The first image of a black hole
Luciano Rezzolla Institute for Theoretical Physics, Frankfurt Event Horizon Telescope (EHT) Collaboration
Milano 09.10.19 Plan of the talk
✴ The first image of a black hole: M87*
✴ How do you take a picture of a BH: observations?
✴ How do you take a picture of a BH: theory?
✴ Alternatives to Einstein and to black holes M87,The firstcenter image of the of aVirgo black cluster hole
How was this accomplished? ESO VLBI: Very Long Baseline Interferometry
wavelength resolution = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ telescope size wavelength
smaller wavelengths (higher frequencies) technology progress (GHz → THz)
GRMHD ray- traced simulation EHT angular size
•The shorter the wavelength, the smaller the emitting source •At 1.3 mm the source becomes of the size of the horizon mas = milli-arcsecond = 5 ×10-9 rad µas = micro-arcsecond = 5 ×10-12 rad VLBI: Very Long Baseline Interferometry
The Event Horizon Telescope IRAM PdB CARMA (NOEMA) Pico Veleta Create a virtual radio telescope the size of SMT the Earth sensitive to SMA mm wavelengths.
LMT
ALMA
SPT 1.3 mm (radio waves) resolution = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯—————— intercontinental ??? distances Mexico Arizona (LMT) (SMT)
Hawaii (SMA/JCMT)
South Pole (SPT) Spain Chile (IRAM 30m, (ALMA/APEX) Pico Veleta) The Black Hole Shadow in M 87 Cover Pages
The image has soon gone around the world… becoming a great resource for social media…
seen from Bologna Elliptical galaxy in center of Virgo cluster 55 Million light years away 9 There is evidence for a central dark mass of 3-6×10 Msun
image in the optical Large-scale radio map (few cm wavelengths) 240.000lightyears small-scale radio map of the core (cm wavelength) Elliptical galaxy in center of Virgo cluster 55 Million light years away 9 There is evidence for a central dark mass of 3-6×10 Msun
shadow’s size 240.000lightyears small-scale radio map of the core (cm wavelength) 3 light years de Gasperin et al. (LOFAR), 2012 … to have an idea of the scales…
https://xkcd.com/2135/ How do we do this in practice? Observations How do we do this in practice? Observations
(u, v) : complex visibilities V image plane 2⇡i(ux+vy) (u, v)= e I(x, y)dxdy V ZZ
(x, y) : angular coordinates on the sky (u, v) : projected baseline coordinates on the sky I(x, y) : brigthness distribution
2⇡ift (f)= e I(t)dt
V
(u,Observations v) : complex visibilities V 2⇡i(ux+vy) (u, v)= e I(x, y)dxdy V ZZ
(x, y) : angular coordinates on the sky (u, v) : projected baseline coordinates on the sky I(x, y) : brigthness distribution
The four teams used multiple software packages and were set to work blindly from each other. All of the teams recovered a very similar images: asymmetric ring is a robust feature of the image M87 was observed for several days (eight) and lead to four distinct images.
The images are slightly different but show again that the asymmetric ring emission is stable, as expected on these timescales. How do we do this in practice? Theory
BlackHoleCam: Bonn (Kramer), Frankfurt (LR), Nijmegen (Falcke) Three basic steps are needed: (1) GRMHD simulations in arbitrary spacetimes (2) ray-traced, radiative-transfer, deconvolved images (3) comparison with observations. BlackHoleCam (LR, Falcke, Kramer), has developed a complex and complete computational infrastructure: BHAC/BHOSS/GENA C. Fromm R. Gold Y. Mizuno H. Olivares O. Porth Z. Younsi
now UA now UCL System of equations to solve…
µ⌫ µT =0, (cons. energy/momentum) r
µ⌫ µ µ⌫ F = I , ⇤F =0, (Maxwell equations) r
µ⌫ µT =0, (cons. energy/momentum) r
µ⌫ µ µ⌫ F = I , ⇤F =0, (Maxwell equations) r
I
•Opted for agnostic approach and built a description able ↵ ↵ to describe all theories: gµ⌫ (x ) gµ⌫ (x ,ai,bi)
LR, Zhidenko, 2014; Konoplya, LR, Zhidenko, 2016 Tracing photons near a BH is not easy…
black hole
direct image
i direct image
high-order image
thin disk photographic plate Younsi, LR 2019 To be even clearer… source of light
photon event horizon circular orbit “shadow” 2GM 3GM GM r = r = ; r := b = p27 EH 2 co 2 c c rco 2
a
circle when seen from the pole shadow’s size depends also on the inclination
Müller, Pössel, Weih, LR In reality, the disk is not geometrically thin but geometrically thick, optically thin… Plasma dynamics: a typical GRMHD simulation…
A three-dimensional simulation of a Kerr black hole (a=0.9375) in Kerr-Schild coordinates and an MRI unstable torus would produce results of this type… L. Weih, LR Space of parameters ✴Plasma dynamics and properties
black-hole spin (plasma dynamics depends on it): • 2 Ti p 1 = Rhigh 2 + 2 Te 1+ 1+ SANE models MAD models black-hole rotation axis R = 10 R = 160 ISCO Kerr black hole, a MAD: mostly from the equatorial plane SANE: can switch from equatorial plane to funnel wall R = 10 R = 160 Rhigh = 10 Rhigh = 160 6 6 Where do MAD MAD mm-long photons 4 to observer 4 2 2 originate? ] ] 2 2 0 0 GM/c GM/c [ ISCO [ 2 2 Kerr black hole, 4 locus of photon 4 a 2 2 SANE: equatorial 4 4 plane is essentially 6 6 depleted 0 2 4 6 8 10 12 0 2 4 6 8 10 12 [GM/c2] [GM/c2] Image is combination of emissions… •Image decomposed in: midplane, nearside, and farside •MAD: midplane emission always dominates •SANE with low Rhigh: midplane emission dominates •SANE with high Rhigh: farside emission dominates •Given physical assumptions (spin, magnetisation), 3D GRMHD simulations were made: ~ 50 high-res simulations. •From each simulation several scenarios are constructed by changing the thermodynamics of the electrons: ~ 400 scenarios. SANE models MAD models •From each scenario synthetic images are constructed after radiative transfer and light bending: ~ 60,000 images. •Genetic algorithms and MCMC pipelines find best match. Fitting the images to the data visibility amplitude (VA) Closure phase (CP) GRMHD image (left) and convolved image (right) Fromm, Younsi, LR The match is found in the visibility space, but can also be found in image space. In the image space this would correspond to searching a face in a stadium full of people… OBSERVATIONS THEORETICAL MODEL •Degeneracies present in physical conditions and scenarios. Good: robustness of conclusions (BHs produce ring) Bad: more accurate observations to determine BH spin The AstrophysicalWhat Journal we Letters, measured…875:L1 (17pp), 2019 April 10 The EHT Collaboration et al. Table 1 our measurement of the black hole mass in M87* is not Parameters of M87* inconsistent with all of the prior mass measurements, this allows Parameter Estimate us to conclude that the null hypothesis of the Kerr metric a (Psaltis et al. 2015; Johannsen et al. 2016), namely, the Ring diameter d 42± 3 μas assumption that the black hole is described by the Kerr metric, Ring width a <20m as has not been violated. Fourth, the observed emission ring Crescent contrast b > 10:1 Axial ratio a < 4:3 reconstructed in our images is close to circular with an axial Orientation PA 150°–200° east of north ratio 4:3; similarly, the time average images from our 2 c qg = GM Dc 3.8± 0.4 μas GRMHD simulations also show a circular shape. After d +0.5 associating to the shape of the shadow a deviation from the aq= d g 11-0.3 c 9 circularity—measured in terms of root-mean-square distance M (6.5± 0.7)×10 Me from an average radius in the image—that is 10%, we can set Parameter Prior Estimate an initial limit of order four on relative deviations of the D e (16.8± 0.8) Mpc quadrupole moment from the Kerr value (Johannsen & Psaltis e +1.1 9 M(stars) 6.2-0.6 ´ 10 Me 2010). Stated differently, if Q is the quadrupole moment of a e +0.9 9 M(gas) 3.5-0.3 ´ 10 Me Kerr black hole and ΔQ the deviation as deduced from circularity, our measurement—and the fact that the inclination Notes. angle is assumed to be small—implies that ΔQ/Q4 a Derived from the image domain. (ΔQ/Q= ε in Johannsen & Psaltis 2010). b Derived from crescent model fitting. Finally, when comparing the visibility amplitudes of M87* c The mass and systematic errors are averages of the three methods (geometric with 2009 and 2012 data(Doeleman et al. 2012; Akiyama et al. models, GRMHD models, and image domain ring extraction). d fl 2015), the overall radio core size at a wavelength of 1.3 mm The exact value depends on the method used to extract d, which is re ected has not changed appreciably, despite variability in total flux in the range given. e Rederived from likelihood distributions (Paper VI). density. This stability is consistent with the expectation that the size of the shadow is a feature tied to the mass of the black hole and not to properties of a variable plasma flow. It is also straightforward to reject some alternative astrophysical procedure, we infer values of θg and α for regularized interpretations. For instance, the image is unlikely to be produced maximum likelihood and CLEAN reconstructed images. by a jet-feature as multi-epoch VLBI observations of the plasma Combining results from all methods, we measure emission jet in M87 (Walker et al. 2018) on scales outside the horizon do region diameters of 42 3 μas, angular sizes of the gravita- ± not show circular rings. The same is typically true for AGN jets in tional radius θ = 3.8± 0.4 μas, and scaling factors in the g large VLBI surveys (Lister et al. 2018).Similarly,werethe range α= 10.7–11.5, with associated errors of ∼10%. For the apparent ring a random alignment of emission blobs, they should distance of 16.8± 0.8 Mpc adopted here, the black hole mass −1 9 also have moved away at relativistic speeds, i.e., at ∼5 μas day is M= (6.5± 0.7)×10 Me; the systematic error refers to the 68% confidence level and is much larger than the statistical (Kim et al. 2018b),leadingtomeasurablestructuralchangesand 9 sizes. GRMHD models of hollow jet cones could show under error of 0.2×10 Me. Moreover, by tracing the peak of the emission in the ring we can determine the shape of the image extreme conditions stable ring features (Pu et al. 2017),butthis and obtain a ratio between major and minor axis of the ring that effect is included to a certain extent in our Simulation Library for models with R > 10. Finally, an Einstein ring formed by is 4:3; this corresponds to a 10% deviation from circularity high in terms of root-mean-square distance from an average radius. gravitational lensing of a bright region in the counter-jet would fi Table 1 summarizes the measured parameters of the image require a ne-tuned alignment and a size larger than that measured features and the inferred black hole properties based on data in 2012 and 2009. fi from all bands and all days combined. The inferred black hole At the same time, it is more dif cult to rule out alternatives mass strongly favors the measurement based on stellar to black holes in GR, because a shadow can be produced by dynamics(Gebhardt et al. 2011). The size, asymmetry, bright- any compact object with a spacetime characterized by unstable ness contrast, and circularity of the reconstructed images and circular photon orbits(Mizuno et al. 2018). Indeed, while the geometric models, as well as the success of the GRMHD Kerr metric remains a solution in some alternative theories of simulations in describing the interferometric data, are consis- gravity (Barausse & Sotiriou 2008; Psaltis et al. 2008), non- tent with the EHT images of M87* being associated with Kerr black hole solutions do exist in a variety of such modified strongly lensed emission from the vicinity of a Kerr black hole. theories (Berti et al. 2015). Furthermore, exotic alternatives to black holes, such as naked singularities(Shaikh et al. 2019), boson stars (Kaup 1968; Liebling & Palenzuela 2012), and 8. Discussion gravastars (Mazur & Mottola 2004; Chirenti & Rezzolla 2007), A number of elements reinforce the robustness of our image are admissible solutions within GR and provide concrete, albeit and the conclusion that it is consistent with the shadow of a contrived, models. Some of such exotic compact objects can black hole as predicted by GR. First, our analysis has used already be shown to be incompatible with our observations multiple independent calibration and imaging techniques, as given our maximum mass prior. For example, the shadows of well as four independent data sets taken on four different days naked singularities associated with Kerr spacetimes with in two separate frequency bands. Second, the image structure ∣a*∣ > 1 are substantially smaller and very asymmetric matches previous predictions well (Dexter et al. 2012; compared to those of Kerr black holes(Bambi & Freese 2009). Mościbrodzka et al. 2016) and is well reproduced by our Also, some commonly used types of wormholes (Bambi 2013) extensive modeling effort presented in Section 6. Third, because predict much smaller shadows than we have measured. 8 Ring Asymmetry and Black Hole Spin Conclusions on the spin can still be drawn if one combines “other” information on jet power and orientation accretion flow observer Ring Asymmetry and Black Hole Spin accretion flow Note that the in the images providing the best match, the emitting material is close to the jet funnel and coronating with the black hole Moving away from Kerr black holes: accretion onto a dilaton black hole Mizuno+ 2018 Dilaton vs Kerr black hole 1.0 •Fair comparison requires that basic Horizon 0.9 Photon Orbit features of the flow are matched. 0.8 ISCO 0.7 •Three most important are: horizon 0.6 0.5 radius, photon orbit, ISCO 0.4 0.3 Dilaton parameter [M] •In general, larger dilaton parameter 0.2 reduces horizon radius, photon 0.1 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 orbit, and ISCO (cf. spin in Kerr). Kerr spin parameter [M] •Different matches possible but ISCO is most critical since most of the emission comes from around ISCO. GRMHD simulations 3D GRMHD simulations of magnetized torus with a weak poloidal magnetic field loop accreting onto Kerr BH (a=0.6) and ISCO-matched dilaton BH (b=0.5) cf. Sgr A* with scatter convolved GRRT Kerr images; emission features smeared by beam; crescent reveals presence of BH. BSMEM dilaton reconstructed image with scattering; again, presence of a crescent reveals BH. Overall, at present not possible to distinguish the two BHs Moving away from Kerr black holes: accretion onto a boson star Olivares+ 2019 Accretion onto a boson star ‣ Self-gravitating horizonless compact objects composed of scalar field (boson stars) have long since been considered potential candidates for Sgr A* (dark-matter cusp). ‣ Previous work has considered whether emission from boson stars can be distinguished from that of a black hole. ✴Using spectral features: not possible to distinguish (Guzman+ 2010) ✴Using shadow image of a boson star surrounded by torus: not possible to distinguish (Vincent+ 2016). ‣These works did not consider effects of accretion. ‣ We performed first GRMHD simulations of accreting nonrotating boson stars. L. Weih, H. Olivares, LR ‣Simulations show considerable differences in the dynamics of the accretion flow. ‣In the case of the boson star, matter reaches very close to the origin, forming a stalled accretion torus (MRI is quenched). density (x,z) density (x,y) side view top view ✴compactness is quite high: := M /R =0.11 ˙ 0.1 M 0.6 0.2 0.4 8950 9000 9050 20 0.2 0.0 10 0.2 ] M [ 0 1.0 b Boson star z 10 Kerr BH,a=0.9375 4 4 4 4 0.8 20 2 2 2 2 0.6 ˙ 30 0 0 0 0 0.4 2 2 2 2 0.2 40 4 4 4 4 8 6 4 2 0 0 2 4 6 8 8 6 4 2 0 0 2 4 6 8 0.0 50 0 2000 4000 6000 8000 10000 50 40 30 20 10 0 10 20 30 40 50 50 40 30 20 10 0 10 20 30 40 50 magnetic flux t [M] x [M] x [M] ✴Mass-accretion rate: positive for black hole but oscillating for boson star. ✴Oscillations produced by stalled torus; correspond to epicyclic frequency. ✴No evacuated funnel in polar region in the case of boson star. ✴Slow wind flowing from hot and dense interior: no jet from boson star. S/SSmax/Smax 0 0 0.20.2 0.40.4 0.60.6 0.80.8 1 1 GRRTGRRT GRRTGRRT(convolved(convolved) ) EHTEHT 2017 2017(6h(,6hreconst, reconst., scatter., scatter) ) KerrKerr a = a 0=.9370.937 KerrKerr a = a 0=.9370.937 KerrKerr a = a 0=.9370.937 ⇤ ⇤ ⇤ ⇤ ⇤ ⇤ •Left: GRRT images; as] 50as] 50 µ µ sharp emission from photon ring visible 0 0 50 50 for BH. Relative Declination [ Relative Declination [ DSSIM=0.126DSSIM=0.126 SmaxS=0.12max=0.12 mJy mJy SmaxS=1.55max=1.55 mJy mJy SmaxS=1.22max=1.22 mJy mJy BosonBoson star star BosonBoson star star BosonBoson star star as] 50as] 50 •Right: reconstructed µ µ image with scattering 0 0 and conditions of EHT 50 50 Relative Declination [ Relative Declination [ 2017 campaign. DSSIM=0.060DSSIM=0.060 SmaxS=0.22max=0.22 mJy mJy SmaxS=2.42max=2.42 mJy mJy SmaxS=1.84max=1.84 mJy mJy 50 50 0 0 50 50 50 50 0 0 50 50 50 50 0 0 50 50 RelativeRelative R.A R..[Aµas]. [µas] RelativeRelative R.A R..[Aµas]. [µas] RelativeRelative R.A R..[Aµas]. [µas] Reconstructed images shows differences, both in size and structure BH image exhibits crescent; boson star emission from inner regions. Overall, from images alone it is possible to distinguish them Conclusions ✴BlackHoleCam covered all aspects of these observations, has played a major role in the EHT campaign and analysis. ✴Accretion onto Kerr black holes has been explored extensively in various physical and thermodynamical regimes. ✴Exploration of accretion onto alternatives to Kerr BHs has started: boson stars can be distinguished, other BHs cannot. ✴EHT has provided first evidence existence of SMBHs and boosted our understanding of accretion in strong gravity. EHT observations of SMBHs is now possible! A new era of astrophysics has started. Much more to come! EXTRAS Looking into the future: going into space 15,000 km Martin-Neira, V.Kudriashov (ESA) Roelofs+ 2019 Looking into the future: going into space 690 GHz 690 GHz Moscibrodzka+ 690 GHz 690 GHz 4m dishes in space 4m dishes in space 1 month 6 months Roelofs+ 2019 Accretion onto a gravastar ● Non-rotating gravastar with compactness := M/R =0.478 C ● Also in this case, dynamics of matter very different. ● Mass accretion is reduced by a factor ~ 5 with respect to the Schwarzschild case ● Interaction with surface produces violent outbursts as matter is out of equilibrium once accreted (“nova” bursts). ● Oscillations and outward-moving spiral shocks are sent into the accreting material. ● Although shadow is very similar to black hole, accretion is not. Multi-wavelength observations will tell difference. Representative GRMHD Model Image of M87 Simulated image Simulated image EHT2017 image from GRMHD model convolved with 20 �as beam M87 April 6 GRMHD Blurred GRMHD 40 µas 0 1 2 3 4 5 6 0 10 20 30 0 1 2 3 4 5 6 Brightness Temperature (109 K) Distribution of Best-Fit Black Hole Angular Size GENA 1% Themis 1% 0.8 0.8 GENA 10% Themis 10% GENA 100% Themis 100% 0.6 0.6 0.4 0.4 dp/d(M/D) dp/d(M/D) 0.2 0.2 0.0 0.0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 M/D (µas) M/D (µas) • Distribution of M/D from fitting Image Library snapshots to 2017 April 6th EHT data • Results by Themis & GENA pipelines are qualitatively similar • The distribution peaks close to M/D ~ 3.6 �as with a width of ~0.5 �as • The models are broadly consistent with stellar mass estimate Distribution of M/D MAD SANE 6 10.1 ) 1 • Distribution of M/D of different as) = M µ 4 6.7 9 D( high BH spin and Rhigh for SANE & / R M 2 3.4 M (10 MAD models 6 10.1 ) 10 as) M µ = 4 6.7 9 D( / high M M (10 • BH mass is calculated with R 2 3.4 6 10.1 ) 20 as) D=16.9 Mpc M µ = 4 6.7 9 D( / high M M (10 R 2 3.4 • 6 10.1 Most individual models favour ) 40 as) M µ = 4 6.7 9 D( M/D close to 3.6 as / � high M M (10 R 2 3.4 6 10.1 ) 80 as) M µ = • a < 0, SANE, Rhigh=1 model 4 6.7 9 D( / high M M (10 favours M/D ∼ 2 as due to R 2 3.4 � 6 10.1 Themis ) GENA as) 160 M µ 9 outer ring at scale of = 4 6.7 D( / high M 2 3.4 M (10 counterrotating disk ISCO R 0.94 0.5 0 0.5 0.94 0.94 0.5 0 0.5 0.94 a a ⇤ ⇤ • a =0.94, SANE favors M/D > 3.6 �as due to secondary inner ring Distribution of Model Best-Fit Position Angle • Large scale jet orientation lies on the shoulder of the BH spin vector poin ng away from Earth spin-away models (⟨PA⟩ ∼ 0.010 Themis 1% GENA 1% 0.010 Themis 10% GENA 10% 0.008 Themis 100% GENA 100% 200 deg, PA ∼ 55 deg) 0.008 � 0.006 0.006 dp/dPA 0.004 dp/dPA 0.004 0.002 0.002 • Large scale jet orientation 0.000 0.000 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 lies off the shoulder of the PA(deg.) PA(deg.) BH spin vector poin ng toward Earth spin-toward models 0.010 0.012 Themis Reflected 1% GENA Reflected 1% Themis Reflected 10% GENA Reflected 10% 0.010 Themis Reflected 100% 0.008 GENA Reflected 100% • BH spin-away models are 0.008 0.006 0.006 dp/dPA dp/dPA strongly favored 0.004 0.004 0.002 0.002 0.000 0.000 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 • Width of distributions arises PA(deg.) PA(deg.) from brightness fluctuations in the ring Average Image Scoring Summary • Compare: data - ⟨model⟩ model - ⟨model⟩ using Themis-AIS • Rejects a = -0.94 MAD models • This model exhibit highest morphological variability Other Constraints Apply three additional constraints: 1. Close to radiative equilibrium 2. Must not overproduce X-rays 3. Must produce jet power > minimal jet power = 1042 erg/sec Radiative Equilibrium ✏ L /(Mc˙ 2) • Calculate radiative efficiency, • Reject model if ε > ε(classical thin disk model); inconsistent; would cool quickly • Lbol: calculated by Monte Carlo code grmonty • Rejects MAD models with a ≥ 0 and Rhigh = 1 (hot midplane electrons) X-ray Constraint • X-ray data: simultaneously Chandra, NuSTAR observations during EHT2017 Campaign • 2-10 keV luminosity: Lx= 4.4 ± 0.1 x 1040 erg/s • Compare data to SEDs generated from simulations • X-ray flux is produced by inverse Compton scattering of synchrotron photons • Reject models that consistently overproduce X-ray • Overluminous model: mostly SANE with Rhigh <= 20. • LX is sensitive to Rhigh, very low values of Rhigh are disfavored. Jet Power • M87’s jet power (Pjet) estimates range from 1042 to 1045 erg/s • Adopt conservative lower limit on jet power, Pjet,min = 1042 erg/s • Pjet defined as total energy flux in polar regions where �� > 1 • Pout defined as energy flux in all polar outflow regions (includes wide-angle, low velocity wind) • Pout is maximal definition of jet power Jet Power • Constraint Pjet > Pjet,min = 1042 erg/s rejects all a=0 models (Pjet =0). These models also have Pout < 1042 erg/s • SANE models with |a| < 0.5 rejected • Most |a| > 0 MAD models acceptable • Pjet dominated by Poynting flux; driven by extraction of black hole spin energy through Blandford-Znajek process Constraint Summary • Applied AIS, consistency SANE MAD of radiative equilibrium, max X-ray luminosity, and minimum jet power • Most SANE models fail, except a=-0.94 and a=0.94 models with large Rhigh • Large fraction of MAD model pass, except a = 0 models and small Rhigh models Pjet/Pout vs ��cut cut cut 0.995 0.707 0.100 0.010 0.995 0.707 0.100 0.010 1.0 MAD a=-0.94 1.0 MAD a=-0.5 MAD a=0 MAD a=+0.5 0.8 MAD a=+0.94 0.8 0.6 0.6 out out /P /P jet jet P 0.4 P 0.4 0.2 0.2 SANE a=-0.94 SANE a=-0.5 SANE a=0 SANE a=+0.5 0.0 0.0 SANE a=+0.94 1 0 1 2 1 0 1 2 10 10 10 10 10 10 10 10 cut cut MAD SANE • Pjet depends on βγ cutoff used in definition • Pjet small for a = 0 because energy flux in relativistic outflow is small BH Mass Distance 1 Rs Source (Msolar) (Mpc) (μas) Sgr A* 4 x 106 0,008 10 3.3 - 6.2 x 3.6 - 7.3 M87 16,8 109 7.6 M104 1 x 109 10 2 Cen A 5 x 107 4 0,25 Stellar Mass: 6.2 x 109 Msun Gas Mass: 3.5 x 109 Msun (Gebhardt et al. 2011) (Walsh et al. 2013) Black Hole:4.84- 5.2 Rg Black Hole: 4.84-5.2 Rg Worm Hole: ~2.7 Rg (e.g., Bambi 2013) Naked Singularity: 1 Rg (superspinar) (e.g., Bambi & Freese 2009) 6.5 Billion Solar Mass Black Hole MAD vs SANE (GRMHD Simulations) RIAF model, two extreme situationdensity plasma beta magnetisation 3D GRMHD side simulations with view a=0.94 SANE MAD top view GRRT Image at 230 GHz • MAD, a=+0.94, Rhigh=160 • i=163 deg • each frame corresponds to 1M (~0.35 day) (Paper V) SANE averaged GRRT images i=163 deg outer ring black hole counter-clockwise clockwise rotational axis *the forward jet is pointed to the right bright top uniform bright bottom in all panels inner ring (Paper V) • EHT observed M87 Polarization polarization in Semi-analytic force-free 2017 (Sgr A*, GRMHD simulation jet model (Broderick & Loeb M87, + AGN (SANE, i=20 deg, Rhigh=40) 09) sources) • Polarization map (linear & circular), rotation measure, total polarization degree color: intensity tick: polarization map • Given additional constraint for theoretical model Moscibrodzka et al. (17) Movie of Sgr A* • Sgr A* is more complicated due to time variability & light curve scattering during EHT observation period (~6h) • Image snapshot => Movie GRMHD + GRRT + scattering (SANE, a=0.6, i=60 deg) Extend EHT: space VLBI (EHT+satellite) • Consider EHT ground VLBI array + 1 orbiting satellite ⇒ increase Frommresolution et al. (2019) • Question: which orbit to use? Stellar orbit • 6 orbital elements semi major axis: a, eccentricity: e, # inclina on: i, right ascension of the ascending node: Ω, argument of perigee: ω, true anomaly: θ • Set constraints: • keep beam nearly circular • fill uv-plane within 24 hours • optimise orbit for Sgr A* observations Figure 4.1.4-9. Classic Orbital Elements (COEs). Here we show four of the six COEs. We ⇒ constrained non-linear optimisationuse the COEs to visualize an orbitby and locateusing a spacecraft Genetic in it. The other two COEs,Algorithm semimajor axis, a, and eccentricity, e, specify the size and shape of an orbit. (GA) Table 4.1.4-3.Summary of Classic Orbital Elements. Element Name Description Range of Values Undefined a Semimajor axis Size Depends on the Never conic section e Eccentricity Shape e = 0: circle Never 0 < e < 1: ellipse i Inclination Tilt, angle from Kˆ unit vector to 0 ≤ i ≤ 180° Never specific angular momentum vector h Ω Right ascension of Swivel, angle from vernal equinox 0 ≤ Ω < 360° When i = 0 or 180° the ascending to ascending node (equatorial orbit) node ω Argument of Angle from ascending node to 0 ≤ ω < 360° When i = 0 or 180° (equatorial perigee perigee orbit) or e = 0 (circular orbit) ν Tr ue anomaly Angle from perigee to the 0 ≤ ν < 360° When e = 0 (circular orbit) spacecraft’s position 4.1.4-160 GA Results for Satellite Orbit number of individuals: 1000 number of generations: 10 Calculated by C. Fromm animation: iteration until best orbit (last frame) Method can be easily adopted and modified for: • different sources (M87 or M87+Sgr A*) • different observations schedules (6h,12h,18h,…) • modification of ground array (where to add new antennas) Primary Target for EHT Psaltis (2018) Slowly Building Up Data Lo-band eht-imaging on April 11 Credit: Palumbo & Wielgus Closure Phases: Mildly asymmetric & time-variable structure The Astrophysical Journal Letters, 875:L1 (17pp), 2019 April 10 The EHT Collaboration et al. The array has a nominal angular resolution of λ/L,whereλ is the The Astrophysical Journal Letters, 875:L4 (52pp), 2019 April 10 The EHT Collaboration et al. observing wavelength and L is the maximum projected baseline length between telescopes in the array (Thompson et al. 2017).In this way, VLBI creates a virtual telescope that spans nearly the full diameter of the Earth. To measure interferometric visibilities, the widely separated telescopes simultaneously sample and coherently record the radiation field from the source. Synchronization using the Global Positioning System typically achieves temporal align- ment of these recordings within tens of nanoseconds. Each station is equipped with a hydrogen maser frequency standard. With the atmospheric conditions during our observations the coherent integration time was typically 10 s (see Figure 2 in Paper II). Use of hydrogen maser frequency standards at all EHT sites ensures coherence across the array over this timescale. After observations, recordings are staged at a central location, aligned in time, and signals from each telescope-pair are cross-correlated. While VLBI is well established at centimeter and millimeter wavelengths (Boccardi et al. 2017; Thompson et al. 2017) and can be used to study the immediate environments of black holes (Krichbaum et al. 1993; Doeleman et al. 2001), the extension of VLBI to a wavelength of 1.3 mm has required long-term Figure 3. Selected closure phases from coherently averaged visibilities on three triangles as a function of Greenwich Mean Sidereal Time (GMST) using data from all technical developments. Challenges at shorter wavelengths fourFigure days. 1. ErrorEight stations bars of denote the EHT± 20171σ campaignuncertainties over six geographic from thermal noise. The trivial ALMA–APEX–SMT triangle (left panel) has closure phases near zero on all days, as include increased noise in radio receiver electronics, higher expectedlocations because as viewed from this the triangle equatorial plane. includes Solid baselines an intra-site represent mutual baseline. Deviations from zero arise from a combination of thermal and systematic errors (Paper III). The ALMA– atmospheric opacity, increased phase fluctuations caused by visibility on M87* (+ 12° declination). The dashed baselines were used for the (Paper IV) atmospheric turbulence, and decreased efficiency and size of LMTcalibration–SMT source triangle 3C279 (seemiddle Papers III paneland IV)).shows persistent structure across all days, while the large LMT–SMA–SMT triangle (right panel) shows source evolution between radio telescopes in the millimeter and submillimeter observing the first two days and last two days. bands. Started in 2009 (Doeleman et al. 2009a), the EHT began median zenith atmospheric opacities at 230 GHz ranging from a program to address these challenges by increasing array 0.03 to 0.28 over the different locations. The observations were sensitivity. Development and deployment of broadband VLBI scheduled as a series4. of Pre-imaging scans of three to sevenConsiderations minutes in can also lead to uncertainties in the a priori calibration for other systems (Whitney et al. 2013; Vertatschitsch et al. 2015) led to * data recording rates that now exceed those of typical cm-VLBI duration, with M87 scans interleaved with those on the quasar sources observed during the same time period, such as 3C 279. In this section, we analyze the* measured M87 visibilities arrays by more than an order of magnitude. Parallel efforts to 3C 279. The number of scans obtained on M87 per night However, pointing errors for 3C 279 are expected to be less support infrastructure upgrades at additional VLBI sites, ranged from 7 (April 10) to 25 (April 6) as a result of different directly to assess what conclusions* are supported by the data including the Atacama Large Millimeter/submillimeter Array observing schedules. A description of the M87 observations, severe, as it is bright enough for the LMT to point directly on- irrespective of choices madefi in the imaging procedures. This (ALMA; Matthews et al. 2018; Goddi et al. 2019) and the their correlation, calibration, and validated nal data products is source prior to VLBI scans. Thus, the corrections needed for Atacama Pathfinder Experiment telescope (APEX) in Chile non-imagingpresented in Paper analysisIII and brie providesfly summarized estimates here. of the quality of the (Wagner et al. 2015), the Large Millimeter Telescope Alfonso At each station, the astronomical signal in both polarizations the LMT are expected to better match the a priori amplitude apriori calibration, the level of non-closing systematic errors, Serrano (LMT) in Mexico (Ortiz-León et al. 2016), the IRAM and two adjacent 2 GHz wide frequency bands centered at error budget during observations of 3C 279 (mostly correcting 30 m telescope on Pico Veleta (PV) in Spain (Greve et al. 1995), and227.1 the and degree 229.1 GHz of were temporal converted variability to baseband using in the source. It also the Submillimeter Telescope Observatory in Arizona (SMT; standard heterodyne techniques, then digitized and recorded for focus errors) than during observations of M87 (correcting guides the generation of realistic synthetic data sets Baars et al. 1999), the James Clerk Maxwell Telescope (JCMT) at atotal rate of 32 Gbps. Correlation of the data was carried for both focus and pointing errors). and the Submillimeter Array (SMA) in Hawai’i (Doeleman et al. (Sectionout using6.1 a software) and correlator motivates(Deller et the al. 2007 choice) at the MIT of imaging parameters 2008; Primiani et al. 2016; Young et al. 2016), and the South Haystack Observatory and at the Max-Planck-Institut für In Section 8.1 and Appendix F, we compare estimated Pole Telescope (SPT) in Antarctica (Kim et al. 2018a), extended (e.g., the FOV of reconstructed images) used to define Radioastronomie, each handling one of the two frequency residual gains for the SMT and the LMT from imaging M87 the range of EHT baselines and coverage, and the overall parameterbands. Differences ranges between in the two the independent imaging correlators parameter surveys collecting area of the array. These developments increased the were shown to be negligible through the exchange of a few and 3C 279. In Paper VI, we compare these results with the sensitivity of the EHT by a factor of ∼30 over early experiments (Sectionidentical6.2 scans). for cross comparison. At correlation, signals that confirmed horizon-scale structures in M87* and Sgr A* fi were aligned to a common time reference using an apriori estimated residual gains when tting parametric models to the (Doeleman et al. 2008, 2012; Akiyama et al. 2015; Johnson et al. Earth geometry and clock model. 2015; Fish et al. 2016; Lu et al. 2018). interferometric data. Asubsequentfringe-fitting step identified detections in For the observations at a wavelength of 1.3 mm presented correlated4.1. signal Expected power while Amplitude phase calibrating Calibration the data for Limitations here, the EHT collaboration fielded a global VLBI array of eight stations over six geographical locations. Baseline lengths Theresidual amplitude delays and atmospheri calibrationceffects.UsingALMAasahighly error budget is determined from 4.2. Estimates of Non-closing Systematic Errors ranged from 160 m to 10,700 km toward M87*, resulting in an sensitive reference station enabled critical corrections for iono- array with a theoretical diffraction-limit resolution of ∼25 μas uncertaintiesspheric and tropospheric on individual distortions at the measurements other sites. Fringe of station perfor- Apart from the thermal errors, which are well understood (see Figures 1 and 2, and Paper II). fitting was performed with three independent automated pipelines, mance,each tailored as described to the specifi inccharacteristicsoftheEHT Paper III. The error budget is only and can be evaluated from first principles, there are several observations, such as the wide bandwidth, susceptibility to 4. Observations, Correlation, and Calibration representative of global station performance and is not sources of additional systematic error present in the EHT data. atmosphericfi turbulence, and array heterogeneity (Blackburn et al. We observed M87* on 2017 April 5, 6, 10, and 11 with the speci2019;Janssenetal.ed for individual2019,PaperIII) measurements..Thepipelinesmadeuseof While this procedure These include polarimetric leakage (proportional to the EHT. Weather was uniformly good to excellent with nightly is adequatestandard software for for stationsthe processing with of radio-interferometric stable performance data and weather magnitude of station-dependent leakage terms and the source during3 the observing run, the error budget may be under- fractional polarization), residual polarimetric-gain calibration estimated for stations with variable performance. The SMT, offsets, loss of amplitude with long coherent averaging, the PV, SMA, JCMT, APEX, and ALMA stations are well effects of biased S/N estimators, and the limitations of alinear characterized either through years of studies or via network error propagation model for closure quantities. calibration. More recent additions to the EHT (the LMT and the These systematic errors can affect both visibilities and SPT) may have more variable behavior, as their observing closure quantities. While these effects are small, in avery high systems are not yet well exercised and because they do not S/N regime systematic uncertainties may dominate over fi have suf ciently close sites to permit network calibration. thermal uncertainties. In Paper III, we quantified the magnitude fi Speci cally for M87, the LMT is the most under- of systematic uncertainties in the EHT 2017 data both with a characterized station. The LMT began observing M87 in the series of statistical tests on the distributions of trivial closure evening, when the dish is still affected by thermal gradients in quantities and with cross-validation tests of data products the back-up structure or panel distortions from daytime heating, across different frequency bands and polarizations. For M87, fi both of which are signi cant for open-air telescopes. These the characteristic magnitude of systematic errors was found to effects are common for sensitive millimeter-wave dishes and be only a fraction of the thermal errors, even for heavily cause surface instability. In addition, evening conditions are averaged data. In the case of 3C 279, which has significant inadequate for accurate pointing and focusing of the telescope intrinsic polarization, systematic errors can dominate over the (particularly on weaker sources), leading to performance that thermal errors. In both cases the characteristic magnitudes are can vary substantially across scans and from day to day. A small: less than 2° for closure phases, and less than 4% for defocused dish can measure persistently low amplitudes on closure amplitudes. baselines to that station between focus attempts (typically every one to two hours). Changes in telescope pointing can cause 4.3. Constraints on the Total Compact Flux Density amplitudes to fluctuate significantly from scan to scan (from the telescope moving to and from the source) and between pointing EHT baselines sample angular scales in M87 that span attempts (typically every half-hour). Issues in telescope focus nearly five orders of magnitude. The largest gap in coverage 7 • X-ray data: simultaneouslyX-ray constraint Chandra, NuSTAR observations during EHT2017 Campaign • 2-10 keV luminosity: Lx= 4.4 ± 0.1 x 1040 erg/s • Compare data to SEDs generated from simulations • X-ray flux is produced by inverse Compton scattering of synchrotron photons • Reject models that consistently overproduce X-ray • Overluminous model: mostly SANE with Rhigh ≤ 20. • LX is sensitive to Rhigh, very low values of Rhigh are disfavored. • M87’s jet power (Pjet) estimatesJet Power range from 1042 to 1045 erg/s • Adopt conservative lower limit on jet power, Pjet,min = 1042 erg/s • Pjet defined as total energy flux in polar regions where �� > 1 • Pout defined as energy flux in all polar outflow regions (includes wide-angle, low velocity wind) • Pout is maximal definition of jet power • Constraint Pjet > Pjet,min = 1042 erg/s rejects all a=0 models (Pjet =0). These models also have Pout < 1042 erg/s • SANE models with |a| < 0.5 rejected • Most |a| > 0 MAD models acceptable • Pjet dominated by Poynting flux; driven by extraction of black hole spin energy through Blandford-Znajek process Pjet/Pout vs ��cut cut cut 0.995 0.707 0.100 0.010 0.995 0.707 0.100 0.010 1.0 MAD a=-0.94 1.0 MAD a=-0.5 MAD a=0 MAD a=+0.5 0.8 MAD a=+0.94 0.8 0.6 0.6 out out /P /P jet jet P 0.4 P 0.4 0.2 0.2 SANE a=-0.94 SANE a=-0.5 SANE a=0 SANE a=+0.5 0.0 0.0 SANE a=+0.94 1 0 1 2 1 0 1 2 10 10 10 10 10 10 10 10 cut cut • Pjet depends on βγ cutoff used in definition • Pjet small for a = 0 because energy flux in relativistic outflow is small Black Hole Photon Ring Johnson et al. (2019) Blue: perpendicular intersection to BH spin axis Red: parallel intersection to BH spin axis Decomposition of subrings by the number n of photon half-orbits from turning points in θ. subring flux ratio n+1 n F /Fring e Time-average image of BH shadow, 3DMAD, a=0.94, i=17 deg : Lyapunov exponent �a=1 case: n=1 subring for M87 contribute ~10% of total luminosity Black Hole Photon Ring Johnson et al. (2019) visibility amplitude of time-averaged GRMHD Blue:simulation perpendicular for M87 intersection (i=163 deg) to BH spin axis Red: parallel intersection to BH spin axis LEO: low Earth Orbit: < 2000 km short baseline: complex structure reflected disk/jet emissionMEO: Medium Earth Orbit: 2000-36,000 km long baseline (>20G�): dominated by photon ring (n=1,2,…)GEO: Geostationary orbit: 36,000 km Effect of Changing Mass Snapshot image of GRMHD simulation MAD, spin a=0.94, Rhigh=160 Changing mass between 3 x 109 and 6 x 109 Msun Credit: G. Wong, B. Prather, C. Gammie (Illinois) Effect of Changing Inclination Snapshot image of GRMHD simulation MAD, spin a=0.94, Rhigh=160 Changing inclination from163 to 0 degree Credit: G. Wong, B. Prather, C. Gammie (Illinois) M87 Theoretical Images Movies of time evolution of GRRT image of M87 GRMHD simulation, SANE, a=0.94 Movie: Z. Younsi, L. Weih, C. Fromm, L. Rezzolla Frankfurt BHCam team M87 Theoretic al Images Movies of time evolution of GRRT & convolved images of M87 GRMHD simulation, SANE, a=0.94 Movie: Z. Younsi, C. Fromm, L. Weih, L. Rezzolla Frankfurt BHCam team Effect of Changing Inclination Snapshot image of GRMHD simulation SANE, a=0.94 Changing inclination angle (from 163º) Movie: Z. Younsi, L. Weih, C. Fromm, L. Rezzolla Frankfurt BHCam team Spherical Projection of Density Evolution color shows log(ρ) MAD, a=0 SANE, a=0 on surface r = 10 GM/c2 pole to equator contrast ~ 105 Credit: G. Wong, B. Prather, C. Gammie (Illinois) Spherical Projection of Density Evolution color shows MAD, a = -0.94 MAD, a= +0.94 log(ρ) retrograde prograde on surface r = 10 GM/c2 pole to equator contrast ~ 105 BH spin: clockwise BH spin: counter-clockwise matter: counter-clockwise matter: counter-clockwise Credit: G. Wong, B. Prather, C. Gammie (Illinois) Spherical Projection of Density Evolution color shows log(ρ) SANE, a = -0.94 SANE, a= +0.94 on surface r = 10 GM/c2 pole to equator contrast ~ 105 BH spin: clockwise BH spin: counter-clockwise matter: counter-clockwise matter: counter-clockwise Credit: G. Wong, B. Prather, C. Gammie (Illinois) Credit: Dom Pesce (Paper VI) Credit: Dom Pesce diameter and uncertainty (Paper VI) Credit: Dom Pesce Image (Paper VI) domain Credit: Dom Pesce Image (Paper VI) domain Geometric Simulatio models ns*