scholarly journals Ultra-deep tidal disruption events: prompt self-intersections and observables

2019 ◽  
Vol 488 (4) ◽  
pp. 5267-5278 ◽  
Author(s):  
Siva Darbha ◽  
Eric R Coughlin ◽  
Daniel Kasen ◽  
Chris Nixon
Keyword(s):  
Close Agreement ◽  
Tidal Disruption ◽  
X Ray ◽  
Analytic Estimate ◽  
Smoothed Particle ◽  
Solar Type ◽  
General Relativistic ◽  
Low Mass ◽  
Smoothed Particle Hydrodynamic ◽  
Schwarzschild Radius

ABSTRACT A star approaching a supermassive black hole (SMBH) can be torn apart in a tidal disruption event (TDE). We examine ultra-deep TDEs, a new regime in which the disrupted debris approaches close to the black hole’s Schwarzschild radius, and the leading part intersects the trailing part at the first pericentre passage. We calculate the range of penetration factors β versus SMBH masses M that produce these prompt self-intersections using a Newtonian analytic estimate and a general relativistic (GR) geodesic model. We find that significant self-intersection of Solar-type stars requires β ∼ 50–127 for M/M⊙ = 104, down to β ∼ 5.6–5.9 forM/M⊙ = 106. We run smoothed particle hydrodynamic (SPH) simulations to corroborate our calculations and find close agreement, with a slightly shallower dependence on M. We predict that the shock from the collision emits an X-ray flare lasting t ∼ 2 s with L ∼ 1047 erg s−1 at E ∼ 2 keV, and the debris has a prompt accretion episode lasting t ∼ several minutes. The events are rare and occur with a rate $\dot{N} \lesssim 10^{-7}$ Mpc−3 yr−1. Ultra-deep TDEs can probe the strong gravity and demographics of low-mass SMBHs.

scholarly journals Near-Eddington Luminosity Flares from Quiescent Supermassive Black Holes

2009 ◽  
Vol 5 (S267) ◽  
pp. 319-324
Author(s):  
Suvi Gezari
Keyword(s):  
Black Hole ◽  
Thermal Emission ◽  
Rare Event ◽  
Light Curves ◽  
Spectral Energy ◽  
Wide Field ◽  
Tidal Disruption ◽  
X Ray ◽  
Solar Type ◽  
Detection Capabilities

AbstractA dormant supermassive black hole lurking in the center of a galaxy will be revealed when a star passes within its tidal disruption radius, is disrupted, and a flare of electromagnetic radiation is emitted when the bound stellar debris is accreted. Although the tidal disruption of a star is a rare event in a galaxy, ~ 10−4 yr−1, observational candidates have emerged in all-sky X-ray and deep UV surveys in the form of luminous UV/X-ray flares from otherwise quiescent galaxies. We present the light curves and broadband properties of three tidal disruption candidates discovered in the UV by GALEX, and find that (1) the light curves are well-fitted by the power-law decline expected for the fallback of debris from a tidally disrupted solar-type star, and (2) the UV/optical spectral energy distributions can be attributed to thermal emission from an envelope of debris located at ten times the tidal disruption radius of the central black hole. We use the observed peak absolute optical magnitudes of the flares to predict the detection capabilities of the next generation of wide-field optical synoptic surveys.

scholarly journals The Peculiar X-Ray Transient Swift J0840.7−3516: An Unusual Low-mass X-Ray Binary or a Tidal Disruption Event?

2021 ◽  
Vol 910 (2) ◽  
pp. 144
Author(s):  
Megumi Shidatsu ◽  
Wataru Iwakiri ◽  
Hitoshi Negoro ◽  
Tatehiro Mihara ◽  
Yoshihiro Ueda ◽  
...  
Keyword(s):  
Tidal Disruption ◽  
X Ray ◽  
Low Mass ◽  
Disruption Event

scholarly journals Gravitational wave emission from unstable accretion discs in tidal disruption events

2019 ◽  
Vol 489 (1) ◽  
pp. 699-706 ◽  
Author(s):  
Martina Toscani ◽  
Giuseppe Lodato ◽  
Rebecca Nealon
Keyword(s):  
Gravitational Wave ◽  
Hydrodynamic Instability ◽  
Maximum Amplitude ◽  
Accretion Discs ◽  
Tidal Disruption ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Solar Type ◽  
Measured Strain ◽  
Mass Quadrupole

Abstract Gravitational waves can be emitted by accretion discs if they undergo instabilities that generate a time varying mass quadrupole. In this work we investigate the gravitational signal generated by a thick accretion disc of 1 M⊙ around a static supermassive black hole of 106 M⊙, assumed to be formed after the tidal disruption of a solar type star. This torus has been shown to be unstable to a global non-axisymmetric hydrodynamic instability, the Papaloizou–Pringle instability, in the case where it is not already accreting and has a weak magnetic field. We start by deriving analytical estimates of the maximum amplitude of the gravitational wave signal, with the aim to establish its detectability by the Laser Interferometer Space Antenna (LISA). Then, we compare these estimates with those obtained through a numerical simulation of the torus, made with a 3D smoothed particle hydrodynamics code. Our numerical analysis shows that the measured strain is two orders of magnitude lower than the maximum value obtained analytically. However, accretion discs affected by the Papaloizou–Pringle instability may still be interesting sources for LISA, if we consider discs generated after deeply penetrating tidal disruptions of main-sequence stars of higher mass.

scholarly journals Eccentric tidal disruption event discs around supermassive black holes: dynamics and thermal emission

2020 ◽  
Vol 499 (4) ◽  
pp. 5562-5577
Author(s):  
J J Zanazzi ◽  
Gordon I Ogilvie
Keyword(s):  
Thermal Emission ◽  
Tidal Disruption ◽  
X Ray ◽  
General Relativistic ◽  
Emission Models ◽  
Heating Model ◽  
Energy Dissipated ◽  
Far Ultraviolet ◽  
Nested Sequence ◽  
Disruption Event

ABSTRACT After the tidal disruption event (TDE) of a star around a supermassive black hole (SMBH), if the stellar debris stream rapidly circularizes and forms a compact disc, the TDE emission is expected to peak in the soft X-ray or far ultraviolet (UV). The fact that many TDE candidates are observed to peak in the near UV and optical has challenged conventional TDE emission models. By idealizing a disc as a nested sequence of elliptical orbits that communicate adiabatically via pressure forces, and are heated by energy dissipated during the circularization of the nearly parabolic debris streams, we investigate the dynamics and thermal emission of highly eccentric TDE discs, including the effect of general-relativistic apsidal precession from the SMBH. We calculate the properties of uniformly precessing, apsidally aligned, and highly eccentric TDE discs, and find highly eccentric disc solutions exist for realistic TDE properties (SMBH and stellar mass, periapsis distance, etc.). Taking into account compressional heating (cooling) near periapsis (apoapsis), we find our idealized eccentric disc model can produce emission consistent with the X-ray and UV/optical luminosities of many optically bright TDE candidates. Our work attempts to quantify the thermal emission expected from the shock-heating model for TDE emission, and finds stream–stream collisions are a promising way to power optically bright TDEs.

scholarly journals Massive discs around low-mass stars

2020 ◽  
Vol 494 (3) ◽  
pp. 4130-4148 ◽  
Author(s):  
Thomas J Haworth ◽  
James Cadman ◽  
Farzana Meru ◽  
Cassandra Hall ◽  
Emma Albertini ◽  
...  
Keyword(s):  
Thermal Evolution ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Star Mass ◽  
Smoothed Particle ◽  
Low Mass ◽  
Self Gravity ◽  
Stellar Masses ◽  
Smoothed Particle Hydrodynamic

ABSTRACT We use a suite of smoothed particle hydrodynamic simulations to investigate the susceptibility of protoplanetary discs to the effects of self-gravity as a function of star–disc properties. We also include passive irradiation from the host star using different models for the stellar luminosities. The critical disc-to-star mass ratio for axisymmetry (for which we produce criteria) increases significantly for low-mass stars. This could have important consequences for increasing the potential mass reservoir in a proto Trappist-1 system, since even the efficient Ormel et al. formation model will be influenced by processes like external photoevaporation, which can rapidly and dramatically deplete the dust reservoir. The aforementioned scaling of the critical Md/M* for axisymmetry occurs in part because the Toomre Q parameter has a linear dependence on surface density (which promotes instability) and only an $M_*^{1/2}$ dependence on shear (which reduces instability), but also occurs because, for a given Md/M*, the thermal evolution depends on the host star mass. The early phase stellar irradiation of the disc (for which the luminosity is much higher than at the zero age main sequence, particularly at low stellar masses) can also play a key role in significantly reducing the role of self-gravity, meaning that even solar mass stars could support axisymmetric discs a factor two higher in mass than usually considered possible. We apply our criteria to the DSHARP discs with spirals, finding that self-gravity can explain the observed spirals so long as the discs are optically thick to the host star irradiation.

scholarly journals Modelling Planet Formation by Capture-Theory Interactions

2004 ◽  
Vol 202 ◽  
pp. 244-246
Author(s):  
Michael M. Woolfson ◽  
Stephen Oxley
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Planet Formation ◽  
Open Cluster ◽  
Brown Dwarfs ◽  
Low Mass Stars ◽  
Capture Theory ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Solar Type ◽  
Low Mass

Diffuse low-mass stars and brown dwarfs coexist with condensed solar-type stars in the embedded stage of a developing open cluster. It is shown by smoothed-particle-hydrodynamics modelling that interactions between stars and protostars leads to disruption of the protostar to form protoplanets that can then be captured by the star.

A GENERAL RELATIVISTIC MODEL FOR SAX J1808.4-3658

2002 ◽  
Vol 17 (14) ◽  
pp. 827-838 ◽  
Author(s):  
R. SHARMA ◽  
S. MUKHERJEE ◽  
MIRA DEY ◽  
JISHNU DEY
Keyword(s):  
Equation Of State ◽  
Space Time ◽  
Strange Star ◽  
Compact Stars ◽  
Relativistic Model ◽  
X Ray ◽  
General Relativistic ◽  
Low Mass ◽  
The One ◽  
Stellar Configuration

We discuss the physical applicability of a model for a class of compact stars, employing Vaidya–Tikekar12 geometry of space–time. It is shown that the model can generate an equation of state (EOS) very similar to the one obtained by earlier workers for SAX J1808.4-3658 (SAX in short), assumed to be a strange star. The stellar configuration, as described by the model, is shown to be stable under radial perturbations. This may explain why the star SAX is known to be very stable compared to other low mass binary X-ray emitters.

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