Periastron shift of compact stellar orbits from general relativistic and tidal distortion effects near Sgr A*

2021 ◽  
Vol 502 (3) ◽  
pp. 3761-3768
Author(s):  
P C Lalremruati ◽  
Sanjeev Kalita
Keyword(s):  
Black Hole ◽  
Tidal Effect ◽  
High Mass ◽  
Orbital Inclination ◽  
Stellar Orbits ◽  
Tidal Distortion ◽  
Gravitational Theories ◽  
Love Numbers ◽  
Sgr A ◽  
Large Telescopes

ABSTRACT The Galactic Centre (Sgr A*), hosting a supermassive black hole, carries sufficient potential for testing gravitational theories. Existing astrometric facilities on Very Large Telescope (VLT) and the Keck Telescope have enabled astronomers to study stellar orbits near Sgr A* and perform new astronomical tests of gravitational theories. These observations have provided strong field tests of gravity (ϕ/c2 ∼ 10−3, which is much greater than ϕ/c2 for the Solar system). In this work, we have estimated magnitudes of various contributions to the periastron shift of compact stellar orbits near Sgr A* for pericentre distance in the range rp = (0.3 – 50)au at a fixed orbital inclination, i = 90°. We take the spin of the black hole as χ = 0.1, 0.44, and 0.9 and eccentricities of the orbit as e = 0.9. The relativistic effects including orders beyond 1PN and spin induced effects are incorporated in the contributions. Effect of tidal distortion on periastron shift has also been added into the estimation by considering gravitational Love numbers for polytropic models of the stars. For the tidal effect, we have considered updated mass–radii relations for low-mass stars and high-mass stars. It has been found that the tidal effect on periastron shift arising from stars represented by polytropes of indices n = 1 and n  = 3 terminate above rp ∼ 2 au and rp ∼ 1 au, respectively. The periastron shift angle for the stars has been compared with the astrometric capabilities of existing large telescopes and upcoming extremely large telescopes. Challenges and prospects associated with the estimations are highlighted.

scholarly journals Dynamical constraints on a dark matter spike at the Galactic centre from stellar orbits

2018 ◽  
Vol 619 ◽  
pp. A46 ◽  
Author(s):  
Thomas Lacroix
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Spectroscopic Data ◽  
Galactic Centre ◽  
Stellar Orbits ◽  
Supermassive Black Hole ◽  
Dynamical Constraints ◽  
Sgr A

In this work I use astrometric and spectroscopic data on the S2 star at the Galactic centre (GC) up to 2016 to derive specific constraints on the size of a dark matter (DM) spike around the central supermassive black hole Sgr A*. These limits are the best direct constraints on a DM spike at the GC for non-annihilating dark matter and exclude a spike with radius greater than a few tens of parsecs for cuspy outer halos and a few hundred parsecs for cored outer halos.

scholarly journals On the Origin of the Galactic Center S Stars

2009 ◽  
Vol 5 (S267) ◽  
pp. 330-330
Author(s):  
Evgeny Griv
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Galactic Rotation ◽  
Concentrated Mass ◽  
Stellar Orbits ◽  
Supermassive Black Hole ◽  
Disk Rotation ◽  
Single Disk ◽  
Sgr A ◽  
Central Parsec

Most, if not all, galaxies with a significant bulge component harbor a central supermassive black hole. In our own Milky Way Galaxy, a disk of stars at a distance r ~ 0.05–1 pc orbits the radio source Sgr A* at the center. Stellar orbits show that the gravitational potential on a scale of ~ 0.5 pc is dominated by a concentrated mass of MBH ≈ 3.6 × 106M⊙, which is associated with a supermassive black hole. In addition to the black hole, the models require the presence of an extended mass of (0.5–1.5) × 106M⊙ in the central parsec, which can be explained well by the mass of the stars that make up the cluster. Thus, the Galactic center star cluster is composed of a central supermassive black hole and a self-gravitating disk that is several Gyrs old and comprised of late-type CO absorption stars. Significant disk rotation in the sense of the general Galactic rotation has been detected. This system is probably a strongly warped, thin single disk; the mean eccentricity of the observed stellar orbits in the disk is e ≈ 0.36 ± 0.06.

scholarly journals MONITORING STELLAR ORBITS AROUND THE MASSIVE BLACK HOLE IN THE GALACTIC CENTER

2009 ◽  
Vol 692 (2) ◽  
pp. 1075-1109 ◽  
Author(s):  
S. Gillessen ◽  
F. Eisenhauer ◽  
S. Trippe ◽  
T. Alexander ◽  
R. Genzel ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Massive Black Hole ◽  
Stellar Orbits

scholarly journals Morphological evolution of supermassive black hole merger hosts and multimessenger signatures

2021 ◽  
Vol 503 (3) ◽  
pp. 3629-3642
Author(s):  
Colin DeGraf ◽  
Debora Sijacki ◽  
Tiziana Di Matteo ◽  
Kelly Holley-Bockelmann ◽  
Greg Snyder ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Star Formation ◽  
Morphological Evolution ◽  
Full Range ◽  
High Mass ◽  
Morphological Evidence ◽  
Galaxy Mergers ◽  
Host Galaxies ◽  
Supermassive Black Hole

ABSTRACT With projects such as Laser Interferometer Space Antenna (LISA) and Pulsar Timing Arrays (PTAs) expected to detect gravitational waves from supermassive black hole mergers in the near future, it is key that we understand what we expect those detections to be, and maximize what we can learn from them. To address this, we study the mergers of supermassive black holes in the Illustris simulation, the overall rate of mergers, and the correlation between merging black holes and their host galaxies. We find these mergers occur in typical galaxies along the MBH−M* relation, and that between LISA and PTAs we expect to probe the full range of galaxy masses. As galaxy mergers can trigger star formation, we find that galaxies hosting low-mass black hole mergers tend to show a slight increase in star formation rates compared to a mass-matched sample. However, high-mass merger hosts have typical star formation rates, due to a combination of low gas fractions and powerful active galactic nucleus feedback. Although minor black hole mergers do not correlate with disturbed morphologies, major mergers (especially at high-masses) tend to show morphological evidence of recent galaxy mergers which survive for ∼500 Myr. This is on the same scale as the infall/hardening time of merging black holes, suggesting that electromagnetic follow-ups to gravitational wave signals may not be able to observe this correlation. We further find that incorporating a realistic time-scale delay for the black hole mergers could shift the merger distribution towards higher masses, decreasing the rate of LISA detections while increasing the rate of PTA detections.

scholarly journals Hunting for intermediate-mass black holes in globular clusters: an astrometric study of NGC 6441

2021 ◽  
Vol 503 (1) ◽  
pp. 1490-1506
Author(s):  
Maximilian Häberle ◽  
Mattia Libralato ◽  
Andrea Bellini ◽  
Laura L Watkins ◽  
Jörg-Uwe Pott ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Velocity Dispersion ◽  
Angular Resolution ◽  
Hubble Space Telescope ◽  
High Mass ◽  
High Angular Resolution ◽  
Stellar Kinematics ◽  
Intermediate Mass ◽  
The Core ◽  
Large Telescopes

ABSTRACT We present an astrometric study of the proper motions (PMs) in the core of the globular cluster NGC 6441. The core of this cluster has a high density and observations with current instrumentation are very challenging. We combine ground-based, high-angular-resolution NACO@VLT images with Hubble Space Telescope ACS/HRC data and measure PMs with a temporal baseline of 15 yr for about 1400 stars in the centremost 15 arcsec of the cluster. We reach a PM precision of ∼30 µas yr−1 for bright, well-measured stars. Our results for the velocity dispersion are in good agreement with other studies and extend already existing analyses of the stellar kinematics of NGC 6441 to its centremost region never probed before. In the innermost arcsecond of the cluster, we measure a velocity dispersion of (19.1 ± 2.0) km s−1 for evolved stars. Because of its high mass, NGC 6441 is a promising candidate for harbouring an intermediate-mass black hole (IMBH). We combine our measurements with additional data from the literature and compute dynamical models of the cluster. We find an upper limit of $M_{\rm IMBH} \lt 1.32 \times 10^4\, \textrm{M}_\odot$ but we can neither confirm nor rule out its presence. We also refine the dynamical distance of the cluster to $12.74^{+0.16}_{-0.15}$ kpc. Although the hunt for an IMBH in NGC 6441 is not yet concluded, our results show how future observations with extremely large telescopes will benefit from the long temporal baseline offered by existing high-angular-resolution data.

scholarly journals Observational manifestations of ‘cosmological dinosaurs’ at redshifts z ∼ 20

2021 ◽  
Vol 503 (2) ◽  
pp. 3081-3088
Author(s):  
V K Dubrovich ◽  
Yu N Eroshenko ◽  
S I Grachev
Keyword(s):  
Black Hole ◽  
Atomic Hydrogen ◽  
Radiation Transfer ◽  
Ring Width ◽  
High Mass ◽  
Primordial Black Hole ◽  
Array Type ◽  
Local Sources ◽  
Order Of Magnitude ◽  
Very High

ABSTRACT We consider a primordial black hole of very high mass, $10^9\!-\!10^{10}\, \mathrm{M}_\odot$, surrounded by the dark matter and bayonic halo at redshifts z ∼ 20 without any local sources of energy release. Such heavy and concentrated objects in the early Universe were previously called ‘cosmological dinosaurs’. Spectral distribution and spatial variation of the brightness in the 21-cm line of atomic hydrogen are calculated with the theory of radiation transfer. It is shown that a narrow and deep absorption arises in the form of the spherical shell around the primordial black hole at the certain radius. The parameters of this shell depend almost exclusively on the mass of the black hole. The angular diameter 18 arcsec of the absorption ring at z ∼ 20 is well within the current technical possibilities of the Square Kilometre Array type telescopes. But the observation of the ring width itself requires an order of magnitude better resolution.

scholarly journals Testing the black hole no-hair theorem with Galactic Center stellar orbits

2021 ◽  
Vol 103 (8) ◽  
Author(s):  
Hong Qi ◽  
Richard O’Shaughnessy ◽  
Patrick Brady
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Stellar Orbits

scholarly journals Relative depolarization of the black hole photon ring in GRMHD models of Sgr A* and M87*

2021 ◽  
Vol 503 (3) ◽  
pp. 4563-4575
Author(s):  
A Jiménez-Rosales ◽  
J Dexter ◽  
S M Ressler ◽  
A Tchekhovskoy ◽  
M Bauböck ◽  
...  
Keyword(s):  
Black Hole ◽  
Relativistic Effects ◽  
Image Features ◽  
Black Hole Mass ◽  
Magnetic Turbulence ◽  
Intensity Images ◽  
General Relativistic ◽  
Sharp Image ◽  
Sgr A ◽  
Magnetohydrodynamic Simulations

ABSTRACT Using general relativistic magnetohydrodynamic simulations of accreting black holes, we show that a suitable subtraction of the linear polarization per pixel from total intensity images can enhance the photon ring feature. We find that the photon ring is typically a factor of ≃2 less polarized than the rest of the image. This is due to a combination of plasma and general relativistic effects, as well as magnetic turbulence. When there are no other persistently depolarized image features, adding the subtracted residuals over time results in a sharp image of the photon ring. We show that the method works well for sample, viable GRMHD models of Sgr A* and M87*, where measurements of the photon ring properties would provide new measurements of black hole mass and spin, and potentially allow for tests of the ‘no-hair’ theorem of general relativity.

scholarly journals Central Molecular Zone of the Milky Way: Star Formation in an extreme Environment

2015 ◽  
Vol 11 (S315) ◽  
pp. 163-166
Author(s):  
Jens Kauffmann
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Spatial Scales ◽  
Extreme Environment ◽  
Average Density ◽  
High Mass ◽  
Density Structure ◽  
Star Formation Activity ◽  
Order Of Magnitude ◽  
Sgr A

AbstractThe Central Molecular Zone (CMZ; inner ~100 pc) hosts some of the most dense and massive molecular clouds of the Milky Way. These clouds might serve as local templates for dense clouds seen in nearby starburst galaxies or in the early universe. The clouds have a striking feature: they form stars at a very slow pace, considering their mass and high average density. Here we use interferometer data from ALMA and the SMA to show that this slow star formation is a consequence of the cloud density structure: CMZ clouds have a very flat density structure. They might, for example, exceed the average density of the Orion A molecular cloud by an order of magnitude on spatial scales ~5 pc, but CMZ “cores” of ~0.1 pc radius have masses and densities lower than what is found in the Orion KL region. This absence of highest–density gas probably explains the suppression of star formation. The clouds are relatively turbulent, and ALMA observations of H2CO and SiO indicate that the turbulence is induced by high–velocity shocks. We speculate that these shocks might prevent the formation of high–mass cores. It has been argued that the state of CMZ clouds depends on their position along the orbit around Sgr A*. Our incomplete data indicate no evolution in the density structure, and only a modest evolution in star formation activity per unit mass.

scholarly journals HOLLOWGRAPHY DRIVEN HOLOGRAPHY: BLACK HOLE WITH VANISHING VOLUME INTERIOR

2010 ◽  
Vol 19 (14) ◽  
pp. 2345-2351 ◽  
Author(s):  
AHARON DAVIDSON ◽  
ILYA GURWICH
Keyword(s):  
Phase Transition ◽  
General Relativity ◽  
Black Hole ◽  
Degrees Of Freedom ◽  
Schwarzschild Solution ◽  
Entropy Formula ◽  
Gravitational Theories ◽  
Hollow Interior ◽  
Spatial Volume ◽  
Self Similar

Hawking–Bekenstein entropy formula seems to tell us that no quantum degrees of freedom can reside in the interior of a black hole. We suggest that this is a consequence of the fact that the volume of any interior sphere of finite surface area simply vanishes. Obviously, this is not the case in general relativity. However, we show that such a phenomenon does occur in various gravitational theories which admit a spontaneously induced general relativity. In such theories, due to a phase transition (one-parameter family degenerates) which takes place precisely at the would-have-been horizon, the recovered exterior Schwarzschild solution connects, by means of a self-similar transition profile, with a novel "hollow" interior exhibiting a vanishing spatial volume and a locally varying Newton constant. This constitutes the so-called "hollowgraphy" driven holography.

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