Foundations of Physics

, Volume 47, Issue 5, pp 553–624 | Cite as

The Milky Way’s Supermassive Black Hole: How Good a Case Is It?

A Challenge for Astrophysics & Philosophy of Science
  • Andreas EckartEmail author
  • Andreas Hüttemann
  • Claus Kiefer
  • Silke Britzen
  • Michal Zajaček
  • Claus Lämmerzahl
  • Manfred Stöckler
  • Monica Valencia-S
  • Vladimir Karas
  • Macarena García-Marín


The compact and, with \({\sim }4.3\pm 0.3\times 10^6\) M\(_{\odot }\), very massive object located at the center of the Milky Way is currently the very best candidate for a supermassive black hole (SMBH) in our immediate vicinity. The strongest evidence for this is provided by measurements of stellar orbits, variable X-ray emission, and strongly variable polarized near-infrared emission from the location of the radio source Sagittarius A* (SgrA*) in the middle of the central stellar cluster. Simultaneous near-infrared and X-ray observations of SgrA* have revealed insights into the emission mechanisms responsible for the powerful near-infrared and X-ray flares from within a few tens to one hundred Schwarzschild radii of such a putative SMBH. If SgrA* is indeed a SMBH it will, in projection onto the sky, have the largest event horizon and will certainly be the first and most important target for very long baseline interferometry observations currently being prepared by the event horizon telescope (EHT). These observations in combination with the infrared interferometry experiment GRAVITY at the very large telescope interferometer and other experiments across the electromagnetic spectrum might yield proof for the presence of a black hole at the center of the Milky Way. The large body of evidence continues to discriminate the identification of SgrA* as a SMBH from alternative possibilities. It is, however, unclear when the ever mounting evidence for SgrA* being associated with a SMBH will suffice as a convincing proof. Additional compelling evidence may come from future gravitational wave observatories. This manuscript reviews the observational facts, theoretical grounds and conceptual aspects for the case of SgrA* being a black hole. We treat theory and observations in the framework of the philosophical discussions about “(anti)realism and underdetermination”, as this line of arguments allows us to describe the situation in observational astrophysics with respect to supermassive black holes. Questions concerning the existence of supermassive black holes and in particular SgrA* are discussed using causation as an indispensable element. We show that the results of our investigation are convincingly mapped out by this combination of concepts.


Black holes: mass, spin, charge Sources: Sagittarus A* Galaxies: active Philosophy of science: (anti)realism, underdetermination, causality Causality 



We thank Sybille Anderl (IPAG Grenoble) for valuable comments and support on the philosophy of science sections, Georgi Dvali (LMU Munich) for constructive and valuable discussions and input, and Grischa Karssen (University of Cologne) for contributing Fig. 12 and part of the corresponding discussion. We also thank Rainer Schödel (IAA Granada, CSIC Spain) for valuable comments. This work was supported in part by the Deutsche Forschungsgemeinschaft (DFG) via the Cologne Bonn Graduate School (BCGS), the Max Planck Society through the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics. Part of this work was supported by fruitful discussions with members of the European Union funded COST Action MP0905: Black Holes in a Violent Universe and the Czech Science Foundation DFG collaboration (No.  14-37086G) and with members of the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement No. 312789, Strong Gravity: Probing Strong Gravity by Black Holes Across the Range of Masses.


  1. 1.
    Aasi, J., Abadie, J., Abbott, B.P., Abbott, R., Abbott, T., Abernathy, M.R., Accadia, T., Acernese, F., Adams, C., Adams, T., et al.: Directed search for continuous gravitational waves from the Galactic center. Phys. Rev. D 88(10), 102002 (2013). arXiv:1309.6221 ADSCrossRefGoogle Scholar
  2. 2.
    Aasi, J., Abbott, B.P., Abbott, R., Abbott, T., Abernathy, M.R., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., et al.: Search for gravitational wave ringdowns from perturbed intermediate mass black holes in LIGO-Virgo data from 2005–2010. Phys. Rev. D 89(10), 102006 (2014). arXiv:1403.5306 ADSCrossRefGoogle Scholar
  3. 3.
    Abbott, B.P., Abbott, R., Abbott, T.D., Abernathy, M.R., Acernese, F., Ackley, K.: Observation of gravitational waves from a binary black hole merger. Phys. Rev. Lett. 116, 061102 (2016). doi: 10.1103/PhysRevLett.116.061102 ADSCrossRefGoogle Scholar
  4. 4.
    Abdolrahimi, S., Mann, R.B., Tzounis, C.: Distorted local shadows. Phys. Rev. D 91(8), 084052 (2015)ADSMathSciNetCrossRefGoogle Scholar
  5. 5.
    Abramowicz, M.A., Kluźniak, W., Lasota, J.P.: No observational proof of the black-hole event-horizon. A&A 396, L31–L34 (2002). arXiv:astro-ph/0207270 ADSzbMATHCrossRefGoogle Scholar
  6. 6.
    Amaro-Seoane, P., Gair, J.R., Freitag, M., Miller, M.C., Mandel, I., Cutler, C.J., Babak, S.: Topical review: intermediate and extreme mass-ratio inspirals astrophysics, science applications and detection using LISA. Class. Quantum Gravity 24, R113–R169 (2007)ADSzbMATHCrossRefGoogle Scholar
  7. 7.
    Amaro-Seoane, P., Aoudia, S., Babak, S., et al.: Low-frequency gravitational-wave science with ELISA/NGO. Class. Quantum Gravity 29(12), 124016 (2012)ADSCrossRefGoogle Scholar
  8. 8.
    Anderl, S.: Astronomy and astrophysics in the philosophy of science. (2015). arXiv:1510.03284
  9. 9.
    Anderl, S.: Astronomy and Astrophysics. In: Humphreys, P. (ed.) The Oxford Handbook of Philosophy of Science. Oxford University Press, Oxford (2016). doi: 10.1093/oxfordhb/9780199368815.013.45
  10. 10.
    Arca-Sedda, M.: On the formation of compact, massive subsystems in stellar clusters and its relation with intermediate-mass black holes. MNRAS 455, 35–50 (2016). arXiv:1502.01242
  11. 11.
    Armstrong, D. (ed.): A World of States of Affairs, p. 41. Cambridge University Press, Cambridge (2001). ISBN-13:9780521580649, ISBN-10:0521580641Google Scholar
  12. 12.
    Baganoff, F.K., Bautz, M.W., Brandt, W.N., Chartas, G., Feigelson, E.D., Garmire, G.P., Maeda, Y., Morris, M., Ricker, G.R., Townsley, L.K., Walter, F.: Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic centre. Nature 413, 45–48 (2001)ADSCrossRefGoogle Scholar
  13. 13.
    Baganoff, F.K., Maeda, Y., Morris, M., Bautz, M.W., Brandt, W.N., Cui, W., Doty, J.P., Feigelson, E.D., Garmire, G.P., Pravdo, S.H., Ricker, G.R., Townsley, L.K.: Chandra X-ray spectroscopic imaging of Sagittarius A* and the central parsec of the galaxy. ApJ 591, 891–915 (2003)ADSCrossRefGoogle Scholar
  14. 14.
    Bahcall, J.N., Wolf, R.A.: Star distribution around a massive black hole in a globular cluster. ApJ 209, 214–232 (1976)ADSCrossRefGoogle Scholar
  15. 15.
    Balick, B., Brown, R.L.: Intense sub-arcsecond structure in the galactic center. ApJ 194, 265–270 (1974)ADSCrossRefGoogle Scholar
  16. 16.
    Barbour, J.B., Pfister, H. (eds.): Mach’s Principle: From Newton’s Bucket to Quantum Gravity. Birkhäuser, Boston (1995). ISBN 978-0-8176-3823-8zbMATHGoogle Scholar
  17. 17.
    Bardeen, J.M.: Rapidly rotating stars, disks, and black holes. In: DeWitt, C., DeWitt, B.S. (eds.) Black Holes (Les Astres Occlus), pp. 241–289 (1973)Google Scholar
  18. 18.
    Bardeen, J.M., Wagoner, R.V.: Relativistic disks. I. Uniform rotation. ApJ 167, 359 (1971)Google Scholar
  19. 19.
    Barrau, A., Rovelli, C., Vidotto, F.: Fast radio bursts and white hole signals. Phys. Rev. D 90(12), 127503 (2014)ADSCrossRefGoogle Scholar
  20. 20.
    Barrau, A., Bolliet, B., Schutten, M., Vidotto, F.: Bouncing black holes in quantum gravity and the Fermi gamma-ray excess. (2016). arXiv:1606.08031
  21. 21.
    Barrière, N.M., Tomsick, J.A., Baganoff, F.K., Boggs, S.E., Christensen, F.E., Craig, W.W., Dexter, J., Grefenstette, B., Hailey, C.J., Harrison, F.A., Madsen, K.K., Mori, K., Stern, D., Zhang, W.W., Zhang, S., Zoglauer, A.: NuSTAR detection of high-energy X-ray emission and rapid variability from Sagittarius A* flares. ApJ 786, 46 (2014). arXiv:1403.0900 ADSCrossRefGoogle Scholar
  22. 22.
    Bartusiak, M.: Black Hole. Yale University Press, New Haven (2015). ISBN 9780300210859zbMATHGoogle Scholar
  23. 23.
    Berti, E., Barausse, E., Cardoso, V., Gualtieri, L., Pani, P., Sperhake, U., Stein, L.C., Wex, N., Yagi, K., Baker, T., Burgess, C.P., Coelho, F.S., Doneva, D., De Felice, A., Ferreira, P.G., Freire, P.C.C., Healy, J., Herdeiro, C., Horbatsch, M., Kleihaus, B., Klein, A., Kokkotas, K., Kunz, J., Laguna, P., Lang, R.N., Li, T.G.F., Littenberg, T., Matas, A., Mirshekari, S., Okawa, H., Radu, E., O’Shaughnessy, R., Sathyaprakash, B.S., Van Den Broeck, C., Winther, H.A., Witek, H., Emad Aghili, M., Alsing, J., Bolen, B., Bombelli, L., Caudill, S., Chen, L., Degollado, J.C., Fujita, R., Gao, C., Gerosa, D., Kamali, S., Silva, H.O., Rosa, J.G., Sadeghian, L., Sampaio, M., Sotani, H., Zilhao, M.: Testing general relativity with present and future astrophysical observations. Class. Quantum Gravity 32(24), 243001 (2015)Google Scholar
  24. 24.
    Berti, E., Sesana, A., Barausse, E., Cardoso, V., Belczynski, K.: Spectroscopy of Kerr Black Holes with Earth- and Space-based interferometers. Phys. Rev. Lett. 117(10), 101102 (2016)ADSCrossRefGoogle Scholar
  25. 25.
    Bethge, K., Gruber, G., Stöhlker, T. (eds.): Physik der Atome und Moleküle: Eine Einfhrung, p. 4445. Wiley, New York (2012). ISBN 978-3-527-66255-5Google Scholar
  26. 26.
    Bilic, N., Tupper, G.B., Viollier, R.D.: Supermassive fermion balls and constraints from stellar dynamics near Sgr A*. Astrophysics (2003). arXiv:astro-ph/0310172
  27. 27.
    Bird, S., Cholis, I., Muñoz, J.B., Ali-Haïmoud, Y., Kamionkowski, M., Kovetz, E.D., Raccanelli, A., Riess, A.G.: Did LIGO detect dark matter? Phys. Rev. Lett. (2016). arXiv:1603.00464
  28. 28.
    Blais, D., Kiefer, C., Polarski, D.: Can primordial black holes be a significant part of dark matter? Phys. Lett. B 535, 11–16 (2002). arXiv:astro-ph/0203520 ADSCrossRefGoogle Scholar
  29. 29.
    Blandford, R.D., Begelman, M.C.: On the fate of gas accreting at a low rate on to a black hole. MNRAS 303, L1–L5 (1999). arXiv:astro-ph/9809083 ADSCrossRefGoogle Scholar
  30. 30.
    Boehle, A., Ghez, A.M., Schödel, R., Meyer, L., Yelda, S., Albers, S., Martinez, G.D., Becklin, E.E., Do, T., Lu, J.R., Matthews, K., Morris, M.R., Sitarski, B., Witzel, G.: An improved distance and mass estimate for Sgr A* from a multistar orbit analysis. ApJ 830, 17 (2016). arXiv:1607.05726
  31. 31.
    Bogdanović, T.: Supermassive Black Hole Binaries: The Search Continues. In: Astrophysics and Space Science Proceedings, vol. 40, p. 103 (2015). arXiv:1406.5193
  32. 32.
    Branham, R.L.: The distance to the Galactic center determined by OB stars. Ap&SS 353, 179–190 (2014)ADSCrossRefGoogle Scholar
  33. 33.
    Britzen, S., Eckart, A., Lämmerzahl, C., et al.: Jet signatures of black holes: from Sgr A* to active galactic nuclei. Astronomische Nachrichten 5(2015), 471–476 (2015)ADSCrossRefGoogle Scholar
  34. 34.
    Broderick, A.E., Loeb, A.: Imaging bright-spots in the accretion flow near the black hole horizon of Sgr A*. MNRAS 363, 353–362 (2005). arXiv:astro-ph/0506433 ADSCrossRefGoogle Scholar
  35. 35.
    Broderick, A.E., Loeb, A.: Imaging optically-thin hotspots near the black hole horizon of Sgr A* at radio and near-infrared wavelengths. MNRAS 367, 905–916 (2006). arXiv:astro-ph/0509237 ADSCrossRefGoogle Scholar
  36. 36.
    Broderick, A.E., Narayan, R.: Where are all the gravastars? Limits upon the gravastar model from accreting black holes. Class. Quantum Gravity 24, 659–666 (2007). arXiv:gr-qc/0701154
  37. 37.
    Broderick, A.E., Johannsen, T., Loeb, A., Psaltis, D.: Testing the no-hair theorem with event horizon telescope observations of Sagittarius A*. ApJ 784, 7 (2014)ADSCrossRefGoogle Scholar
  38. 38.
    Broderick, A.E., Narayan, R., Kormendy, J., Perlman, E.S., Rieke, M.J., Doeleman, S.S.: The event horizon of M87. ApJ 805, 179 (2015)ADSCrossRefGoogle Scholar
  39. 39.
    Brown, E.: Ann E. Ewing, 89, Washington Post, Sunday, August 1, 2010, p. 39, (2010). wp-dyn/content/article/
  40. 40.
    Buchholz, R.M., Schödel, R., Eckart, A.: Composition of the galactic center star cluster. Population analysis from adaptive optics narrow band spectral energy distributions. A&A 499, 483–501 (2009). arXiv:0903.2135
  41. 41.
    Bursa, M., Abramowicz, M.A., Karas, V., Kluźniak, W., Schwarzenberg-Czerny, A.: The timescale of encircling light. In: Hledík, S., Stuchlík, Z. (eds.) Proceedings of RAGtime 8/9: Workshops on Black Holes and Neutron Stars, pp. 21–25 (2007)Google Scholar
  42. 42.
    Calmet, X.: Quantum Aspects of Black Holes. Springer, Heidelberg (2015). ISBN 978-3-319-10852-0zbMATHCrossRefGoogle Scholar
  43. 43.
    Cardoso, V., Crispino, L.C.B., Macedo, C.F.B., Okawa, H., Pani, P.: Light rings as observational evidence for event horizons: long-lived modes, ergoregions and nonlinear instabilities of ultracompact objects. Phys. Rev. D 90(4), 044069 (2014)ADSCrossRefGoogle Scholar
  44. 44.
    Cardoso, V., Franzin, E., Pani, P.: Is the gravitational-wave ringdown a probe of the event horizon? Phys. Rev. Lett. 116(171101), 116 (2016)Google Scholar
  45. 45.
    Carnap, R.: Logische Syntax der Sprache (1968). ISBN 978-3-662-25376-2(e-book), ISBN 978-3-662-23331-3; 1934 by Julius Springer, 2. AuflageGoogle Scholar
  46. 46.
    Chakravartty, A.: A Metaphysics for Scientific Realism: Knowing the Unobservable (2010) ISBN 978-0-521-13009-7; 2015 Paperback: ISBN-10: 1508932867, ISBN-13: 978-1508932864Google Scholar
  47. 47.
    Chandrasekhar, S.: The mathematical theory of black holes. Oxford University PressGoogle Scholar
  48. 48.
    Chapline G (2003) Quantum Phase Transitions and the Failure of Classical General Relativity. International Journal of Modern Physics A 18:3587–3590, gr-qc/0012094Google Scholar
  49. 49.
    Christodoulou, M., Rovelli, C., Speziale, S., Vilensky, I.: Planck star tunneling time: An astrophysically relevant observable from background-free quantum gravity. Phys. Rev. D 94(8), 084035 (2016)ADSCrossRefGoogle Scholar
  50. 50.
    Clavel, M., Terrier, R., Goldwurm, A., Morris, M.R., Ponti, G., Soldi, S., Trap, G.: Echoes of multiple outbursts of Sagittarius A revealed by Chandra. A&A 558, A32 (2013). 1307.3954Google Scholar
  51. 51.
    Cleland, C.: Living with the abstract: realism and models. Philosophy of Science 69, 474–496 (2002)CrossRefGoogle Scholar
  52. 52.
    Colbert, E.J.M., Mushotzky, R.F.: The Nature of Accreting Black Holes in Nearby Galaxy Nuclei. ApJ 519, 89–107 (1999). astro-ph/9901023ADSCrossRefGoogle Scholar
  53. 53.
    Colpi, M., Shapiro, S.L., Wasserman, I.: Boson stars - Gravitational equilibria of self-interacting scalar fields. Phys. Rev. Lett. 57, 2485–2488 (1986)ADSMathSciNetCrossRefGoogle Scholar
  54. 54.
    Colyvan, M.: Can the eleatic principle be justified? Canad. J. Philos. 28, 313–335 (1998)CrossRefGoogle Scholar
  55. 55.
    Colyvan, M.: The Indispensability of Mathematics; Oxford University Press, Oxford (2001)(1983). ISBN 0-19-513754-XGoogle Scholar
  56. 56.
    Contini, M.: The low-luminosity active galactic nucleus in the centre of the Galaxy. MNRAS 418, 1935–1947 (2011). arXiv:1104.1282 ADSCrossRefGoogle Scholar
  57. 57.
    Cumpa, J., Tegtmeier, E.: Phenomenological Realism Versus Scientific Realism. In: Cumpa, J., Tegtmeier, E. (eds.) Metaphysical Correspondences. Ontos Verlag, Heusenstamm (2009). ISBN 978-3-86838-051-4Google Scholar
  58. 58.
    Cunha, P.V.P., Herdeiro, C.A.R., Radu, E., Rúnarsson, H.F.: Shadows of Kerr Black Holes with Scalar Hair. Phys. Rev. Lett. 115(21), 211102 (2015). arXiv:1509.00021
  59. 59.
    Danzmann, K.: ELISA and the Gravitational Universe. In: IAU General Assembly , vol. 22, p. 2248153 (2015)Google Scholar
  60. 60.
    De Paolis, F., Ingrosso, G., Nucita, A.A., Orlando, D., Capozziello, S., Iovane, G.: Astrophysical constraints on a possible neutrino ball at the Galactic Center. A&A 376, 853–860 (2001). arXiv:astro-ph/0107497 ADSCrossRefGoogle Scholar
  61. 61.
    Deccock, L., Horsten, L.: Quine, Naturalized Epistemology, Perceptual Knowledge and Ontology. In: Lieven, D., Leon, H. (eds.). Editions Rodopi B.V. Amsterdam, Atlanta, GA (2000). ISBN 90-420-1241-2Google Scholar
  62. 62.
    Dékány, I., Minniti, D., Catelan, M., Zoccali, M., Saito, R.K., Hempel, M., Gonzalez, O.A.: VVV survey near-infrared photometry of known bulge RR lyrae stars: the distance to the galactic center and absence of a barred distribution of the metal-poor population. ApJL 776, L19 (2013)ADSCrossRefGoogle Scholar
  63. 63.
    DeWitt C, DeWitt BS (1973) Black holes. In: DeWitt, C., DeWitt, B.S. (eds.)Lectures Delivered at the Summer School of Theoretical Physics of the University of Grenoble at Les Houches. Gordon and Breach, New YorkGoogle Scholar
  64. 64.
    Dexter, J., Fragile, P.C.: Tilted black hole accretion disc models of Sagittarius A*: time-variable millimetre to near-infrared emission. MNRAS 432, 2252–2272 (2013)ADSCrossRefGoogle Scholar
  65. 65.
    Dexter, J., O’Leary, R.M.: The peculiar pulsar population of the central parsec. ApJL 783, L7 (2014)ADSCrossRefGoogle Scholar
  66. 66.
    Dexter, J., Agol, E., Fragile, P.C., McKinney, J.C.: The submillimeter bump in Sgr A* from relativistic MHD simulations. ApJ 717, 1092–1104 (2010)ADSCrossRefGoogle Scholar
  67. 67.
    Dexter, J., Agol, E., Fragile, P.C., McKinney, J.C.: Radiative models of Sagittarius A* and M87 from relativistic MHD simulations. J. Phys. Conf. Ser. 372(1), 012023 (2012a). 1202.0348CrossRefGoogle Scholar
  68. 68.
    Dexter, J., McKinney, J.C., Agol, E.: The size of the jet launching region in M87. MNRAS 421, 1517–1528 (2012b). arXiv:1109.6011
  69. 69.
    Do, T., Ghez, A.M., Morris, M.R., Lu, J.R., Matthews, K., Yelda, S., Larkin, J.: High angular resolution integral-field spectroscopy of the galaxy’s nuclear cluster: a missing stellar cusp? ApJ 703, 1323–1337 (2009). arXiv:0908.0311
  70. 70.
    Do, T., Martinez, G.D., Yelda, S., Ghez, A., Bullock, J., Kaplinghat, M., Lu, J.R., Peter, A.H.G., Phifer, K.: Three-dimensional stellar kinematics at the galactic center: measuring the nuclear star cluster spatial density profile, black hole mass, and distance. ApJL 779, L6 (2013)ADSCrossRefGoogle Scholar
  71. 71.
    Dobler, G., Finkbeiner, D.P., Cholis, I., Slatyer, T., Weiner, N.: The fermi haze: a gamma-ray counterpart to the microwave haze. ApJ 717, 825–842 (2010). arXiv:0910.4583
  72. 72.
    Doeleman, S.S., Lonsdale, C.J., Greenhill, L.J.: VLBI imaging of the 86 GHz SiO maser emission in the circumstellar envelope of VX sagittarii. ApJ 494, 400–408 (1998)ADSCrossRefGoogle Scholar
  73. 73.
    Doeleman, S.S., Weintroub, J., Rogers, A.E.E., Plambeck, R., Freund, R., Tilanus, R.P.J., Friberg, P., Ziurys, L.M., Moran, J.M., Corey, B., Young, K.H., Smythe, D.L., Titus, M., Marrone, D.P., Cappallo, R.J., Bock, D.C.J., Bower, G.C., Chamberlin, R., Davis, G.R., Krichbaum, T.P., Lamb, J., Maness, H., Niell, A.E., Roy, A., Strittmatter, P., Werthimer, D., Whitney, A.R., Woody, D.: Event-horizon-scale structure in the supermassive black hole candidate at the galactic centre. Nature 455, 78–80 (2008)ADSCrossRefGoogle Scholar
  74. 74.
    Doeleman, S.S., Fish, V.L., Broderick, A.E., Loeb, A., Rogers, A.E.E.: Detecting flaring structures in Sagittarius A* with high-frequency VLBI. ApJ 695, 59–74 (2009)ADSCrossRefGoogle Scholar
  75. 75.
    Dvali, G., Gomez, C.: Black Hole’s Quantum N-Portrait. (2011). FortschPhys. 61 742–767 (2013) arXiv:1112.3359
  76. 76.
    Dvali, G., Gomez, C.: Black hole’s 1/N hair. Phys. Lett. B 719, 419–423 (2013). arXiv:1203.6575
  77. 77.
    Dvali, G., Gomez, C., Lüst, D.: Black hole quantum mechanics in the presence of species. Fortsch. Phys. 61(7–8), 768–778 (2013). arXiv:1206.2365
  78. 78.
    Dvali, G., Gomez, C., Lüst, D.: Classical limit of black hole quantum N-portrait and BMS symmetry. Phys. Lett. B 753, 173–177 (2016). arXiv:1509.02114
  79. 79.
    Earnshaw, H.M., Roberts, T.P., Heil, L.M., Mezcua, M., Walton, D.J., Done, C., Harrison, F.A., Lansbury, G.B., Middleton, M.J., Sutton, A.D.: A variable ULX and possible IMBH candidate in M51a. MNRAS 456, 3840–3854 (2016). arXiv:1512.04825
  80. 80.
    Eatough, R., Lazio, T.J.W., Casanellas, J., Chatterjee, S., Cordes, J.M., Demorest, P.B., Kramer, M., Lee, K.J., Liu, K., Ransom, S.M., Wex, N.: Observing radio pulsars in the galactic centre with the square kilometre array. Advancing Astrophysics with the Square Kilometre Array (AASKA14), vol. 45 (2015). arXiv:1501.00281
  81. 81.
    Eatough, R.P., Falcke, H., Karuppusamy, R., Lee, K.J., Champion, D.J., Keane, E.F., Desvignes, G., Schnitzeler, D.H.F.M., Spitler, L.G., Kramer, M., Klein, B., Bassa, C., Bower, G.C., Brunthaler, A., Cognard, I., Deller, A.T., Demorest, P.B., Freire, P.C.C., Kraus, A., Lyne, A.G., Noutsos, A., Stappers, B., Wex, N.: A strong magnetic field around the supermassive black hole at the centre of the Galaxy. Nature 501, 391–394 (2013). arXiv:1308.3147
  82. 82.
    Eckart, A., Genzel, R.: Observations of stellar proper motions near the Galactic Centre. Nature 383, 415–417 (1996)ADSCrossRefGoogle Scholar
  83. 83.
    Eckart, A., Genzel, R.: Stellar proper motions in the central 0.1 PC of the galaxy. MNRAS 284, 576–598 (1997)ADSCrossRefGoogle Scholar
  84. 84.
    Eckart, A., Genzel, R., Ott, T., Schödel, R.: Stellar orbits near Sagittarius A*. MNRAS 331, 917–934 (2002)ADSCrossRefGoogle Scholar
  85. 85.
    Eckart, A., Moultaka, J., Viehmann, T., Straubmeier, C., Mouawad, N., Genzel, R., Ott, T., Schödel, R., Baganoff, F.K., Morris, M.R.: Monitoring Sagittarius A* in the MIR with the VLT. Astron. Nachr. Suppl. 324, 557–561 (2003)ADSCrossRefGoogle Scholar
  86. 86.
    Eckart, A., Schödel, R., Straubmeier, C.: The black hole at the center of the Milky Way / Andreas Eckart, Rainer Schödel, Christian Straubmeier. Imperial College Press, London (2005)Google Scholar
  87. 87.
    Eckart, A., Baganoff, F.K., Schödel, R., Morris, M., Genzel, R., Bower, G.C., Marrone, D., Moran, J.M., Viehmann, T., Bautz, M.W., Brandt, W.N., Garmire, G.P., Ott, T., Trippe, S., Ricker, G.R., Straubmeier, C., Roberts, D.A., Yusef-Zadeh, F., Zhao, J.H., Rao, R.: The flare activity of Sagittarius A*. New coordinated mm to X-ray observations. A&A 450, 535–555 (2006a)ADSCrossRefGoogle Scholar
  88. 88.
    Eckart, A., Schödel, R., Meyer, L., Trippe, S., Ott, T., Genzel, R.: Polarimetry of near-infrared flares from Sagittarius A*. A&A 455, 1–10 (2006b)ADSCrossRefGoogle Scholar
  89. 89.
    Eckart, A., Schödel, R., Straubmeier, C., Bertram, T., Pott, J.U., Muzic, K., Meyer, L., Moultaka, J., Viehmann, T., Rost, S., Herbst, T.: Interferometric observations of the galactic center: LBT and VLTI. In: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, vol. 6268 (2006c)Google Scholar
  90. 90.
    Eckart, A., Zamaninasab, M., Straubmeier, C., Fischer, S., Araujo-Hauck, C., Garcia-Marin, M., Wiest, M., Witzel, G., Buchholz, R.M., Sabha, N., Muzic, K., Eisenhauer, F., Paumard, T., Yazici, S., Perrin, G., Brandner, W., Perraut, K., Amorim, A., Schöller, M.: Signatures of strong gravity with GRAVITY. In: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, vol . 7734 (2010)Google Scholar
  91. 91.
    Eckart, A., Britzen, S., Horrobin, M., Zamaninasab, M., Muzic, K., Sabha, N., Shahzamanian, B., Yazici, S., Moser, L., Zuther, J., Garcia-Marin, M., Valencia-S, M., Bursa, M., Karssen, G., Karas, V., Jalali, B., Vitale, M., Bremer, M., Fischer, S., Smajic, S., Rauch, C., Kunneriath, D., Moultaka, J., Straubmeier, C., Rashed, Y.E., Iserlohe, C., Busch, G., Markakis, K., Borkar, A., Zensus, A.J.: The Galactic Center as a pradigm for low-luminosity nuclei? What can be learned from SgrA* for the central engine and conditions of star formation in nuclei of Seyfert galaxies and low luminosity nearby QSOs. The K-band identification of the DSO/G2 source from VLT and Keck data. In: Proceedings of Nuclei of Seyfert galaxies and QSOs—Central Engine and Conditions of Star Formation (Seyfert 2012), 6–8 November, 2012. Max-Planck-Insitut fuer Radioastronomie (MPIfR), Bonn, Germany (2012a). arXiv:1311.2743
  92. 92.
    Eckart, A., García-Marín, M., Vogel, S.N., Teuben, P., Morris, M.R., Baganoff, F., Dexter, J., Schödel, R., Witzel, G., Valencia-S, M., Karas, V., Kunneriath, D., Straubmeier, C., Moser, L., Sabha, N., Buchholz, R., Zamaninasab, M., Mužić, K., Moultaka, J., Zensus, J.A.: Millimeter to X-ray flares from Sagittarius A*. A&A 537, A52 (2012b)ADSCrossRefGoogle Scholar
  93. 93.
    Eckart, A., García-Marín, M., Vogel, S.N., Teuben, P., Morris, M.R., Baganoff, F., Dexter, J., Schödel, R., Witzel, G., Valencia-S, M., Karas, V., Kunneriath, D., Straubmeier, C., Moser, L., Sabha, N., Buchholz, R., Zamaninasab, M., Mužić, K., Moultaka, J., Zensus, J.A.: Millimeter to X-ray flares from Sagittarius A*. A&A 537, A52 (2012c)ADSCrossRefGoogle Scholar
  94. 94.
    Eckart, A., Sabha, N., Witzel, G., Straubmeier, C., Shahzamanian, B., Valencia-S, M., García-Marín, M., Horrobin, M., Moser, L., Zuther, J., Fischer, S., Rauch, C., Rost, S., Iserlohe, C., Yazici, S., Smajic, S., Wiest, M., Araujo-Hauck, C., Wank, I.: Beating the confusion limit: the necessity of high angular resolution for probing the physics of Sagittarius A* and its environment: opportunities for LINC-NIRVANA (LBT), GRAVITY (VLTI) and and METIS (E-ELT). In: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, vol. 8445 (2012d). arXiv:1208.1129
  95. 95.
    Einstein, A.: Lens-like action of a star by the deviation of light in the gravitational field. Science 84, 506–507 (1936)ADSzbMATHCrossRefGoogle Scholar
  96. 96.
    Einstein, A.: On a stationary system with spherical symmetry consisting of many gravitating masses. Ann. Math. 40, 922 (1939)ADSMathSciNetzbMATHCrossRefGoogle Scholar
  97. 97.
    Eisenhauer, F., Schödel, R., Genzel, R., Ott, T., Tecza, M., Abuter, R., Eckart, A., Alexander, T.: A geometric determination of the distance to the galactic center. ApJL 597, L121–L124 (2003)ADSCrossRefGoogle Scholar
  98. 98.
    Eisenhauer, F., Genzel, R., Alexander, T., Abuter, R., Paumard, T., Ott, T., Gilbert, A., Gillessen, S., Horrobin, M., Trippe, S., Bonnet, H., Dumas, C., Hubin, N., Kaufer, A., Kissler-Patig, M., Monnet, G., Ströbele, S., Szeifert, T., Eckart, A., Schödel, R., Zucker, S.: SINFONI in the galactic center: young stars and infrared flares in the central light-month. ApJ 628, 246–259 (2005). arXiv:astro-ph/0502129
  99. 99.
    Eisenhauer, F., Perrin, G., Brandner, W., Straubmeier, C., Richichi, A., Gillessen, S., Berger, J.P., Hippler, S., Eckart, A., Schöller, M., Rabien, S., Cassaing, F., Lenzen, R., Thiel, M., Clénet, Y., Ramos, J.R., Kellner, S., Fédou, P., Baumeister, H., Hofmann, R., Gendron, E., Boehm, A., Bartko, H., Haubois, X., Klein, R., Dodds-Eden, K., Houairi, K., Hormuth, F., Gräter, A., Jocou, L., Naranjo, V., Genzel, R., Kervella, P., Henning, T., Hamaus, N., Lacour, S., Neumann, U., Haug, M., Malbet, F., Laun, W., Kolmeder, J., Paumard, T., Rohloff, R.R., Pfuhl, O., Perraut, K., Ziegleder, J., Rouan, D., Rousset, G.: GRAVITY: getting to the event horizon of Sgr A*. In: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, vol. 7013 (2008). arXiv:0808.0063
  100. 100.
    Ellis, H.G.: Ether flow through a drainhole: a particle model in general relativity. J. Math. Phys. 14, 104–118 (1973)ADSMathSciNetCrossRefGoogle Scholar
  101. 101.
    Emmanoulopoulos, D.: Pinpointing the base of the AGN jets through general relativistic X-ray reverberation studies. In: Massaro, F., Cheung, C.C., Lopez, E., Siemiginowska, A. (eds.) IAU Symposium, vol. 313, pp. 346–351 (2015). arXiv:1411.0727
  102. 102.
    Esteban, E.P., Ramos, E.: Rotating black hole in an external electromagnetic field. Phys. Rev. D 38, 2963–2971 (1988)ADSMathSciNetCrossRefGoogle Scholar
  103. 103.
    Ewing, E.A.: ’Black Holes’ in Space for Science S, the Public (edn) Science News Letters, January 18, p. 39 (1964)Google Scholar
  104. 104.
    Falcke, H., Markoff, S.: The jet model for Sgr A*: radio and X-ray spectrum. A&A 362, 113–118 (2000)ADSGoogle Scholar
  105. 105.
    Falcke, H., Melia, F., Agol, E.: Viewing the shadow of the black hole at the galactic center. ApJL 528, L13–L16 (2000)ADSCrossRefGoogle Scholar
  106. 106.
    Falcke, H., Markoff, S., Bower, G.C.: Jet-lag in Sagittarius A*: what size and timing measurements tell us about the central black hole in the Milky Way. A&A 496, 77–83 (2009)ADSCrossRefGoogle Scholar
  107. 107.
    Ferrarese, L., Côté, P., Dalla Bontà, E., Peng, E.W., Merritt, D., Jordán, A., Blakeslee, J.P., Haşegan, M., Mei, S., Piatek, S., Tonry, J.L., West, M.J.: A fundamental relation between compact stellar nuclei, supermassive black holes, and their host galaxies. ApJL 644, L21–L24 (2006). arXiv:astro-ph/0603840
  108. 108.
    Ferré-Mateu, A., Mezcua, M., Trujillo, I., Balcells, M., van den Bosch, R.C.E.: Massive relic galaxies challenge the co-evolution of super-massive black holes and their host galaxies. ApJ 808, 79 (2015). arXiv:1506.02663
  109. 109.
    Finkelstein, D.: Past-future asymmetry of the gravitational field of a point particle. Phys. Rev. 110(965), 110 (1958)zbMATHGoogle Scholar
  110. 110.
    Fish, V.L., Doeleman, S.S., Beaudoin, C., Blundell, R., Bolin, D.E., Bower, G.C., Chamberlin, R., Freund, R., Friberg, P., Gurwell, M.A., Honma, M., Inoue, M., Krichbaum, T.P., Lamb, J., Marrone, D.P., Moran, J.M., Oyama, T., Plambeck, R., Primiani, R., Rogers, A.E.E., Smythe, D.L., SooHoo, J., Strittmatter, P., Tilanus, R.P.J., Titus, M., Weintroub, J., Wright, M., Woody, D., Young. K.H., Ziurys, L.M.: 1.3 mm wavelength VLBI of Sagittarius A*: detection of time-variable emission on event horizon scales. ApJL 727, L36 (2011)Google Scholar
  111. 111.
    Fish, V.L., Johnson, M.D., Lu, R.S., Doeleman, S.S., Bouman, K.L., Zoran, D., Freeman, W.T., Psaltis, D., Narayan, R., Pankratius, V., Broderick, A.E., Gwinn, C.R., Vertatschitsch, L.E.: Imaging an event horizon: mitigation of scattering toward Sagittarius A*. ApJ 795, 134 (2014). arXiv:1409.4690
  112. 112.
    Fish, V.L., Johnson, M.D., Doeleman, S.S., Broderick, A.E., Psaltis, D., Lu, R.S., Akiyama, K., Alef, W., Algaba, J.C., Asada, K., Beaudoin, C., Bertarini, A., Blackburn, L., Blundell, R., Bower, G.C., Brinkerink, C., Cappallo, R., Chael, A.A., Chamberlin, R., Chan, C.K., Crew, G.B., Dexter, J., Dexter, M., Dzib, S.A., Falcke, H., Freund, R., Friberg, P., Greer, C.H., Gurwell, M.A., Ho, P.T.P., Honma, M., Inoue, M., Johannsen, T., Kim, J., Krichbaum, T.P., Lamb, J., León-Tavares, J., Loeb, A., Loinard, L., MacMahon, D., Marrone, D.P., Moran, J.M., Mościbrodzka, M., Ortiz-León, G.N., Oyama, T., Özel, F., Plambeck, R.L., Pradel, N., Primiani, R.A., Rogers, A.E.E., Rosenfeld, K., Rottmann, H., Roy, A.L., Ruszczyk, C., Smythe, D.L., SooHoo, J., Spilker, J., Stone, J., Strittmatter, P., Tilanus, R.P.J., Titus, M., Vertatschitsch, L., Wagner, J., Wardle, J.F.C., Weintroub, J., Woody, D., Wright, M., Yamaguchi, P., Young, A., Young, K.H., Zensus, J.A., Ziurys, L.M.: Persistent asymmetric structure of Sagittarius A* on event horizon scales. ApJ 820, 90 (2016)ADSCrossRefGoogle Scholar
  113. 113.
    Francis, C., Anderson, E.: Two estimates of the distance to the Galactic Centre. MNRAS 441, 1105–1114 (2014)ADSCrossRefGoogle Scholar
  114. 114.
    Franklin, A.: What Makes a Good Experiment? University of Pittsburgh Press, Pittsburgh (2016). ISBN-13 9780822944416Google Scholar
  115. 115.
    Freitag, M.: Gravitational waves from stars orbiting the Sagittarius A* black hole. Astrophys. J. Lett. 583(1), L21 (2003)ADSCrossRefGoogle Scholar
  116. 116.
    Fritz, T.K., Gillessen, S., Dodds-Eden, K., Martins, F., Bartko, H., Genzel, R., Paumard, T., Ott, T., Pfuhl, O., Trippe, S., Eisenhauer, F., Gratadour, D.: GC-IRS13E—a puzzling association of three early-type stars. ApJ 721, 395–411 (2010). arXiv:1003.1717
  117. 117.
    Gair, J.R., Barack, L., Creighton, T., Cutler, C., Larson, S.L., Phinney, E.S., Vallisneri, M.: Event rate estimates for LISA extreme mass ratio capture sources. Class. Quantum Gravity 21, S1595–S1606 (2004)ADSzbMATHCrossRefGoogle Scholar
  118. 118.
    Gair, J.R., Vallisneri, M., Larson, S.L., Baker, J.G.: Testing general relativity with low-frequency, space-based gravitational-wave detectors. Liv. Rev. Relat. 16, 7 (2013)CrossRefGoogle Scholar
  119. 119.
    Galison, P.: How Experiments End. The University of Chicago Press, Chicago (1987). ISBN: 9780226279152Google Scholar
  120. 120.
    García Díaz, A.: Magnetic generalization of the Kerr-Newman metric. J. Math. Phys. 26, 155–156 (1985)ADSMathSciNetCrossRefGoogle Scholar
  121. 121.
    Genzel, R., Pichon, C., Eckart, A., Gerhard, O.E., Ott, T.: Stellar dynamics in the Galactic Centre: proper motions and anisotropy. MNRAS 317, 348–374 (2000). arXiv:astro-ph/0001428
  122. 122.
    Genzel, R., Schödel, R., Ott, T., Eckart, A., Alexander, T., Lacombe, F., Rouan, D., Aschenbach, B.: Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre. Nature 425, 934–937 (2003). arXiv:astro-ph/0310821
  123. 123.
    Genzel, R., Eisenhauer, F., Gillessen, S.: The Galactic Center massive black hole and nuclear star cluster. Rev. Mod. Phys. 82, 3121–3195 (2010) arXiv:1006:0064
  124. 124.
    Ghez, A., Morris, M., Lu, J., Weinberg, N., Matthews, K., Alexander, T., Armitage, P., Becklin, E., Brown, W., Campbell, R., Do, T., Eckart, A., Genzel, R., Gould, A., Hansen, B., Ho, L., Lo, F., Loeb, A., Melia, F., Merritt, D., Milosavljevic, M., Perets, H., Rasio, F., Reid, M., Salim, S., Schödel, R., Yelda, S.: The galactic center: a laboratory for fundamental astrophysics and galactic nuclei. In: astro2010: The Astronomy and Astrophysics Decadal Survey, Astronomy (2009). arXiv:0903.0383
  125. 125.
    Ghez, A.M., Klein, B.L., Morris, M., Becklin, E.E.: High proper-motion stars in the vicinity of Sagittarius A*: evidence for a supermassive black hole at the center of our galaxy. ApJ 509, 678–686 (1998). arXiv:astro-ph/9807210
  126. 126.
    Ghez, A.M., Duchene, G., Morris, M., Becklin, E.E., Hornstein, S.D., Tanner, A., Kremenek, T., Matthews, K., Thompson, D., Soifer, B.T., Larkin, J., McLean, I.: Full 3-D orbital solutions for stars making a close approach to the supermassive black hole at the center of the galaxy. In: American Astronomical Society Meeting Abstracts, Bulletin of the American Astronomical Society, vol. 34, p. 1219 (2002)Google Scholar
  127. 127.
    Ghez, A.M., Wright, S.A., Matthews, K., Thompson, D., Le Mignant, D., Tanner, A., Hornstein, S.D., Morris, M., Becklin, E.E., Soifer, B.T.: Variable infrared emission from the supermassive black hole at the Center of the Milky Way. ApJL 601, L159–L162 (2004). arXiv:astro-ph/0309076
  128. 128.
    Ghez, A.M., Salim, S., Weinberg, N.N., Lu, J.R., Do, T., Dunn, J.K., Matthews, K., Morris, M.R., Yelda, S., Becklin, E.E., Kremenek, T., Milosavljevic, M., Naiman, J.: Measuring distance and properties of the Milky Way’s central supermassive black hole with stellar orbits. ApJ 689, 1044–1062 (2008)ADSCrossRefGoogle Scholar
  129. 129.
    Ghisellini, G., Foschini, L., Volonteri, M., Ghirlanda, G., Haardt, F., Burlon, D., Tavecchio, F.: The blazar S5 0014+813: a real or apparent monster? MNRAS 399, L24–L28 (2009). arXiv:0906.0575
  130. 130.
    Ghisellini, G., Della Ceca, R., Volonteri, M., Ghirlanda, G., Tavecchio, F., Foschini, L., Tagliaferri, G., Haardt, F., Pareschi, G., Grindlay, J.: Chasing the heaviest black holes of jetted active galactic nuclei. MNRAS 405, 387–400 (2010). arXiv:0912.0001
  131. 131.
    Giannios, D., Lorimer, D.R.: Flares from Galactic Centre pulsars: a new class of X-ray transients? MNRAS 459, L95–L99 (2016)ADSCrossRefGoogle Scholar
  132. 132.
    Giddings, S.B.: Possible observational windows for quantum effects from black holes. Phys. Rev. D 90(12), 124033 (2014). arXiv:1406.7001
  133. 133.
    Gillessen, S., Eisenhauer, F., Quataert, E., Genzel, R., Paumard, T., Trippe, S., Ott, T., Abuter, R., Eckart, A., Lagage, P.O., Lehnert, M.D., Tacconi, L.J., Martins, F.: Variations in the Spectral Slope of Sagittarius A* during a Near-Infrared Flare. ApJL 640, L163–L166 (2006). arXiv:astro-ph/0511302
  134. 134.
    Gillessen, S., Eisenhauer, F., Fritz, T.K., Bartko, H., Dodds-Eden, K., Pfuhl, O., Ott, T., Genzel, R.: The orbit of the star S2 Around SGR A* from very large telescope and keck data. ApJL 707, L114–L117 (2009a)ADSCrossRefGoogle Scholar
  135. 135.
    Gillessen, S., Eisenhauer, F., Trippe, S., Alexander, T., Genzel, R., Martins, F., Ott, T.: Monitoring stellar orbits around the massive black hole in the Galactic Center. ApJ 692, 1075–1109 (2009b)ADSCrossRefGoogle Scholar
  136. 136.
    Graham, A.W., Scott, N., Schombert, J.M.: Super-massive black hole mass scaling relations. Publ. Kor. Astron. Soc. 30, 335–339 (2015). arXiv:1411.1438
  137. 137.
    Grenzebach, A., Perlick, V., Lämmerzahl, C.: Photon regions and shadows of accelerated black holes. Int. J. Mod. Phys. D 24, 1542024 (2015)ADSMathSciNetzbMATHCrossRefGoogle Scholar
  138. 138.
    Guedes, J., Madau, P., Mayer, L., Callegari, S.: Recoiling massive black holes in gas-rich galaxy mergers. ApJ 729, 125 (2011). arXiv:1008.2032
  139. 139.
    Gwinn, C.R., Kovalev, Y.Y., Johnson, M.D., Soglasnov, V.A.: Discovery of Substructure in the Scatter-broadened Image of Sgr A*. ApJL 794, L14 (2014). arXiv:1409.0530
  140. 140.
    Hacking, I. (ed.): Representing and Intervening, p. 24. Cambridge University Press, Cambridge (1983)Google Scholar
  141. 141.
    Hacking, I.: Extragalactic reality: the case of gravitational lensing. Philos. Sci. 56, 555–581 (1989)MathSciNetCrossRefGoogle Scholar
  142. 142.
    Haggard, H.M., Rovelli, C.: Quantum-gravity effects outside the horizon spark black to white hole tunneling. Phys. Rev. D 92(10), 104020 (2015)ADSMathSciNetCrossRefGoogle Scholar
  143. 143.
    Hawking, S.: Information preservation and waether forcasting for black holes (2014). arXiv:1401.5761
  144. 144.
    Hawking, S., Penrose, R.: The Nature of Space and Time. Princeton University Press, Princeton (1996)zbMATHGoogle Scholar
  145. 145.
    Hawking, S.W., Israel, W.: Three Hundred Years of Gravitation. Cambridge University Press, Cambridge (1987)zbMATHGoogle Scholar
  146. 146.
    Herdeiro, C.A.R., Radu, E.: Kerr black holes with scalar hair. Phys. Rev. Lett. 112(22), 221101 (2014). arXiv:1403.2757
  147. 147.
    Heusler, M.: Black Hole Uniqueness Theorems. Cambridge University Press, Cambridge (1996)zbMATHCrossRefGoogle Scholar
  148. 148.
    Hoefer, C., Smeenk, C.: Philosophy of the physical sciences. In: Humphreys, P. (ed.) Oxford Handbook of the Philosophy of Science. Oxford University Press, Oxford (2016)Google Scholar
  149. 149.
    Hopman, C., Alexander, T.: Resonant relaxation near a massive black hole: the stellar distribution and gravitational wave sources. ApJ 645, 1152–1163 (2006)ADSCrossRefGoogle Scholar
  150. 150.
    Horrobin, M., Eisenhauer, F., Tecza, M., Thatte, N., Genzel, R., Abuter, R., Iserlohe, C., Schreiber, J., Schegerer, A., Lutz, D., Ott, T., Schödel, R.: First results from SPIFFI. I: the galactic center. Astron. Nachr. 325, 88–91 (2004)ADSCrossRefGoogle Scholar
  151. 151.
    Hughes, S.A.: Evolution of circular, nonequatorial orbits of Kerr black holes due to gravitational-wave emission. Phys. Rev. D 61(8), 084004 (2000)ADSMathSciNetCrossRefGoogle Scholar
  152. 152.
    Hughes, S.A.: Evolution of circular, nonequatorial orbits of Kerr black holes due to gravitational-wave emission. II. Inspiral trajectories and gravitational waveforms. Phys. Rev. D 64(6), 064004 (2001)ADSCrossRefGoogle Scholar
  153. 153.
    Israel, W.: Dark stars: the evolution of an idea. In: Hawking, S.W., Israel, W. (eds.) Three Hundred Years of Gravitation, pp. 199–276 (1987)Google Scholar
  154. 154.
    Iwata, K., Yamazaki, S., Mutombo, P., Hapala, P., Ondráček, M., Jelínek, P., Sugimoto, Y.: Chemical structure imaging of a single molecule by atomic force microscopy at room temperature. Nat. Commun. 6, 7766 (2015)ADSCrossRefGoogle Scholar
  155. 155.
    Jaroszynski, M.: Prospects for the Determination of Star Orbits near the Galactic Center. ApJ 521, 591–596 (1999). arXiv:astro-ph/9903354
  156. 156.
    Johannsen, T.: Sgr A* and general relativity. (2015) arXiv:1512.03818
  157. 157.
    Johannsen, T.: Testing the no-hair theorem with observations of black holes in the electromagnetic spectrum. Class. Quantum Gravity 33(12), 124001 (2016). arXiv:1602.07694
  158. 158.
    Johnson, M.D., Fish, V.L., Doeleman, S.S., Marrone, D.P., Plambeck, R.L., Wardle, J.F.C., Akiyama, K., Asada, K., Beaudoin, C., Blackburn, L., Blundell, R., Bower, G.C., Brinkerink, C., Broderick, A.E., Cappallo, R., Chael, A.A., Crew, G.B., Dexter, J., Dexter, M., Freund, R., Friberg, P., Gold, R., Gurwell, M.A., Ho, P.T.P., Honma, M., Inoue, M., Kosowsky, M., Krichbaum, T.P., Lamb, J., Loeb, A., Lu, R.S., MacMahon, D., McKinney, J.C., Moran, J.M., Narayan, R., Primiani, R.A., Psaltis, D., Rogers, A.E.E., Rosenfeld, K., SooHoo, J., Tilanus, R.P.J., Titus, M., Vertatschitsch, L., Weintroub, J., Wright, M., Young, K.H., Zensus, J.A., Ziurys, L.M.: Resolved magnetic-field structure and variability near the event horizon of Sagittarius A*. Science 350, 1242–1245 (2015). arXiv:1512.01220
  159. 159.
    Karas, V., Vokrouhlický, D.: On interpretation of the magnetized Kerr-Newman black hole. J. Math. Phys. 32, 714–716 (1991)ADSMathSciNetzbMATHCrossRefGoogle Scholar
  160. 160.
    Karas, V., Huré, J.M., Semerák, O.: TOPICAL REVIEW: Gravitating discs around black holes. Classical and Quantum Gravity 21, 1 (2004). arXiv:astro-ph/0401345
  161. 161.
    Karas, V., Kopáček, O., Kunneriath, D.: Influence of frame-dragging on magnetic null points near rotating black holes. Class. Quantum Gravity 29(3), 035010 (2012). arXiv:1201.0009
  162. 162.
    Kardashev, N.S., Andreyanov, V.V., Gromov, V.D., Buyakas, V.I., Gvamichava, A.S., Kotik, A.N., Kurt, V.G., Lazareva, G.S., Mironova, E.N., Myshonkova, N.V., Slysh, V.I., Trubnikov, A.G., Vinogradov, I.S., Troitsky, V.F., Puryaev, D.T., Usyukin, V.I.: The millimetron project. In: Kardashev, N.S., Dagkesamanskii, S.A. (eds.) Radioastronomical Tools and Techniques, p 111 (2007)Google Scholar
  163. 163.
    Kardashev, N.S., Novikov, I.D., Lukash, V.N., Pilipenko, S.V., Mikheeva, E.V., Bisikalo, D.V., Wiebe, D.S., Doroshkevich, A.G., Zasov, A.V., Zinchenko, I.I., Ivanov, P.B., Kostenko, V.I., Larchenkova, T.I., Likhachev, S.F., Malov, I.F., Malofeev, V.M., Pozanenko, A.S., Smirnov, A.V., Sobolev, A.M., Cherepashchuk, A.M., Shchekinov, Y.A.: Review of scientific topics for the Millimetron space observatory. Phys. Usp. 57, 1199–1228 (2014)ADSCrossRefGoogle Scholar
  164. 164.
    Kaup, D.J.: Klein-Gordon geon. Phys. Rev. 172, 1331–1342 (1968)ADSCrossRefGoogle Scholar
  165. 165.
    Kerr, R.P.: Gravitational field of a spinning mass as an example of algebraically special metrics. Phys. Rev. Lett. 11, 237–238 (1963)ADSMathSciNetzbMATHCrossRefGoogle Scholar
  166. 166.
    Kiefer, C.: Thermodynamics of black holes and Hawking radiation. In: Fré, P., Gorini, V., Magli, G., Moschella, U. (eds.) Classical and Quantum Black Holes, pp. 17–74. Institute of Physics Publishing, Bristol (1999)Google Scholar
  167. 167.
    Kiefer, C.: Quantum Gravity, 3rd edn. Oxford University Press, Oxford (2012)zbMATHGoogle Scholar
  168. 168.
    Kiefer, C.: Quantum black hole without singularity. In: BH6 Session at the Marcel Grossmann Conference MG14 on General Relativity and Quantum Cosmology, WSPC Proceedings (2015). arXiv:1512.08346
  169. 169.
    Kiefer, C., Marto, J., Moniz, P.V.: Indefinite oscillators and black hole evaporation. Ann. Phys. (Berlin) 18, 722 (2009)Google Scholar
  170. 170.
    King, A.: How big can a black hole grow? MNRAS 456, L109–L112 (2016)ADSCrossRefGoogle Scholar
  171. 171.
    Kiziltan, B., Baumgardt, H., Loeb, A.: An intermediate-mass black hole in the centre of the globular cluster 47 Tucanae. Nature 542, 203–205 (2017). arXiv:1702.02149
  172. 172.
    Kormendy, J., Ho, L.C.: Coevolution (Or Not) of supermassive black holes and host galaxies. ARA&A 51, 511–653 (2013)ADSCrossRefGoogle Scholar
  173. 173.
    Krabbe, A., Genzel, R., Eckart, A., Najarro, F., Lutz, D., Cameron, M., Kroker, H., Tacconi-Garman, L.E., Thatte, N., Weitzel, L., Drapatz, S., Geballe, T., Sternberg, A., Kudritzki, R. The nuclear cluster of the milky way: star formation and velocity dispersion in the central 0.5 parsec. ApJL 447, L95 (1995)Google Scholar
  174. 174.
    Laudan, L., Leplin, J.: Empirical equivalence and underdetermination larry laudan & jarrett leplin journal of philosophy 88 (9):449–472 (1991). J. Philos. 88, 449–472 (1991)MathSciNetCrossRefGoogle Scholar
  175. 175.
    Leinert, C., Graser, U.: MIDI: a mid-infrared interferometric instrument for the VLTI. In: Reasenberg, R.D. (ed) Astronomical Interferometry, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, vol. 3350, pp 389–393 (1998)Google Scholar
  176. 176.
    Li, Z., Morris, M.R., Baganoff, F.K.: Evidence for a parsec-scale jet from the galactic center black hole: interaction with local gas. ApJ 779, 154 (2013)ADSCrossRefGoogle Scholar
  177. 177.
    Löckmann, U., Baumgardt, H.: Tracing intermediate-mass black holes in the Galactic Centre. MNRAS 384, 323–330 (2008). arXiv:0711.1326
  178. 178.
    Lu, R.S., Roelofs, F., Fish, V.L., Shiokawa, H., Doeleman, S.S., Gammie, C.F., Falcke, H., Krichbaum, T.P., Zensus, J.A.: Imaging an event horizon: mitigation of source variability of Sagittarius A*. ApJ 817 173 (2016). arXiv:1512.08543
  179. 179.
    Lu, Y., Torres, D.F.: The Relativistic Iron K\(\alpha \) Line from an Accretion Disc Onto a Static Non-Baryonic Compact Object. International Journal of Modern Physics D 12, 63–77 (2003). arXiv:astro-ph/0205418
  180. 180.
    Luminet, J.P.: Image of a spherical black hole with thin accretion disk. A&A 75, 228–235 (1979)ADSGoogle Scholar
  181. 181.
    Maillard, J.P., Paumard, T., Stolovy, S.R., Rigaut, F.: The nature of the Galactic Center source IRS 13 revealed by high spatial resolution in the infrared. A&A 423, 155–167 (2004)ADSCrossRefGoogle Scholar
  182. 182.
    Majaess, D.J., Turner, D.G., Lane, D.J.: Characteristics of the galaxy according to cepheids. MNRAS 398, 263–270 (2009)ADSCrossRefGoogle Scholar
  183. 183.
    Malkin, Z.M.: Analysis of determinations of the distance between the sun and the galactic center. Astron. Rep. 57, 128–133 (2013)ADSCrossRefGoogle Scholar
  184. 184.
    Maoz, E.: Dynamical constraints on alternatives to supermassive black holes in galactic nuclei. ApJL 494, L181–L184 (1998). arXiv:astro-ph/9710309
  185. 185.
    Marcus, R.: The eleatic and the indispensabilist. THEORIA 30(3), 415–429 (2015)MathSciNetCrossRefGoogle Scholar
  186. 186.
    Markakis, K., Dierkes, J., Eckart, A., Nishiyama, S., Britzen, S., García-Marín, M., Horrobin, M., Muxlow, T., Zensus, J.A.: Subaru and e-Merlin observations of NGC 3718. Diaries of a supermassive black hole recoil? A&A 580, A11 (2015)ADSCrossRefGoogle Scholar
  187. 187.
    Markoff, S.: Sagittarius A* in context: daily flares as a probe of the fundamental X-ray emission process in accreting black holes. ApJL 618, L103–L106 (2005)ADSCrossRefGoogle Scholar
  188. 188.
    Markoff, S., Bower, G.C., Falcke, H.: How to hide large-scale outflows: size constraints on the jets of Sgr A*. MNRAS 379, 1519–1532 (2007)ADSCrossRefGoogle Scholar
  189. 189.
    Markoff, S., Nowak, M.A., Maitra, D., Wilms, J., Gallo, E., Hynes, R., Plotkin, R.: Fitting along the fundamental plane: new comparisons of jet physics across the black hole mass scale. In: Romero, G.E., Sunyaev, R.A., Belloni, T. (eds.) Jets at All Scales, IAU Symposium, vol. 275, pp. 250–254 (2011)Google Scholar
  190. 190.
    Matsuoka, Y., Strauss, M.A., Shen, Y., Brandt, W.N., Greene, J.E., Ho, L.C., Schneider, D.P., Sun, M., Trump, J.R.: The sloan digital sky survey reverberation mapping project: post-starburst signatures in quasar host galaxies at z \({<}\) 1. ApJ 811, 91 (2015). arXiv:1506.07535
  191. 191.
    Mazur, P.O., Mottola, E.: Gravitational condensate stars: an alternative to black holes. ArXiv General Relativity and Quantum Cosmology arXiv:gr-qc/0109035 (2001)
  192. 192.
    Melia, F., Falcke, H.: The supermassive black hole at the galactic center. ARA&A 39, 309–352 (2001)ADSCrossRefGoogle Scholar
  193. 193.
    Menten, K.M., Reid, M.J., Eckart, A., Genzel, R.: The position of Sagittarius A*: accurate alignment of the radio and infrared reference frames at the galactic center. ApJL 475, L111–L114 (1997)ADSCrossRefGoogle Scholar
  194. 194.
    Merritt, D.: The distribution of stars and stellar remnants at the Galactic Center. ApJ 718, 739–761 (2010). arXiv:0909.1318
  195. 195.
    Merritt, D., Alexander, T., Mikkola, S., Will, C.M.: Testing properties of the Galactic center black hole using stellar orbits. Phys. Rev. D 81(6), 062002 (2010)ADSCrossRefGoogle Scholar
  196. 196.
    Meyer, L., Schödel, R., Eckart, A., Karas, V., Dovčiak, M., Duschl, W.J.: K-band polarimetry of an Sgr A* flare with a clear sub-flare structure. A&A 458, L25–L28 (2006)ADSCrossRefGoogle Scholar
  197. 197.
    Meyer, L., Schödel, R., Eckart, A., Duschl, W.J., Karas, V., Dovčiak, M.: On the orientation of the Sagittarius A* system. A&A 473, 707–710 (2007)ADSCrossRefGoogle Scholar
  198. 198.
    Mielke, E.W., Schunck, F.E.: Boson stars: alternatives to primordial black holes? Nucl. Phys. B 564, 185–203 (2000) arXiv:gr-qc/0001061
  199. 199.
    Mielke, E.W., Schunck, F.E.: Boson and Axion Stars. In: Gurzadyan, V.G., Jantzen, R.T., Ruffini, R. (ed.). The Ninth Marcel Grossmann Meeting, pp. 581–591 (2002)Google Scholar
  200. 200.
    Miller, J.M., Tomsick, J.A., Bachetti, M., Wilkins, D., Boggs, S.E., Christensen, F.E., Craig, W.W., Fabian, A.C., Grefenstette, B.W., Hailey, C.J., Harrison, F.A., Kara, E., King, A.L., Stern, D.K., Zhang, W.W.: New constraints on the black hole low/hard state inner accretion flow with NuSTAR. ApJL 799, L6 (2015). arXiv:1411.1921
  201. 201.
    Miller, M.C.: Constraints on alternatives to supermassive black holes. MNRAS 367, L32–L36 (2006). arXiv:astro-ph/0512194
  202. 202.
    Misner, C., Thorne, K., Wheeler, J.: Gravitation. W. H. Freeman, San Francisco (1973). ISBN 978-0-7167-0344-0Google Scholar
  203. 203.
    Montero, B.: Varieties of causal closure. In: Walter, S., Heckmann, H.-D. (eds.) Physicalism and Mental Causation: The Metaphysics of Mind and Action, Chapt. 8. Imprint Academic, Charlottesville, VA (2003). ISBN 0907845460Google Scholar
  204. 204.
    Mori, K., Gotthelf, E.V., Zhang, S., An, H., Baganoff, F.K., Barrière, N.M., Beloborodov, A.M., Boggs, S.E., Christensen, F.E., Craig, W.W., Dufour, F., Grefenstette, B.W., Hailey, C.J., Harrison, F.A., Hong, J., Kaspi, V.M., Kennea, J.A., Madsen, K.K., Markwardt, C.B., Nynka, M., Stern, D., Tomsick, J.A., Zhang, W.W.: NuSTAR discovery of a 3.76 s transient magnetar near Sagittarius A*. ApJL 770, L23 (2013). arXiv:1305.1945
  205. 205.
    Morris, M., Howard, C., Muno, M., Baganoff, F.K., Park, S., Feigelson, E., Garmire, G., Brandt, N.: The hot interstellar medium of the galactic center: observations with Chandra. In: Pfalzner, S., Kramer, C., Staubmeier, C., Heithausen, A. (eds.) The Dense Interstellar Medium in Galaxies. Springer, Berlin (2004)Google Scholar
  206. 206.
    Mościbrodzka, M., Falcke, H.: Coupled jet-disk model for Sagittarius A*: explaining the flat-spectrum radio core with GRMHD simulations of jets. A&A 559, L3 (2013)ADSCrossRefGoogle Scholar
  207. 207.
    Mościbrodzka, M., Falcke, H., Shiokawa, H., Gammie, C.F.: Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: application to Sagittarius A*. A&A 570, A7 (2014)ADSCrossRefGoogle Scholar
  208. 208.
    Mossoux, E., Grosso, N., Vincent, F.H., Porquet, D.: Study of the X-ray activity of Sagittarius A* during the 2011 XMM-Newton campaign. A&A 573, A46 (2015)ADSCrossRefGoogle Scholar
  209. 209.
    Mou, G., Yuan, F., Bu, D., Sun, M., Su, M.: Fermi Bubbles Inflated by Winds Launched from the Hot Accretion Flow in Sgr A*. ApJ 790, 109 (2014). arXiv:1403.2129
  210. 210.
    Mou, G., Yuan, F., Gan, Z., Sun, M.: The accretion wind model of fermi bubbles. II. Radiation. ApJ 811, 37 (2015). arXiv:1505.00892
  211. 211.
    Mužić, K., Eckart, A., Schödel, R., Meyer, L., Zensus, A.: First proper motions of thin dust filaments at the Galactic center. A&A 469, 993–1002 (2007)ADSCrossRefGoogle Scholar
  212. 212.
    Mužić, K., Eckart, A., Schödel, R., Buchholz, R., Zamaninasab, M., Witzel, G.: Comet-shaped sources at the Galactic center. Evidence of a wind from the central 0.2 pc. A&A 521, A13 (2010)ADSCrossRefGoogle Scholar
  213. 213.
    Nakamura, M., Asada, K.: The parabolic jet structure in M87 as a magnetohydrodynamic nozzle. ApJ 775, 118 (2013). arXiv:1308.1436
  214. 214.
    Narayan, R., Yi, I., Mahadevan, R.: Explaining the spectrum of Sagittarius A\(^{*}\) with a model of an accreting black hole. Nature 374, 623–625 (1995)ADSCrossRefGoogle Scholar
  215. 215.
    Narayan, R., Mahadevan, R., Grindlay, J.E., Popham, R.G., Gammie, C.: Advection-dominated accretion model of Sagittarius A\(^{*}\): evidence for a black hole at the Galactic center. ApJ 492, 554–568 (1998)ADSCrossRefGoogle Scholar
  216. 216.
    Natarajan, P., Treister, E.: Is there an upper limit to black hole masses? MNRAS 393, 838–845 (2009). arXiv:0808.2813
  217. 217.
    Nayakshin, S., Power, C., King, A.R.: The observed M-\(\sigma \) relations imply that super-massive black holes grow by cold chaotic accretion. ApJ 753, 15 (2012). arXiv:1203.3450
  218. 218.
    Neilsen, J., Markoff, S., Nowak, M.A., Dexter, J., Witzel, G., Barrière, N., Li, Y., Baganoff, F.K., Degenaar, N., Fragile, P.C., Gammie, C., Goldwurm, A., Grosso, N., Haggard, D.: The X-ray flux distribution of Sagittarius A* as seen by Chandra. ApJ 799, 199 (2015a)ADSCrossRefGoogle Scholar
  219. 219.
    Neilsen, J., Markoff, S., Nowak, M.A., Dexter, J., Witzel, G., Barrière, N., Li, Y., Baganoff, F.K., Degenaar, N., Fragile, P.C., Gammie, C., Goldwurm, A., Grosso, N., Haggard, D.: The X-ray flux distribution of Sagittarius A* as Seen by Chandra. ApJ 799, 199 (2015b). arXiv:1412.3106
  220. 220.
    Nelson, O.J.: Hume’s ’new scene of thought’ and the several faces of David Hume in the dialogues concerning natural religion; with a preface by Jeff Broome; University Press of America, New York (2010). ISBN 978-0-7618-4735-9Google Scholar
  221. 221.
    Neugebauer, G., Meinel, R.: The Einsteinian gravitational field of the rigidly rotating disk of dust. ApJL 414, L97–L99 (1993)ADSCrossRefGoogle Scholar
  222. 222.
    Newmann, A.: The correspondence theory of truth; an essay on the metaphysics of predication; part of Cambridge studies in philosophy. University of Nebraska, Omaha (2002). ISBN: 9780521811392Google Scholar
  223. 223.
    Nordström, G.: On the energy of the gravitation field in Einstein’s theory. K. Ned. Akad. Wet. Proc. Ser. B 20, 1238–1245 (1918)ADSGoogle Scholar
  224. 224.
    Oka, T., Mizuno, R., Miura, K., Takekawa, S.: Signature of an intermediate-mass black hole in the central molecular zone of our galaxy. ApJL 816, L7 (2016)ADSCrossRefGoogle Scholar
  225. 225.
    Oppenheimer, J.R., Snyder, H.: On continued gravitational contraction. Phys. Rev. 56, 455–459 (1939)ADSzbMATHCrossRefGoogle Scholar
  226. 226.
    Oppenheimer, J.R., Volkoff, G.M.: On massive neutron cores. Phys. Rev. 55, 374–381 (1939)ADSzbMATHCrossRefGoogle Scholar
  227. 227.
    Ostriker, J.: The equilibrium of self-gravitating rings. ApJ 140, 1067 (1964)ADSMathSciNetCrossRefGoogle Scholar
  228. 228.
    de Oteyza, D., Gorman, P., et al.: Direct imaging of covalent bond structure in single-molecule chemical reactions. Science 340, 1434 (2013)ADSCrossRefGoogle Scholar
  229. 229.
    Parsa, M., Eckart, A., et al.: Investigating relativistic motion of stars near the supermassive black hole in the Galactic center. A&A (2017, in preparation)Google Scholar
  230. 230.
    Pasham, D.R., Strohmayer, T.E., Mushotzky, R.F.: A 400-solar-mass black hole in the galaxy M82. Nature 513, 74–76 (2014)ADSCrossRefGoogle Scholar
  231. 231.
    Paumard, T., Perrin, G., Eckart, A., Genzel, R., Lena, P., Schoedel, R., Eisenhauer, F., Mueller, T., Gillessen, S.: Scientific prospects for VLTI in the Galactic Centre: getting to the Schwarzschild radius. Astron. Nachr. 326, 568–568 (2005)ADSGoogle Scholar
  232. 232.
    Paumard, T., Perrin, G., Eckart, A., Genzel, R., Léna, P., Schödel, R., Eisenhauer, F., Müller, T., Gillessen, S.: Scientific prospects for VLTI in the Galactic Centre: getting to the Schwarzschild radius. In: Richichi, A., Delplancke, F., Paresce, F., Chelli, A. (eds.) The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation (2008)Google Scholar
  233. 233.
    Peters, P.C., Mathews, J.: Gravitational radiation from point masses in a Keplerian orbit. Phys. Rev. 131, 435–440 (1963)ADSMathSciNetzbMATHCrossRefGoogle Scholar
  234. 234.
    Pierro, V., Pinto, I.M., Spallicci, A.D., Laserra, E., Recano, F.: Fast and accurate computational tools for gravitational waveforms from binary stars with any orbital eccentricity. MNRAS 325, 358–372 (2001). arXiv:gr-qc/0005044
  235. 235.
    Plewa, P.M., Gillessen, S., Eisenhauer, F., Ott, T., Pfuhl, O., George, E., Dexter, J., Habibi, M., Genzel, R., Reid, M.J., Menten, K.M.: Pinpointing the near-infrared location of SgrA* by correcting optical distortion in the NACO imager. MNRAS 453, 3234–3244 (2015). doi: 10.1093/mnras/stv1910
  236. 236.
    Poisson, E.: A Relativist’s Toolkit—the Mathematics of Black-Hole Mechanics. A Relativist’s Toolkit—The Mathematics of Black-Hole Mechanics. Cambridge University Press, Cambridge (2004)zbMATHCrossRefGoogle Scholar
  237. 237.
    Pollney, D., Reisswig, C.: Gravitational memory in binary black hole mergers. ApJL 732, L13 (2011) arXiv:1004.4209
  238. 238.
    Porquet, D., Grosso, N., Predehl, P., Hasinger, G., Yusef-Zadeh, F., Aschenbach, B., Trap, G., Melia, F., Warwick, R.S., Goldwurm, A., Bélanger, G., Tanaka, Y., Genzel, R., Dodds-Eden, K., Sakano, M., Ferrando, P.: X-ray hiccups from Sagittarius A* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day. A&A 488, 549–557 (2008)ADSCrossRefGoogle Scholar
  239. 239.
    Pott, J.U., Eckart, A., Glindemann, A., Viehmann, T., Schodel, R., Straubmeier, C., Leinert, C., Feldt, M., Genzel, R., Robberto, M.: VLTI Observations of IRS 3: The brightest compact MIR source at the Galactic Centre. Messenger 119, 43–44 (2005). arXiv:astro-ph/0505189
  240. 240.
    Pott, J.U., Eckart, A., Glindemann, A., Schödel, R., Viehmann, T., Robberto, M.: The enigma of GCIRS 3. Constraining the properties of the mid-infrared reference star of the central parsec of the Milky Way with optical long-baseline interferometry. A&A 480, 115–131 (2008)ADSCrossRefGoogle Scholar
  241. 241.
    Price, H.: Quining naturalism. J. Philos. 104, p375–p402 (2007)CrossRefGoogle Scholar
  242. 242.
    Psaltis, D.: The influence of gas dynamics on measuring the properties of the black hole in the center of the Milky Way with stellar orbits and pulsars. ApJ 759, 130 (2012). arXiv:1112.0026
  243. 243.
    Psaltis, D., Narayan, R., Fish, V.L., Broderick, A.E., Loeb, A., Doeleman, S.S.: Event horizon telescope evidence for alignment of the black hole in the center of the Milky Way with the inner stellar disk. ApJ 798, 15 (2015)ADSCrossRefGoogle Scholar
  244. 244.
    Psaltis, D., Wex, N., Kramer, M.: A quantitative test of the no-hair theorem with Sgr A* using stars, pulsars, and the event horizon telescope. ApJ 818, 121 (2016a). arXiv:1510.00394
  245. 245.
    Psaltis, D., Wex, N., Kramer, M.: A quantitative test of the no-hair theorem with Sgr A* using stars, pulsars, and the event horizon telescope. ApJ 818, 121 (2016b). arXiv:1510.00394
  246. 246.
    Psillos, S.: Living with the abstract: realism and models. Synthese 180, 3–17 (2011a)CrossRefGoogle Scholar
  247. 247.
    Psillos, S.: Making contact with molecules: on Perrin and Achinstein. In: Morgan, G.J. (ed.) Philosophy of Science Matters: The Philosophy of Peter Achinstein, pp. 177–190. Oxford University Press, Oxford (2011b)CrossRefGoogle Scholar
  248. 248.
    Quataert, E.: Radiatively Inefficient Accretion Flow Models of Sgr A*. Astron. Nachr. Suppl. 324, 435–443 (2003). arXiv:astro-ph/0304099
  249. 249.
    Quine, W.: On what there is. Rev. Metaphys. 2(1948/1949), p21–38 (1948)Google Scholar
  250. 250.
    Rauch, C., Ros, E., Krichbaum, T.P., Eckart, A., Zensus, J.A., Shahzamanian, B., Mužić, K.: Wisps in the Galactic center: near-infrared triggered observations of the radio source Sgr A* at 43 GHz. A&A 587, A37 (2016)ADSCrossRefGoogle Scholar
  251. 251.
    Rees, M.J.: Black hole models for active galactic nuclei. ARA&A 22, 471–506 (1984)ADSCrossRefGoogle Scholar
  252. 252.
    Reid, M.J.: The distance to the center of the Galaxy. ARA&A 31, 345–372 (1993)ADSCrossRefGoogle Scholar
  253. 253.
    Reid, M.J., Menten, K.M., Genzel, R., Ott, T., Schödel, R., Brunthaler, A.: The position, motion, and mass of Sgr A*. Astron. Nachr. Suppl. 324, 505–511 (2003a)ADSCrossRefGoogle Scholar
  254. 254.
    Reid, M.J., Menten, K.M., Genzel, R., Ott, T., Schödel, R., Eckart, A.: The position of Sagittarius A*. II. Accurate positions and proper motions of stellar SiO masers near the Galactic Center. ApJ 587, 208–220 (2003b). arXiv:astro-ph/0212273
  255. 255.
    Reissner, H.: Über die Eigengravitation des elektrischen Feldes nach der Einsteinschen Theorie. Ann. Phys. 355, 106–120 (1916)CrossRefGoogle Scholar
  256. 256.
    Renn, J., Sauer, T.: In the limelight of stars. Einstein, Mandl, and the origins of gravitational lens research (German Title: Im Rampenlicht der Sterne. Einstein, Mandl und die Ursprünge der Gravitationslinsenforschung). Acta Hist. Astron. 27, 210–239 (2005)ADSGoogle Scholar
  257. 257.
    Revnivtsev, M.G., Churazov, E.M., Sazonov, S.Y., Sunyaev, R.A., Lutovinov, A.A., Gilfanov, M.R., Vikhlinin, A.A., Shtykovsky, P.E., Pavlinsky, M.N.: Hard X-ray view of the past activity of Sgr A* in a natural Compton mirror. A&A 425, L49–L52 (2004)ADSCrossRefGoogle Scholar
  258. 258.
    Reynolds, C.S.: Measuring black hole spin using X-ray reflection spectroscopy. Space Sci. Rev. 183, 277–294 (2014). arXiv:1302.3260
  259. 259.
    Ricarte, A., Dexter, J.: The event horizon telescope: exploring strong gravity and accretion physics. MNRAS 446, 1973–1987 (2015)ADSCrossRefGoogle Scholar
  260. 260.
    Roedig, C., Sesana, A.: Origin and implications of high eccentricities in massive black hole binaries at sub-pc scales. J. Phys. Conf. Ser. 363(1), 012035 (2012). arXiv:1111.3742
  261. 261.
    Rovelli, C., Vidotto, F.: Planck stars. Int. J. Mod. Phys. D 23, 1442026 (2014)ADSCrossRefGoogle Scholar
  262. 262.
    Rozanska, A., Kunneriath, D., Czerny, B., Adhikari, T.P., Karas, V.: Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster. MNRAS 464, 2090–2102 (2017)ADSCrossRefGoogle Scholar
  263. 263.
    Rubilar, G.F., Eckart, A.: Periastron shifts of stellar orbits near the Galactic Center. A&A 374, 95–104 (2001)ADSCrossRefGoogle Scholar
  264. 264.
    Ruffini, R., Bonazzola, S.: Systems of self-gravitating particles in general relativity and the concept of an equation of state. Phys. Rev. 187, 1767–1783 (1969)ADSCrossRefGoogle Scholar
  265. 265.
    Sabha, N., Eckart, A., Merritt, D., Zamaninasab, M., Witzel, G., García-Marín, M., Jalali, B., Valencia-S, M., Yazici, S., Buchholz, R., Shahzamanian, B., Rauch, C., Horrobin, M., Straubmeier, C.: The S-star cluster at the center of the Milky Way. On the nature of diffuse NIR emission in the inner tenth of a parsec. A&A 545, A70 (2012)ADSCrossRefGoogle Scholar
  266. 266.
    Sakai, N., Saida, H., Tamaki, T.: Gravastar shadows. Phys. Rev. D 90(10), 104013 (2014). arXiv:1408.6929
  267. 267.
    Salpeter, E.E.: Accretion of interstellar matter by massive objects. ApJ 140, 796–800 (1964)ADSCrossRefGoogle Scholar
  268. 268.
    Sandell, M.: Astronomy and experimentation. Techné 14, 252–269 (2010)Google Scholar
  269. 269.
    Schnittman, J.D.: Astrophysics of super-massive black hole mergers. Classical and Quantum Gravity 30(24), 244007 (2013). arXiv:1307.3542
  270. 270.
    Schödel, R., Ott, T., Genzel, R., Hofmann, R., Lehnert, M., Eckart, A., Mouawad, N., Alexander, T., Reid, M.J., Lenzen, R., Hartung, M., Lacombe, F., Rouan, D., Gendron, E., Rousset, G., Lagrange, A.M., Brandner, W., Ageorges, N., Lidman, C., Moorwood, A.F.M., Spyromilio, J., Hubin, N., Menten, K.M.: A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way. Nature 419, 694–696 (2002)ADSCrossRefGoogle Scholar
  271. 271.
    Schödel, R., Eckart, A., Iserlohe, C., Genzel, R., Ott, T.: A black hole in the Galactic Center complex IRS 13E? ApJL 625, L111–L114 (2005). arXiv:astro-ph/0504474
  272. 272.
    Schödel, R., Eckart, A., Alexander, T., Merritt, D., Genzel, R., Sternberg, A., Meyer, L., Kul, F., Moultaka, J., Ott, T., Straubmeier, C.: The structure of the nuclear stellar cluster of the Milky Way. A&A 469, 125–146 (2007)ADSCrossRefGoogle Scholar
  273. 273.
    Schödel, R., Gallego-Cano, E., Dong, H., Nogueras-Lara, F., Gallego-Calvente, A.T., Amaro-Seoane, P., Baumgardt, H.: The distribution of stars around the Milky Way’s central black hole II: diffuse light from sub-giants and dwarfs. A&A (2017). arXiv:1701.03817
  274. 274.
    Schwarzschild, K.: Über das Gravitationsfeld eines Massenpunktes nach der Einstein’schen Theorie (On the gravitational field of a mass point according to Einstein’s theory). Abh Königl Preuss Akad Wissenschaften, math-phys Klasse, 424 (1916). arXiv:physics/9912033 [physics.hist-ph]
  275. 275.
    Sellars, W.: Science, perception and reality. Ridgeview Publishing Company, Atascadero, CA (1963)Google Scholar
  276. 276.
    Sesana, A., Gair, J., Berti, E., Volonteri, M.: Reconstructing the massive black hole cosmic history through gravitational waves. Phys. Rev. D 83(4), 044036 (2011). 1011.5893ADSCrossRefGoogle Scholar
  277. 277.
    Shahzamanian, B., Eckart, A., Valencia-S, M., Witzel, G., Zamaninasab, M., Sabha, N., García-Marín, M., Karas, V., Karssen, G.D., Borkar, A., Dovčiak, M., Kunneriath, D., Bursa, M., Buchholz, R., Moultaka, J., Straubmeier, C.: Polarized light from Sagittarius A* in the near-infrared K\(_{s}\)-band. A&A 576, A20 (2015a)ADSCrossRefGoogle Scholar
  278. 278.
    Shahzamanian, B., Eckart, A., Valencia-S, M., Witzel, G., Zamaninasab, M., Sabha, N., García-Marín, M., Karas, V., Karssen, G.D., Borkar, A., Dovčiak, M., Kunneriath, D., Bursa, M., Buchholz, R., Moultaka, J., Straubmeier, C.: Polarized light from Sagittarius A* in the near-infrared K\(_{s}\)-band. A&A 576, A20 (2015b)ADSCrossRefGoogle Scholar
  279. 279.
    Shapiro, S., Teukolsky, S.: Black Holes, White Dwarfs, and Neutron Stars: The Physics of Compact Objects. Wiley, New York (1983). ISBN 0-471-87317-9CrossRefGoogle Scholar
  280. 280.
    Shcherbakov, R.V., Penna, R.F.: McKinney JC (2012) Sagittarius A* accretion flow and black hole parameters from general relativistic dynamical and polarized radiative modeling. ApJ 755, 133 (2012). arXiv:1007.4832
  281. 281.
    Shen, Y., Greene, J.E., Ho, L.C., Brandt, W.N., Denney, K.D., Horne, K., Jiang, L., Kochanek, C.S., McGreer, I.D., Merloni, A., Peterson, B.M., Petitjean, P., Schneider, D.P., Schulze, A., Strauss, M.A., Tao, C., Trump, J.R., Pan, K., Bizyaev, D.: The sloan digital sky survey reverberation mapping project: no evidence for evolution in the M -\(\sigma \) relation to z   1. ApJ 805, 96 (2015). arXiv:1502.01034
  282. 282.
    Shen, Z.Q., Lo, K.Y., Liang, M.C., Ho, P.T.P., Zhao, J.H.: A size of \(\sim \)1AU for the radio source Sgr A* at the centre of the Milky Way. Nature 438, 62–64 (2005)ADSCrossRefGoogle Scholar
  283. 283.
    Slaný, P., Kovář, J., Stuchlík, Z., Karas, V.: Charged Tori in spherical gravitational and dipolar magnetic fields. ApJS 205, 3 (2013). arXiv:1302.2356
  284. 284.
    Smeenk, C.: False vacuum: early universe cosmology and the development of inflation. In: Eisenstaedt, J., Kox, A.J. (eds.) The Universe of General Relativity. Einstein Studies, vol. 11. Birkhauser, Boston (2005)Google Scholar
  285. 285.
    Spitler, L.G., Lee, K.J., Eatough, R.P., Kramer, M., Karuppusamy, R., Bassa, C.G., Cognard, I., Desvignes, G., Lyne, A.G., Stappers, B.W., Bower, G.C., Cordes, J.M., Champion, D.J., Falcke, H.: Pulse broadening measurements from the Galactic Center pulsar J1745–2900. ApJL 780, L3 (2014). arXiv:1309.4673
  286. 286.
    Su, M., Slatyer, T.R., Finkbeiner, D.P.: Giant gamma-ray bubbles from fermi-LAT: active galactic nucleus activity or bipolar galactic wind? ApJ 724, 1044–1082 (2010). arXiv:1005.5480
  287. 287.
    Sunyaev, R., Churazov, E.: Equivalent width, shape and proper motion of the iron fluorescent line emission from molecular clouds as an indicator of the illuminating source X-ray flux history. MNRAS 297, 1279–1291 (1998). arXiv:astro-ph/9805038
  288. 288.
    Synge, J.L.: The escape of photons from gravitationally intense stars. MNRAS 131, 463 (1966)ADSCrossRefGoogle Scholar
  289. 289.
    Terrier, R., Ponti, G., Bélanger, G., Decourchelle, A., Tatischeff, V., Goldwurm, A., Trap, G., Morris, M.R., Warwick, R.: Fading hard X-ray emission from the Galactic Center molecular cloud Sgr B2. ApJ 719, 143–150 (2010). arXiv:1005.4807
  290. 290.
    The eLISA Consortium: Seoane PAea: The Gravitational Universe. (2013). arXiv:1305.5720
  291. 291.
    The L.I.G.O. Scientific Collaboration; The Virgo Collaboration.: Properties of the binary black hole merger GW150914. (2016). arXiv:1602.03840
  292. 292.
    Torres, D.F., Capozziello, S., Lambiase, G.: Supermassive boson stars: prospects for observational detection. (2000). ArXiv:gr-qc/0012031
  293. 293.
    Trippe, S., Paumard, T., Ott, T., Gillessen, S., Eisenhauer, F., Martins, F., Genzel, R.: A polarized infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots. MNRAS 375, 764–772 (2007). arXiv:astro-ph/0611737
  294. 294.
    Tsupko, O.Y., Bisnovatyi-Kogan, G.S.: Gravitational lensing in plasma: relativistic images at homogeneous plasma. Phys. Rev. D 87(12), 124009 (2013)ADSCrossRefGoogle Scholar
  295. 295.
    van Fraassen, C.: Images of Science: Essays on Realism and Empiricism; Churchland, P.M. (ed.). University Of Chicago Press, Chicago (1985). ISBN-13: 978-0226106540Google Scholar
  296. 296.
    Vanhollebeke, E., Groenewegen, M.A.T., Girardi, L.: Stellar populations in the Galactic bulge. Modelling the Galactic bulge with TRILEGAL. A&A 498, 95–107 (2009)ADSCrossRefGoogle Scholar
  297. 297.
    Vasudevan, R.V., Fabian, A.C.: Piecing together the X-ray background: bolometric corrections for active galactic nuclei. MNRAS 381, 1235–1251 (2007)ADSCrossRefGoogle Scholar
  298. 298.
    Verozub, L.: Sgr A* as probe of the theory of supermassive compact objects without event horizon. Astron. Nachr. 327, 355 (2006)ADSCrossRefGoogle Scholar
  299. 299.
    Vincent, F.H., Paumard, T., Perrin, G., Mugnier, L., Eisenhauer, F., Gillessen, S. (2011a) Astrometric study of the complex environment of Sgr A* in imaging mode with the VLTI/GRAVITY instrument. In: Morris, M.R., Wang, Q.D., Yuan, F. (eds.) The Galactic Center: A Window to the Nuclear Environment of Disk Galaxies, Astronomical Society of the Pacific Conference Series, vol. 439, p. 275Google Scholar
  300. 300.
    Vincent, F.H., Paumard, T., Perrin, G., Mugnier, L., Eisenhauer, F., Gillessen, S.: Performance of astrometric detection of a hotspot orbiting on the innermost stable circular orbit of the Galactic Centre black hole. MNRAS 412, 2653–2664 (2011b). arXiv:1011.5439
  301. 301.
    Vincent, F.H., Paumard, T., Perrin, G., Varniere, P., Casse, F., Eisenhauer, F., Gillessen, S., Armitage, P.J.: Distinguishing an ejected blob from alternative flare models at the Galactic Centre with GRAVITY. MNRAS 441, 3477–3487 (2014). arXiv:1404.6149
  302. 302.
    Vincent, F.H., Meliani, Z., Grandclement, P., Gourgoulhon, E., Straub, O.: Imaging a boson star at the Galactic center. (2015). arXiv:1510.04170
  303. 303.
    Viollier, R.D., Leimgruber, F.R., Trautmann, D.: Halos of heavy neutrinos around baryonic stars. Phys. Lett. B 297, 132–137 (1992)ADSCrossRefGoogle Scholar
  304. 304.
    Wald, R.: General Relativity. The University of Chicago Press, Chicago (1984). ISBN: 9780226870335Google Scholar
  305. 305.
    Walker, S.A., Fabian, A.C., Russell, H.R., Sanders, J.S.: The effect of the quasar H1821+643 on the surrounding intracluster medium: revealing the underlying cooling flow. MNRAS 442, 2809–2816 (2014). arXiv:1405.7522
  306. 306.
    Walsh, J.L., Barth, A.J., Ho, L.C., Sarzi, M.: The M87 black hole mass from gas-dynamical models of space telescope imaging spectrograph observations. ApJ 770, 86 (2013). arXiv:1304.7273
  307. 307.
    Wang, X., Loeb, A.: Detecting floating black holes as they traverse the gas disc of the Milky Way. MNRAS 441, 809–812 (2014)ADSCrossRefGoogle Scholar
  308. 308.
    Wharton, R.S., Chatterjee, S., Cordes, J.M., Deneva, J.S., Lazio, T.J.W.: Multiwavelength constraints on pulsar populations in the Galactic Center. ApJ 753, 108 (2012). arXiv:1111.4216
  309. 309.
    Will, C.M.: Perturbation of a slowly rotating black hole by a stationary axisymmetric ring of matter. I. Equilibrium configurations. ApJ 191, 521–532 (1974)ADSCrossRefGoogle Scholar
  310. 310.
    Witzel, G., Eckart, A., Bremer, M., Zamaninasab, M., Shahzamanian, B., Valencia-S, M., Schödel, R., Karas, V., Lenzen, R., Marchili, N., Sabha, N., Garcia-Marin, M., Buchholz, R.M., Kunneriath, D., Straubmeier, C.: Source-intrinsic near-infrared properties of Sgr A*: total intensity measurements. ApJS 203, 18 (2012a)ADSCrossRefGoogle Scholar
  311. 311.
    Witzel, G., Eckart, A., Bremer, M., Zamaninasab, M., Shahzamanian, B., Valencia-S, M., Schödel, R., Karas, V., Lenzen, R., Marchili, N., Sabha, N., Garcia-Marin, M., Buchholz, R.M., Kunneriath, D., Straubmeier, C.: Source-intrinsic near-infrared properties of Sgr A*: total intensity measurements. ApJS 203, 18 (2012b). arXiv:1208.5836
  312. 312.
    Wollman, E.R., Geballe, T.R., Lacy, J.H., Townes, C.H., Rank, D.M.: NE II 12.8 micron emission from the galactic center. II. ApJL 218, L103–L107 (1977)ADSCrossRefGoogle Scholar
  313. 313.
    Wrobel, J.M., Miller-Jones, J.C.A., Middleton, M.J.: A very large array search for intermediate-mass black holes in globular clusters in M81. Astron. J. 152, 22 (2016)ADSCrossRefGoogle Scholar
  314. 314.
    Wu, Q., Czerny, B., Grzedzielski, M., Janiuk, A., Gu, W.M., Aj, Dong, Cao, X.F., You, B., Yan, Z., Sun, M.Y.: The universal heartbeat; oscillations in black hole systems across the mass-scale. ApJ 833, 79 (2016)Google Scholar
  315. 315.
    Wyithe, J.S.B., Loeb, A.: Low-Frequency Gravitational Waves from Massive Black Hole Binaries: Predictions for LISA and Pulsar Timing Arrays. ApJ 590, 691–706 (2003). arXiv:astro-ph/0211556
  316. 316.
    Yagi, K., Stein, L.C.: Black hole based tests of general relativity. Class. Quantum Gravity 33(5), 054001 (2016). arXiv:1602.02413
  317. 317.
    Yuan, F., Narayan, R.: Hot accretion flows around black holes. ARA&A 52, 529–588 (2014)ADSCrossRefGoogle Scholar
  318. 318.
    Yuan, F., Quataert, E., Narayan, R.: Nonthermal electrons in radiatively inefficient accretion flow models of Sagittarius A*. ApJ 598, 301–312 (2003). arXiv:astro-ph/0304125
  319. 319.
    Yuan, F., Bu, D., Wu, M.: Numerical simulation of hot accretion flows. II. Nature, origin, and properties of outflows and their possible observational applications. ApJ 761, 130 (2012) arXiv:1206.4173
  320. 320.
    Yunes, N., Siemens, X.: Gravitational-wave tests of general relativity with ground-based detectors and pulsar-timing arrays. Liv. Rev. Relat. 16, 9 (2013)CrossRefGoogle Scholar
  321. 321.
    Yusef-Zadeh, F., Wardle, M., Miller-Jones, J.C.A., Roberts, D.A., Grosso, N., Porquet, D.: Rapid intrinsic variability of SGR A* at radio wavelengths. ApJ 729, 44 (2011)ADSCrossRefGoogle Scholar
  322. 322.
    Yusef-Zadeh, F., Arendt, R., Bushouse, H., Cotton, W., Haggard, D., Pound, M.W., Roberts, D.A., Royster, M., Wardle, M.: A 3 pc scale jet-driven outflow from Sgr A*. ApJL 758, L11 (2012a)ADSCrossRefGoogle Scholar
  323. 323.
    Yusef-Zadeh, F., Wardle, M., Dodds-Eden, K., Heinke, C.O., Gillessen, S., Genzel, R., Bushouse, H., Grosso, N., Porquet, D.: An inverse compton scattering origin of X-ray flares from Sgr A*. AJ 144, 1 (2012b)ADSCrossRefGoogle Scholar
  324. 324.
    Yusef-Zadeh, F., Wardle, M., Cotton, W., Schödel, R., Royster, M.J., Roberts, D.A., Kunneriath, D.: Tidal distortion of the envelope of an AGB star IRS 3 near Sgr A*. (2017)Google Scholar
  325. 325.
    Zajacek, M., Karas, V., Kunneriath, D.: Galactic Center minispiral: interaction modes of neutron stars. Acta Polytech. 55, 203–214 (2015)ADSCrossRefGoogle Scholar
  326. 326.
    Zakharov, A.F.: Constraints on a charge in the Reissner-Nordström metric for the black hole at the Galactic Center. Phys. Rev. D 90(6), 062007 (2014)ADSCrossRefGoogle Scholar
  327. 327.
    Zamaninasab, M., Eckart, A., Witzel, G., Dovciak, M., Karas, V., Schödel, R., Gießübel, R., Bremer, M., García-Marín, M., Kunneriath, D., Mužić, K., Nishiyama, S., Sabha, N., Straubmeier, C., Zensus, A.: Near infrared flares of Sagittarius A*. Importance of near infrared polarimetry. A&A 510, A3 (2010)ADSCrossRefGoogle Scholar
  328. 328.
    Zeh, H.D.: The Physical Basis of the Direction of Time, Fifth edn. Springer, Berlin (2007). ISBN 978-3-540-68000-0Google Scholar
  329. 329.
    Zel’dovich, Y.B., Novikov, I.D.: The radiation of gravity waves by bodies moving in the field of a collapsing star. Sov. Phys. Dokl. 9, 246 (1964)ADSGoogle Scholar
  330. 330.
    Zubovas, K., Nayakshin, S., Markoff, S.: Sgr A* flares: tidal disruption of asteroids and planets? MNRAS 421, 1315–1324 (2012). arXiv:1110.6872

Copyright information

© European Union 2017

Authors and Affiliations

  • Andreas Eckart
    • 1
    • 2
    Email author
  • Andreas Hüttemann
    • 3
  • Claus Kiefer
    • 4
  • Silke Britzen
    • 2
  • Michal Zajaček
    • 1
    • 2
  • Claus Lämmerzahl
    • 5
  • Manfred Stöckler
    • 6
  • Monica Valencia-S
    • 1
  • Vladimir Karas
    • 7
  • Macarena García-Marín
    • 8
  1. 1.I. Physikalisches InstitutUniversität zu KölnCologneGermany
  2. 2.Max-Planck-Institut für RadioastronomieBonnGermany
  3. 3.Philosphisches SeminarCologneGermany
  4. 4.Institut für Theoretische PhysikCologneGermany
  5. 5.Center for Applied Space Technology and Microgravity (ZARM)Am FallturmBremenGermany
  6. 6.Institut für PhilosophieUniversität BremenBremenGermany
  7. 7.Astronomical InstituteAcademy of SciencesPragueCzech Republic
  8. 8.European Space Agency (ESA/STScI)BaltimoreUSA

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