GRAVITY: Astrometry on the galactic center and beyond

Bartko, H.; Perrin, G.; Brandner, W.; Straubmeier, C.; Richichi, A.; Gillessen, S.; Paumard, T.; Hippler, S.; Eckart, A.; Schöller, M.; Eisenhauer, F.; Haubois, X.; Lenzen, R.; Rabien, S.; Clénet, Y.; Ramos, J.; Thiel, Markus; Berger, J.‐P.; Baumeister, Harald; Kellner, S.; Cassaing, F.; Böhm, A.; Hofmann, R.; Gendron, É.; Klein, Ralf; Dodds-Eden, K.; Houairi, K.; Hormuth, F.; Gräter, A.; Kervella, P.; Naranjo, V.; Genzel, R.; Fédou, P.; Henning, Th.; Hamaus, Nico; Jocou, L.; Neumann, Udo; Haug, M.; Lacour, S.; Laun, W.; Kolmeder, J.; Malbet, Fabien; Rohloff, R.-R.; Pfuhl, O.; Perraut, K.; Ziegleder, J.; Rouan, D.; Rousset, G.; Amorim, A.; Lima, Jorge

doi:10.1016/j.newar.2010.07.002

Cited by 12 publications

(17 citation statements)

References 36 publications

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“…DISCUSSION 5.1. Comparisons with GRAVITY The possibility of microarcsecond astrometry with the EHT nicely complements the similar efforts using the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI)(Eisenhauer et al 2008;Bartko…”

mentioning

confidence: 80%

RELATIVE ASTROMETRY OF COMPACT FLARING STRUCTURES IN Sgr A* WITH POLARIMETRIC VERY LONG BASELINE INTERFEROMETRY

Johnson

Fish

Doeleman

et al. 2014

ApJ

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We demonstrate that polarimetric interferometry can be used to extract precise spatial information about compact polarized flares of Sgr A*. We show that, for a faint dynamical component, a single interferometric baseline suffices to determine both its polarization and projected displacement from the quiescent intensity centroid. A second baseline enables two-dimensional reconstruction of the displacement, and additional baselines can self-calibrate using the flare, enhancing synthesis imaging of the quiescent emission. We apply this technique to simulated 1.3-mm wavelength observations of a "hot spot" embedded in a radiatively inefficient accretion disk around Sgr A*. Our results indicate that, even with current sensitivities, polarimetric interferometry with the Event Horizon Telescope can achieve ∼5 µas relative astrometry of compact flaring structures near Sgr A* on timescales of minutes.

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confidence: 80%

RELATIVE ASTROMETRY OF COMPACT FLARING STRUCTURES IN Sgr A* WITH POLARIMETRIC VERY LONG BASELINE INTERFEROMETRY

Johnson

Fish

Doeleman

et al. 2014

ApJ

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“…However, if a star can be detected within ∼1000 Schwarzschild radii of Sgr A * and if it can be monitored over a sufficiently long period of time, this technique may also measure the spin (see Figure 6; [30]) and even the quadrupole moment [30,80] together with the already obtained mass [37,38]. Future instruments, such as GRAVITY [81], may be able to resolve the orbits of such stars providing an independent test of the no-hair theorem.…”

Section: Combining Strong-field With Weak-field Tests Of the No-hair mentioning

confidence: 99%

Testing the No-Hair Theorem with Sgr A*

Johannsen

2012

Advances in Astronomy

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The no-hair theorem characterizes the fundamental nature of black holes in general relativity. This theorem can be tested observationally by measuring the mass and spin of a black hole as well as its quadrupole moment, which may deviate from the expected Kerr value. Sgr A*, the supermassive black hole at the center of the Milky Way, is a prime candidate for such tests thanks to its large angular size, high brightness, and rich population of nearby stars. In this paper, I discuss a new theoretical framework for a test of the no-hair theorem that is ideal for imaging observations of Sgr A* with very long baseline interferometry (VLBI). The approach is formulated in terms of a Kerr-like spacetime that depends on a free parameter and is regular everywhere outside of the event horizon. Together with the results from astrometric and timing observations, VLBI imaging of Sgr A* may lead to a secure test of the no-hair theorem.

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“…We study gravitational lensing by a pair of black holes and show that this system can exhibit novel features which are quite unprecedented and absent in any other gravitational lensing configuration studied so far. The analysis of the gravitational lensing is also a timely from the point of view of Event Horizon Telescope and Gravity collaborations which would in near future take snapshots of supermassive black holes at the center of our and nearby galaxies [5], [6], [7], [8], [9], [11], [12].…”

Section: Introductionmentioning

confidence: 99%

Curious case of gravitational lensing by binary black holes: A tale of two photon spheres, new relativistic images, and caustics

2017

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Binary black holes have been in limelight off late due to the detection of a gravitational waves from coalescing compact binaries in the events GW150914 and GW151226. In this paper we study gravitational lensing by the binary black holes modelled as an equal mass Majumdar-Papapetrou di-hole metric and show that this system displays features that are quite unprecedented and absent in any other lensing configuration investigated so far in the literature. We restrict our attention to the light rays which move on the plane midway between the two identical black holes, which allows us to employ various techniques developed for the equatorial lensing in the spherically symmetric spacetimes. If distance between the two black holes is below a certain threshold value, then the system admits two photon spheres. As in the case of single black hole, infinitely many relativistic images are formed due to the light rays which turn back from the region outside the outer (unstable) photon sphere, all of which lie beyond a critical angular radius with respect to the lens.However in the presence of the inner (stable) photon sphere, the effective potential after admitting minimum turns upwards and blows up for the smaller values of radii and the light rays that enter the outer photon sphere can turn back, leading to the formation of a new set of infinitely many relativistic images, all of which lie below the critical radius from the lens mentioned above. As the distance between the two black hole is increased, two photon spheres approach one another, merge and eventually disappear. In the absence of the photon sphere, apart from the formation of a finite number of discrete relativistic images, the system remarkably admits a radial caustic, which has never been observed in the context of relativistic lensing before. Thus the system of binary black hole admits novel features both in the presence and absence of photon spheres. We discuss possible observational signatures and implications of the binary black hole lensing.

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GRAVITY: Astrometry on the galactic center and beyond

Cited by 12 publications

References 36 publications

RELATIVE ASTROMETRY OF COMPACT FLARING STRUCTURES IN Sgr A* WITH POLARIMETRIC VERY LONG BASELINE INTERFEROMETRY

RELATIVE ASTROMETRY OF COMPACT FLARING STRUCTURES IN Sgr A* WITH POLARIMETRIC VERY LONG BASELINE INTERFEROMETRY

Testing the No-Hair Theorem with Sgr A*

Curious case of gravitational lensing by binary black holes: A tale of two photon spheres, new relativistic images, and caustics

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