PoS(FRAPWS2018)050 , E. is 2 , p 1 r https://pos.sissa.it/ , C. 1 , M. Zajacek 4 , 1 , M. Valencia-S. is the Schwarzschild radius and 1 s r 2 B. Shahzamanian 3 , N. Sabha 1 , A. Zensus 2 , E. Mossoux 2 , 1 , F. Peissker 1 , S. Britzen 5 , M. Parsa ∗ 2 , 1 could be derived for star S2. The quantity , V. Karas 1 p r , M. Subroweit / 2 s , r 1 = [email protected] Speaker. We report on the nature ofrespect to prominent the sources Bremsstrahlung of X-ray emission light of andcasts the shadow a hot in plasma ’shadow’. in the The that Galactic region ’shadow’ the Center.a is Galactic distance caused With Center of by about the 1 Circumphysical to Nuclear properties 2 Disk of parsec. that the surrounds This surroundings SgrA*of detection of at allows high the us velocity super to massive stars do black orbitingprobe a hole. for the detailed the Further central investigation gravitational potential of in, super and the the massive theRecently, cluster degree three black of of hole relativity the that SgrA* one closest represents caninvestigations. stars attribute an (S2, to In ideal this S38, addition area. and to S55/S0-102)as the have black been hole used mass to and conduct distance these a relativistic parameter defined the pericenter distance of the orbitingand star. significance Here, of in this this result. publication,to If we get one highlight aims closer the at to robustness investigating SgrA*. strongerinformation relativistic can Here, effects be one one obtained can by needs modeling use lightcurveson the of the emission bright shadow X-ray of of flares. plasma the Finally, SgrA* blobs we black comment that hole orbit expected due SgrA*. to This light bending and boosting in its vicinity. ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Hosseini Straubmeier Frontier Research in Astrophysics - III 28 May - 2 June, 2018 Palermo, Italy Andreas Eckart 1) I. Physikalisches Institut der Universität2) zu Max-Planck-Institut Köln, für Zülpicher Radioastronomie, Str. Auf 77, dem3)Space D-50937 Hügel sciences, Köln, 69, Technologies Germany; D-53121 and Bonn, Astrophysics Germany; Research (STAR)Allée Institute, du Université 6 de Août, Liège, 19c, Bât4) B5c, Instituto 4000 de Liège, Astrofisica Belgium; de AndaluciaSpain (CSIC), Glorieta de la Astronomia5) s/n, Astronomical 18008 Institute Granada, of the AcademyPraha of 4, Sciences Czech Prague, Republic Bocni IIE-mail: 1401/1a, CZ-141 31 Light and shadow in the GalacticOn the Center detection of the relativistic periastron shift of star S2 in the Galactic Center PoS(FRAPWS2018)050 2 , 1 of the hot gas is Andreas Eckart 2 − cm 22 10 × 1 . Getting close to the last stable orbit around the SMBH

The Galactic Center is a very active region. It is filled with stars, dust, gas at different tempera- The SgrA complex at the center of the Milky Way consists of several components like the The shadow inspired us to define several regions (inside, on, and outside the CND in addition tures and different ionization states, andcenter an accreting of super the massive region, black i.e. hole Sagittariusto (SMBH) A* at the (SgrA*, the large very for mass an of overviewis see, SgrA*, also e.g., it subjected Eckart amounts et to to al. relativistic aboutSgrA*. effects, 2017). which 4 Due This can million leads be solar to used a masses,dilution to situation the act map in at motion out which the and space many same radiation competitive time. timeshadow. sources in Hence, In of the the this radiation region vicinity brief can and overview, of be we extinction thought begin or the of the X-ray as discussion an at Bremsstrahlung interplay a radiation between scale of light ofis and several the embedded. parsecs plasma, and Further in investigate in which(2008) we SgrA* confirmed detect and that the the the star relativistic central S2 motion stellarmain-sequence is of (ZAMS) a cluster main-sequence mass the star of luminous of 19.5M star spectral type S2. B0-2.5 V Martins with et a zero-age al. 1.1 Shadow of the Circum Nuclear Disk SMBH SgrA*, the mini-spiral, andobserved the in Circum the Nuclear radio/sub-millimeter, Disk infrared (CND). andand The X-ray as source wavelength a complex domain. part can of However, be untilto SgrA now the East, 4.6 the CND Ms had ofEckart only Chandra (2018), been observations we detected of were now in the able the Galactic toemission radio Center detect of an and region, X-ray far the as ”shadow” infrared. entire described of the region. by Thanks CNDan Mossoux against Mossoux absorber the & & for diffuse X-ray Eckart the (2018) diffusecentral aimed X-ray stellar at emission cluster. finding or The out as basis if adata for covering the barrier this the CND for investigation time acts are the interval the as between plasmaX-ray ACIS-I 1999 close emission and and to from 2012. ACIS-S/HETG Sgr Chandra the Subtracting A* image, a andgives smooth inverting an it, model the image of clipping of the it the diffuse at CND zerodiffuse with X-ray intensity, identifiable emission and subcomponents. model. smoothing The the result result is rather insensitive to the to regions off the entiretemperatures structure) and for column which densities. webest extracted fits spectra. The to general the Fromtemperature picture spectra the model are Mossoux spectra with obtained we 1.8 & keV assuming derived Eckart and a total (2018) two local get column temperature density is plasma. of that 2.3 For the CND a single Light and Shadow in the GC 1. Introduction we have indications for plasma movingto at see relativistic speed the and shadow finally of there the may SMBH be as the it possibility bends the light generated in its accretion zone. obtained. Inside the CND temperaturestemperatures of of 1 0.35 keV keV and and 1.3 5in keV keV Table are are 1 indicated. needed. Details by of Similarly Mossouxcooler the for & in MCMC the general fitting Eckart outside results and (2018). are may given inCND. We fact find act that as a the barrier plasma between at the hot the plasma location insight of and outside the of CND the is PoS(FRAPWS2018)050 2 , 1 Andreas Eckart X−ray ’shadow’ 0.5−8 keV 2 X−ray 0.5 − 8 keV 120 arcsec = 4.68 pc The Chandra image of the X-ray diffuse emission at the Galactic Center as shown by Mossoux SgrA* and central star cluster location of depressions of indicating the shadow Disk the Circum Nuclear Figure 1: & Eckart (2018) andbeen as carried obtained out for between 1999 theis and half energy 2012. an interval arcsecond. between Correspondingscale The to 0.5 implying image the that and intensity Chandra the 8 represents brightest angular areas keV. thecentral resolution The are stellar count the represented cluster observations rate. as pixel is have the shown. size It darkest TheIn is regions. dashed Mossoux shown The line & in shows location Eckart depressions of an (2018) due SgrA* invertedshadow to we and logarithmic into the explain the an shadowing the image effect algorithm of by that it. theimage allowed CND. The us of inset to shows the the transform CND. image these of Itscluster indications the (see of inner shadow figures which the edge in looks is Mossoux very similar & identical to Eckart to the 2018). ALMA the circumference of the bright part of the central stellar Light and Shadow in the GC PoS(FRAPWS2018)050 2 , 1 ) we derived 2 S38 and a distance Andreas Eckart

M 6 between the pre- and 10 ω × orbital shift ∆ ) . See also text and animation ω 57 . ∆ 0 Most of the relativistic shift happens during periapse ± 13 . 0 ± 15 . 4 = ( 3 BH M . The possibility of the detection of faint stars inside the S2 kpc . We also calculated the periastron shift u 34 a . ∆ 0 S2 / l ± a ∆ 11 . 0 and ± u S0−102/S55 e 19 . ∆ This is a region where the orbital shift can clearly be measured 8 / l e = ∆ Orbital fits for the high velocity stars S2, S38, and S0-103/S55 orbiting the Galactic Center SMBH 0 R The S-star cluster that surrounds the supermassive black hole SgrA* in the Galactic center in Parsa et al. (2017) a black hole mass of Figure 2: SgrA* as taken from Parsaimprinted et onto the al. orbit and (2017). wherezoom the We depicts effects indicated the can regions be (projected) seen in prograde easily advance which in of the comparison the to relativistic orbit the periastron by larger shift scale the orbit. is amount The is ideally suited to investigateallows the us physics to close perform to dynamical this teststhree peculiar high of object. velocity general stars relativity. In with Using the particular positions shortest such and periods a radial (S2, study velocities S38, of and S55/S0-102; see Fig. in the ESO press Announcemant ann17051 (http://www.eso.org/public/announcements/ann17051/). 2. Relativistic motion of star S2 to it of orbit is discussed in Zajacek &investigated Tursunov via (2018). The a relativistic first-order character of post-Newtoniana simulated approximation large orbits to was range calculate ofelements stellar periapse that orbits distances. were that obtained cover from Thesethe fits eccentricity calculations to and different the were semi-major sections used axis of obtainedthese to the from are orbits. fits derive to Here changes the we lower in andpost-periapse used upper orbital part changes part of in of the the orbits, orbit. Parsa et al. (2017) could show that these quantities are correlated Light and Shadow in the GC PoS(FRAPWS2018)050 ) 2 p , 3 r 1 . As an ex- s ∆ -ratios as well 00065 derived . a 0 Andreas Eckart between lower and u = a ∆ -, and / e l a ∆ , u e =0,+0.5,-0.5 mas (see Fig. s ∆ / ∆ l e ∆ is the Schwarzschild radius and s r . The corresponding histograms are shown ω . Here, ∆ p r and the ratios of the S2 orbit) and the data from the literature. / s 4 ω r ω ∆ ∆ = = 0.5 mas (in the projected view of the orbit). Hence, we s ∆ , and the periastron shift l a ∆ / u a ∆ 00080. This value is consistent with the expected value of , . l 0 e ∆ ± / u e value were obtained by transporting the uncertainties from the measurements, via the ∆ Sketch depicting the randomization of the shifts for the four orbital sections by ω 00088 . ∆ 0 In Parsa et al. (2017) we present a qualitative analysis of the robustness and significance of the = is the pericenter distance ofthe the corresponding data orbiting from star. stardegree After S2 of establishing relativity to that these derive is its correlations shownof relativistic by we its parameter could orbit. and, use For hence, S2 determine Parsa et the al. (2017) were able to derive a value with respect to the nominalprojected position view in of the the deprojected orbit. Newtonianquantities orbit, For i.e., each less orbit than that that we in generate the with this procedure we calculate the Figure 3: for the star S2 usingis the most SgrA* likely black not hole dominated mass. bypositions, possible rotation Parsa perturbing of et influences the al. such field as (2017) thathole noise argue was in on imaged position. that the at this derived different derived stellar epochs, value and possible drifts of the black ample of effective variations in the periastron shift We then find a mean uncertaintyal. of 2017) 1.4 have about mas 5 for data an pointsuncertainty individual per for position. quarter each of Knowing quarter the that three of dimensional we about randomize orbit (Parsa we the et derive position a positioning of each orbital segment by placing it at results in chapter 5.3. Here, wecomparison present to the a results fully of noise a dominated numerical calculation scenario. of The the uncertainties significance for in the Light and Shadow in the GC with the relativistic parameter we defined as upper orbital fits are shown.assumption Orbital of fits a to fully these noise configurations dominated were case. used to obtain the distributions for the as the reference frames to the final statement.as As well, we used for only the images stars inquantities in which in order SgrA* the to could measure be central the detected arcsecondcase deviation and from the estimate a positional the Newtonian uncertainties orbit. uncertainties relative We are todirection assume it. the a (essential noise We in most use dominated the the important measurement combination of of our the uncertainty in R.A. PoS(FRAPWS2018)050 2 , 1 obtained for result. Parsa ω σ ∆ Andreas Eckart of the distributions (see above). Taking σ s ∆ -ratios and a - and e excursions turn into a 4-6 σ 5 obtained from the orbits with randomization of the shifts ω ∆ into account the 3-4 o excursions including the 3D application of under the assumption of a fully noise dominated Newtonian case. s σ ∆ . These diagrams can now be used to determine an uncertainty 5 Distribution of the periastron shift and 4 Karssen et al. (2017) could show that the lightcurves of bright X-ray SgrA* flares have the exact shape one expects from plasma blobstrue orbiting for the the SMBH four close bright to flares theby discussed last Ponti by stable Karssen et orbit. et al. This al. is (2017) (2017)et and al. (see the also (2015) recent scenario Eckart bright that et flare explainswith reported al. the the SgrA* 2018). theory flares of in Li, solar a Yuan magneto-hydrodynamic flares.and & model. leading This Wang via analogous involved (2017) reconnection magnetic elaborate of field on the loops fieldsolar the originating lines physics. Li in to the the These accretion well bright known flow ejections coronal& close mass Wang ejection to (2017) described may the in be the an accretionemission explanation flow so for or well. the disk Recently, orbiting the (see blobs orbiting Fig.1 that spot in model explain Li, has the Yuan obtained observed compelling X-ray observational flare support Figure 4: 2.1 Relativistic motion of plasma blobs star S2 represent at leastthe 3-4 inclination of S2 of aboutet 137 al. (2017) shows thatthe the stellar inclusion cluster of does a possibleTab.8 not in small change Parsa proper the et motion al. result of 2017).to on SgrA* the the with Hence, noise respect it relativistic dominated to also Newtonian periastron case. does shift not (see effect our in evaluation particular of the result with respect for the four orbital sections by Light and Shadow in the GC in Figs. and compare those to the values measured off for star S2. The PoS(FRAPWS2018)050 2 , 1 Andreas Eckart under the assumption of a fully s ∆ ) with the theoretical light curves and 3 c / GM between lower and upper orbital fits obtained from u 6 a ∆ / l a ∆ , u e ∆ / l e ∆ Distribution of the ratios Since the bright X-ray flares are correlated with synchronous NIR flares (see e.g. Eckart et al. One of the goals of the Event Horizon Telescope project (EHT) is to get a high angular reso- the orbits with randomization of the shifts for the four orbital sections by Figure 5: 2012) the finding by Karssen et al.X-ray (2017) domain, probably flares also occur holds at for a theflares low NIR overlap rate domain. the than bright However, in in flare the events the resulting NIR.orbiting in Therefore, blobs. a it clearer In is agreement the with less NIR lightcurves likely flares expectedblob that are from much faint light more X-ray frequent curve and undisturbed it isblobs by less stay secondary likely stable to flare for obtain a events. a substantial cleanlight single fraction The curves of is assumption a that single that they orbit. goesthe all The boosting in show characteristics dominated a is of light shoulder these that curve due theoretical found the (The to in lensing boosting the observed amplification sets lighcurves on in of thethe before all flare bright ascending the curves X-ray part lensing scale flares of free occurs). as (in well. gravitational This Reassuring time can is scales also be that by fitting lution image at mm-wavelengths of SgrA*This in shadow order results to from measure the the following sobending effect: called of Luminous shadow plasma of light is the by orbiting SMBH. the the SMBH SMBH. there Due to is the the possibility that in addition to a bright Doppler boosted Light and Shadow in the GC noise dominated Newtonian case. through the infrared interferometric detection of orbitalnear motions the of a last dominant stable emission circular component orbit ofthe the submillimeter massive black interferometric hole imaging SgrA* of (Gravityaround Collaboration a 2018) the ring and super of massive emitting black blobs2019b). hole close in to M87 the (Event last Horizon stable Telescope orbit Collaboration; 2019a and then scaling them by introducing the observedThis flare can time be in understood seconds one by obtains therather the fact the mass that of event the SgrA*. horizon) black size,i.e., holein mass our with scales model. the linearly orbital Hence, with thematter time being is black able scale another hole to and, indication (or explain for therefore, the the the high X-ray degree flare flare of time shapes relativity via scale in2.2 the the vicinity assumption Shadow of of of SgrA*. the orbiting supermassive black hole PoS(FRAPWS2018)050 2 , 1 as and µ ratios as well as Andreas Eckart − a and − e as. However, if one is able to see it or not µ 7 result, and it appears to be highly unlikely that the common effect seen in all σ 4 ≥ The first EHT results were recently published by Ru-Sen Lu et al. (2018). The authors report Luminous stars and plasma blobs can be used to map the space time close to SgrA*. While With Parsa et al. (2017) we used three stars to derive the mass and distance of SgrA* in a In addition we report on the ’shadow’ the Galactic Center casts with respect to the X-ray represent a value lie close to the values expected for S2 and the SgrA* mass (see Iorio 2017). Here we give ω ω on a detection of intrinsic source structure at about 3 Schwarzschild radii, i.e., about 30 will critically depend on the actuala observational and feature geometrical uniquely situation associated (The shadow to isIn Black also order holes not only to - see seemust this detailed be shadow discussion well one in ordered needs Eckart andimpression et to not al. one have chaotic, a gets 2017). and special from itthat orientation the would the of be orbiting scattering best the material. screen if system, along there Another1 the the is mm. problem line accretion no may of Hence, jet sight also that it justobservations result may may becomes at from disturb be transparent optical the the around that and fact a multiple infraredwill wavelength simultaneous wavelengths) make of images it may (like difficult occur. to the get All speckle a of effect clear view known these of from effects the and immediate environment influences of SgrA*. the presence of the plasma blobsthe close light to the curves last the stable stars orbit cansurrounding needs be the to observed SMBH. be directly. Due inferred The to from plasma light the blobsof bending shape would effects the of that be black structure part hole. is of potentially the showing structure a shadow Newtonian and post-Newtonian solution.Newtonian A fits new to the and lower, simple upper, pre-, methodthe and that degree post-periapse of parts compares of relativity. properties the For orbits of the allows high us velocity to star determine S2 the values for the Light and Shadow in the GC part of the source thereThe may expected appear size a of dark that region region is in of the the overall order structure of (see 30-50 Falcke et al. 2000). therefore on the expected sizeimage scale for structures the that shadow one ofmeasurements. would the The black expect variations hole. in from the Their based datathe Fig.5 and on the expectation shows the appearance of possible of current a the shadow, models amplitudeorbiting however, are and detailed matter also consistent with images closure with indications that phase of would a show shadow that have disk not yet structure been due published. to 3. Summary and Conclusion Bremsstrahlung emission of the plasmaby in The the local Circum for- Nuclear and Disksubdivide background. that the surrounds The hot ’shadow’ SgrA* is casts nuclear caused models a plasma and ’shadow’ estimates into that of allows the areas column us inside, density to give at, effectively us a and clear picture outside of the the physical CND. conditions of Two the temperature ∆ an analysis of the uncertaintiessituation. for these In quantities this with case∆ respect the to deviations a are noise significant dominated andthree Newtonian quantities the originates S2 from values a for purelyfirst noise the star dominated with e- scenario. a and resolvable Accepting a-ratios orbit thisthe around and result, near a S2 future SMBH is for these the which results a willGRAVITY test become at for more the relativity significant VLTI can using (e.g., be interferometric Gravity performed. data Collaboration as In 2017, obtained Mérand by et al. 2017). PoS(FRAPWS2018)050 2 , 1 Andreas Eckart Terrestrial Labs Hulse−Taylor Pulsar Precession of Mercury Orbit of S2 (Parsa et al. 2017) Orbit of S2 (Parsa Deflection of light/ Shapiro Delay Orbiting spots (Karssen et al. 2018) Orbiting spots (Karssen et al. 2016) GW150914 (Abbott Stellar black hole QPOs 8 log (Mass/gr) Black Hole We received funding from the European Union Seventh Framework Pro- The gravitational potential that is measured by a number of tests of gravity presented in compar-





























































































































































































. This comparison is based on Fig.6 in Psaltis et al. (2004; see also Fig.1 in Hees et al. 6 25 30 35 40 45 25 30 35 40 0 2

−8 −6 −2 −4 The probes of the gravitational potential as they have been presented by Parsa et al. (2017) log (Potential/c^2) log −10 gram (FP7/2007-2013) under grant agreement No.ity 312789 by - Black Strong Holes gravity: Across Probing theForschungsgemeinschaft Strong Range (DFG) Grav- of via Masses. the This Cologne work Bonn was Graduate supported School in (BCGS), part the by Max the Planck Deutsche and Karssen et al. (2017) andin summarized in Fig. the present publication can2017, be and compared to Figs.4 other and tests 5 innow Eckart be et probed al. over 2010). 9 orders ThisThese figure of results shows magnitude can that for the still masses gravitational be covering potential more improvedmm-wavelength can with than and 10 infrared currently orders regime. running of interferometry magnitude. experiments in the radio Acknowledgements: plasma. The CND appears tostellar cluster act and as close a to blocking the agent super that massive black keeps hole the SgrA*. hot plasma inside the central Figure 6: ison to the mass responsibleprecession for of the Mercury, potential light (based deflection onQSO Psaltis and QPOs, 2004). the and Shapiro We have delay the selectedthe in gravitational terrestrial results the wave labs, for solar detection the the system, GW150914 Galactic thepresented (Abbott Center Hulse-Taylor by S2 et pulsar, Karssen orbit al. et presented al. by 2016). (2017). Parsa et In al. addition (2017) we and show the X-ray lightcurve fitting Light and Shadow in the GC PoS(FRAPWS2018)050 2 , 1 Andreas Eckart 9 16-19 PhysRevLett.116.061102. [2] Eckart, A., Schödel, R.; Garcia-Marin, M.;[3] Witzel, G.; etEckart, al. A.; 2008, Zamaninasab, A&A M.; 492, Straubmeier, C.; 337 [4] et al., 2010,Eckart, 2010SPIE.7734E..0XE A.; Garcia-Marin, M.; Vogel, S. N.;[5] Teuben, P.; etEckart, al., A.; 2012, Hüttemann, A&A A.; 537, Kiefer, C.; 52 [6] Britzen, S.; 2017,Eckart, FoPh A., 47, M. 553 Zajacek, M. Parsa,[7] et al.Event 2018, Horizon arXiv:1806.00284 Telescope Collaboration; 2019a, ApJ 875,[8] L1 Event Horizon Telescope Collaboration; 2019b, ApJ 875,[9] L5 Falcke, H.; Melia, F.; Agol, E., 2000, ApJ 528, L13 [1] Abbott, Benjamin P.; et al. (LIGO Scientific Collaboration and Virgo Collaboration) (2016). [10] Gravity Collaboration 2017, A&A 602, 94 [11] Gravity Collaboration 2018, A&A 618, L10 [12] Hees, A.; Do, T.; Ghez, A.[13] M.; Martinez, G.Iorio, D.; L., et 2017, al., MNRAS 2017, 472, PhRvL.118u1101H 2249 [14] Karssen G.D., Bursa M., Eckart A.,[15] Valencia-S M., etMossoux, al., E. 2017, & MNRAS Eckart, 472, A., 4422 2018,[16] MNRAS 474,Parsa, 3787 M.; Eckart, A.; Shahzamanian, B.;[17] 2017, ApJPonti, 845, G.; 22 George, E.; Scaringi, S.;[18] Zhang, S.;Psaltis, et D., al.; Wex, 2017, N. MNRAS & 468, Kramer, 2447 M.[19] 2016, ApJMartins, 818, F., 121 Gillessen, S., Eisenhauer, F., et[20] al. 2008,Mérand, ApJ A.; 672, Berger, L119 J.-P.; de Wit, W.-J.; Eisenhauer, F.; et al. 2017, The[21] Messenger, vol. 170,Li, p. Y.-P. et al., 2015, ApJ, 810,[22] 19 Li, Y.-P.; Yuan, F.; Wang, Q.D.; 2017, MNRAS 468, 2552 Light and Shadow in the GC Society through the International Maxtrophysics, Planck as Research well School as (IMPRS) special forand funds Impact Astronomy through of and the Star As- Formation. University of E.Foundation Hosseini Cologne - is and DFG members SFB of collaboration 956 the (No. IMPRS. -(DAAD) We 13-00070J) Conditions for thank - the support and Czech under Science the COPRAG2015 Germansented Academic (No.57147386). at Exchange the Service The ’Stellar result DynamicsStudy, on in in Princeton, S2 Galactic NJ, Nuclei’ has between workshop, also NovemberBlack held 29 been Hole and at Initiative pre- December Conference the 1, on Institute Black 2017, for Holes’mander and (Harvard Advanced at Hotel, University), the held 16 ’Second at Annual the Garden Sheraton2018. Street, Com- Cambridge, MA, Wednesday, May 9 through Friday, MayReferences 11, PoS(FRAPWS2018)050 2 , 1 Andreas Eckart 10 ApJ (Carlsbad, https://www.ibws.cz/), 2018arXiv180411014Z [23] Lu, Ru-Sen; Krichbaum, Thomas P.; Roy, Alan L.; et al., 2018, 2018arXiv180509223L, in[24] press with Zajacek, M., & Tursunov, A., 2018, contribution to the proceedings of the IBWS 2018 workshop Light and Shadow in the GC