Presentation of the article "Questionable black hole"
French translation:
Doubts about the existence of black holes.
To directly access the scientific article
Authors:
Jean-Pierre Petit, Observatoire de Marseille Pierre Midy, CRI d'Orsay.
This work represents the culmination of ten years of effort. For thirty years, astrophysicists have only one word on their lips: "black holes". The word fascinates the general public. Many books have been written about the subject. Yet, observational confirmations are lacking: black holes "shine by their absence". However, we know that the cosmos is vast. Our galaxy alone contains at least 100 to 200 billion stars.
The existence of certain objects has been revealed by observation, such as quasars, for example. We now know of more than four thousand. This does not mean that we know exactly what these objects are, how they form, how they evolve, or what their lifespan is. In fact, we know nothing about them. They are simply catalogued, like the "nebulae" of the time of the astronomer Messier.
Apparently, some quasars are located at the center of galaxies with a galactic shape. These galaxies therefore have an "active nucleus", which means everything and nothing at the same time, since we know nothing about the nature of this activity, for example, what is the source of energy.
Contemporary astrophysics seems to be satisfied with little. To the question
- What is a quasar?
The astrophysicist will answer:
- It is the nucleus of an active galaxy.
And to the question:
- What is an active galaxy?
He will answer:
- It is a galaxy that has a quasar at its center.
More recently, a few years ago, "gamma-ray bursts" were discovered, one per day. The magazine Ciel et Espace once had on its cover "Gamma-ray bursts: an enigma finally solved". The answer in the columns of the newspaper: they had just located a small bright spot in place of a gamma-ray burst that had just been detected. Therefore, to solve an enigma means to know that the areas of the sky that emit these bursts also emit light...
Isn't that a bit... meager?
Conversely, there are other objects whose existence was conjectured, often with considerable precision, even before they were observed. The classic example is the supernova, described as early as 1931 by the American (Swiss-born) astrophysicist Fritz Zwicky, during a famous lecture at Caltech, USA. Zwicky explained at the time that stars sufficiently massive, whose mass would exceed, say, twenty solar masses, should have a paroxysmal end, with a rapid rise in a few days, the entire phenomenon lasting about twenty days. It was a remarkable prediction, although it was not taken seriously at the time. But Zwicky, persistent, discovered the first supernovae. Several hundred are currently recorded. The same goes for neutron stars, identified later as pulsars (rotating neutron stars) and white dwarfs. Again, the menagerie, the species counts several hundred identified individuals.
The black hole was proposed as an answer to a problem: the fate of a neutron star exceeding a certain "critical mass". These properly identified neutron stars would resemble huge atomic nuclei, without protons. Why are these objects composed solely of neutrons?
It is considered that the neutron star is what remains of the iron core of a massive star after it has exploded. A massive star is a star in which many types of fusion reactions occur during its history. It ends up producing iron, which can no longer undergo any exo-energetic fusion reaction. This iron, heavy, falls to the center of the star, like ash in a fireplace. When the star suddenly runs out of fusion fuel (something Zwicky had understood), it collapses on itself at 80,000 kilometers per second (approximately a few kilometers per second, of course). As it falls on the iron core, this gas is strongly compressed. Not only does it bounce off it, but during the passage, numerous fusion reactions occur, which no longer need to be exo-energetic, since the energy now comes from the abrupt contraction of the star on itself. All possible and imaginable nuclear species are then created, including many radioactive atoms with very varied lifetimes. We know that in 1987, the observation of the explosion of the star Sanduleak, in the Magellanic Cloud, provided a definitive confirmation of the existence of such phenomena (only 150,000 light-years away).
The phenomenon completely crushes the iron core, breaking up its atoms. It is then so compressed on itself that the electrons no longer have enough space to move between the nucleons. Trapped, they combine with protons to give neutrons and neutrinos.
Normally, when a gas is compressed, a phenomenon called pressure opposes this compression. This also applies to a liquid or a solid (everything is compressible). This is what happens, for example, when a young star is born. The protostar is a mass of gas that compresses on itself. But it heats up and the pressure force limits its contraction. It is a poor radiator and will have to lose energy by radiation (infrared) before it can compress sufficiently to become a real star. Unless its mass is insufficient, in which case it will become "a large Jupiter" (this giant planet continues to radiate more energy than it receives from the Sun, but will never become a star).
When the supernova explosion compresses the iron core, it emits a fantastic amount of ... neutrinos. At this point, the scenario changes completely: the radiative cooling is instant, since the neutrinos escape easily. Therefore, no counter-pressure force. The iron fragment is crushed lamentably. What remains is a pile of neutrons, packed together, like Japanese in their metro during rush hour.
Why a critical mass? Because neutrons cannot withstand a pressure higher than a maximum value. Like electric bulbs stacked in a mine shaft. Beyond a certain height of bulbs, the glass breaks and a cloud of broken glass collapses to the bottom of the shaft.
When a neutron star has a mass exceeding a little more than two times the mass of the Sun, its pressure at the core becomes too strong. The neutrons can no longer support it. Then it is supposed to collapse on itself without any known physical phenomenon being able to counteract this collapse, this "gravitational collapse". A frightening prospect for a physicist.
Even before it collapses, a neutron star is "relativistic", in contrast to a "Newtonian object". This is reflected in the shape of the trajectories of "test particles" nearby (any mass m, an atom, for example). We know that the phenomenon of space-time curvature causes the precession of Mercury's elliptical orbit. But this precession is minimal. However, the following drawing, extracted from computer calculations, shows the strong precession of a quasi-elliptical trajectory aut...