Abstract
From an observational perspective, supermassive black holes (SMBHs) are nearly ubiquitous in nearby galactic nuclei. These massive objects (\(\sim 10^{5-10} M_{\odot}\)) generally reside at the center of their host galaxy’s stellar bulge, and can be observed either through the luminous accretion of gas, or via gravitational interactions with surrounding stellar populations. In this thesis, we focus on strong, disruptive tidal encounters between SMBHs and nearby stars, but SMBHs themselves are objects of much intrinsic interest, as we outline in this introductory section.
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Notes
- 1.
However, electric charge is expected to be negligibly small for any astrophysical black hole.
- 2.
Which would be falsified by the discovery of a single SMBH with super-extremal spin.
- 3.
The black hole quadrupole moment is uniquely determined by mass and spin in GR, but not in many alternative theories of gravity (Johannsen and Psaltis 2010).
- 4.
We also have examined an analogous scenario, in which a neutron star is tidally disrupted by a stellar mass black hole, producing a short gamma ray burst (Stone et al. 2013a). However, that type of tidal disruption is beyond the scope of this book.
- 5.
This terminology was taken by analogy from plasma kinetic theory in the 1970s (Cohn and Kulsrud 1978). At the time, American fusion research focused on magnetic confinement devices known as magnetic mirrors, which eventually proved nonviable due to plasma leaks from a geometrically conical region of phase space.
- 6.
It has recently been argued (Brem et al. 2012) that a subpopulation of very high eccentricity EMRIs may successfully penetrate the barrier; these were previously disregarded because it was thought they would plunge directly into the horizon. Properly accounting for SMBH spin shows that many of these “plunge” EMRIs can in fact accumulate high SNR in the LISA band (Amaro-Seoane et al. 2013).
- 7.
James Guillochon, Morgan MacLeod, and Enrico Ramirez-Ruiz, private communication.
- 8.
This argument could break down if a large fraction of the debris re-collapses due to gravitational instability, but it is not clear whether that would aid or hinder nozzle-driven circularization (it would certainly hinder GR-driven circularization, by reducing the stream cross-section and magnifying the impact of nodal GR precession). This is because the collapsed streams will see a higher effective β, but will likely have a lower specific internal energy than the original star.
- 9.
The SPH simulations of Ayal et al. (2000) appear to capture nozzle-driven circularization in \(e=1\), \(M_{\rm BH}=10^6M_{\odot}\) TDEs. However, the reliability of these results may be limited by (i) the difficulty of accurately capturing shocks in SPH codes, (ii) the low particle resolution (\(N=5000\)) of these simulations, and (iii) the particle-splitting algorithm employed to address resolution issues, since the vertical compression of the star will be sensitive to spurious changes in stream geometry. If vertical compression at pericenter is under-resolved, the net effect will be unphysical velocity perturbations in the orbital plane (Guillochon et al. 2009; Stone et al. 2013b) and correspondingly unphysical apsidal precession.
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Stone, N. (2015). Introduction. In: The Tidal Disruption of Stars by Supermassive Black Holes. Springer Theses. Springer, Cham. https://doi.org/10.1007/978-3-319-12676-0_1
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DOI: https://doi.org/10.1007/978-3-319-12676-0_1
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