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In the recently released photo of a black hole shown above, which was created by using data from EHT, why is the lower region brighter than the one above? Is it because of the rotation of the accretion disk? Also what is the orientation of the accretion disk? Are we looking at it head on?

No, you aren't seeing the shape of the accretion disk and its plane is aligned with main N-S asymmetry. The reason for this asymmetry is almost entirely due to Doppler beaming and boosting of radiation arising in matter travelling at relativistic speeds. This in turn is almost entirely controlled by the orientation of the black hole spin. The black hole sweeps up material and magnetic fields almost irrespective of the orientation of any accretion disk.

The pictures below from the fifth event horizon telescope paper makes things clear.

The black arrow indicates the direction of black hole spin. The blue arrow indicates the initial rotation of the accretion flow. The jet of M87 is more or less East-West (projected onto the page), but the right hand side is pointing towards the Earth. It is assumed that the spin vector of the black hole is aligned (or anti-aligned) with this.

The two left hand plots show agreement with the observations. What they have in common is that the black hole spin vector is into the page (anti-aligned with the jet). Gas is forced to rotate in the same way and results in projected relativistic motion towards us south of the black hole and away from us north of the black hole. Doppler boosting and beaming does the rest.

As the paper says:

the location of the peak flux in the ring is controlled by the black hole spin: it always lies roughly 90 degrees counterclockwise from the projection of the spin vector on the sky.

In the paper: "First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring", (Apr 10 2019), by The Event Horizon Telescope Collaboration, Kazunori Akiyama, Antxon Alberdi, Walter Alef, Keiichi Asada, Rebecca Azulay, Anne-Kathrin Baczko, David Ball, Mislav Baloković, John Barrett, et al., in one of several papers recently published they explain:

(4) The ring is brighter in the south than the north. This can be explained by a combination of motion in the source and Doppler beaming. As a simple example we consider a luminous, optically thin ring rotating with speed v and an angular momentum vector inclined at a viewing angle i > 0° to the line of sight. Then the approaching side of the ring is Doppler boosted, and the receding side is Doppler dimmed, producing a surface brightness contrast of order unity if v is relativistic. The approaching side of the large-scale jet in M87 is oriented west–northwest (position angle $mathrmPAapprox 288^circ ;$ in Paper VI this is called $mathrmPA_mathrmFJ$), or to the right and slightly up in the image.

Figure 5 from that paper is included in Rob Jeffries answer.

The conclusion that they reach, in part, is:

"... The results of this comparison are consistent with the hypothesis that the compact 1.3 mm emission in M87 arises within a few $r_rmg$ of a Kerr black hole, and that the ring-like structure of the image is generated by strong gravitational lensing and Doppler beaming. The models predict that the asymmetry of the image depends on the sense of black hole spin. If this interpretation is accurate, then the spin vector of the black hole in M87 points away from Earth (the black hole spins clockwise on the sky). The models also predict that there is a strong energy flux directed away from the poles of the black hole, and that this energy flux is electromagnetically dominated. If the models are correct, then the central engine for the M87 jet is powered by the electromagnetic extraction of free energy associated with black hole spin via the Blandford–Znajek process.".

First Draft:

The article: "Ergoregion instability of exotic compact objects: electromagnetic and gravitational perturbations and the role of absorption", (Feb 15 2019), by Elisa Maggio, Vitor Cardoso, Sam R. Dolan, and Paolo Pani explains that this is due to rotational superradiance on page 10:

"... the instability can be understood in terms of waves trapped within the photon-sphere barrier and amplified by superradiant scattering$^[43]$
[43] R. Brito, V. Cardoso, and P. Pani, Lect. Notes Phys. 906, pp.1 (2015), arXiv:1501.06570.

In the article "Superradiance", (above) while considerably longer, maybe much more approachable. On page 38 where they explain the Penrose Process they offer a diagram which probably makes the understanding of this easier:

"Figure 7: Pictorial view of the original Penrose processes. A particle with energy E$_0$ decays inside the ergosphere into two particles, one with negative energy E$_2$ < 0 which falls into the BH, while the second particle escapes to infinity with an energy higher than the original particle, E$_1$ > E$_0$.".

From page 41:

"Figure 8: The carousel analogy of the Penrose process. A body falls nearly from rest into a rotating cylinder, whose surface is sprayed with glue. At the surface the body is forced to co-rotate with the cylinder (analog therefore of the BH ergosphere, the surface beyond which no observer can remain stationary with respect to infinity). The negative energy states of the ergoregion are played by the potential energy associated with the sticky surface. If now half
the object (in reddish) is detached from the first half (yellowish), it will reach infinity with more (kinetic) energy than it had initially, extracting rotational energy out of the system.".

A further more complicated model, believed to be beyond what was asked, from page 46:

"Figure 9: Pictorial view of the different collisional Penrose processes. Left: initial particleswith ingoing radial momentum (p$^r
_1$ < 0 and p$^r_2$ < 0). Particle 3 has initial ingoing radial
momentum, but eventually finds a turning point and escapes to infinity. The maximum efficiency for this was shown to be quite modest η ∼ 1.5 $^[168, 169, 170, 171]$. Right: initial particles with p$^r_1$ > 0 and p$^r_2$ < 0. In this case particle 1 must have p$^r_1$ > 0 inside the ergosphere. For this process the efficiency can be unbound for extremal BHs $^[172, 173]$.

[168] T. Piran and J. Shaham, “Upper Bounds on Collisional Penrose Processes Near Rotating Black Hole Horizons,” Phys.Rev. D16 (1977) 1615–1635.

[169] T. Harada, H. Nemoto, and U. Miyamoto, “Upper limits of particle emission from high-energy collision and reaction near a maximally rotating Kerr black hole,” Phys.Rev. D86 (2012) 024027, arXiv:1205.7088 [gr-qc].

[170] M. Bejger, T. Piran, M. Abramowicz, and F. Hakanson, “Collisional Penrose process near the horizon of extreme Kerr black holes,” Phys.Rev.Lett. 109 (2012) 121101, arXiv:1205.4350 [astro-ph.HE].

[171] O. Zaslavskii, “On energetics of particle collisions near black holes: BSW effect versus Penrose process,” Phys.Rev. D86 (2012) 084030, arXiv:1205.4410 [gr-qc].

[172] J. D. Schnittman, “A revised upper limit to energy extraction from a Kerr black hole,” arXiv:1410.6446 [astro-ph.HE].

[173] E. Berti, R. Brito, and V. Cardoso, “Ultra-high-energy debris from the collisional Penrose process,” arXiv:1410.8534 [gr-qc].

There is a summary on page 170 (nowhere near the end of the paper) which explains:

"In gravitational theories, superradiance is intimately connected to tidal acceleration, even at Newtonian level. Relativistic gravitational theories predict the existence of BHs, gravitational vacuum solutions whose event horizon behaves as a one-way viscous membrane. This allows superradiance to occur in BH spacetimes, and to extract energy from vacuum even at the classical level. When semiclassical effects are taken into account, superradiance occurs
also in static configurations, as in the case of Hawking radiation from a Schwarzschild BH.

The efficiency of superradiant scattering of GWs by a spinning (Kerr) BH can be larger than 100% and this phenomenon is deeply connected to other important mechanisms associated to spinning compact objects, such as the Penrose process, the ergoregion instability, the Blandford-Znajek effect, and the CFS instability. Rotational superradiance might be challenging to observe in the laboratory, but its BH counterpart is associated with a number
of interesting effects and instabilities, which may leave an observational imprint. We have presented a unified treatment of BH superradiant phenomena including charged BHs, higher dimensions, nonasymptotically flat spacetimes, analog models of gravity and theories beyond GR.".

I believe we are seeing one of the effects of the accretion disk rotating at very high speeds. This is called relativistic beaming, and it occurs because particles (in this case matter in the accretion disk) that are travelling at relativistic speeds (say, upwards of .2c), tend to preferentially emit their radiation in a cone towards the direction of motion.

This suggests that the matter at the bottom of the picture (the brightest blobs) are travelling towards us, and the darker parts are travelling away. Since the black hole tends to warp light around itself, I'm not sure from the photo of the orientation of the accretion disk.