Don't Be Deceived: There Is No Such Thing As A Photo Of A "Black Hole"

The much circulated image above - purported to be of a black hole in the center of the galaxy M87- is nothing of the sort.

As usual, the mainstream media - in an effort to grab clicks or reads- has misrepresented the recently circulated image claimed to be of a "black hole" in the Virgo galaxy M87.   Of course, this is impossible. One cannot get a photo or other image of a black hole itself.  That is invisible - or better "un-seeable" - at any wavelength, including radio..   What one has in the image, is not the black hole per se, but its event horizon which is somewhat different.

TO fix ideas, the image in question was captured by a global network of 8 radio telescopes, appropriately called the "Event Horizon Telescope" or  EHT.  The effective aperture essentially formed one giant radio telescope "dish" stretching from Spain in the north to Antarctica in the south.  The mass associated with the M87 black hole  is the equivalent of 6.5 billion Suns.  That implies its event horizon would have quite a significant scale.

What is this event horizon? It is basically an "infinite redshift" surface from which no signal, no light or radiation of any kind, can escape. The key cut off occurs at what's called the Schwarzschild radius or:

R(s) = 2GM/c²

where G is the Newtonian gravitational constant, c is the speed of light in vacuo, and M is the gravitating mass.   In this case - and for a "Schwarzschild solution" all observers will agree that the surface r = R(s) is an "event horizon".  It defines the boundary or edge at which all outgoing signals are cut off so they cannot have any external manifestation - whether as radio waves or optical ones.  

A good algebraic way to show how signals are cut off  at the r = R(s) Schwarzschild event horizon has been given by Ohanian and Ruffini ('Gravitation & Spacetime', p. 445).  Thus, one considers a radio signal propagating in the radial or r direction. Then the velocity of this signal, say with respect to r, t (radius, time) coordinates can be expressed:

dr/ dt =  + {1  -   r/ R(s)}

Now note what happens when the signal approaches the critical boundary, i.e. r = R(s).  Then we see:

dr/ dt =   + {1  -   r/ R(s)}   =   + {1  -   R(s) / R(s)} =  1 - 1   =  0

The graph shown in the same text (op. cit, p. 446, Fig. 8.3) can also help to illuminate the situation vis-a-vis interior and exterior to the black hole.   We see that in the exterior of the black hole (r > R(s))  the axis of the light cones is parallel to the time (t) axis.  But in the interior of the black hole (r < R(s)) the axis of the light cones is parallel to the r- axis.  The reversal is a direct result of r being a "time-like coordinate" and t space -like.   The existence of an event horizon at r = R(s) is "obvious from the inspection of the light cones in Fig. 8.3."  as noted by the authors. (Ibid.)  Hence, any kind of signal must travel in a spacetime direction that lies within a light cone. And "since the light cones in the black hole region are oriented toward r = 0 any signal in this region is unavoidably pulled toward decreasing values of r."

Thus, all such signals can never leave the black hole, hence we cannot obtain them from outside . This is no matter how many radio telescopes we assemble in a global network, as in the case of the EHT.

Bottom line, the EHT captured exactly what its title designated: the event horizon of a monster black hole in galaxy M87.  But not the black hole itself! Think of what we are seeing as an impenetrable 'cosmic curtain' impeding our accessing the actual black hole.

'Interstellar' - A Film Not To Miss! (Warning: Some Spoilers!)

In some early reviews the new science fiction film 'Interstellar' has been compared to Stanley Kubrick's '2001- A Space Odyssey' which is not too far off. As in that 1968 film there are segments of this one that leave the viewer spellbound and often in wonderment (and mystery) at being enfolded in an almost metaphysical realm (especially one sequence where the astronaut 'Coop' finds himself inside a hyper-dimensional tesseract.)

The film, directed by Christopher Nolan, stars Matthew McConaughey, Anne Hathaway, Jessica Chastain, and Michael Caine. It is basically about a team of space travelers who travel through a wormhole in search of a new habitable planet. The opening scenes (roughly 20 minutes) show why. The Earth is now ravaged by monstrous dust storms and all its grain crops are dying out or have already become extinct because of a blight.

The scenes are realistic as we see people covered in dust, which gets into every nook and cranny, and also invades living spaces, smothers tables, linens, and incites chronic coughs. One of the most upsetting scenes occurs during a baseball game when a giant Haboob bears down and all the spectators must run for cover.

We don't know how the planet came to be this way or what caused the blight affecting the crops, but it doesn't take a lot of imagination to think that it has been spawned from radical climate change, at a time when even the seasons have stopped. The film cites the population being "9 billion" which would put the year at about 2040. (David Suzuki's projection for the first "year of no seasons" - marking the beginning of the runaway greenhouse effect).

Ultimately, the has-been astronaut Coop gets a new lease on his astronaut life when he ends up locating (using Morse code decoding of a gravimetric signal in his home) the only existing NASA facility. It is surrounded by barbed wire and kept ultra-secret, because as Prof. Brand (Michael Caine's character) tells him, you can't be spending billions on space ships when the world is starving and the only surviving grain crop is corn - which is also on its way out.

In this hidden enclave, Coop learns that 12 earlier "Lazarus" missions have been sent out - using a wormhole discovered near Saturn. Some have sent back signals indicating planets that might be able to support human life. These planets are all located in another galaxy, so clearly conventional rocket power would never be adequate to reach them. Thus has Coop been recruited to pilot Endurance, an experimental spacecraft, to follow the Lazarus Missions, through the wormhole to survey potential planets' long-term habitability. (By the time of Coop's launch the data from the Lazarus Mission has given NASA three potentially habitable planets: Miller, Edmunds, and Mann, named after the astronauts who carried out the surveys.)

The Endurance trek to the vicinity of Saturn alone takes two years, requiring all the astronauts to enter a hibernation condition to save oxygen. The wormhole itself is really a sphere, and by now the astronauts are awake as Coop enters through it - with incredible cgi graphics images depicting the transition.

The remainder of the film depicts astronauts Coop, Brand (Prof. Brand's daughter, played by Anne Hathaway) and Bromley trying their best to at least get to one more habitable world - after a disaster befalls them on Miller's planet (where one hour equals 7 years because of the gravitational slowing of time) and the craft is upended by a monstrous tidal wave some half- mile high, killing one of their original team.

A key segment, which I won't go into as it gives too much away, is the plan to pilot Endurance to a "gentle" black hole's ergosphere, jettison an AI designed robot into the event horizon and have it send data regarding the singularity within the black hole back to Earth.

What impressed me the most about the film is how realistically it depicted what an interstellar voyage would really be like, even assisted by a convenient wormhole and relativity. Bottom line: No picnic! Unlike most such portrayals of locating an alter-Earth (cf. the TV series 'Earth Two') there are no flora -abundant, hospitable planets, but mostly barren and hostile - with t he possible exception of "Edmund's planet".  We understand from the get- go life will largely be a matter of survival not simply landing in 'paradise' in the midst of avocado and mango trees.

One other point: Some reviews, for example in The Financial Times, have complained about needing "a baccalaureate degree in astrophysics" to understand the scientific interjections "about once every fifteen minutes". But first, the references were not that frequent (more like once every half hour) and second, they were totally within the grasp of a reasonably scientifically literate person - say who has read Hawking's 'Brief History of Time' or similar works.  Nor were any equations actually used in the explanations, we only see them occasionally when the blackboard is shown in Prof. Brand's (the elder's) office. All the equations are based on actual astrophysical theory and were pre-prepared by Kip Thorne of Caltech, one of the pre-eminent researchers of black holes and one of the film advisors.

By all means, if you have the chance to see this film, see it. It offers hope that one day, indeed, we may actually transfer the vision of settling other words to really doing so - as opposed to waiting for a monster, planet-killing asteroid (or something else) to take us out.