Stars dancing with black holes in the Milky Way

Just recently a joint press release from European Southern Observatory (ESO) and theEvent Horizon Telescope (EHT) has announced that on May 12, 2022 there will be an online conference, at 3:00 p.m. in France, which will report new results and in particular about the supermassive black hole of the Milky Way. It contains just over 4 million masses solar and as for all the others black holes supermassive, we do not know how it was formed. We are also not certain that thestar compact flushed out to the center of our Galaxy with this mass is indeed a black hole even if it seems very probable.

On the other hand, we know many other stars of this kind, but much less massive, which are also considered to be black holes in the Milky Way. Their origin is much less mysterious since they are so-called stellar-mass black holes generally containing between 5 and 15 times the mass of the Sun.

Let’s make a few reminders about these stellar black holes taking up what Futura had explained about them in a previous article.

When a star more than 8 solar masses is gravitationally collapsing after exhausting its nuclear fuel and still contains at least several solar masses despite the winds end-of-life violent stellar particles that ejected a significant part of its initial mass and especially its explosion in supernova SN II at that time, thespace-time inside this star becomes dynamic and looks very similar to that of theUniverse observable during big Bang. The big difference being of course that in the first case the space is in contraction whereas in the second it is in expansion.

L’collapse of the star will sometimes lead its matter to go under the surface of theevent horizon black hole of mass equivalent to that of the final star, which means in fact that the star becomes a black hole. In the early 1960s, two teams of researchers, American and Russian, showed on computer that the formation of this horizon was entirely credible based solely on the laws of physical known at the time. On the contrary, these numerical simulations and other analytical calculations didn’t really tell what happened at the end of the gravitational collapse, below the event horizon.

Black holes, laboratories for fundamental physics

It’s the Nobel Prize Roger Penrose who will finally demonstrate in 1965 that if we believe in equations of the theory of general relativitya point of infinite density and curvature of space-time which is just as much, must appear a singularity of space-time, and this contrary to the calculations of two physicists legendary Russians who claimed the opposite, Evgeny Lifshitz and Isaak Khalatnikov.

However, quantum effects and new physics of matter and forces were to intervene and were likely to change the situation. However, just as the collapse of a star into a black hole is in a way the reverse of the expansion of the observable Universe at the time of the Big Bang, a gravitational singularity must have appeared at the very beginning of the existence of the cosmos or precisely be avoided. Probably due to the laws of a quantum theory of gravitation able to describe what John Wheelerthe inventor of the word black hole, called thespace-time foam and which is the subject of the last work of Jean Pierre Luminet.

Black holes are among the most opaque objects in the Universe. Fortunately, however, they are among the most attractive, and it is by their excessive power of attraction that we can detect them. Giant black holes are the most monstrous ogres in the cosmic zoo, but they are not weapons of mass destruction. The jets of matter they produce would have helped to ignite the first stars and form the first galaxies. Hubert Reeves and Jean-Pierre Luminet, specialists in contemporary cosmology, answer all your questions. To find out more, visit the site From the big bang to the living. © ECP-YouTube Group

From the end of the 1960s, the program to be carried out to understand the origin of the Universe and to cast a new light on that of Man and its place in Nature was therefore clear, it was necessary to study the physics of black holes and understand the final state of the collapse of matter-space-timeto use the title of the famous general relativity course ofHerman Weyl.

But, as a preamble to this program, a question naturally arose. Do these black holes really exist?

A first element of response arrived during the year 1971 when observations made possible by the development of radio astronomy and X-ray astronomy began to accredit the idea that the compact star exceeding the mass limit authorized by the existence of a neutron starand who was in orbit around a blue supergiant star in the Milky Way towards the Cygnus Constellation, could be a black hole. The source X detected, and by extension the black hole and even the binary system containing it, was called Cygnus X1.

As Jean-Pierre Luminet explains in the video above, it is the X-radiation emitted by matter torn from a companion star by tidal forces and which is heated by forces of viscous friction forming an accretion disk while spiraling towards the black hole which betrays its presence. An isolated stellar black hole would not emit against any radiation, not even according to the process discovered by stephen hawking because in the current Universe it is still too cold compared to the cosmic radiation.

A zoo of stellar black holes in the Milky Way

Other candidates for the title of stellar black holes have since been discovered in the Milky Way, always flushed out by emissions of X-rays. NASA presents them to us today with a series of animations showing around twenty X-ray binary systems that host confirmed black holes. These systems are shown at the same scale but with the gears companion stars in orbit accelerated about 22,000 times. The view of each system reflects how we see it from Earth. Temperatures rise as they approach the edge of the accretion disk with consequent emissions in the visible, theultraviolet and finally X-rays.

Star colors ranging from blue-white to reddish represent temperatures 5 times hotter to 45% cooler than the surface of our Sun. In most of these systems, a flow of material from the star and torn by tidal forces forms an accretion disk around the black hole. In others, like the famous system called Cygnus X-1, the star produces a kind of strong wind of matter which is partly captured by the gravity of the black hole to form a disc there too. Accretion disks use a different color palette because they sport even higher temperatures than stars. The largest disc represented, belonging to a binary called GRS 1915, extends over a distance greater than that separating Mercury from our Sun. The black holes themselves, however, are depicted larger than they actually are using scaled spheres to reflect their masses. © NASA’s Goddard Space Flight Center and Scientific Visualization Studio

Here are some more specific examples taken from the previous video and with indications of distance to the Solar systemthe masses of black holes and companion stars, often giants which will evolve rapidly in a few million years before exploding in a supernova, which could give rise to binary black holes, but not always, already because the additional stellar corpse could be a neutron star and that the explosion could separate the two celestial bodies.

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