Circularization" vs. Accretion -- What Powers Tidal Disruption Events? (original) (raw)

General Relativistic Hydrodynamic Simulation of Accretion Flow from a Stellar Tidal Disruption

The Astrophysical Journal, 2015

We study how the matter dispersed when a supermassive black hole tidally disrupts a star joins an accretion flow. Combining a relativistic hydrodynamic simulation of the stellar disruption with a relativistic hydrodynamics simulation of the tidal debris motion, we track such a system until 80% of the stellar mass bound to the black hole has settled into an accretion flow. Shocks near the stellar pericenter and also near the apocenter of the most tightly-bound debris dissipate orbital energy, but only enough to make the characteristic radius comparable to the semi-major axis of the most-bound material, not the tidal radius as previously thought. The outer shocks are caused by post-Newtonian effects, both on the stellar orbit during its disruption and on the tidal forces. Accumulation of mass into the accretion flow is non-monotonic and slow, requiring 3 − 10× the orbital period of the most tightly-bound tidal streams, while the inflow time for most of the mass may be comparable to or longer than the mass accumulation time. Deflection by shocks does, however, remove enough angular momentum and energy from some mass for it to move inward even before most of the mass is accumulated into the accretion flow. Although the accretion rate rises sharply and then decays roughly as a power-law, its maximum is 0.1× the previous expectation, and the duration of the peak is 5× longer than previously predicted. The geometric mean of the black hole mass and stellar mass inferred

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.

Magnetohydrodynamical simulations of a tidal disruption in general relativity

2015

We perform hydro- and magnetohydrodynamical general relativistic simulations of a tidal disruption of a 0.1 M_ red dwarf approaching a 10^5 M_ non-rotating massive black hole on a close (impact parameter β=10) elliptical (eccentricity e=0.97) orbit. We track the debris self-interaction, circularization, and the accompanying accretion through the black hole horizon. We find that the relativistic precession leads to the formation of a self-crossing shock. The dissipated kinetic energy heats up the incoming debris and efficiently generates a quasi-spherical outflow. The self-interaction is modulated because of the feedback exerted by the flow on itself. The debris quickly forms a thick, almost marginally bound disc that remains turbulent for many orbital periods. Initially, the accretion through the black hole horizon results from the self-interaction, while in the later stages it is dominated by the debris originally ejected in the shocked region, as it gradually falls back towards th...

The signature of tidal disruption phenomena in the vicinity of a black hole

Tidal effects on clumps of material during random non-stationary accretion onto a black hole produce phenomena with distinct temporal characteristics in observed light-curves. During such non-stationary accretion events, the shape of the accreting object evolves in time, and observable quasi-periodic phenomena with variable quasi-periods are produced. A number of characteristic light-curves, obtained with numerical simulations, will be shown. Their relevance to observed phenomena will be briefly discussed.

Tidal disruption rate of stars by supermassive black holes obtained by direct N-body simulations

Monthly Notices of the Royal Astronomical Society, 2011

The disruption rate of stars by supermassive black holes (SMBHs) is calculated numerically with a modified version of Aarseth's NBODY6 code. Equal-mass systems without primordial binaries are treated. The initial stellar distribution around the SMBH follows a Sérsic n = 4 profile representing bulges of late type galaxies as well of early type galaxies without central light deficits, i.e. without cores. In order to infer relaxation driven effects and to increase the statistical significance, a very large set of N-body integrations with different particle numbers N, ranging from 10 3 to 0.5 · 10 6 particles, is performed. Three different black hole capture radii are taken into account, enabling us to scale these results to a broad range of astrophysical systems with relaxation times shorter than one Hubble time, i.e. for SMBHs up to M • ≈ 10 7 M ⊙ . The computed number of disrupted stars are driven by diffusion in angular momentum space into the loss cone of the black hole and the rate scales with the total number of particles as dN dt ∝ N b , where b is as large as 0.83. This is significantly steeper than the expected scaling dN dt ∝ ln(N ) derived from simplest energy relaxation arguments. Only a relatively modest dependence of the tidal disruption rate on the mass of the SMBH is found and we discuss our results in the context of the M • − σ relation. The number of disrupted stars contribute a significant part to the mass growth of black holes in the lower mass range as long as a significant part of the stellar mass becomes swallowed by the SMBH. This also bears direct consequences for the search and existence of IMBHs in globular clusters. For SMBHs similar to the galactic center black hole Sgr A ⋆ , a tidal disruption rate of 55 ± 27 events per Myr is deduced. Finally relaxation driven stellar feeding can not account for the masses of massive black holes M • ≥ 10 7 M ⊙ in complete agreement with conventional gas accretion and feedback models.

Mass-loss from advective accretion disc around rotating black holes

Monthly Notices of the Royal Astronomical Society, 2015

We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter, PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (E) and specific angular momentum (λ) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole (a k) plays an important role in deciding the outflow rate Rṁ (ratio of mass flux of outflow and inflow), in particular, Rṁ is directly correlated with a k for the same set of inflow parameters. It is found that a large range of the inflow parameters allows global accretion-ejection solutions and the effective area of the parameter space (E, λ) with and without outflow decreases with black hole spin (a k). We compute the maximum outflow rate (R maẋ m) as function of black hole spin (a k) and observe that R maẋ m weakly depends on a k that lies in the range ∼ 10% − 18% of the inflow rate for the adiabatic index (γ) with 1.5 γ 4/3. We present the observational implication of our approach while studying the steady/persistent Jet activities based on the accretion states of black holes. We discuss that our formalism seems to have the potential to explain the observed Jet kinetic power for several Galactic Black Hole sources (GBHs) and Active Galactic Nuclei (AGNs).

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 ...

Dissipative accretion flows around a rotating black hole

Monthly Notices of the Royal Astronomical Society, 2008

We study the dynamical structure of a cooling dominated rotating accretion flow around a spinning black hole. We show that non-linear phenomena such as shock waves can be studied in terms of only three flow parameters, namely, the specific energy (E), the specific angular momentum (λ) and the accretion rate (ṁ) of the flow. We present all possible accretion solutions. We find that a significant region of the parameter space in the E − λ plane allows global accretion shock solutions. The effective area of the parameter space for which the Rankine-Hugoniot shocks are possible is maximum when the flow is dissipation free. It decreases with the increase of cooling effects and finally disappears when the cooling is high enough. We show that shock forms further away when the black hole is rotating compared to the solution around a Schwarzschild black hole with identical flow parameters at a large distance. However, in a normalized sense, the flow parameters for which the shocks form around the rotating black holes are produced shocks closer to the hole. The location of the shock is also dictated by the cooling efficiency in that higher the accretion rate (ṁ), the closer is the shock location. We believe that some of the high frequency quasi-periodic oscillations may be due to the flows with higher accretion rate around the rotating black holes.

Light Curves of Partial Tidal Disruption Events

The Astrophysical Journal, 2021

Tidal disruption events (TDEs) can uncover the quiescent black holes (BHs) at the center of galaxies and also offer a promising method to study them. In a partial TDE (PTDE), the BH's tidal force cannot fully disrupt the star, so the stellar core survives and only a varied portion of the stellar mass is bound to the BH and feeds it. We calculate the event rate of PTDEs and full TDEs (FTDEs). In general, the event rate of PTDEs is higher than that of FTDEs, especially for the larger BHs. And the detection rate of PTDEs is about dozens per year by Zwicky Transient Factory (ZTF). During the circularization process of the debris stream in PTDEs, no outflow can be launched due to the efficient radiative diffusion. The circularized debris ring then experiences viscous evolution and forms an accretion disk. We calculate the light curves of PTDEs contributed by these two processes, along with their radiation temperature evolution. The light curves have double peaks and the spectra peak in UV. Without obscuration or reprocessing of the radiation by an outflow, PTDEs provide a clean environment to study the circularization and transient disk formation in TDEs.