The Event Horizon Telescope (EHT) has added a larger number of observatories to the global network of radio telescopes, and the first image of our galaxy’s black hole can be obtained in less than a year.
"Early next spring, Event Horizon will reproduce the image of a black hole in the center of the Milky Way," said Avery E. Broderick, assistant professor of physics and astronomy at the University of Waterloo, during a presentation at the Perimeter Institute at a conference on convergence on June 23, 2015.
Broderick, who is also a teacher at this institute, shared some of the mind-blowing opportunities to explore the temporary space around a supermassive black hole in the center of the Milky Way, called Sagittarius * (or Sagittarius A *), so the EHT will focus on learning strong gravity.
"There are only two places in the universe where you can explore strong gravity on a large, very large scale and around compact objects," he added.
Referring to the study of the general theory of relativity by Albert Einstein, who formulated it 100 years ago - from the beginning of the maps created by sailors, Broderick said that there are many “monsters” in the unexplored depths of space, one of which is the gravitational conditions surrounding a black hole. But this theory may change for the first time in the history of mankind.
Angle Resolution of Event Horizon
EHT consists of many radio observatories around the world. With Very Long Baseline Interferometry (an ultra-long-base interferometer or VLBI) technology, many independent radio antennas, separated by hundreds or thousands of miles, can be used together to create a "virtual" telescope with the diameter of our planet. The possibilities of the most powerful optical telescopes on the planet are severely limited in the observation of even the most massive objects known in the universe. And black holes are extremely compact, appearing like tiny specks of dust in the sky. During their activity, supermassive black holes, as is known, exist in the nuclei of most galaxies, can overshadow them and generate huge areas of explosive relativistic gases in the intergalactic space. They can also have powerful effects on the evolution of galaxies, so the observation of these gravitational "hippopotamuses" is one of the most important goals of modern astrophysics.
To observe Sagittarius A * through Event Horizon, an extremely small angular resolution is required. With this telescope, these figures are estimated at 50 arc-seconds (micro μas) in diameter. One of the most powerful optical infrared observatories on the planet (two Keck telescopes atop Mauna Kea in Hawaii) can have an angular resolution of up to 20000 μas. It is planned that the thirty-meter telescope (TMT) will be able to provide indicators at 7000 μas. Although these resolutions are amazing for optical astronomy, these resources are not quite enough for full-fledged research in this area, Broderick added.
After completion of the preparation for the project, the EHT will work at a resolution of 10 μas, and these indicators are very good for solving the problem. These characteristics suggest some intriguing possibilities not only to obtain the first image of a black hole, but also to test Einstein’s general theory of relativity, and they will also help lift the curtain on physics beyond the general theory of relativity.
“This is not a future experiment, it is happening now,” said Broderick, pointing out that the “prototype” of the EHT already has 9 years of work experience. But the observations of Sagittarius A * so far come only from three sections of the radio antennas EHT, and this data was too scarce to create a clear view of the “ring” of a black hole. These observations, however, make a serious contribution to understanding the characteristics of the black hole, helping theoretical physicists to guess what Sagittarius A * is, but many questions remain unanswered. Even with regard to the black hole in the center of the Milky Way, there are serious uncertainties regarding the understanding of the geometry and dynamics of the area.
The “classical” black hole theory includes a point of no return — an area where the gravitational deformation is so great that even light cannot avoid the gravitational pull of a black hole, called the event horizon. There is also an accretion disk, where the material falls on the areas surrounding the event horizon; this is the generation of high energies. But we don’t really know what an accretion disk is - big, small, thin or thick. We also do not know whether this disk is angled relative to the back of a black hole (astrophysicists are certain that Sagittarius A * is a rotating black hole). Perhaps any of our black holes is also a disk? At present, the morphology of the structures surrounding a black hole remains a mystery.
This secret appears as a kind of "existential crisis" for the EHT - warns Broderick.
“The name of the Event Horizon Telescope telescope is far from accidental, it was given to check for the presence of an event horizon in a black hole, if this theory were refuted, the telescope would be renamed,” he added, “fortunately, the EHT found the best proof on today, that's true, and horizons of events exist. "
Sagittarius A * flickers, flickers
Currently, with the exception of the unlikely turn of physics, there is an event horizon, and physicists have managed to narrow the concept of how it will look - a small set of variables and current models, and this is consistent with the data that is starting to come from the EHT.
“I’m not sure if I’m glad or I’m depressed, I was hoping that we would find some unexpected things now, although everything is fine,” Broderick joked. Although the EHT is already producing results and hopes for getting the first images of Sagittarius A * soon, are high, there is still a long way to go and problems to overcome.
One of the problems pointed out by Broderick is a problem for all ground observatories. When a look passes through the atmosphere, we see the twinkling of stars. This flicker is caused by many atmospheric influences, including turbulence in the upper atmosphere and moisture. When a supermassive black hole is observed, a similar effect appears in the center of our Galaxy - Sagittarius A * also “flickers”.
When stars and interstellar plasma pass between us and Sgr. *, Scintillations in the received signal may occur, creating small anomalies that need to be corrected immediately. After a few years, when the EHT conducts full-scale operations, his research will be crucial to understanding what drives the accretion flow around the black hole. But if scintillation effects are not taken into account, then such a phenomenon as magnetohydrodynamic turbulence near a black hole may become too diffuse to study.
Similar to ground-based observatories that have lasers in the upper atmosphere for measuring the amount of turbulence and tuning using adaptive optics, the EHT will adopt an adaptive optics scheme (but without lasers) to remove this effect when analyzing the results.
Tomography of space
Perhaps the most beneficial use of EHT is to study SGR outbreaks. *. It is known that they are periodically generated there.
About once a day, several observatories observed a clarification of emissions from Sgr. * and this phenomenon also changes the structure of the emitted area. This flash was interpreted as a “hot spot” in the accretion stream near the event horizon. When the EHT is fully operational, it will be able to track these hot spots, tracing their origins and looking at the process of reducing them. Astronomers also hope to use hot spots as an indicator in order to outline the structure of temporary space in this strong gravity environment. "This opens the door to the possibility of a temporary space tomography - these spots move, they arise in different areas of the temporary space," Broderick said. "And the way it happens once a day, you can see quite a few of these flashes."
How deeply we would not have probed the unknown in this unique gravitational region, and we think that we have a pretty good platform in the theory of black hole dynamics, but I want to think that EHT could find something new and, possibly, exotic about a highly unpredictable space nearest supermassive black hole.
"I would like to think that as soon as we get the image, we will see that it will look like the version of the beginning of the 21st century - a pale blue dot, maybe with more sinister overtones ... There are monsters that are hiding in darkness "- this conclusion did Broderick.
