The first image of a black hole: what is fitting so far

L/upd: 2019/05/25
In the article is studied the splendid outcome achieved by the Event Horizon Telescope team and made public on April 10, 2019, through the release of the by now famous pic of M87* black hole, as well as through the release of a series of related articles. With regard to them we analyze a few features concerning our theory of the holostar, showing its relativistic nature of Kerr object.

As summarized briefly in my previous article, we finally succeeded in direct observing what we can define the shadow of the event horizon of a black hole, to be exact of the gigantic and supermassive black hole M87* (to be read M87 star), which is located at the center of the namesake elliptical galaxy M87 (or Virgo A: it is the largest galaxy of our reference supercluster, the Virgo one). The relative pic went all over the world and has rightly been named the pic of the century. The team of scientists of the EHT (Event Horizon Telescope) project, announced this epochal success on April 10, 2019, at once with the release of the pic which we all have seen, and with the publication of a remarkable series of highly detailed scientific articles.
So, the April 10 event (which surprised everyone in this respect) did not refer to Sagittarius A*, the central black hole of our galaxy. Instead, the lesser-known previous image, released at the beginning of 2019, was referred to Sgr A* (real pic too, about which, during the present by now long lack of new feedback, we discuss within the mentioned article, giving also useful links).

Observations made known within the April 10th event not only led to the first direct and effective pic of the shadow of the event horizon of a black hole, but also to an estimation of M87*’s mass, equal to about 6,5 billion solar masses (over 1,500 times Sagittarius A*’s mass).
Rumors consequently say that M87* was chosen by the EHT team for its mass (mass, being directly proportional, we recall, to the Schwarzschild radius, for its part proportionate to the shadow we all have seen in the pic, gives us to detect something over 1,500 times larger – see Footnote 1). However, this one cannot be sufficient as a reason, since M87* is almost 2,000 times farther than Sgr A* (almost 60 million light years compared to just over 26,000 of Sgr A*).
So, the most plausible reason is that the M87 galaxy is known to show a jet of plasma, coming out from its galactic center, and so powerful that it extends for at least 5,000 light years. M87* was therefore chosen because it was known at the outset that this monstrous black hole shows an enormous emission of matter (expelled at relativistic speed precisely as a result of the “congestion” or “funnel” created by the circular crowded fall of so much other matter towards the hole, nearby its horizon), while Sgr A* does not manifest such a characteristic at all.
Only an accretion disk formed by so much matter in circular falling (or better in spiral falling), matter accelerated up to a speed enough to let it emit powerful radiation, could provide to a viewer, here from the Earth, that dense ring of light, with respect to which the large event horizon can emerge, by contrast, as a background or a shadow.

In fact, if we start from the assumption that every black hole is surrounded by an event horizon that doesn’t let any light radiation escape, only this boundary light can give us an image that allows us to glimpse the black hole as a relative central absence of light. Without a significant accretion disk, any black hole, being surrounded by its own insurmountable horizon, remains totally invisible (that is totally black).
Let’s use a comparison relative to the Sun and its corona (area surrounding our star and much warmer than the solar surface). If we take an x-ray picture, the sun appears black and the corona appears bright; so, if I had only x-rays available to me, I could see the surface of the star only by contrast with its corona. And, if I were looking for stars to photograph, I would prefer those with a corona, like the Sun.
But what happens if I have not only x-rays available to me, but also visible light? If I detect through the latter, it happens that I see the Sun, that is its surface, without being dazzled by the corona.
Something like this has happened, and I suppose it’s still happening on EHT’s computer desktops, about Sagittarius A*. Still see my article The centre of our galaxy: a holostar.

What we all see in the pic released on April 10, 2019, must therefore be properly interpreted.

A) Einstein’s General Relativity is confirmed in every aspect, as well as his predictions, both regarding the Schwarzschild metric, relative to black holes, and the application of the latter, as seems to be the universal case , to rotating black holes, through the more complex Kerr metric.
B) We cannot however state that we are looking at the shadow of an event horizon.
Let’s see below why.

Among the long and detailed articles published by the Event Horizon Telescope team on April 10th, we are interested in the combined conclusions of the following two:
https://iopscience.iop.org/article/10.3847/2041-8213/ab0ec7/meta
https://iopscience.iop.org/article/10.3847/2041-8213/ab1141/meta
If read carefully, they tell us that the shadow shows emissions “at least 10 times lower” than the average of the “brighter” area of the photo. If you consider the power of the basic emissive phenomenon, which is the one that gives us the boundary and allows us to see the shadow, even if they were a thousand or ten thousand times lower, such emissions of the shadow area would still represent something extremely remarkable, given the incredible gravitational redshift by which the same light would be marked in order to escape from such a massive body/surface. It is precisely the equivalent case of what we were saying above about the solar surface and the corona.
The shadow area has a radius of approximately 2.6 times the Schwarzschild radius. This is consistent with the predictions of the Kerr relativistic metric; however it is not useless to point out such aspect here. In fact, as a consequence, the shadow area is not at all M87*’s event horizon, in contrast to what even serious but perhaps hasty commentators and communicators have made their readers believe.

The EHT team of scientists, while stating that its result is absolutely consistent with Kerr’s metric, says that there are at least two other solutions, in addition to the one that foresees an event horizon, that respect the Kerr metric predictions (without nevertheless foreseeing a horizon), and that would give an equivalent result (that is the same image); I quote from the first of the linked articles:
“Our constraints on deviations from the Kerr geometry rely only on the validity of the equivalence principle and are agnostic about the underlying theory of gravity, but can be used to measure, with ever improved precision, the parameters of the background metric”. After excluding compact-objects theories that do not respect the Kerr metric, among those theories that instead respect it “other compact-object candidates need to be analyzed with more care. Boson stars are an example of compact objects having circular photon orbits but without a surface or an event horizon”. Also “gravastars provide examples of compact objects having unstable photon orbits and a hard surface, but not an event horizon”.
As known, the model proposed by us, i.e. the holostar, is not based on a modification of General Relativity and does not reject the Kerr metric at all, but it is based rather on the emergence of the equivalence principle from inertial dynamics, and, in the more specific case of the holostar, on the consequent space precession. The model does not foresee an event horizon, and outlines something that only apparently can be defined as a surface.
Let’s specify better the reason why we are talking about the last thing. The second of linked articles titles at point 9.4: “Evidence for a Horizon“. By reading it we understand that it is showing the absence of evidence of any radiation (which should be detected at least on the near infrared) due to the thermal impact of matter with a surface, feature that would differentiate it from the continuum of the synchrotron radiation of a beam of accelerated falling matter (the radio waves we have talked about so far).
Now, in the holostar model no particular impact is expected, because the type of movement (and of spiral fall) that both the matter along the accretion disk and the matter on the “surface” of the holostar are doing, are nothing more that the same identical movement, if we consider them on the respective four-dimensional (or spatial-temporal) scale, that is if we keep in our mind the role of time dilation. Each circular sub-level reproduces, on its scale, exactly the dynamics that we observe on a wider level, for example outside the disk: it’s an infinite spiral movement, always equal to itself, and only temporal distortion makes it appear to us as circularly flattened, on the “surface”of the holostar. What matter was doing while getting to that “surface” (in an increasingly collimated way), matter is just doing so even later, but more and more on a different time scale. The shadow zone depends on the enormous gravitational redshift, which can only lead to the detection of ever greater wavelengths, i.e. towards very low frequency radio emissions, and certainly not towards near infrared ones.
Since the free fall motion of the matter of the disk is time-verse, we can say that the matter that we see so bright in the pic is already part of the holostar: it is already part of its verse of common fall, it is already more and more collimating own trajectories and it is already conditioning the radius of the superstar, so that disk and “surface”, in the respective proportions (like the apple and the Earth), are meeting “half way”, going through portions of spiral that are exactly replicated on each zoom of the chosen space-time scale, up to the maximum, that is up to the scale of the “surface” itself, the scale of maximum time dilation for trajectories that can be physically crossed by matter (see Fn 2).

The shadow area (with the strong reduction of emissions, on the chosen radio frequency, that characterizes it) as well as its size together with its respect of the Kerr relativistic metric, all this does not, in any way, question the black hole model described by the holostar.
Under certain characteristics, in fact, the holostar cannot be defined as a compact object, but rather, in a more relativistic sense, a Kerr object. Its density, for a remote external observer, is obtained from the corresponding Schwarzschild density multiplied by R/3 (the ratio volume/surface in a sphere). Proper density is much lower, and it is compatible, in the case of M87*, with the presence of atomic ions.

Another particular feature pointed out in the second article we linked above, feature which is very interesting given the main topic of our articles, is that, like any study for some years now, and for any physical scope it has been conducted, even the one of the EHT team places very low upper limits on the possible presence of a dark matter peak, which instead would be justified, and expected too, given the enormous mass of M87*.

Footnotes:
1) The Schwarzschild radius is the theoretical minimum radius of the sphere within which all the mass of a body should be compressed in order to have an escape velocity on body’s surface equal to or greater than the speed of light; if the body proceeds in its collapse, the Schwarzschild radius remains the radius of the sphere that delimits the event horizon, since no information can come out from within that sphere.
2) For a more detailed and reasoned exposition of the last two paragraphs, refer every time to the more complete article: The centre of our galaxy: a holostar.

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