Image 1 Caption: M87 (NGC 4486) in the Virgo Cluster (near the center of mass???) in constellation Virgo.

M87 is cD or giant elliptical galaxy with relativistic jet that expands into the lobe (77 kpc in length) seen in Image 1.

Image 1 is a collage of true-color visible light and, to emphasize the jet-produced lobe, some other electromagnetic radiation (EMR) from some other electromagnetic spectrum band maybe ultraviolet or radio---or so believes yours truly---the original caption did NOT fully elucidate. The lobe is visible in visible light, but NOT prominently---or so believes yours truly. See Hubblesite: Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87 for some elucidation.

Features:

1. Hubble type: E0-1, pec where 0-1 means intermediate/uncertain between 0 and 1 "pec" stands for peculiar.

2. Distance: 16.40(50) Mpc = 53.5(1.63) (Mly). Lookback time: ∼ 50 Myr.

   For comparison, note that the Andromeda galaxy (M31, NGC 224) (the closest non-dwarf galaxy) is at 0.778(17) Mpc = 2.54(11) Mly.

3. Heliocentric radial velocity: 1307(7) km/s. The heliocentric radial velocity is the sum of the recession velocity due to the expansion of the universe and the peculiar velocity which is a velocity relative to the inertial frame that participates in the mean expansion of the universe at the location of M87.

4. The total redshift = 0.004360(22) which is the sum of the cosmological redshift z and the Doppler effect due to the peculiar velocity.

   Note the value 0.004360(22) << 0.5, and so M87 is well inside the local universe.

5. The luminous matter has mass of about 2.4*10**12 M_☉. The total mass including dark matter is estimated to be about 1.5*10**13 M_☉ (see Wikipedia: M87: Properties).

6. The brightness radius of M87 by some definition is ∼ 40 kpc (see Wikipedia: M87: Properties).

   However, the galactic halo has radius of maybe 150 kpc or more. It is always hard to tell how far the gravitational well (essentially the total galactic halo) of galaxy extends (particularly in dark matter) since you run out of tracers: e.g., very bright stars and globular clusters.

7. Globular cluster population: ∼ 12,000. Many of the pinpricks of light clustered around M87 are globular clusters although knowing which are globular clusters for sure requires an analysis.

   The Milky Way has 150 known globular clusters with maybe 10 to 20 more to be discovered (see Wikipedia: Globular cluster)

8. The relativistic jet extends outward from the core to 1.5 kpc and then extends into the lobe of matter seen in Image 1.

   The lobe extends to out to 77 kpc.

   The relativistic jet is plasma gas with the cosmic composition with metallicity somewhat uncertain???.

   The relativistic jet originates in and is perpendicular to an accretion disk orbiting the M87* (see M87 Supermassive Black Hole First Image below).

   There is evidence for a counter relativistic jet in the opposite direction, but it is hard detect (see Wikipedia: M87: Jet).

   We have dicussed in the preamble the probable collage nature of Image 1.

Image 2 Caption: Behold the black hole: M87 supermassive black hole (M87*)---which is near the center of mass of giant elliptical M87 (see Wikipedia: M87: Supermassive black hole (M87*)). This is M87 Supermassive Black Hole First Image: announcement 2019 Apr10.

Features:

1. Image 2 is taken in the radio band 0.1 cm -- 10**5 km, and so is false color.

2. Image 2 was obtained by the Event Horizon Telescope collaboration (EHT) (2006--).

   EHT has also imaged the Galactic center black hole called Sagittarius A* (Sgr A*). That image will be released in the future (see Time Magazine, 2019 Apr10).

3. EHT uses Very-long-baseline interferometry (VLBI) to obtain high resolution. The baseline that EHT uses is comparable to the Earth's diameter by using radio telescopes located widely spaced over the Earth. Constructing an accurate image from the data is a major task in data analysis and took the EHT collaboration about a year.

4. If yours truly is interpreting the image of the M87* correctly, the dark central region contains the event horizon (but does NOT exactly map out the event horizon) and the surrounding bright ring is the observed accretion disk seen somewhat close to face-on and which has diameter ∼ 1200 AU. The unobserved accretion disk may be much larger.

   In fact, for an isolated black hole you do NOT see the event horizon, but rather you see the black hole shadow---the region from which light CANNOT reach the distant observer. For an explication of black hole shadow, see Black hole file: black_hole_shadow.html. Since M87* is a Kerr black hole (a non-ideal one), it would have slightly different formula for its black hole shadow than that of a Schwarzschild black holes.

   The emission from the accretion disk surrounding M87* partially fills in its black hole shadow in a complicated way.

5. In fact, Image 2 looks very much what one would naively expect a black hole surrounded by an accretion disk seen relatively close to face-on to look like. However, naive interpretations can be mislead.

   The confirmation that we are seeing a black hole surrounded by an accretion disk is the fact that Image 2 matches computer simulations of what the M87* should look like. Thus, Image 2 confirms to near-certainty the existence of the event horizon which is the defining characteristic of black holes, but it is NOT a simple direct confirmation.

6. Note we do NOT see the relativistic bipolar jets that probably are coming roughly to us and away from us. The radio image is somehow insensitive to them at least in an obvious way.

   Note also that the accretion disk probably has temperature of order a few times 10**6 K, and so probably radiates much more strongly in the X-ray band (fiducial range 0.1--100 Å) (see wien_law.html) than in the radio band 0.1 cm -- 10**5 km, but we can only resolve M87* in the radio band.

7. The M87* has mass = 6.5(9)*10**9 M_☉. This is one of largest masses for a SMBH.

8. From the Schwarzschild radius formula R_sch = 2GM/c**2 (see below), we estimate that the event horizon radius to be ∼ 140 AU and the diameter to be ∼ 280 AU.

   The Schwarzschild radius formula applies to non-rotating black holes and one should use the formula for the Kerr-Schwarzschild radius for rotating black holes since the M87* is rotating. However, for crude estimates the Schwarzschild radius formula is probably adequate.

9. For online announcement articles for the M87* image, see BBC News, 2019 Apr10, Guardian, 2019 Apr10, SciAm, 2019 Apr10, Science magazine, 2019 Apr18 (best one), Time Magazine, 2019 Apr10.

10. For reference, the formulae for the Schwarzschild radius are given in the insert below (local link / general link: black_hole_schwarzschild_radius_formulae.html).
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11. Keywords relevant to black holes are given at Black hole keywords below (local link / general link: black_hole_keywords.html):
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Images:

1. Credit/Permission: NASA/HST, before or circa 2009 / Public domain.
   Image link: Wikipedia: File:Messier 87 Hubble WikiSky.jpg.
   
2. Credit/Permission: © Event Horizon Telescope (EHT) 2019 (uploaded to Wikimedia Commons by User:Theklan, 2019) / CC BY-SA 4.0.
   Image link: Wikimedia Commons: File:Black hole - Messier 87.jpg.