Categories: world

Don't let the event horizon steal the border, save a little for the ergosphere

A black hole gravity affects a twist – and twist – with many parts to it. We all know the event horizon because of its wonderful ability to capture "even light" within its envelope, and keep everything inside the catch in absolute darkness as long as the black hole lives. But beyond the event horizon, there is another region with equal – if not more – marvelous abilities that distort reality's perception in its own unique way. Because both of their abilities are activated by gravity, let's begin there. [19659002] The gravitational force is actually an effect that objects seem to experience because of the shape of the spacetime continuum. All objects move on the surface of the continuum, and when the surface is curved, an observer sees the object moving as on a curve. Such deformations are caused by massive bodies: the heavier a body, the more it bends the continuum around itself. So to the observer, it seems that the heavy body causes the easier object to track itself. The Moon orbits the Earth because the Earth's mass has bent the continuity of the scattering around it. In fact, the Moon simply moves on the surface of the continuum, and it seems to be circling the Earth because of the shape of the continuum in that region. Credit: Mysid / Wikimedia Commons, CC BY-SA 3.0 Depending on the mass of the deforming body, this effect can be felt at great distances. Pluto, for example, orbits the sun at…

A black hole gravity affects a twist – and twist – with many parts to it. We all know the event horizon because of its wonderful ability to capture “even light” within its envelope, and keep everything inside the catch in absolute darkness as long as the black hole lives. But beyond the event horizon, there is another region with equal – if not more – marvelous abilities that distort reality’s perception in its own unique way.

Because both of their abilities are activated by gravity, let’s begin there. [19659002] The gravitational force is actually an effect that objects seem to experience because of the shape of the spacetime continuum. All objects move on the surface of the continuum, and when the surface is curved, an observer sees the object moving as on a curve. Such deformations are caused by massive bodies: the heavier a body, the more it bends the continuum around itself. So to the observer, it seems that the heavy body causes the easier object to track itself.

The Moon orbits the Earth because the Earth’s mass has bent the continuity of the scattering around it. In fact, the Moon simply moves on the surface of the continuum, and it seems to be circling the Earth because of the shape of the continuum in that region. Credit: Mysid / Wikimedia Commons, CC BY-SA 3.0

Depending on the mass of the deforming body, this effect can be felt at great distances. Pluto, for example, orbits the sun at an average distance of 5.9 billion km. So Pluto’s average path indicates the deformation that an object as heavy as Pluto is experiencing because of the sun (and other planets as well as the Kuiper belt) at that distance. According to Newton’s Gravity Requirements, the force of force falls off the square of the distance. So, if the force between two bodies is X at a distance of Y, it becomes X / 4 at a distance of 2Y (assuming the gravity constant is the same at Y and 2Y). The strength never falls to zero unless the objects are endless far apart.

If Pluto wanted (for some fantastic reasons) to leave his or her circulation, it would have to move at a certain speed to escape it. Say it was Death Star there instead of Pluto, and Death Star has thrusters. It would have to fire the thrusters to accelerate to such an extent that its velocity grows beyond the limit where the sun can hold Pluto there with its gravity.

The basic setup is the same for a black hole, but the numbers are more extreme. When you look at a black hole, you actually see its event horizon. The gravitational feature of the black hole starts from a point in the center called singularity. This singularity deforms the spacetime continuum in unimaginable ways, although it becomes more and more conceivable the longer you get from the center.

The event horizon is the distance at which the continuum deforms in such a way that you have to travel faster than at the speed of light to escape it – that is, if you were caught right at the event horizon, even traveling at the exact speed of light you just keep on the event horizon and do not lock you in space. (Put differently: this would allow us to work out the speed of light in a certain universe using the rules of ground-white gravity physics and the sizes of black holes in that universe.)

This is also why the event horizon is you see when you see a black hole: it is a literal event. Events that occur on one side cannot be seen on the other side because the light that carries the information you see cannot cross it or return. This would in turn lead to the question of whether there is an area around the black hole where its gravitational effects can be noticed but which do not define “non-return points”. The answer is yes; it is called the ergosphere.

The name itself gives a very utilitarian look to the thought – that it is the area where you can extract work from the black hole – but it is true. The Ergosphere is the region where the spacetime continuum has been deformed by the black hole to such an extent that you can enter and leave if you traveled fast enough (but less than at light speed). But even though the black hole’s effects from singularity to event horizon are properly warped and the event horizon itself is an important – albeit arbitrary limit – the effects of the black hole in the ergosphere are still the senses.

A Part of this is due to an effect of rotating black holes called frame drilling. Imagine that you are (an immortal river) looking at Pluto that orbits the sun from somewhere near Mercury, through a stationary window located between the Neptune and Pluto paths. If you look through the window you will see Pluto pass once every 248 years. Besides the fantasy elements, this scenario is also physically possible because the window is practically stationary. The part of the space-time continuum on which it rests is thus not in motion due to the sun’s rotation. That is, there is a negligible amount of drafts.

But this would not be possible in the ergosphere of a rotating black hole. Say you are just above the event horizon, looking through a window in the distance at an object that orbits the black hole at the inner edge of the ergosphere. Frame drawing would absolutely prevent the window from stopping, along with you and the object as well. This is because the devastating gravity of the black hole – that is, the pernicious deformation of the continuum – is such that it not only deforms the continuum but also draws it as it rotates in the direction of its rotation in a very pronounced manner.

As a result of such a frame drawing, everything that sits on that part of the continuum also seems to be moved even though it did not have any speed in that direction to begin with. It would be like watching your friend who goes west-east on a boat moving east-west at the speed of light: for all practical purposes, she can also go cheese-west! Therefore, a rotating black hole will force an object that angles towards the black hole ergosphere from the opposite direction to act to shift and move toward its rotation.

The test particle, shown in red, first moves toward the ergosphere (in purple) clockwise before the frame pull forces it to act counterclockwise. Credit: Yukterez / Wikimedia Commons, CC BY-SA 4.0

Note the use of “appear”: the object will not need to change the direction of the rotation of the black hole. The changed arrangement of the time period in the region along with the light coming from the object towards the observer will make it appear that way.

If an object, using a certain force, insists that it appears stationary inside the ergosphere, it can but there is a catch. If it is within the ergosphere but above the event horizon, the object has no alternative but to be framed. But just as the event horizon is the surface you would travel in eternity if you traveled at the speed of light, the ergosphere also has a surface where you can avoid being framed if you move at the speed of light.

This picture is one of the pictures in a presentation prepared by Prof Chris Reynolds, UMD [19659006] (Trivia: It is possible to explain the effects of gravity beyond the ergosurface using Newtonian physics Inside you need the theories of relativity.)

The location of both envelopes – the event horizon and ergosurface – is determined by the speed of light. Their shapes are also determined by common factors: the mass of the black hole and the angular momentum. However, they are not affected in the same way. For example, a non-rotating black hole will have a spherical event horizon, but a rotating black hole will have a flat event horizon. On the other hand, a non-rotating black hole will not have an ergosurface while a rotating black hole will have something between an oblate and a pump-shaped ergosurface.

<img class = “wp-image-46758” src = “https://skepticalengine.files.wordpress.com/2019/04/ergosphere_and_event_horizons_of_a_rotating_black_hole.gif” alt = “Credit: Yukterez / Wikimedia Commons, CC BY- SA 4.0 [19659024] Credit: Yukterez / Wikimedia Commons, CC BY-SA 4.0

These are just some of the reasons why the shadow of the black hole in the M87 galaxy looked like it did in the image formed by the Event Horizon Telescope (EHT) Apart from how it was obtained (using techniques such as VLBI), the image contains many distortions originating from the black hole itself, so interpreting it is not a simple activity.

EHT registered and studied radiation only as could get away from the black hole, with a lot of matter accumulating beyond that point and falling into the hole, so what we see in the sum is the hot and magnetized matter, all their radiation and the Doppler effects on them, the effects of the ergosphere frame – drag them and S the shadow of the event horizon.

The shadow (black) and the event horizon and the ergosphere (white) of a black hole rotating from left to right. At a = 0, black does not rotate and at a = 1 it rotates maximally. Credit: Yukterez / Wikimedia Commons, CC BY-SA 4.0

The idea that you can extract work from the ergosphere, which gives the region its current name, can be traced to some examples that various researchers have spelled out over the years. The three best-known examples are the Penrose mechanism, the Hawking radiation and the Blandford-Znajek process. The case of Hawking radiation is the easiest to explain (only because it has been done many times in the popular press so that one can access it immediately), but understand it provides insights into the Penrose option as well.

The vacuum of deep space is not a true vacuum: it contains little energy, including electromagnetic energy from distant stars, which is often converted into a particle-antiparticle pair. That is, these particles are condensations of energy that emerge and reappear as energy again (here is a more detailed than available primer) in a very short time. It is possible that this process also happens near black holes simply because it can. And when it does, something strange follows.

If such a particle pair appears to exist just above the event horizon, one of them may fall into black and the other will be shot into the ergosphere. This push-off happens because of the momentum conservation law, and the energy carried by the pressed particle will be a teeny, tiny bit transformed from the black hole mass. To a distant observer, it will look as if the black hole has just released a particle and lost some of its mass to do so. Stephen Hawking and Jacob Bekenstein first predicted this phenomenon, having called Hawking radiation in 1974. When this process happens over and over again, over many eons, a black hole may have lost all its mass and completely vaporized in nothing.

British mathematician physician Roger Penrose suggested a similar idea which was relatively more practical (and was also used in the film Interstellar ) in 1969. As Suvrat Raju, a theoretical physicist at ICTS Bangalore, explained : Say an object – like a stone – is thrown into the ergosphere. As it approaches the event horizon, it is caused by a deliberate mechanism to break up into two parts so that one bit falls into the event horizon in the direction opposite to the black hole rotation. As a result, the other would speed up his journey through the ergosphere through a “kick” from the black hole.

If orchestrated correctly, the kicked part may come out of the ergosphere with more energy than it had entered – energy supplied by the black hole by converting part of its mass. Researchers have already worked out the average achievable energy improvement in each Penrose mechanism that is trying to be about 21%.

“In classical processes one can never reduce the area of ​​the black hole, but the Penrose process can reduce its mass,” Raju continued. “Science fiction fantasy is that a sufficiently advanced civilization could use rotating black holes for disposal and also gaining some energy in the process through the Penrose process. “The Blandford-Znajek process is less raw and more … involved . Say a star became a little too close A black hole is crushed into pieces that fall into orbit around the event horizon, friction between these pieces warms them up to a very high temperature, and pushes them into a plasma position of matter, these pieces also have electric and magnetic fields, and the electric and magnetic fields. magnetic field lines pass through them even when they whirl around the monster and approaching closer.

Let me now quote the following course material by Daniel Nagasawa, Stanford U niversity, from 2011:

Basically, the black hole acts as a massive conductor spin in a very large magnetic field produced by the accretion disc, where there is a voltage induced between the poles in the black hole and its equator. The final result is that the force breaks down by slowing down the black hole …

To extract energy in this scenario, a path – as set by the user CapnTrippy on Everything2 – is to build a superconductor that orbits the black hole’s poles so that it can separate and remove some of the current flowing from the equator to the poles, rather than allowing it to be deposited in plasma in the ergosphere. Towards the black hole itself, this electrical energy has two sources: its rotational energy and that which remains in plasma. Since a black hole can carry up to 29% of its total mass as its rotational energy, it is also the maximum possible energy that can be extracted in this process. It is not good but it is still fantastic because black holes often weigh enough to be able to deliver power in the ages at the end. According to Nagasawa,

… for a solar mass with a 1 T magnetic field, the generated power is approximately 2.7 × 10 38 W. In perspective, the annual energy consumption is The world is estimated to be around … 5 × 10 20 J. The example case presents more energy in a single second than the whole world can manage in a year. Although this is a bold requirement to do, it is just an example case where not all energy produced is extractable as useful energy. At that point, even a system less than 10 -15 % will be effective enough to provide enough energy to drive the world for a full year.

The Blandford-Znajek process remains an object of active research to this day. Part of this is thankfully due to a cause that has little to do with driving the earth: relativistic jets. These are extremely powerful and narrow rays of radiation that travel at almost the speed of light as astronomers have observed in space. Astrophysicists believe that the Blandford-Znajek process and the Penrose mechanism together can explain how they are formed and shot from the poles of supermassive rotating black holes and travel billions of kilometers. In fact, the galaxy CGCG 049-033, located 680 million light-years from Earth, is believed to host a black hole weighing 2 billion solar masses that shoot floodlights in a dizzying 1.5 million light-years in space.

So the next time you read about black holes, don’t let the event horizon steal all the spotlights (even literally). There is also action and drama over its surface where things are still visible while acting in strange ways, where a gallery of plasma, energy fields, and a moving continuum exposes the gravity technique of the black hole to the complete image of the universe. Just remember that what you see is not what you get.

This article appears first on the author’s blog and has been published here with some changes.


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