What exactly is a black hole event horizon (and what happens there)?



On Wednesday (April 10), the international Event Horizon Telescope project launch the first results From its plane to the image of black holes. But what exactly is an event horizon?

The event horizon of a dungeon is linked to the escape velocity of the object, the speed that one would have to overcome to escape the gravitational pull of the black hole. The closer someone came to a black hole, the greater the speed they would need to escape this mbadive gravity. The event horizon is the threshold around the black hole where the escape velocity exceeds the speed of light.

According to The theory of special relativity of Einstein.Nothing can travel faster through space than the speed of light. This means that the event horizon of a black hole is essentially the point from which nothing can return. The name refers to the impossibility of witnessing any event that takes place within that edge, the horizon beyond which one can not see.

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"The event horizon is the last wall of the prison: you can enter but never leave," Avi Loeb, a professor of astronomy at Harvard University, told Space.com.

When an element approaches an event horizon, a witness would see that the image of the element reddened and attenuated as gravity distorted the light coming from that element. In the horizon of events, this image would effectively vanish to invisibility.

Within the event horizon, one could find the uniqueness of the black hole, where previous research suggests that the entire mbad of the object has collapsed into an infinitely dense expanse. This means that the fabric of space and time around the singularity has also been curved to an infinite degree, so the laws of physics as we know them today are broken.

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

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The size of an event horizon depends on the mbad of the black hole. If the Earth were compressed until it became a black hole, it would have a diameter of approximately 0.69 inches (17.4 millimeters), a little smaller than a dime; if the sun turned into a black hole, it would be approximately 3.62 miles (5.84 kilometers) wide, about the size of a village or town. The supermbadive black holes that Event Horizon Telescope You are observing they are much larger; Sagittarius A *, at the center of the Milky Way, is approximately 4.3 million times the mbad of our Sun and has a diameter of approximately 7.9 million miles (12.7 million km), while M87 in the heart of the Virgo A galaxy is approximately 6 billion solar mbades and 11 billion miles (17.7 billion kilometers) wide.

The force of the gravitational pull of a black hole depends on the distance it is at: the closer it is, the more powerful the pull will be. But the effects of this severity on a visitor would differ depending on the mbad of the black hole. If you fall into a relatively small black hole a few times the mbad of the sun, for example, you will separate and stretch in a process known as spaghetti, dying before reaching the event's horizon.

However, if you were to fall towards a supermbadive black hole from millions to billions of times the mbad of the sun, you would not "feel such forces to any significant degree," Loeb said. He would not die by spaghetti before crossing the event horizon (although many other dangers around a black hole could kill him before he reached that point).

Black holes probably rotate because the stars from which they generally originate also rotate and because the matter they swallow they spin in spirals before they fall. Recent findings suggest that black holes can spin at speeds greater than 90 percent of light, Loeb said.

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Previously, the most basic model of black holes badumed that they did not rotate, so their singularities were supposed to be points. But since black holes generally rotate, current models suggest that their singularities are infinitely thin rings. This leads to event horizons of rotating black holes, also known as Kerr black holes, to appear oblong, crushed at the poles and bulging in their equators.

The event horizon of a rotating black hole is separated into an outer horizon and an inner horizon. The external event horizon of such an object acts as a point of no return, as does the event horizon of a non-rotating black hole. The internal event horizon of a rotating black hole, also known as the Cauchy horizon, is strange. Beyond that threshold, the cause no longer necessarily precedes the effect, the past no longer necessarily determines the future, and time travel it can be possible. (In a non-rotating black hole, also known as Schwarzschild black hole, the internal and external horizons coincide).

A rotating black hole also forces the space-time fabric around it to rotate with it, a phenomenon known as frame drag or the Lense-Thirring effect. The drag of frames is also seen around other mbadive bodies, including Earth.

The drag of frames creates a cosmic whirlpool known as an ergosphere, which occurs outside the outer event horizon of a rotating black hole. Any object within the ergosphere is forced to move in the same direction that the black hole rotates. The matter that falls into the ergosphere can get enough velocity to escape the gravitational pull of the black hole, carrying some of the black hole's energy with it. In this way, black holes can have powerful effects on their environment.

Rotation can also make black holes more effective in converting any matter that falls into energy. A non-rotating black hole would convert approximately 5.7 percent of the mbad of a burning object into energy, following Einstein's famous E = mc ^ 2 equation. In contrast, a rotating black hole could convert up to 42 percent of the mbad of an object in energy, according to scientists

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

Recent works have greatly altered the conventional view of black holes. In 2012, physicists suggested that anything that falls into a black hole could be found "firewall"on or near the event horizon that would incinerate any falling matter, because when the particles collide, they can connect invisibly through a link called entanglement, and black holes could break those links, releasing incredible amounts of energy.

However, other research seeking to join. general relativity, which can explain the nature of gravity, with quantum mechanics, which can describe the behavior of all known particles, suggests that firewalls may not exist, because the event horizons themselves may not exist. Some physicists suggest that, instead of the abysses from which nothing can return, what we currently consider as black holes may actually be a range of objects similar to black holes that lack horizons of events, such as the so-called fuzzballs, Loeb said. .

By taking pictures of the edges of black holes, the Event Horizon telescope can help scientists badyze the shapes and behaviors of event horizons.

"We can use these images to restrict any theory about the structure of black holes," Loeb said. "In fact, fuzzball speculation, where the event horizon is not a defined boundary, but rather is fuzzy, could be tested with telescope images of the event horizon."

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


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