scholarly journals What causes the fragmentation of debris streams in TDEs?

2020 ◽  
Vol 495 (1) ◽  
pp. 1227-1238
Author(s):  
Andrea Sacchi ◽  
Giuseppe Lodato ◽  
Claudia Toci ◽  
Valentina Motta
Keyword(s):  
Black Hole ◽  
Time Scales ◽  
Physical Processes ◽  
Tidal Disruption ◽  
Tidal Forces ◽  
Gaseous Stream ◽  
Gravitational Stability ◽  
Hydrodynamical Simulations ◽  
Self Gravity ◽  
Disruption Event

ABSTRACT A tidal disruption event (TDE) occurs when a star passes too close to a supermassive black hole and gets torn apart by its gravitational tidal field. After the disruption, the stellar debris form an expanding gaseous stream. The morphology and evolution of this stream are particularly interesting as it ultimately determines the observational properties of the event itself. In this work, we perform 3D hydrodynamical simulations of the TDE of a star modelled as a polytropic sphere of index γ = 5/3 and study the gravitational stability of the resulting gas stream. We provide an analytical solution for the evolution of the stream in the bound, unbound, and marginally bound cases, which allows us to describe the stream properties and analyse the time-scales of the physical processes involved, applying a formalism developed in star formation context. Our results are that, when fragmentation occurs, it is fuelled by the failure of pressure in supporting the gas against its self-gravity. We also show that a stability criterion that includes also the stream gas pressure proves to be far more accurate than one that only considers the black hole tidal forces, giving analytical predictions of the time evolution of the various forces associated with the stream. Our results point out that fragmentation occurs on time-scales longer compared with the observational windows of these events and is thus not expected to give rise to significant observational features.

scholarly journals Rapid late-time X-ray brightening of the tidal disruption event OGLE16aaa

2020 ◽  
Vol 639 ◽  
pp. A100 ◽  
Author(s):  
Jari J. E. Kajava ◽  
Margherita Giustini ◽  
Richard D. Saxton ◽  
Giovanni Miniutti
Keyword(s):  
Black Hole ◽  
Host Galaxy ◽  
Late Time ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
X Ray ◽  
Tidal Forces ◽  
Upper Limits ◽  
Optical Light Curve ◽  
Disruption Event

Stars that pass too close to a super-massive black hole may be disrupted by strong tidal forces. OGLE16aaa is one such tidal disruption event (TDE) which rapidly brightened and peaked in the optical/UV bands in early 2016 and subsequently decayed over the rest of the year. OGLE16aaa was detected in an XMM-Newton X-ray observation on June 9, 2016 with a flux slightly below the Swift/XRT upper limits obtained during the optical light curve peak. Between June 16–21, 2016, Swift/XRT also detected OGLE16aaa and based on the stacked spectrum, we could infer that the X-ray luminosity had jumped up by more than a factor of ten in just one week. No brightening signal was seen in the simultaneous optical/UV data to cause the X-ray luminosity to exceed the optical/UV one. A further XMM-Newton observation on November 30, 2016 showed that almost a year after the optical/UV peak, the X-ray emission was still at an elevated level, while the optical/UV flux decay had already leveled off to values comparable to those of the host galaxy. In all X-ray observations, the spectra were nicely modeled with a 50–70 eV thermal component with no intrinsic absorption, with a weak X-ray tail seen only in the November 30 XMM-Newton observation. The late-time X-ray behavior of OGLE16aaa strongly resembles the tidal disruption events ASASSN-15oi and AT2019azh. We were able to pinpoint the time delay between the initial optical TDE onset and the X-ray brightening to 182 ± 5 days, which may possibly represent the timescale between the initial circularization of the disrupted star around the super-massive black hole and the subsequent delayed accretion. Alternatively, the delayed X-ray brightening could be related to a rapid clearing of a thick envelope that covers the central X-ray engine during the first six months.

scholarly journals The diversity and variability of star formation histories in models of galaxy evolution

2020 ◽  
Vol 498 (1) ◽  
pp. 430-463 ◽  
Author(s):  
Kartheik G Iyer ◽  
Sandro Tacchella ◽  
Shy Genel ◽  
Christopher C Hayward ◽  
Lars Hernquist ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Time Scales ◽  
Formation Rate ◽  
Power Laws ◽  
Stellar Mass ◽  
Physical Processes ◽  
Long Time ◽  
Hydrodynamical Simulations ◽  
Star Formation Histories

ABSTRACT Understanding the variability of galaxy star formation histories (SFHs) across a range of time-scales provides insight into the underlying physical processes that regulate star formation within galaxies. We compile the SFHs of galaxies at z = 0 from an extensive set of models, ranging from cosmological hydrodynamical simulations (Illustris, IllustrisTNG, Mufasa, Simba, EAGLE), zoom simulations (FIRE-2, g14, and Marvel/Justice League), semi-analytic models (Santa Cruz SAM) and empirical models (UniverseMachine), and quantify the variability of these SFHs on different time-scales using the power spectral density (PSD) formalism. We find that the PSDs are well described by broken power laws, and variability on long time-scales (≳1 Gyr) accounts for most of the power in galaxy SFHs. Most hydrodynamical models show increased variability on shorter time-scales (≲300 Myr) with decreasing stellar mass. Quenching can induce ∼0.4−1 dex of additional power on time-scales >1 Gyr. The dark matter accretion histories of galaxies have remarkably self-similar PSDs and are coherent with the in situ star formation on time-scales >3 Gyr. There is considerable diversity among the different models in their (i) power due to star formation rate variability at a given time-scale, (ii) amount of correlation with adjacent time-scales (PSD slope), (iii) evolution of median PSDs with stellar mass, and (iv) presence and locations of breaks in the PSDs. The PSD framework is a useful space to study the SFHs of galaxies since model predictions vary widely. Observational constraints in this space will help constrain the relative strengths of the physical processes responsible for this variability.

scholarly journals Tidal disruption event discs around supermassive black holes: disc warp and inclination evolution

2019 ◽  
Vol 487 (4) ◽  
pp. 4965-4984 ◽  
Author(s):  
J J Zanazzi ◽  
Dong Lai
Keyword(s):  
Black Hole ◽  
Equatorial Plane ◽  
Accretion Rate ◽  
Accretion Disc ◽  
Precession Frequency ◽  
Tidal Disruption ◽  
Eigenmode Analysis ◽  
Accretion Rates ◽  
Rigid Disc ◽  
Disruption Event

ABSTRACT After the tidal disruption event (TDE) of a star around a supermassive black hole (SMBH), the bound stellar debris rapidly forms an accretion disc. If the accretion disc is not aligned with the spinning SMBH’s equatorial plane, the disc will be driven into Lense–Thirring precession around the SMBH’s spin axis, possibly affecting the TDE’s light curve. We carry out an eigenmode analysis of such a disc to understand how the disc’s warp structure, precession, and inclination evolution are influenced by the disc’s and SMBH’s properties. We find an oscillatory warp may develop as a result of strong non-Keplarian motion near the SMBH. The global disc precession frequency matches the Lense–Thirring precession frequency of a rigid disc around a spinning black hole within a factor of a few when the disc’s accretion rate is high, but deviates significantly at low accretion rates. Viscosity aligns the disc with the SMBH’s equatorial plane over time-scales of days to years, depending on the disc’s accretion rate, viscosity, and SMBH’s mass. We also examine the effect of fallback material on the warp evolution of TDE discs, and find that the fallback torque aligns the TDE disc with the SMBH’s equatorial plane in a few to tens of days for the parameter space investigated. Our results place constraints on models of TDE emission which rely on the changing disc orientation with respect to the line of sight to explain observations.

scholarly journals Thawing the frozen-in approximation: implications for self-gravity in deeply plunging tidal disruption events

2019 ◽  
Vol 485 (1) ◽  
pp. L146-L150 ◽  
Author(s):  
Elad Steinberg ◽  
Eric R Coughlin ◽  
Nicholas C Stone ◽  
Brian D Metzger
Keyword(s):  
Free Fall ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
High Penetration ◽  
Order Of Magnitude ◽  
Sphere Radius ◽  
Hydrodynamical Simulations ◽  
Self Gravity ◽  
Hydrostatic Balance ◽  
Mesh Technique

ABSTRACT The tidal destruction of a star by a massive black hole, known as a tidal disruption event (TDE), is commonly modelled using the ‘frozen-in’ approximation. Under this approximation, the star maintains exact hydrostatic balance prior to entering the tidal sphere (radius rt), after which point its internal pressure and self-gravity become instantaneously negligible and the debris undergoes ballistic free fall. We present a suite of hydrodynamical simulations of TDEs with high penetration factors β ≡ rt/rp = 5−7, where rp is the pericentre of the stellar centre of mass, calculated using a Voronoi-based moving-mesh technique. We show that basic assumptions of the frozen-in model, such as the neglect of self-gravity inside rt, are violated. Indeed, roughly equal fractions of the final energy spread accumulate exiting and entering the tidal sphere, though the frozen-in prediction is correct at the order-of-magnitude level. We also show that an $\mathcal {O}(1)$ fraction of the debris mass remains transversely confined by self-gravity even for large β which has implications for the radio emission from the unbound debris and, potentially, for the circularization efficiency of the bound streams.

scholarly journals Estimation of the jet inclination angle for the TDE Swift J1644+57

2019 ◽  
Vol 492 (2) ◽  
pp. 1634-1640
Author(s):  
Sudip Chakraborty ◽  
Sudip Bhattacharyya ◽  
Chandrachur Chakraborty ◽  
A R Rao
Keyword(s):  
Black Hole ◽  
Data Analysis ◽  
Inclination Angle ◽  
Jet Physics ◽  
Triggering Mechanism ◽  
Tidal Disruption ◽  
X Ray ◽  
Upper Limit ◽  
The One ◽  
Disruption Event

ABSTRACT An estimate of the jet inclination angle relative to the accreting black hole’s spin can be useful to probe the jet triggering mechanism and the disc–jet coupling. A tidal disruption event (TDE) of a star by a supermassive spinning black hole provides an excellent astrophysical laboratory to study the jet direction through the possibility of jet precession. In this work, we report a new method to constrain the jet inclination angle β and apply it to the well-sampled jetted TDE Swift J1644+57. This method involves X-ray data analysis and comparisons of jet models with broad properties of the observed X-ray dips, to estimate the upper limit of the extent of the contribution of a plausible jet precession to these X-ray dips. From this limit, we find that β is very likely to be less than ∼15° for Swift J1644+57. Such a well-constrained jet inclination angle could be useful to probe the jet physics. The main advantage of our method is that it does not need to assume an origin of the observed X-ray dips, and the conclusion does not depend on any particular type of jet precession (e.g. the one due to the Lense–Thirring effect) or any specific value of precession frequency or any particular jet model. These make this method reliable and applicable to other jetted TDEs, as well as to other jetted accreting systems.

scholarly journals Erratum: Black hole masses of tidal disruption event host galaxies II

2020 ◽  
Vol 493 (1) ◽  
pp. 1498-1499
Author(s):  
Thomas Wevers ◽  
Nicholas C Stone ◽  
Sjoert van Velzen ◽  
Peter G Jonker ◽  
Tiara Hung ◽  
...  
Keyword(s):  
Black Hole ◽  
Host Galaxies ◽  
Tidal Disruption ◽  
Black Hole Masses ◽  
Disruption Event

scholarly journals Observational Progress in Identifying and Characterizing Tidal Disruption Flares

2016 ◽  
Vol 12 (S324) ◽  
pp. 93-98
Author(s):  
S. Bradley Cenko
Keyword(s):  
Black Hole ◽  
Optical Spectra ◽  
Starburst Galaxies ◽  
Electromagnetic Spectrum ◽  
Speed Of Light ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
X Ray ◽  
Tidal Forces

AbstractI present an overview of observational efforts across the electromagnetic spectrum to identify and study tidal disruption flares (TDFs), when a star wanders too close to a super-massive black hole and is torn apart by tidal forces. In particular I will focus on four unexpected surprises that challenge the most basic analytic picture of these events: 1) large inferred radii for the optical/UV-emitting material; 2) the ubiquity of outflows, detected at radio, X-ray, and UV wavelengths, ranging from speeds of 100 km/s to near the speed of light; 3) the peculiar atomic abundances observed in the UV and optical spectra of these objects; and, 4) the preference for these events to occur in post-starburst galaxies.

scholarly journals Tidal disruption as a probe for supermassive black hole binaries

2014 ◽  
Vol 10 (S312) ◽  
pp. 43-47
Author(s):  
Shuo Li ◽  
Fukun Liu ◽  
Peter Berczik ◽  
Rainer Spurzem
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Galactic Center ◽  
Galaxy Mergers ◽  
Tidal Disruption ◽  
Black Hole Binaries ◽  
Supermassive Black Hole ◽  
Before And After ◽  
Many Core ◽  
Disruption Event

AbstractSupermassive black hole binaries (SMBHBs) are the products of frequent galaxy mergers. It is very hard to be detected in quiescent galaxy. By using one million particle direct N-body simulations on special many-core hardware (GPU cluster), we study the dynamical co-evolution of SMBHB and its surrounding stars, specially focusing on the evolution of stellar tidal disruption event (TDE) rates before and after the coalescence of the SMBHB. We find a boosted TDE rate during the merger of the galaxies. After the coalescence of two supermassive black holes (SMBHs), the post-merger SMBH can get a kick velocity due to the anisotropic GW radiations. Our results about the recoiling SMBH, which oscillates around galactic center, show that most of TDEs are contributed by unbound stars when the SMBH passing through galactic center. In addition, the TDE light curve in SMBHB system is significantly different from the curve for single SMBH, which can be used to identify the SMBHB.

scholarly journals A study on tidal disruption event dynamics around an Sgr A*-like massive black hole

2020 ◽  
Vol 642 ◽  
pp. A111
Author(s):  
A. Clerici ◽  
A. Gomboc
Keyword(s):  
Black Hole ◽  
Relativistic Effects ◽  
Dynamical Behaviour ◽  
Return Rate ◽  
Newtonian Potential ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
Orbital Parameters ◽  
Sgr A ◽  
Disruption Event

Context. The number of observed tidal disruption events is increasing rapidly with the advent of new surveys. Thus, it is becoming increasingly important to improve tidal disruption event models using different stellar and orbital parameters. Aims. We study the dynamical behaviour of tidal disruption events produced by an Sgr A*-like massive black hole by changing different initial orbital parameters, taking into account the observed orbits of S stars. Investigating different types of orbits and penetration factors is important since their variations lead to different timescales of the tidal disruption event debris dynamics, making mechanisms such as self-crossing and pancaking act strongly or weakly and thus affecting the circularisation and accretion disc formation. Methods. We performed smoothed particle hydrodynamics simulations. Each simulation consisted of modelling the star with 105 particles, and the density profile is described by a polytrope with γ = 5/3. The massive black hole was modelled with a generalised post-Newtonian potential, which takes into account the relativistic effects of the Schwarzschild space-time. Results. Our analyses find that mass return rate distributions of solar-like stars and S-like stars with the same eccentricities have similar durations, but S-like stars have higher mass return rate distributions, as expected due to their larger masses. Regarding debris circularisation, we identify four types of evolution related to the mechanisms and processes involved during circularisation: in type 1, the debris does not circularise efficiently, hence a disc is not formed or is formed after a relatively long time; in type 2, the debris slowly circularises and eventually forms a disc with no debris falling back; in type 3, the debris circularises relatively quickly and forms a disc while there is still debris falling back; in type 4, the debris quickly and efficiently circularises, mainly through self-crossings and shocks, and forms a disc with no debris falling back. Finally, we find that the standard relation of circularisation radius rcirc = 2rt holds only for β = 1 and eccentricities close to parabolic.

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