Tidal Disruptions of White Dwarfs from Ultra-Close Encounters with Intermediate-Mass Spinning Black Holes (original) (raw)
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Tidal disruption of white dwarfs by intermediate mass black holes
EPJ Web of Conferences, 2012
Modeling ultra-close encounters between a white dwarf and a spinning, intermediate mass black hole requires a full general relativistic treatment of gravity. This paper summarizes results from such a study. Our results show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole spin. On the other hand, the late-time accretion onto the black hole follows the same decay,Ṁ ∝ t −5/3 , estimated from Newtonian gravity disruption studies. The spectrum of the fallback material peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yrs after the disruption. The orientation of the black hole spin has also a profound effect on how the outflowing debris obscures the central region. The disruption produces a burst of gravitational radiation with characteristic frequencies of ∼3.2 Hz and strain amplitudes of ∼10 −18 for galactic intermediate mass black holes.
Tidal Disruption of a Main-sequence Star by an Intermediate-mass Black Hole: A Bright Decade
The Astrophysical Journal, 2018
There has been suggestive evidence of intermediate-mass black holes (IMBHs; 10 3−5 M e) existing in some globular clusters (GCs) and dwarf galaxies, but IMBHs as a population remain elusive. As a main-sequence star passes too close by an IMBH it might be tidally captured and disrupted. We study the long-term accretion and observational consequence of such tidal disruption events. The disruption radius is hundreds to thousands of the BH's Schwarzschild radius, so the circularization of the falling-back debris stream is very inefficient due to weak general relativity effects. Due to this and a high mass fallback rate, the bound debris initially goes through a ∼10 yr long super-Eddington accretion phase. The photospheric emission of the outflow ejected during this phase dominates the observable radiation and peaks in the UV/optical bands with a luminosity of 10 erg s 42 1-. After the accretion rate drops below the Eddington rate, the bolometric luminosity follows the conventional t −5/3 powerlaw decay, and X-rays from the inner accretion disk start to be seen. Modeling the newly reported IMBH tidal disruption event candidate 3XMM J2150-0551, we find a general consistency between the data and predictions. The search for these luminous, long-term events in GCs and nearby dwarf galaxies could unveil the IMBH population.
GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate-Mass Black Hole
The Astrophysical Journal, 2013
A highly unusual pair of a gamma-ray burst (GRB) GRB060218 and an associated supernova SN2006aj has puzzled theorists for years. A supernova shock breakout and a jet from a newborn stellar mass compact object were put forward to explain its multiwavelength signature. We propose that the source is naturally explained by another channel, a tidal disruption of a white dwarf (WD) by an intermediate mass black hole (IMBH). The tidal disruption is accompanied by a tidal pinching, which leads to the ignition of a WD and a supernova. Some debris falls back onto the IMBH, forms a disk, which quickly amplifies the magnetic field, and launches a jet. We successfully fit soft X-ray spectrum with the Comptonized blackbody emission from a jet photosphere. The optical/UV emission is consistent with self-absorbed synchrotron from the expanding jet front. The accretion rate temporal dependenceṀ(t) in a tidal disruption provides a good fit to soft X-ray lightcurve. The IMBH mass is found to be about 10 4 M in three independent estimates: (1) fitting tidal disruptionṀ(t) to soft X-ray lightcurve; (2) computing the jet base radius in a jet photospheric emission model; (3) inferring the central BH mass based on a host dwarf galaxy stellar mass. The supernova position is consistent with the center of the host galaxy, while low supernova ejecta mass is consistent with a WD mass. High expected rate of tidal disruptions in dwarf galaxies is consistent with one source observed by Swift satellite over several years at GRB060218 distance of 150 Mpc. The encounters with the WDs provide a lot of fuel for IMBH growth.
Prompt emission from tidal disruptions of white dwarfs by intermediate mass black holes
EPJ Web of Conferences, 2012
We present a qualitative picture of prompt emission from tidal disruptions of white dwarfs (WD) by intermediate mass black holes (IMBH). The smaller size of an IMBH compared to a supermassive black hole and a smaller tidal radius of a WD disruption lead to a very fast event with high peak luminosity. Magnetic field is generated in situ following the tidal disruption, which leads to effective accretion. Since large-scale magnetic field is also produced, geometrically thick super-Eddington inflow leads to a relativistic jet. The dense jet possesses a photosphere, which emits quasi-thermal radiation in soft X-rays. The source can be classified as a long lowluminosity gamma-ray burst (ll-GRB). Tidal compression of a WD causes nuclear ignition, which is observable as an accompanying supernova. We suggest that GRB060218 and SN2006aj is such a pair of ll-GRB and supernova. We argue that in a flux-limited sample the disruptions of WDs by IMBHs are more frequent then the disruptions of other stars by IMBHs.
Massive disk formation in the tidal disruption of a neutron star by a nearly extremal black hole
Class. Quantum Grav. 30, 135004 (2013)
Black hole-neutron star (BHNS) binaries are important sources of gravitational waves for second-generation interferometers, and BHNS mergers are also a proposed engine for short, hard gamma-ray bursts. The behavior of both the spacetime (and thus the emitted gravitational waves) and the neutron star matter in a BHNS merger depend strongly and nonlinearly on the black hole's spin. While there is a significant possibility that astrophysical black holes could have spins that are nearly extremal (i.e. near the theoretical maximum), to date fully relativistic simulations of BHNS binaries have included black-hole spins only up to S/M2S/M^2S/M2=0.9, which corresponds to the black hole having approximately half as much rotational energy as possible, given the black hole's mass. In this paper, we present a new simulation of a BHNS binary with a mass ratio q=3q=3q=3 and black-hole spin S/M2S/M^2S/M2=0.97, the highest simulated to date. We find that the black hole's large spin leads to the most massive accretion disk and the largest tidal tail outflow of any fully relativistic BHNS simulations to date, even exceeding the results implied by extrapolating results from simulations with lower black-hole spin. The disk appears to be remarkably stable. We also find that the high black-hole spin persists until shortly before the time of merger; afterwards, both merger and accretion spin down the black hole.
Tidal Disruption Events by Relatively Compact Supermassive Black Hole Binaries
2022
Stars can be tidally destroyed or swallowed by supermassive black hole binaries. Using a large number of accurate few-body simulations, we investigate the enhancement and suppression of full and partial disruption and direct capture events by hard supermassive black hole binaries with wide ranges of key parameters, i.e., the primary black hole mass (105−108 M ), the binary mass ratio (10−3 − 1), the ratio of the binary semimajor axis to the hardening radius (10−4 − 1), the binary eccentricity (0.0− 0.9) and the stellar mass (0.3 − 3 M ). This is a significant extension of the parameter space compared to previous work. We show that the encounter probabilities of all three events are well-described by the encounter cross section, which is proportional to the pericenter distance. The probability of full disruptions by supermassive black hole binaries can be enhanced by up to a factor of 40 − 50 or suppressed by up to a factor of 10, relative to that by single black holes, depending on ...
The evolution of Kerr discs and late-time tidal disruption event light curves
Monthly Notices of the Royal Astronomical Society, 2018
An encounter between a passing star and a massive black hole at the centre of a galaxy, a socalled tidal disruption event or TDE, may leave a debris disc that subsequently accretes onto the hole. We solve for the time evolution of such a TDE disc, making use of an evolutionary equation valid for both the Newtonian and Kerr regimes. The late time luminosity emergent from such a disc is of interest as a model diagnostic, as it tends to follow a power law decline. The original simple ballistic fallback model, with equal mass in equal energy intervals, produces a −5/3 power law, while standard viscous disc descriptions yield a somewhat more shallow decline, with an index closer to −1.2. Of four recent, well-observed tidal disruption event candidates however, all had fall-off power law indices smaller than 1 in magnitude. In this work, we revisit the problem of thin disc evolution, solving this reduced problem in full general relativity. Our solutions produce power law indices that are in much better accord with observations. The late time observational data from many TDEs are generally supportive, not only of disc accretion models, but of finite stress persisting down to the innermost stable circular orbit.
Tidal disruption events by compact supermassive black hole binaries
Monthly Notices of the Royal Astronomical Society
Stars can be tidally destroyed or swallowed by supermassive black hole binaries (SMBHBs). Using a large number of few-body simulations, we investigate the enhancement and suppression of full and partial disruption and direct capture events by hard SMBHBs with wide ranges of key parameters, i.e. the primary BH mass ($M_{\rm BH, 1}= 10^{5}{-}10^{8}\, {\rm M}_{\odot }$), the binary mass ratio (10−3–1), the ratio of the binary semimajor axis to the hardening radius (10−4–1), the binary eccentricity (0.0–0.9) and the stellar mass (0.3−3,rmModot)(0.3{-}3\, {\rm M}_{\odot})(0.3−3,rmModot). This is a significant extension of the parameter space compared to previous work. We show that the encounter probabilities of all three events are well-described by the encounter cross-section. The probability of full tidal disruption events (FTDEs) by SMBHBs can be enhanced by up to a factor of 40–50 or suppressed by up to a factor of 10, relative to that by single BHs, depending on the binary parameters. Relativistic effects can ...
Lense–Thirring precession around supermassive black holes during tidal disruption events
Monthly Notices of the Royal Astronomical Society, 2015
A tidal disruption event (TDE) occurs when a star wanders close enough to a black hole to be disrupted by its tidal force. The debris of a tidally disrupted star are expected to form an accretion disc around the supermassive black hole. The light curves of these events sometimes show a quasi-periodic modulation of the flux that can be associated with the precession of the accretion disc due to the Lense-Thirring ("frame-dragging") effect. Since the initial star orbit is in general inclined with respect to the black hole spin, this misalignment combined with the Lense-Thirring effect leads to a warp in the disc. In this paper we provide a simple model of the system composed by a thick and narrow accretion disc surrounding a spinning supermassive black hole, with the aim to: (a) compute the expected precession period as a function of the system parameters, (b) discuss the conditions that have to be satisfied in order to have rigid precession, (c) investigate the alignment process, highlighting how different mechanisms play a role leading the disc and the black hole angular momenta into alignment.
Monthly Notices of the Royal Astronomical Society, 2020
We make use of a new hybrid method to simulate the long-term, multiple-orbit disc formation through tidal disruptions of rocky bodies by white dwarfs, at high-resolution and realistic semimajor axis. We perform the largest yet suite of simulations for dwarf and terrestrial planets, spanning four orders of magnitude in mass, various pericentre distances, and semimajor axes between 3 and 150 au. This large phase space of tidal disruption conditions has not been accessible through the use of previous codes. We analyse the statistical and structural properties of the emerging debris discs, as well as the ejected unbound debris contributing to the population of interstellar asteroids. Unlike previous tidal disruption studies of small asteroids which form ring-like structures on the original orbit, we find that the tidal disruption of larger bodies usually forms dispersed structures of interlaced elliptic eccentric annuli on tighter orbits. We characterize the (typically power law) size d...