the Eddington limit of _\odot$), typically lasting for a few months. The combination
of a peculiar thermonuclear supernova together with an X-ray flare thus
whistle-blows the existence of such moderate-mass black holes. The next
generation of wide field space-based instruments should be able to detect such
events.Comment: 8 pages, 2 figures, EuroWD0
Catching Element Formation In The Act ; The Case for a New MeV Gamma-Ray Mission: Radionuclide Astronomy in the 2020s
High Energy Astrophysic
Massive stars and their supernovae
Stars more massive than about 8-10 solar masses evolve differently from their lower-mass counterparts: nuclear energy liberation is possible at higher temperatures and densities, due to gravitational contraction caused by such high masses, until forming an iron core that ends this stellar evolution. The star collapses thereafter, as insufficient pressure support exists when energy release stops due to Fe/Ni possessing the highest nuclear binding per nucleon, and this implosion turns into either a supernova explosion or a compact black hole remnant object. Neutron stars are the likely compact-star remnants after supernova explosions for a certain stellar mass range. In this chapter, we discuss this late-phase evolution of massive stars and their core collapse, including the nuclear reactions and nucleosynthesis products. We also include in this discussion more exotic outcomes, such as magnetic jet supernovae, hypernovae, gamma-ray bursts and neutron star mergers. In all cases we emphasize the viewpoint with respect to the role of radioactivities