What's a Black Hole event horizon (and what's going on here)?



On Wednesday, April 10th, the international Event Horizon Telescope project will take place publish first results of his plan for the image of black holes. But what is a horizon of events?

The event horizon of one black hole is related to the speed of exit from the object – the speed that would have to exceed to escape the gravitational pull of the black hole. The closer a person approaches a black hole, the greater would be the speed she would need to escape this tremendous gravity. The event horizon is the threshold around the black hole where the output speed exceeds the speed of light.

according to Einstein's theory of special relativitynothing can travel faster in space than the speed of light. This means that the event horizon of a black hole is essentially the point from which nothing can come back. The name refers to the impossibility of attending any event taking place inside this border, the horizon beyond which one can not see.

Related: "Revolutionary Result" coming soon from Event Horizon telescope

"The event horizon is the ultimate wall of the prison – you can get in but never get out of it," Avi Loeb, president of astronomy at the University of California, told Space.com Harvard.

When an element is approaching a horizon of events, a witness finds that the element's image is reddened and sifted by the light deformed by the gravity coming from that element . At the event horizon, this image would gradually disappear in invisibility.

In the event horizon, one would find the singularity of the black hole, where previous research suggested that the entire mass of the object had collapsed into an infinitely dense expanse. This means that the structure of space and time around the singularity has also been bent to infinity, so that the laws of physics as we know them now are collapsing.

"The event horizon protects us from unknown physics close to a singularity," Loeb said.

Related: Images: Black Holes of the Universe

The size of an event horizon depends on the mass of the black hole. If the Earth were compressed until it became a black hole, it would have a diameter of about 17.4 millimeters, a little smaller than a dime; if the sun were converted into a black hole, its width would be about 5.84 kilometers (3.82 km), about the size of a village or city. The supermassive black holes that the Event Horizon Telescope observe are much larger; Sagittarius A *, in the center of the Milky Way, represents about 4.3 million times the mass of our sun and has a diameter of about 12.7 million kilometers (7.9 million miles), while that M87 at the heart of the galaxy of Virgo A is about 6 billion solar masses and 17 billion kilometers wide.

The strength of the gravitational attraction of a black hole depends on the distance that separates it: the closer you are, the stronger the tug is. But the effects of this gravity on a visitor would vary depending on the mass of the black hole. For example, if you fell to a relatively small black hole several times the mass of the sun, you would be separated and stretched into a process known as spaghettification, dying well before reaching the horizon of events .

However, if you fell to a a supermassive black hole Millions to billions of times the mass of the sun, you would not "feel such forces to a significant extent," said Loeb. You would not die spaghettification before having gone through the event horizon (although many other dangers around such a black hole could kill you before you reach this point) .

The black holes probably turn because the stars from which they came are also spun and the matter they swallow spiraled before falling. Recent findings suggest that black holes can rotate at speeds greater than 90% of those of light, explained Loeb.

Related: Black Hole Quiz: How do you know the strangest creations of nature?

Previously, the basic pattern of black holes assumed that they were not spinning and that their singularities were therefore points. But as black holes generally turn, current models suggest that their singularities are infinitely thin rings. This brings the event horizons of rotating black holes, also called Kerr black holes, to appear oblong – crushed at the poles and bulging at their equators.

The horizon of events of a rotating black hole separates into an outer horizon and an inner horizon. The event horizon outside such an object acts as a point of no return, just as the event horizon of a non-rotating black hole. The internal event horizon of a rotating black hole, also called Cauchy's horizon, is unknown. Beyond this threshold, the cause does not necessarily precede the effect, the past does not necessarily determine the future, and time travel may be possible. (In a non-rotating black hole, also called black Schwarzschild hole, the inner and outer horizons coincide.)

A rotating black hole also forces the space-time structure that surrounds it to rotate with it, a phenomenon called drag effect or Lense-Thirring effect. Frame trails are also seen around other massive bodies, including the Earth.

Dragging the frame creates a cosmic vortex called ergosphere, which occurs outside the horizon of external events of a rotating black hole. Any object in the ergosphere is forced to move in the same direction in which the black hole turns. Materials falling into the ergosphere can take enough speed to escape the gravitational pull of the black hole, causing some of its energy. In this way, black holes can have powerful effects on their environment.

Rotation can also make black holes more efficient in converting any material that falls on their heads into energy. A non-rotating black hole would convert about 5.7% of the mass of an infesting object into energy, according to the famous Einstein equation E = mc ^ 2. On the other hand, a rotating black hole can convert up to 42% of the mass of an object in energy, have determined scientists

Related: The weirdest black holes in the universe

"This has important implications for environments around black holes," said Loeb. "The amount of energy from supermassive black holes in the center of virtually all large galaxies can significantly influence the evolution of these galaxies."

Recent work has dramatically changed the conventional vision of black holes. In 2012, physicists suggested that anything that fell to a black hole could end up "firewall"At or near the event horizon that would cremate any matter that would fall in. Indeed, when particles collide, they can become invisibly linked by a link called entanglement, and black holes can break up such links, releasing incredible amounts of energy.

However, other research seeking to unite general relativity, which may explain the nature of gravity, while quantum mechanics, which can describe the behavior of all known particles, suggests that firewalls may not exist – because the horizons of the events themselves may not to exist. Some physicists suggest that instead of abyss from which nothing can come back, what we currently consider to be black holes may actually be a range of objects resembling black holes lacking from event horizons, such as fuzzballs, said Loeb.

By imagining the edges of black holes, the Event Horizon telescope can help scientists analyze the shapes and behaviors of event horizons.

"We can use these images to constrain any theory on the structure of black holes," said Loeb. "Indeed, fuzzball speculation – where the event horizon is not a sharp, but rather fuzzy – boundary could be tested with images from the Event Horizon telescope."

Follow Charles Q. Choi on Twitter @cqchoi. Follow us on twitter. Follow us on twitter @Spacedotcom or Facebook.


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