EinsteinEinstein did not believe in the possibility of the existence of black holes, although this was predicted by his equations of general relativity. Remarkably, he still used his theory's predictions about the propagation of light rays in a gravitational field to show that his theory was more relevant to describing the phenomena than Newton's theory. Today, members of the Event Horizon Telescope (EHT) are also studying the properties of light rays deflected by a suspected supermassive black hole at the center of the galaxy Messier 87, about 55 million miles away, about 55 million miles away.
By combining the images taken by different radio telescopes on the surface of our Blue Planet, it is actually possible to create the equivalent of an instrument the size of the Earth and thus be able to create an image of the surroundings of the suspected compact star to create a black hole at the heart of the large elliptical galaxy. This allows us to test alternatives to Einstein's relativistic theory of gravity and even question the existence of black holes. Could M87* actually be a wormhole connected to another universe? The way the light is deflected and what the resulting image looks like actually depends on the hypotheses considered.
But to move forward and perhaps get answers to these questions, we need ever more efficient instruments and ever longer observations. In 2017, a certain number of radio telescopes were mobilized to obtain a first image. In 2018, a radio telescope in Greenland entered the dance, and astrophysicists today unveil the new image taken by M87* the following year. It takes a long time to process the collected data and then start drawing conclusions for fundamental physics and astrophysics.
In addition to a new image, the members of the EHT have just published an article about their activities and findings in the famous magazine Astronomy & Astrophysics.
The film of turbulent matter around a black hole?
The main features of the 2018 image have not changed compared to 2017, especially with regard to the size of the photon ring, that bright ring surrounding a deep central depression, the “shadow of the black hole”, where its event horizon is located and the What informs us about this is the fundamental physics of the observed object (to learn more about the photonic ring, check out the excellent video below). For M87*, it remains consistent with what Einstein's equations say and with the mathematical theory of black holes they imply, laid out in the impressive paper by Nobel Prize winner in physics Subrahmanyan Chandrasekhar.
On the other hand, the peak of the ring's luminosity has shifted by about 30° compared to the 2017 images, consistent with our theoretical understanding of variability due to turbulent materials around black holes in its disk. Accretion and accretion disk. We know such a disk exists, but we don't see its inner edge in the image. We also know that there are jets of matter driven by accretion and by complex processes of relativistic magnetohydrodynamics in curved space-time (the theory of which has been studied in particular by Yvonne Choquet-Bruhat) of hot plasmas rotating around be accelerated Kerr black hole with its invisible event horizon.
In the press release introducing the new image, Dr. Keiichi Asada, a research fellow at the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan, said that “a fundamental requirement of science is to be able to reproduce the results.” Confirming the ring in a brand new data set is an important milestone for our collaboration and a strong evidence that we are observing the shadow of a black hole and the matter orbiting it.”
His colleague Rohan Dahale, a doctoral student at the Instituto de Astrofísica de Andalucía (IAA-CSIC) in Spain, adds: “To advance scientific efforts, we need to continuously improve data quality and analysis techniques.” Adding the Greenland Telescope to our network has critical gaps in our Earth-sized telescope closed. The upcoming observations in 2021, 2022 and 2024 demonstrate improvements to the network and fuel our enthusiasm to push the boundaries of black hole astrophysics.”
Dr. Britt Jeter, a postdoctoral researcher at the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan, specifies that “the most important change, namely the movement of the peak brightness around the ring, does something that we predicted when we first published the results.” Year 2019. While general relativity suggests that the size of the ring should remain fairly constant, the emission from the turbulent and disordered accretion disk around the black hole will cause the brightest part of the ring to oscillate around a common center. We can use the strength of the oscillations we see over time to test our theories about the magnetic field and plasma environment around the black hole.”
Very good explanations of what the EHT really sees with M87*. To get a reasonably accurate French translation, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then click on “Subtitles” and finally “Auto-translate”. Select “French”. © PBS Spacetime
Spectacular new images of the giant black hole M87*
Article by Laurent SaccoLaurent Sacco published on April 17, 2021
We are still in the early stages of studying and imaging supermassive black holes in detail. Currently, many researchers are focusing on the M87* galaxy and its jet of matter, combining images taken at different wavelengths.
By the early 19th century, physicists had already begun to outline the concept of a black hole and the wave theory of light with the work of Michell and Young in Britain and Laplace and Fresnel in France. Certainly none of them expected the observations made today in a field of electromagnetic waves ranging from radio photons to gamma photons, showing the shadow of the event horizon of the black hole M87* and finally the entire jet of matter rising above its accretion disk , until It leaves the huge elliptical galaxy, at the center of which is the supermassive black hole.
Over two centuries, the noosphere has made amazing advances that today allow members of the Event Horizon Telescope (EHT) collaboration to combine their radio telescope observations with those of their visible light (HubbleHubble and SwiftSwift) and ultraviolet light (Swift) colleagues. and X-rays (ChandraChandra and NuSTAR). The results are spectacular, as we can see in the video below, but also from the article that the astrophysicists have just published in The Astrophysical Journal Letters.
The work presented is in fact the result of collective reflection of humanity yesterday and today, since the data collected from late March to mid-April 2017 required the brains of 760 scientists and engineers from almost 200 institutions in 32 countries or regions. They used observatories funded by agencies and institutions around the world. Remember that the Event Horizon Telescope is a virtual telescope made using Very Long Baseline Interferometry (VLBIVLBI) that allows small instruments to be combined to obtain the equivalent of a very large instrument, in this case a radio telescope with a diameter of more than 5,000 kilometers.
Here's a dramatic zoom showing a nest of images taken by instruments that make observations at different wavelengths and resolutions, showing M87* and its jet of material. Obviously, light years means light years. © The EHT Multi-Wavelength Science Working Group; the EHT collaboration; Alma (ESO/NAOJ/NRAO); EVN; the EAVN cooperation; VLBA (NRAO); the GMVA; the Hubble Space Telescope; the Neil Gehrels Swift Observatory; the Chandra X-ray Observatory; the Nuclear Spectroscopic Telescope Array; the Fermi-LAT Collaboration; the HESS collaboration; the Magic collaboration; the Veritas collaboration; NASA, ESA and ESO; NASA/GSFC/SVS/M.Subbarao & NASA/CXC/SAO/A.Jubett
M87*, a laboratory for black hole physics and astrophysics
The goals are always the same. We know that supermassive black holes are closely linked to the evolution of galaxies and vice versa. However, we do not yet understand the accretion processes that form disks and tori of matter around supermassive black holes as well as we would like.
We also do not yet understand the acceleration processes at the origin of the material jets of these compact stars as well as we would like. Of course, we know that this is related to plasma physics and relativistic magnetohydrodynamics in curved spacetime, in this case rotating Kerr black holes. But as in the case of terrestrial fluids, the equations of this physics are very difficult to solve analytically and the use of computers and experiments – hence observations in astrophysics with stars, which naturally serve as laboratories under various conditions – are necessary to progress.
As a spin-off of this research, we also hope to unravel the mystery of the origin of cosmic rays at high energies, and initial results on neutrinos are already available. A supermassive black hole with 6.5 billion solar masses, as is the case with M87*, is also a good opportunity to test alternatives to Einstein's general theory of relativity (Futura explained this in the previous article below) or even alternatives to this theory Black holes to explain what happens at the heart of active galactic nuclei like quasars.
To achieve the set goals, as shown in the images above, it is necessary to observe the black hole, the black hole's surroundings and its jet of matter on numerous interleaved distance and time scales. It is also necessary to extract information contained in different radiation bands.
Specifically, the smallest image showing the environment near the black hole's horizon is about 0.013 light-years in size (one light-year is about 10,000 billion kilometers), and the world's radio telescopes, including Alma, allow zooming out around 1,000 light-years .
In addition, and as a relay, the X-rays from space observatories such as Swift and Chandra intervene, accompanied by Hubble. Material concentrations in the M87* beam then become clearly visible.
It was the American astronomer Heber Doust Curtis who in 1918 observed a particularly fine and focused jet of material that stretched over at least 5,000 light-years. As Futura explained in a previous article, this beam, like others, caused a lot of ink to flow because it appeared to show movements of matter faster than light. It is not so.
Black Hole: Message from M87* with EHT confirms Einstein's theory
Article by Laurent Sacco published on February 10, 2020
By further analyzing images of the supermassive black hole M87*, members of the Event Horizon Telescope have introduced new constraints on possible alternatives to Einstein's general theory of relativity. It emerges once again strengthened, as does the classic theory of black holes.
The 1960s were not only marked by a revival of theoretical studies on general relativity under the influence of the discovery of quasars, quasars and fossil radiation. At this time we also saw the development of work to test Einstein's theory and even refute it in favor of other theories of gravity, which introduced new field equations while preserving curved spacetime and even added fields other than a metric tensor, in particular one or more scalar fields.
The easiest tests to perform involved the movements of planets, light rays and electromagnetic waves in the solar system. But the astronomy of gravitational waves was already in great development, although in the early 1970s the race to discover it did not yet rely on the construction of an interferometer using laser beams, as was ultimately the case with the Ligo and Virgo detectors . We can get a good overview of the atmosphere at that time, roughly between 1960 and 1975, by consulting the famous MTW by John Wheeler, Charles Misner and the future Nobel Prize winner in physics Kip Thorne.
Today, the most promising ways to discover new physics and move beyond general relativity – perhaps even towards a quantum theory of gravity – are undoubtedly the study of gravitational waves produced by black hole collisions and the study of the images of the members of the event Horizon Telescope collaboration begins to offer. They have just published a new article on this topic in the famous journal Physical Review Letters.
A presentation of the work of the EHT collaboration in releasing the first image of M87* in 2019. For a reasonably faithful French translation, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then click on “Subtitles” and finally “Auto-translate”. Select “French”. © Perimeter Institute for Theoretical Physics
A black hole observed with a virtual radio telescope the size of Earth
Recall that these astronomers captured the first and, for now, only images of the shadow of a black hole's event horizon with the supermassive black hole at the center of the giant elliptical galaxy M87. This galaxy was discovered in 1781 by the French astronomer Charles MessierCharles Messier near the northern border of the constellation Virgo, not far from the constellation Berenice's Hair.
Located just 55 million light-years from the Milky Way, M87 is particularly studied because it is the largest elliptical galaxy closest to Earth and one of the closest radiating radio sources in the sky. This radio source was believed to hide a rotating Kerr black hole with 6.5 billion solar masses called M87*.
On April 10, 2019, observations made with the Event Horizon Telescope (EHT) were finally revealed. At that time, they came from an international network of eight radio telescopes and observatories, including the Atacama Large Millimeter/submillimeter Array (Alma) in Chile and Iram's Pico Veleta radio telescope south of Spain in the Sierra Nevada.
These radio telescopes, spread across the planet, were used to perform Very Long Baseline Interferometry (or VLBI), which is a very large instrument, in this case a radio telescope several thousand kilometers in diameter, as in the video above explained.
Even more limited alternatives to Einstein's theory
It turns out that alternative metric theories to Einstein's general theory of relativity can often be summarized into a formalism that depends on several parameters. Observations in the solar system have made it possible to place limits on these parameters, sometimes leading to the exclusion of certain theories, such as the one originally proposed in 1922 by the great mathematician and philosopher Alfred North Whitehead.
Members of the EHT collaboration report today that the constraints on some of these parameters have become about 500 times stronger by looking closely at the size of the black hole shadow or alternatives to black holes considered in other relativistic theories. Gravity is still believable.
In the diagram above we have shown the circles predicted by its variants, they correspond to the ring of light and the boundary of the images of the accretion disk of M87*. Apparently the general is once again, and perhaps sadly, still victorious.
But we are still only at the beginning of the EHT images saga. In fact, their quality will increase over the years, especially as other radio telescopes join in. So we will receive contributions from the Greenland Telescope, the 12-meter telescope at Kitt Peak near Tucson and the Northern Extended Millimeter Array Observatory in France.
Taiwan's participation in the Greenland Telescope project, which enables the observation of supermassive black holes. © Rti French