Here's what we know about black holes in anticipation of the first image of the Horizon Telescope event

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For hundreds of years, physicists have hypothesized that the Universe should contain black holes. If enough material is collected in a sufficient space of space, the gravitational attraction will be so strong that nothing in the universe & nbsp;– no particles, no antiparticles, not even the light itself & nbsp;– can escape. They are predicted by Newton's and Einstein's theories of gravity, and astrophysicists have observed many candidate objects consistent with black holes and no other explanation.

But we have never seen the horizon of events before: the characteristic signature specific to & nbsp; black holes, of the dark region where nothing can escape. On April 10, 2019, the collaboration between Event Horizon Telescope will publish its very first image from such a horizon of events. Here is what we know now, on the eve of this monumental discovery.

Black holes are an inevitable consequence, at least in theory, of limiting the speed in your universe. Einstein's theory of general relativity, which connects the tissue of space-time to matter and energy present in the universe, also contains an intrinsic relationship between the way whose matter and energy move in space – time. The larger your movement in space, the smaller your movement in time, and vice versa.

But there is a constant that connects this movement: the speed of light. & In general relativity, the physical size of the planned event horizon & nbsp; – the size of the region from which nothing can escape & – is determined by the mass of the black hole and the speed of light. If the speed of light was faster or slower, the expected size of the event horizon would decrease or increase, respectively. If the light moved infinitely fast, there would be no horizon of event.

Astrophysically, black holes are surprisingly easy to create. In our galaxy alone in the Milky Way, there are probably hundreds of millions of black holes. At the present time, we believe that there are three mechanisms capable of training them, even if there may be more.

1. The death of a massive star, where the nucleus of a star much heavier than our sun, rich in heavy elements, collapses under its own gravity. & nbsp; When the external pressure is insufficient to counteract the inner gravitational force, the nucleus implodes. The resulting supernova explosion leads to a central black hole.

2. The direct collapse of a large amount of material, possibly coming from a star or a cloud of gas. If enough material is present in one place in the space, it can directly generate a black hole without supernova or similar cataclysm to trigger its creation.

3. The collision of two neutron stars, which are the densest and most massive objects that do not become black holes. Add enough mass on one, by accretion or (more generally) by melting, and a black hole can occur.

A little more than 0.1% of the stars that formed in the Universe will eventually become black holes in one of these modes. Some of these black holes will only represent a few times the mass of our Sun; others can be hundreds or even thousands of times more massive.

But the more massive ones will do what all the extremely massive objects do when they move in the gravitational collection of masses typical of star clusters and galaxies: they sink in the center, through the astronomical process of mass segregation. When several masses pile up in a well of gravitational potential, the lighter masses tend to take more momentum and are eventually ejected, while the larger ones lose the amount of angular momentum accumulate in the center. There, they can accumulate matter, merge, grow and eventually become the supermassive behemoths that we find today in the center of galaxies.

In addition, black holes do not exist in isolation, but in the messy environment of space itself, filled with various types of materials. When the material approaches a black hole, it undergoes tidal forces. The part of any object that is closer to the black hole experiences a greater gravitational force than the farthest part of the black hole, while the parts that bulge on one side will feel a pinch toward the black hole. center of the object.

Ultimately, this results in a set of stretching forces in one direction and compression in & perpendicular to the perpendicular directions, resulting in the fall of the falling object. "Spaghettify." & Nbsp; The object will be torn into its constituent particles. Due to a number of physical properties and dynamics involved, this will cause a build-up of material around the black hole of the form of a disc: an accretion disk.

These particles constituting the disk are charged and move in orbit around the black hole. When the charged particles move, they create magnetic fields, which in turn accelerate the charged particles. This should lead to a number of observable phenomena, including:

• photons emitted from the entire electromagnetic spectrum, especially radio,
• eruptions appearing at higher energies (as in X-rays) from the moment the material falls into the black hole,
• and jets of accelerated matter and antimatter perpendicular to the accretion disk itself.

All these phenomena have been observed for black holes of various masses and orientations, which further confirms their existence.

In addition, we observed the movements of stars and individual stellar remains around the black hole candidates, which seem to put into orbit large masses that have no viable explanation other than being black holes. In the center of the Milky Way, for example, we observed dozens of stars orbiting an object called Sagittarius A *, whose inferred mass is 4 million suns and which emits flares, radio waves and shows the signatures of positrons (antimatter form) being ejected perpendicular to the galactic plane.

Other black holes have many identical signatures, such as the ultramassive black hole in the center of the M87 galaxy, which would weigh about 6.6 billion solar masses.

Finally, we observed a host of other observational signatures, such as & nbsp; the & nbsp; Direct detection of gravitational waves inspired by fusing black holes, creating a black hole directly from both direct collapse events and neutron star fusions, and flipping. quasars, blazars and microquasars, caused by black holes of varying masses and orientations.

Upon entering the event, we have every reason to believe that black holes exist, are compatible with general relativity and are surrounded by materials that accelerate and emit radiation that we should be able to detect.

The major advance of the Horizon Event Telescope lies in its ability to ultimately solve the event horizon itself. & Nbsp; In this region, there should be no matter and no radiation should be emitted. There should beside effects inherent to the black holes themselves observable with this telescope, including the fact that the most internal circular stable orbit should be about three times larger than the event horizon itself, and that radiation should be emitted around the The horizon of events, because of the presence of accelerated matter.

There are many questions to which the first direct image of the event horizon of a black hole should be ready to answer, and you can check what we can potentially learn here. But the biggest advance is this: he will test the predictions of general relativity in a totally new way. If our understanding of gravity needs to be revisited near black holes, this observation will tell us the way.

For hundreds of years, humanity has been waiting for the existence of black holes. In our lives, we have collected a whole series of evidences that suggest not only their existence, but also a fantastic agreement between their expected theoretical properties and what we have observed. But maybe the most important prediction of all & nbsp; – the existence of the event horizon and its properties & nbsp; – has never been directly tested before.

With simultaneous observations of hundreds of telescopes around the world, scientists have finished rebuilding an image, based on real data, of the largest black hole seen from Earth: the $ 4 million solar mass monster located at center of the Milky Way. What we will see & nbsp; April 10th will further confirm general relativity or encourage us to rethink everything we believe in gravity. Eager to anticipate, the world is waiting now.

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For hundreds of years, physicists have hypothesized that the Universe should contain black holes. If enough material is collected in a space of space sufficiently small, the gravitational attraction will be so strong that nothing in the Universe – no particles, no antiparticles, not even the light itself – can escape. They are predicted by Newton's and Einstein's theories of gravity, and astrophysicists have observed many candidate objects consistent with black holes and no other explanation.

But we have never seen the horizon of events before: the characteristic signature peculiar to black holes, to the dark region where nothing can escape. On April 10, 2019, the Event Horizon Telescope collaboration will publish its very first image of such a horizon of events. Here is what we know now, on the eve of this monumental discovery.

Black holes are an inevitable consequence, at least in theory, of limiting the speed in your universe. Einstein's theory of general relativity, which connects the tissue of space-time to matter and energy present in the universe, also contains an intrinsic relationship between the way whose matter and energy move in space – time. The larger your movement in space, the smaller your movement in time, and vice versa.

But there is one constant concerning this movement: the speed of light. In general relativity, the physical size of the expected event horizon – the size of the region from which nothing can escape – is defined by the mass of the black hole and the speed of light. If the speed of light was faster or slower, the expected size of the event horizon would decrease or increase, respectively. If the light moved infinitely fast, there would be no horizon of event.

Astrophysically, black holes are surprisingly easy to create. In our galaxy alone in the Milky Way, there are probably hundreds of millions of black holes. At the present time, we believe that there are three mechanisms capable of training them, even if there may be more.

1. The death of a massive star, where the nucleus of a star much heavier than our Sun, rich in heavy elements, collapses under its own gravity. When the external pressure is insufficient to counter the inner gravitational force, the nucleus implodes. The resulting supernova explosion leads to a central black hole.

2. The direct collapse of a large amount of material, possibly coming from a star or a cloud of gas. If enough material is present in one place in the space, it can directly generate a black hole without supernova or similar cataclysm to trigger its creation.

3. The collision of two neutron stars, which are the densest and most massive objects that do not become black holes. Add enough mass on one, by accretion or (more generally) by melting, and a black hole can occur.

A little more than 0.1% of the stars that formed in the Universe will eventually become black holes in one of these modes. Some of these black holes will only represent a few times the mass of our Sun; others can be hundreds or even thousands of times more massive.

But the more massive ones will do what all the extremely massive objects do when they move in the gravitational collection of masses typical of star clusters and galaxies: they sink in the center, through the astronomical process of segregation of the masses. When several masses pile up in a well of gravitational potential, the lighter masses tend to take more momentum and are eventually ejected, while the larger ones lose the amount of angular momentum accumulate in the center. There, they can accumulate matter, merge, grow and eventually become the supermassive behemoths that we find today in the center of galaxies.

In addition, black holes do not exist in isolation, but in the messy environment of space itself, filled with various types of materials. When the material approaches a black hole, it undergoes tidal forces. The part of any object that is closer to the black hole experiences a greater gravitational force than the farthest part of the black hole, while the parts that bulge on one side will feel a pinch toward the black hole. center of the object.

In total, this results in a set of forces of stretch in one direction and compression in a perpendicular direction, which causes the "spaghettification" of the infesting object. The object will be torn into its constituent particles. Due to a number of physical properties and dynamics involved, this will cause a build-up of material around the black hole of the form of a disc: an accretion disk.

These particles constituting the disk are charged and move in orbit around the black hole. When the charged particles move, they create magnetic fields, which in turn accelerate the charged particles. This should lead to a number of observable phenomena, including:

• photons emitted from the entire electromagnetic spectrum, especially radio,
• eruptions appearing at higher energies (as in X-rays) from the moment the material falls into the black hole,
• and jets of accelerated matter and antimatter perpendicular to the accretion disk itself.

All these phenomena have been observed for black holes of various masses and orientations, which further confirms their existence.

In addition, we observed the movements of stars and individual stellar remains around the black hole candidates, which seem to put into orbit large masses that have no viable explanation other than being black holes. In the center of the Milky Way, for example, we observed dozens of stars orbiting an object called Sagittarius A *, whose inferred mass is 4 million suns and which emits flares, radio waves and shows the signatures of positrons (antimatter form) being ejected perpendicular to the galactic plane.

Other black holes show a lot of identical signatures, like the ultramassive black hole in the center of the M87 galaxy, which would weigh about 6.6 billion solar masses.

Finally, we have witnessed a host of other observational signatures, such as the direct detection of gravitational waves from inspiring and merged black holes, the creation of a black hole directly from direct collapse events and of neutron star fusions, and start-up. quasars, blazars and microquasars, which would be caused by black holes of varying masses and orientations.

Upon entering the event, we have every reason to believe that black holes exist, are compatible with general relativity and are surrounded by materials that accelerate and emit radiation that we should be able to detect.

The great advance of the Event Horizon telescope will be the ability to ultimately resolve the event horizon itself. From within this region, no material should exist and no radiation should be issued. There must be subtle intrinsic effects to the black holes themselves, observable with this telescope, including the fact that the most stable circular internal orbit must be about three times larger than the horizon of events itself. same and that radiation must be emitted around the event horizon. , because of the presence of accelerated matter.

There are many questions to which the first direct image of the event horizon of a black hole should be able to answer, and you can check what we can potentially learn here. But the biggest advance is this: he will test the predictions of general relativity in a totally new way. If our understanding of gravity needs to be revisited near black holes, this observation will tell us the way.

For hundreds of years, humanity has been waiting for the existence of black holes. In our lives, we have collected a whole series of evidences that suggest not only their existence, but also a fantastic agreement between their expected theoretical properties and what we have observed. But perhaps the most important prediction of all – that of existence and properties of the event horizon – has never been tested directly before.

Avec des observations simultanées de centaines de télescopes à travers le monde, les scientifiques ont fini de reconstruire une image, basée sur des données réelles, du plus grand trou noir vu de la Terre: le monstre de masse solaire de 4 millions de dollars situé au centre de la Voie lactée. Ce que nous verrons le 10 avril confirmera davantage la relativité générale ou nous incitera à repenser tout ce que nous pensons de la gravité. Désireux d&#39;anticiper, le monde attend maintenant.