Perets, Hagai B., Gualandris, Alessia, Kupi, Gabor, Merritt, David, Alexander, Tal
We use N-body simulations to study the evolution of the orbital eccentricities of stars deposited near (
Accretion disk warping by resonant relaxation: The case of maser disk NGC4258 (2009)
Bregman, Michal, Alexander, Tal
The maser disk around the massive black hole (MBH) in active galaxy NGC 4258 exhibits an O(10 deg) warp on the O(0.1 pc) scale. The physics driving the warp are still debated. Suggested mechanisms...
Probing Stellar Dynamics in Galactic Nuclei (2009)
Miller, M. Coleman, Alexander, Tal, Amaro-Seoane, Pau, Barth, Aaron J., Cutler, Curt, Gair, Jonathan R., ...
Electromagnetic observations over the last 15 years have yielded a growing appreciation for the importance of supermassive black holes (SMBH) to the evolution of galaxies, and for the intricacies of...
Analytic study of mass segregation around a massive black hole (2009)
Keshet, Uri, Hopman, Clovis, Alexander, Tal
We analyze the distribution of stars of arbitrary mass function g(m) around a massive black hole (MBH). Unless g is strongly dominated by light stars, the steady-state distribution function...
The Galactic potential and the asymmetric distribution of hypervelocity stars (2008)
Perets, Hagai B., Wu, Xufen, Zhao, HongSheng, Famaey, Benoit, Gentile, Gianfranco, Alexander, Tal
In recent years several hypervelocity stars (HVSs) have been observed in the halo of our Galaxy. Such HVSs have possibly been ejected from the Galactic center and then propagated in the Galactic...
Strong mass segregation around a massive black hole (2008)
Alexander, Tal, Hopman, Clovis
We show that the mass-segregation solution for the steady state distribution of stars around a massive black hole (MBH) has two branches: the known weak segregation solution (Bahcall & Wolf 1977),...
Dynamical evolution of the young stars in the Galactic center (2008)
Perets, Hagai. B., Gualandris, Alessia, Merritt, David, Alexander, Tal
Recent observations of the Galactic center revealed a nuclear disk of young OB stars near the massive black hole (MBH), in addition to many similar outlying stars with higher eccentricities and/or...
The Galactic Center as a laboratory for extreme mass ratio gravitational wave source dynamics (2008)
The massive Galactic black hole and the stars around it are a unique laboratory for studying how relaxation processes lead to close interactions of stars and compact remnants with the central massive...
The efficiency of resonant relaxation around a massive black hole (2008)
Eilon, Ehud, Kupi, Gábor, Alexander, Tal
Resonant relaxation (RR) is a rapid relaxation process that operates in the nearly-Keplerian potential near a massive black hole (MBH). RR dominates the dynamics of compact remnants that inspiral...
Dynamical evolution of the young stars in the Galactic center (2008)
Perets, Hagai, Gualandris, Alessia, Merritt, David, Alexander, Tal
Also archived in arXiv:0807.2340 v1 Jul 15, 2008. Proceedings from The Central Kiloparsec: Active Nuclei And Their Hosts from Ierapetra, Crete, Greece, June 4-6, 2008
Getting a kick out of the stellar disk(s) in the galactic center (2007)
Perets, Hagai B., Kupi, Gabor, Alexander, Tal
Recent observations of the Galactic center revealed a nuclear disk of young OB stars, in addition to many similar outlying stars with higher eccentricities and/or high inclinations relative to the...
Beaming Binaries - a New Observational Category of Photometric Binary Stars (2007)
Zucker, Shay, Mazeh, Tsevi, Alexander, Tal
The new photometric space-borne survey missions CoRoT and Kepler will be able to detect minute flux variations in binary stars due to relativistic beaming caused by the line-of-sight motion of their...
Stellar Relaxation Processes Near the Galactic Massive Black Hole (2007)
The massive black hole (MBH) in the Galactic Center and the stars around it form a unique stellar dynamics laboratory for studying how relaxation processes affect the distribution of stars and...
Massive perturbers and the efficient merger of binary massive black holes (2007)
Perets, Hagai B., Alexander, Tal
We show that dynamical relaxation in the aftermath of a galactic merger and the ensuing formation and decay of a binary massive black hole (MBH), are dominated by massive perturbers (MPs) such as...
Massive perturbers in the galactic center (2006)
Perets, Hagai B., Hopman, Clovis, Alexander, Tal
We investigate the role of massive perturbers, such as giant molecular clouds or stellar clusters, in supplying low-angular momentum stars that pass very close to the central massive black hole (MBH)...
Spectroscopic Binary Mass Determination using Relativity (2006)
High-precision radial-velocity techniques, which enabled the detection of extrasolar planets are now sensitive to relativistic effects in the data of spectroscopic binary stars (SBs). We show how...
Massive perturber-driven interactions of stars with a massive black hole (2006)
Perets, Hagai B., Hopman, Clovis, Alexander, Tal
We study the role of massive perturbers (MPs) in deflecting stars and binaries to almost radial ("loss-cone") orbits, where they pass near the central massive black hole (MBH), interact with it at...
Resonant Relaxation near the Massive Black Hole in the Galactic Center (2006)
Hopman, Clovis, Alexander, Tal
The coherent torques between stars on orbits near massive black holes (MBHs) lead to resonant angular momentum relaxation. Due to the fact that orbits are Keplerian to good approximation, the torques...
The effect of mass-segregation on gravitational wave sources near massive black holes (2006)
Hopman, Clovis, Alexander, Tal
Gravitational waves (GWs) from the inspiral of compact remnants (CRs) into massive black holes (MBHs) will be observable to cosmological distances. While a CR spirals in, 2-body scattering by field...
Hopman, Clovis, Alexander, Tal
Resonant relaxation (RR) of orbital angular momenta occurs near massive black holes (MBHs) where the stellar orbits are nearly Keplerian and so do not precess significantly. The resulting coherent...
Probing Post-Newtonian Gravity near the Galactic Black Hole with Stellar Doppler Measurements (2005)
Zucker, Shay, Alexander, Tal, Gillessen, Stefan, Eisenhauer, Frank, Genzel, Reinhard
Stars closely approaching the massive black hole in the center of the Galaxy provide a unique opportunity to probe post-Newtonian physics in a yet unexplored regime of celestial mechanics. Recent...
Stellar Processes Near the Massive Black Hole in the Galactic Center (2005)
A massive black hole resides in the center of most, perhaps all galaxies. The one in the center of our home galaxy, the Milky Way, provides a uniquely accessible laboratory for studying in detail the...
Hopman, Clovis, Alexander, Tal
We study the orbital parameters distribution of stars that are scattered into nearly radial orbits and then spiral into a massive black hole (MBH) due to dissipation, in particular by emission of...
Inward bound: high resolution AO observations of the galactic center (2005)
Genzel, Reinhard, Ott, Thomas, Eckart, Andreas, Schödel, Reiner, Alexander, Tal
Orbital capture of stars by a massive black hole via exchanges with compact remnants (2004)
We propose a dynamical mechanism for capturing stars around a massive black hole (MBH), which is based on the accumulation there of a very dense cluster of compact stellar remnants. This study is...
Scott, Jennifer E., Kriss, Gerard A., Lee, Julia C., Arav, Nahum, Ogle, Patrick, Roraback, Kenneth, ...
We present a study of the intrinsic X-ray and far-ultraviolet absorption in the Seyfert 1.5 galaxy Markarian 279 using simultaneous observations from the Chandra X-ray Observatory, the Space...
Ultraluminous X-ray Sources as Intermediate Mass Black Holes Fed by Tidally Captured Stars (2003)
Hopman, Clovis, Zwart, Simon F. Portegies, Alexander, Tal
The nature of ultraluminous X-ray sources (ULXs) is presently unknown. A possible explanation is that they are accreting intermediate mass black holes (IBHs) that are fed by Roche lobe overflow from...
Squeezars: Tidally powered stars orbiting a massive black hole (2003)
We propose that there exists a class of transient sources, "squeezars", which are stars caught in highly eccentric orbits around a massive (m
Orbital inspiral into a massive black hole in a galactic center (2003)
Alexander, Tal, Hopman, Clovis
A massive black hole (MBH) in a galactic center drives a flow of stars into nearly radial orbits to replace those it destroyed. Stars whose orbits cross the event horizon r_s or the tidal disruption...
Stellar Tidal Processes Near Massive Black Holes (2003)
Close tidal interactions of stars with a central massive black hole (MBH) or with other stars in the high density cusp around it can affect a significant fraction of the stellar population within the...
Stars and singularities: Stellar phenomena near a massive black hole (2002)
This is a pedagogical review of recent results on the interactions of central massive black holes with stars very near them, focused on the black hole in the center of the Milky Way. Table of...
Tidal scattering of stars on supermassive black holes in galactic centers (2001)
Some of the mass that feeds the growth of a massive black hole (BH) in a galactic center is supplied by tidal disruption of stars that approach it on unbound, low angular momentum orbits. For each...
The Cosmic Baryon Fraction and the Extragalactic Ionizing Background (2001)
Hui, Lam, Haiman, Zoltan, Zaldarriaga, Matias, Alexander, Tal
We reassess constraints on the cosmological baryon density from observations of the mean decrement and power spectrum of the Lyman-alpha forest, taking into account uncertainties in all free...
Pinpointing the massive black hole in the Galactic Center with gravitationally lensed stars (2001)
A new statistical method for pinpointing the massive black hole (BH) in the Galactic Center on the IR grid is presented and applied to astrometric IR observations of stars close to the BH. This is of...
Enhanced Microlensing by Stars Around the Black Hole in the Galactic Center (2000)
The effect of stars on the lensing properties of the supermassive black hole in the Galactic Center is similar to the effect of planets on microlensing by a star. We show that the dense stellar...
Tidal spin-up of stars in dense stellar cusps around massive black holes (2000)
We show that main-sequence stars in dense stellar cusps around massive black holes are likely to rotate at a significant fraction of the centrifugal breakup velocity due to spin-up by hyperbolic...
Infrared spectroscopy of NGC 1068: Probing the obscured ionizing AGN continuum (2000)
Alexander, Tal, Lutz, Dieter, Sturm, Eckhard, Genzel, Reinhard, Sternberg, Amiel, Netzer, Hagai
The ISO-SWS 2.5-45 um infrared spectroscopic observations of the nucleus of the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a compilation of UV to IR narrow emission line data...
The distribution of stars near the super-massive black hole in the Galactic Center (1999)
We analyze three sets of infrared star counts in the inner ~0.5 pc of the Galactic Center. We perform statistical tests on the star counts and model in detail the extinction field and the effects of...
Near-Infrared Microlensing of Stars by the Super-Massive Black Hole in the Galactic Center (1998)
Alexander, Tal, Sternberg, Amiel
We investigate microlensing amplification of faint stars in the dense stellar cluster in the Galactic Center (GC) by the super-massive black hole (BH). Such events would appear very close to the...
Infrared spectroscopy of NGC4151: Probing the obscured ionizing AGN continuum (1998)
Alexander, Tal, Sturm, Eckhard, Lutz, Dieter, Sternberg, Amiel, Netzer, Hagai, Genzel, Reinhard
The ISO-SWS infrared spectroscopic observations of the nucleus of Seyfert galaxy NGC4151, which are described in a companion paper, are used together with a compilation of UV to IR narrow emission...
Peterson, Bradley M., Wanders, Ignaz, Horne, Keith, Collier, Stefan, Alexander, Tal, Kaspi, Shai, ...
We describe a model-independent method of assessing the uncertainties in cross-correlation lags determined from AGN light curves, and use this method to investigate the reality of lags between UV and...
Bloated Stars as AGN Broad Line Clouds: The Emission Lines Response to Continuum Variations (1996)
The `Bloated Stars Scenario' proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS). Alexander and Netzer (1994, 1996) established that ~ 5e4 BSs with dense,...
Bloated Stars as AGN Broad Line Clouds: The Emission Line Profiles (1996)
The Bloated Stars Scenario proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS). Alexander and Netzer (1994) established that ~ 5e4 BSs with dense,...
The Signature of Microlensing in QSO Variability-Redshift Correlations (1995)
A recently discovered inverse correlation between QSO redshift and long-term continuum variability timescales was suggested to be the signature of microlensing on cosmological scales (Hawkins 1993)....
Bloated Stars as AGN Broad Line Clouds: The Emission Line Spectrum (1994)
The Bloated Stars Scenario proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS). Its main advantage over BLR cloud models is the gravitational confinement...