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User:Scientrifica/Black hole

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A black hole is a place in space where from nothing, not even light, can escape. In general relativity,[1] if enough matter is packed into a tiny enough space, a black hole would be made. A black hole is black because light cannot escape to let us see it. Under quantum mechanics, black holes have a temperature. This because black holes release Hawking radiation, which makes them slowly get smaller.

Picture of a supermassive black hole

Because we cannot see black holes, people use other ways to find them. Because black holes have very strong gravity, stars and matter near them, can orbit them. This is how astronomers found a supermassive black hole of more than four million solar masses (four million of our sun) at the center of our Milky Way galaxy.[2] People can find black holes when gas moves around a black hole. This is because as the gas moves around the black hole, friction makes it hot and also makes it very bright. This can be seen by telescopes on Earth or in space such as Chandra or XMM Newton.

How black holes are made

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Gravitational collapse

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See the main article: Gravitational collapse

When very big stars run out of fuel for nuclear fusion they are crushed by their own gravity. This can also happen if more matter is added to the star, but it doesn't get hot enough to fuse that new matter.[3]

If the star wasn't big enough, it would become a white dwarf or a neutron star. But if the star was really big like more than 3-4 times the mass of our sun, it can turn into a black hole. When this happens, nothing can stop it from becoming a black hole. Some theories say it might become a quark star. But eventually, it becomes a black hole anyway.[3]

If you were watching a star turn into a black hole, you wouldn't see the event horizon being made. This is because for us, as the star collapses, the matter falling in, slows down and stops outside the event horizon because of gravitational time dilation. The light from the matter takes forever to reach you, so you would never see the event horizon being made. The matter falling into the black hole would look redder, and slowly disappear because of gravitational redshift.[4] But for the matter, it doesn't slow down or disappear, but falls into the black hole.

Primordial black holes and the Big Bang

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See the main article: Primordial black hole
 
Formation of the universe without (above) and with (below) primordial black holes

Black holes are made when a lot of matter is packed into a very tiny place. In our universe today, this happens when very big stars die. But, in the early universe, after the Big Bang, matter was packed very close together. If any place had more matter than other places a black hole would be made. These are called primordial black holes.

We have not found any primordial black holes but scientists think they might be real. We think primordial black holes may come in lots of different sizes, from super tiny to very big.[5]

High energy collisions

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A collision in which a micro black hole may be created

Scientists think if two particles are smashed together very hard, a black hole could be made. But, we have not seen this happen even in very powerful particle accelerators like LHC. This might be telling us, there is a mass needed to make a black hole.[6]

We think the smallest mass for a black hole is around the Planck mass. This means, any process here on Earth, no matter how high energy it is, might not be able to make black holes.[7] But, some ideas in quantum gravity say this smallest mass for a black hole could be much lower.[8] If this is true, then super tiny black holes could be made when cosmic rays hit Earth's atmosphere or in particle colliders like the Large Hadron Collider.

But, we don't know if these theories are true and many scientists think that black holes cannot be made in these ways.[9] But, even if we could make these black holes, they will disappear very fast, because of hawking radiation. This is because hawking radiation causes the black to get smaller. The smaller the black hole, the faster the hawking radiation escapes. So there is no danger to Earth.[10]

Growing Black Holes

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Black hole feeding on star

After a black hole is made, it can keep growing by eating matter. This matter can be gas, dust, and other stuff around it. This might be one way of creating the supermassive black holes we see at the center of most galaxies. But we do not really know how these black holes are made and we are still trying to understand them.[11] The same thing happens to intermediate-mass black holes, which are found in groups of stars called globular clusters. These black holes might have grown by eating up matter.[12]

Black holes can also smash into other black holes to create an even bigger black hole. This could also be how supermassive black holes are made.[13] This merging of black holes may have also created some intermediate-mass black holes.[14]

Quasi-stars

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See the main article: Quasi-star

In the early universe, there could have been very big stars. These stars were so big, their cores became black holes. The black hole at the center of these stars slowly ate the star from the inside making black holes that were as big as 1000 solar masses. These black holes may have become the supermassive black holes we have found in the centers of most galaxies.[15]

Properties of black holes

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See the main article: No-hair theorem

In the no hair theorem, black holes have only three properties that we can measure: mass, charge, and spin. If this is true, then if two black holes had the same mass, electric charge and spin then they would be the same. But, we do not know if the no hair theorem is true for real black holes.[16]

These properties are special, because we can measure them from outside the black hole. The mass can be found using Gauss's law but for gravity. We can also find the electric charge and how fast a black hole is spinning.[17] The angular momentum or spin can also be measured from far away.[18]

When anything falls into a black hole, we can still find out the mass, electric charge and how fast the object was spinning. But, we cannot find out what the object was made out of and other information about that object. It's as if the information disappeared. Imagine throwing a book into a black hole. We cannot know the shape, the cover, the atoms that made that book all erased. All we can know is the mass, spin and electric charge of that book which doesn't help. This is a very big problem because physics tells us information cannot just disappear. This puzzle is called the black hole information loss paradox.[19] [20]

Types of black holes

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The simplest types of black holes are called Schwarzschild black holes. These were discovered by Karl Schwarzschild in 1916. They have mass but don't spin or have an electric charge. We also have black holes that spin, black holes with electric charge and black holes with mass, spin and electric charge.[21]

Only spinning black holes are real.[further explanation needed] This is because black holes, come from very big, spinning stars that don't have any electric charge. This means that real black holes have mass, and can spin but don't have electric charge. But this also mean, there are no Schwarzschild black holes in the real universe. Some of these black holes spin very fast. For example, GRS 1915+105 is a black hole spinning at close to 90% the speed of light.[22]

When we talk about the size of a black hole, we use something called the Schwarzschild radius. To understand this, imagine that the black hole is a circle. If you draw a line from the center of the circle to the edge that is the Schwarzchild radius of the black hole. The heavier the black hole, the bigger its Schwarzschild radius. But, if a black hole spins really fast or has an electric charge, the Schwarzchild radius would be smaller than it is supposed to be. This is why the Schwarzchild radius only works for Schwarzschild black holes. These are black holes that do not spin and do not have electric charge which are not real.[21]

For example, the Schwarzchild radius of a black hole the mass of the Sun is 3 km.

Parts of a Black Hole

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Artistic depiction of a black hole and its features

The Event Horizon

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See the main article: Event Horizon
 
Far from the black hole, a particle can move anywhere
 
When the particle gets closer to the black hole, the space around it starts to bend or warp. This bending makes the particle to move to the black hole. But it can still escape
 
When the particle crosses the event horizon, it can only go to the center of the black hole. There is no way for the particle to escape from the black hole

A black hole is separated from the rest of the Universe by an invisible border called the event horizon. Anything which crosses the event horizon cannot escape, not even light. This means, if anything happens inside the event horizon, we cannot see it from outside the black hole because light cannot escape to allow us to see it.

Near a black hole, time appears to slow down. This is known as gravitational time dilation. This happens because gravity affects time. The stronger the gravity, the slower time passes. Objects seem to turn red and fade away when they reach the event horizon. This is known as gravitational redshift. A black hole is separated from the rest of the Universe by its event horizon. The Event Horizon is a border which separates the black hole from the rest of the Universe. Anything which crosses it cannot escape, not even light. We cannot see anything that happens inside the Event Horizon.[23][24]

The shape of the event horizon for non-rotating black holes is spherical and slightly flattened for spinning ones. Near a black hole, we would see objects slowing down. This is because gravity affects time. The stronger the gravity, the slower time is. This is what we call gravitational time dilation. We would also see the objects turn red and fade away when they reach the event horizon. This happens very fast and is what we call gravitational redshift.[25][26] But, anything falling into a black hole, would not feel itself slowing down or turning red.

The Event horizon for non-rotating black holes is circular and a little bit like an egg for spinning black holes.[27][28][29]

The Singularity

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See the main article: Gravitational singularity

At the center of a black hole, is the singularity. This is a point where the curvature of spacetime becomes infinite and density becomes infinite. In non-spinning black holes, this singularity is just a single point, while in spinning black holes, it's stretched into a ring shape.[30][31]

If someone falls into a non-spinning black hole, they will always be pulled towards the singularity once they cross the event horizon, no matter what you do.

For a charged or spinning black hole, you could be transported to another place in the universe or a different universe.[32] But this idea is mostly theoretical. There's also a weird situation where one could travel back in time around a rotating black hole, which would cause a lot of paradoxes.[33]

Because of the ridiculous gravitational forces near a black hole, any object falling into the black hole is stretched out into a noodle-like shape. This is known as "spaghettification."[34]

Singularities are a problem because they show that general relativity doesn't work in these extreme conditions. So singularities might not even exist or be something totally different. We think that a new theory that combines quantum mechanics and gravity would fix everything. But we haven't been able to create one.[35]

The Ergosphere

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See the main article: Ergosphere
 
The ergosphere is a place outside the event horizon, where objects cannot stay in one place

Spinning black holes have a special place around them called the "ergosphere." In this place, it's impossible to stay in one place because of "frame-dragging." According to general relativity, anything that spins will twist the spacetime around it. This is frame dragging. So, near a rotating black hole, things start spin around it. For a spinning black hole, frame-dragging is so strong that to stay in one place, you'd have to move backward faster than the speed of light, which is impossible.[3]

Inside the objects and energy can escape. But through the Penrose process, objects can actually come out of the ergosphere with more energy than when they went in. This energy comes from the spin of the black hole causing it to slow down.

In some cases with very strong magnetic fields, a special type of the Penrose process called Blandford-Znajek process is thought to be the cause of the extreme brightness and fast jets of matter in quasars and other active galactic nuclei.

Photon sphere

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See the main article: Photon sphere

Imagine a sphere around a black hole. We call it the "photon sphere." If a photon moves along the edge of this sphere, it gets stuck going in a circle around the black hole. However, the photon's orbit is not stable. Any small disturbance, like a tiny bit of matter falling in, will make the photon either escape from the black hole or fall into the black hole.[36]

When we see light from the photon sphere, it actually comes from objects which are between the photon sphere the event horizon.[36] If the black hole is spinning, how big the photonsphere is and it's properties depend on the black hole's spin and which way the photon is moving.[37]

Innermost Stable Circular Orbit

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See the main article: Innermost Stable Circular Orbit

In Newtonian gravity, objects were able to orbit a celestial body at any distance without any major issues. However, Albert Einstein's theory of general relativity changed everything. In his theort, we have what we call an "innermost stable circular orbit," or ISCO. This is the closest an object can safely orbit a black hole.

What makes the ISCO very interesting is that any slight disturbance, whether it's pushing an object into a black hole or pushing an object out into space, will affect the object a lot. An object pushed in towards the black hole will fall into it while an object pushed out into space depending on how much you push it, may fall into the black hole, start orbiting somewhere else around the black hole or just escape.[38]

Where the ISCO is, depends on how fast the black hole is spinning. The faster a black hole spins, the closer the ISCO while the slower the black hole spins the farther away the ISCO is. Where the ISCO is for an object is also depends on whether the object is moving with the black hole's spin or in the opposite direction.[39]

Hawking radiation

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See the main article: Hawking Radiation

In 1974, Stephen Hawking thought of an interesting idea: black holes aren't completely black; they emit a tiny amount of heat-like radiation called Hawking radiation. This radiation is because of the effects of quantum mechanics near black holes.[40]

Hawking radiation is black body radiation which is emitted by black hole, due to quantum effects near the event horizon. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974.[41]

Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as black hole evaporation. This happens because of the virtual particle-antiparticle pairs. Due to quantum fluctuations, this is when one of the particles falls in and the other gets away with the energy/mass. Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish. Micro black holes (MBHs) are predicted to be larger net emitters of radiation than larger black holes and should shrink and dissipate faster.

Properties of black holes

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See the main article: No-hair theorem

The no hair theorem basically says that once a black hole has formed, it only has three physical properties that we can measure: mass, charge, and spin. If this is true, then if two black holes had the same mass, charge and spin then they will look the same. As of 2020, it is unclear if the no hair theorem is true for real black holes.[42]

The properties are special, because all of them can be measured from outside the black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, far away from the black hole.[43] The angular momentum or spin can also be measured from far away.[44]

For instance, a black hole with the mass of our Sun has an incredibly low Hawking temperature, much colder than the cosmic microwave background. So, it would absorb more heat from its surroundings than it emits, and it would grow, not shrink.

To find a black hole that could actually evaporate and disappear, you'd need one much smaller than the Moon, with a tiny diameter. If it were as massive as a car, it would evaporate in a fraction of a second with a burst of intense radiation.

However, when black holes get this tiny, the effects of quantum gravity become crucial. Some theories suggest these miniature black holes could be stable, but current research doesn't confirm that.

Detecting Hawking radiation from big black holes is incredibly tough, and we've mostly focused on primordial black holes. These tiny black holes, if they exist, might emit bursts of gamma rays as they evaporate, but we haven't found them yet.

If black holes do evaporate through Hawking radiation, it would take an insanely long time. A black hole the mass of our Sun would take 10^64 years to disappear. Supermassive black holes in the centers of galaxies could grow huge but would still evaporate over an even longer timescale.

Some theories in quantum gravity suggest that Hawking's description might need modifications, especially when it comes to how black holes lose mass and charge.

Finding Black Holes

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We cannot see black holes. This is because they don't give off any kind of light or radiation that we can see directly, except for the theoretical Hawking radiation. So, when scientists want to find black holes, they have to use other ways.

One way to find a black hole is by watching the how stars and gas are moving because black holes have very strong gravity that can affect the things around it. For example, if you see a star or gas moving around something invisible, but that something has a strong pull on these objects, it's a good bet that there's a hidden black hole in the middle. Scientists use these to find and study the black holes in the universe.[45]

The EH Telescope

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The Event Horizon Telescope (EHT) is a project that allows us to get a close look at black holes, such as the one in the center of our Milky Way galaxy. In 2017, it started watching the black hole in a galaxy called Messier 87, and in April 2019, it showed us the first direct image of a black hole.[46][47][48]

 
The Event Horizon Telescope image of the Messier 87 Black Hole

The image doesn't show the black hole itself because it's entirely dark. What we actually see are the gases going around the black hole. But these are shown in shades of orange and red, which are fake colors added for us to see it better. These colors help scientists understand the it better.[49]

The brighter part of the bottom of the image above is because of Doppler beaming. This happens because the matter near the black hole is moving very fast, almost at the speed of light. As the matter moves fast, it makes it look brighter.[50]

The image makes it look like we're looking at the top of the black hole, but in the truth is, we are looking at the side of the black hole. The strong gravity around black holes affects light which changes how we see the black hole.

 
Sagittarius A* taken a picture of by the Event Horizon Telescope in 2017, released in 2022

In May 2022, EHT gave us another picture, this time of Sagittarius A*, the supermassive black hole at the center of our Milky Way. It looks similar to the M87 black hole, with a ring-like structure and a dark center. But taking a picture of Sagittarius A* was even harder because Sagittarius A* is much smaller and less massive than the black hole in M87.[51][52]

In 2015, EHT found magnetic fields outside the event horizon of Sagittarius A* and learned some things about them. These fields were a mix of ordered and tangled lines, confirming what theories had said about magnetic fields around black holes.[53]

Gravitational Waves

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On September 14, 2015, something groundbreaking happened at the LIGO observatory. They found gravitational waves for the first time ever. These waves came from two black holes merging. One black hole with about 36 times the mass of our Sun and the other around 29 solar masses. What we saw showed that black holes are real.

What's really amazing is that they also found something called the "post-merger ringdown." This is the signal produced as the newly merged black hole settles into a stable state. It's a direct way to see a black hole in action. From this signal, scientists were able to calculate the mass and spin of the final black hole, and this was the same as what they thought would happen using computer simulations of black hole mergers.

We also found the presence of a photon sphere using this observation. However, this discovery couldn't rule out some other things that it might be, but we think black holes are the more likely reasons for this.

This observation was a huge deal because it provided the first real hard evidence of two black hole with masses of 25 times the Sun or more. Since then, scientists have found many more events involving gravitational waves, opening a new way to study the universe.

Stars and Sagittarius A*

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The movements of stars near the center of our Milky Way galaxy provide strong proof that they are orbiting something incredibly massive, which is most likely a supermassive black hole. Since 1995, astronomers have closely tracked the motions of 90 stars circling around an invisible object that lines up with a radio source known as Sagittarius A*.

By studying these star movements and fitting them into a mathematical pattern called Keplerian orbits, scientists made a significant discovery in 1998. They calculated that an object with a mass of about 2.6 million times the mass of our Sun is concentrated in a tiny area with a radius of just 0.02 light-years. This hidden object is what causes the stars to move the way they do.

What's even more fascinating is that one of these stars, known as S2, has completed a full orbit. From S2's journey, astronomers fine-tuned their calculations, revealing that the mass of the hidden object is actually about 4.3 million times the mass of our Sun, and it's squeezed into a region smaller than 0.002 light-years across.

Although we can't directly confirm whether this object is smaller than its Schwarzschild radius (a measure related to the size of a black hole), these observations strongly suggest that it's a supermassive black hole. There aren't any other reasonable explanations for how so much invisible mass could be confined within such a tiny space.

Furthermore, there's some evidence suggesting that this object might have something called an "event horizon," which is a unique feature of black holes.

Accretion Disk

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When gas falls towards a massive object in space, like a neutron star or a black hole, it tends to form a flat, disk-like structure around that object because of the conservation of angular momentum. This disk is called an accretion disk. An accretion disk looks something like the rings of Saturn. As it gets sucked in, the matter gets very hot and shoots x-ray radiation into space. Think of this as the water spinning around the hole before it falls in.

Inside this disk, something interesting happens. Friction between the gas particles causes the angular momentum to be transported outward. This means that gas can fall further inward, getting closer to the massive object. As it gets closer, it releases potential energy and heats up, reaching extremely high temperatures.

When the gas is very close to a neutron star or a black hole, it moves at incredibly fast speeds due to the strong gravity of the compact object. The friction within the disk generates so much heat that it emits a tremendous amount of electromagnetic radiation, particularly X-rays. Telescopes can detect these bright X-ray sources in space.

This process of accretion, where matter falls onto a compact object and emits energy in the form of X-rays, is one of the most efficient ways to produce energy in the universe. It can convert up to 40% of the mass of the accreted material into radiation, which is much more efficient than nuclear fusion, where only about 0.7% of the mass is turned into energy.

In some cases, accretion disks are accompanied by jets of material that shoot out along the poles of the compact object at nearly the speed of light, carrying away a significant portion of the energy. However, scientists still don't fully understand how these jets are created.

Because of this accretion process, many energetic phenomena in the universe are associated with the matter falling onto black holes. Active galactic nuclei, quasars, and X-ray binaries are examples where this process is believed to play a significant role. Some ultraluminous X-ray sources may also be related to accretion disks around intermediate-mass black holes.

In November 2011, astronomers made a groundbreaking discovery by directly observing a quasar's accretion disk around a supermassive black hole. This observation provided valuable insights into the workings of these systems.

X-ray Binaries

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X-ray binaries are pairs of stars that mostly emit X-ray radiation. This happens because one star, which can be very compact, pulls material from its companion star. Scientists use these systems to investigate the central object and determine if it might be a black hole.

If signals from the system can be traced directly to the compact object, it's not a black hole. However, if there's no such signal, it could still be a black hole or a neutron star. Scientists look at the companion star to learn about the system's orbit and estimate the mass of the compact object. If that mass is way larger than what a regular star can have without collapsing, it's probably a black hole.

The first strong candidate for a black hole was found in 1972, but there were doubts because the companion star was much heavier.

Today, scientists search for better black hole candidates in a group of X-ray binaries called soft X-ray transients. These systems have companion stars with lower mass, making it easier to estimate the black hole's mass accurately. They also only emit a lot of X-rays for a few months every decade or so. During the quieter times, scientists can closely study the companion star. V404 Cygni is a good example of this.

Quasi-Periodic Oscillations

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When we observe X-ray emissions from accretion disks around compact objects, we sometimes notice flickering at specific frequencies. These flickering signals are known as quasi-periodic oscillations (QPOs). Scientists believe they occur because material is moving near the inner edge of the accretion disk, which is the closest point where matter can stably orbit around the compact object.

These QPOs have frequencies that are related to the mass of the compact object. So, when we detect these oscillations, they can serve as an alternative method to estimate the mass of a suspected black hole. By analyzing the frequency of these flickers, scientists can get insights into the mass of the object in question. It's like a cosmic fingerprint that helps us identify the mass of the candidate black hole.

Active Galactic Nucleus

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See the main article: Active galactic nucleus
See the main article: Quasar

Astronomers use the term "active galaxy" to describe galaxies that stand out due to unusual characteristics like peculiar spectral line emissions and strong radio emissions. These unique features are often linked to the presence of supermassive black holes called quasars at the center of these galaxies.

These supermassive black holes can be millions or even billions of times more massive than our Sun and shine brighter than an entire galaxy full of stars. Quasars are believed to be powered by gravity collecting material into supermassive black holes in the centers of distant galaxies. Light cannot escape the SBHs at the center of quasars, so the escaping energy is made outside the event horizon by gravitational stresses and immense friction on the incoming material.[54]

The theoretical models of these active galactic nuclei (AGN) typically consist of three main components: a colossal black hole at the center, surrounded by an accretion disk made of gas and dust, and two jets that shoot out perpendicularly (90 degrees) from the disk.

While it's expected that most AGN host supermassive black holes, researchers have closely examined only a select few galaxies' centers to identify and measure the actual masses of these central supermassive black hole candidates. Some notable galaxies with these candidates include the Andromeda Galaxy, M32, M87, NGC 3115, NGC 3377, NGC 4258, NGC 4889, NGC 1277, OJ 287, APM 08279+5255, and the Sombrero Galaxy.

In recent years, it has become widely accepted that nearly every galaxy, not just the active ones, houses a supermassive black hole at its core. There is a strong connection between the mass of this black hole and the velocity dispersion of the galaxy's central bulge, known as the M–sigma relation. This suggests a profound link between the formation of the supermassive black hole and the galaxy itself.

Gravitational Lensing

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See the main article: Gravitational lensing
 
Gravitational lensing of the galaxy by a black hole

When light from stars or galaxies far away moves close to a black hole, its gravity bends and changes the way light moves. This bending makes the distant stars or galaxies look funny or appear in a different place than were they actually are. It's similar to how a magnifying glass bends light to make things look bigger. This is known as gravitational lensing. It helps us see black holes that are far away, all by themselves.

Microlensing is another way that we find black holes. They are like a short and bright flash of light in the night sky. This happens when there's a black hole, moves between us and a star very far away. Even though we can't see the black hole, we can see the tiny, quick bright flash it makes as it moves in front of the star. It's as if someone turned on a very bright flashlight for a very short time in the night sky. In January 2022, astronomers saw what they think was the first ever time we have microlensing caused by a black hole.

Other things that might be Black Holes

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For small black holes, they form by the collapse of really heavy stars. There's a mass limit for a dense object to turn into a black hole. However, others suggest other things might exist like free quarks or preons.

According to the famous theory called general relativity, says that any object, no matter what it is made of, could become a black hole if it becomes too large.

Now, big black holes at the centers of galaxies are a bit different. They're easier to explain using our current physics knowledge. We have thought about other ideas, like groups of dark things, but those ideas usually don't match with what we see in space.

The fact that we've found both small and huge black holes tells us that our main theory of gravity, called general relativity, needs some changes when we start thinking about very tiny things, like particles. Scientists are working on a new theory called quantum gravity to understand black holes better. This new theory should help us deal with the weird stuff happening inside black holes, the crushing point called a singularity and the invisible boundary called an event horizon.

Some people have suggested other things instead of black holes, like gravastars, black stars, and dark-energy stars, but we have not seen these in space yet, so we're still figuring things out.

Some questions

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Information Paradox

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See the main article: Black hole information paradox

When things fall into a black hole, only the information about the mass, charge, and spin of that object is saved, but the rest of the information, like the shape and the atoms that made it are destroyed. This is a very big problem because physics tells us information cannot be destroyed. This problem is what we call the black hole information paradox. At first, we thought that black holes would live forever. If this was true then the information was just hiding inside the black hole which means information is not destroyed. But then Stephen Hawking came and said black holes do not live forever but slowly evaporate through hawking radiation. This meant information was destroyed.

Ever since then, scientists have tried to solve this problem. One idea is the lost information was on the surface of the black hole, which is what we call the holographic principle. Another idea is, there is a firewall inside the black hole which destroys anything that falls in. Which idea is correct is still hot topic of debate among scientists.[55] [56]

The Cosmic Censorship Hypothesis

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See the main article: Cosmic censorship hypothesis

Black holes are very extreme objects in the Universe. They can get ridiculously massive, nothing can escape and some can spin at up to 90% the speed of light. But things can get too extreme for a black hole. Black holes have only three properties: mass, electric charge and spin. If the black holes spin too fast or have too much electric charge, their event horizon would disappear and we would be able to see the singularity. These are known as naked singularities. If these exist, they could break physics as we know it.

Because of this, scientists think that something prevents the universe from having a naked singularity. Scientists think that something always makes sure that every singularity is hidden behind an event horizon. This is what we call the cosmic censorship hypothesis. But we are not sure if this is true or not.

References

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  1. ↑ Wald, Robert M. 1984. General Relativity. University of Chicago Press. ISBN 978-0-226-87033-5
  2. ↑ "Scientists find proof a black hole is lurking at the centre of our galaxy". Metro. 2018-10-31. Retrieved 2018-10-31.
  3. ↑ 3.0 3.1 3.2 Carroll, Sean M. (1973). Spacetime and geometry: an introduction to general relativity (Nachdr. ed.). San Francisco Munich: Addison-Wesley. ISBN 978-0-8053-8732-2.
  4. ↑ Penrose, Roger 2002 (2002). "Gravitational collapse:the role of general relativity" (PDF). General Relativity and Gravitation. 34 (7): 1141. Bibcode:2002GReGr..34.1141P. doi:10.1023/A:1016578408204. S2CID 117459073. Archived from the original (PDF) on 2013-05-26. Retrieved 2013-01-05.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  5. ↑ Suzuki, H., ed. (2006). Inflating horizons of particle astrophysics and cosmology: proceedings of the Yamada Conference LIX, held on June 20 - 24, 2005, in Tokyo, Japan. Frontiers science series. Tokyo: Universal Acadademy Press, Inc. ISBN 978-4-946443-94-7.
  6. ↑ Giddings, Steven B.; Thomas, Scott (2002-02-12). "High energy colliders as black hole factories: The end of short distance physics". Physical Review D. 65 (5). doi:10.1103/PhysRevD.65.056010. ISSN 0556-2821.
  7. ↑ Harada, Tomohiro (2006-10-04). "Is there a black hole minimum mass?". Physical Review D. 74 (8). doi:10.1103/PhysRevD.74.084004. ISSN 1550-7998.
  8. ↑ Arkani–Hamed, Nima; Dimopoulos, Savas; Dvali, Gia (1998). "The hierarchy problem and new dimensions at a millimeter". Physics Letters B. 429 (3–4): 263–272. doi:10.1016/S0370-2693(98)00466-3.
  9. ↑ Ellis, John; Giudice, Gian; Mangano, Michelangelo; Tkachev, Igor; Wiedemann, Urs; LHC Safety Assessment Group (2008-11-01). "Review of the safety of LHC collisions". Journal of Physics G: Nuclear and Particle Physics. 35 (11): 115004. doi:10.1088/0954-3899/35/11/115004. ISSN 0954-3899.
  10. ↑ "Particle accelerators as black hole factories? — Einstein Online". web.archive.org. 2013-05-08. Retrieved 2023-09-10.
  11. ↑ Rees, Martin J.; Volonteri, Marta (2006). "Massive black holes: formation and evolution". Proceedings of the International Astronomical Union. 2 (S238): 51–58. doi:10.1017/S1743921307004681. ISSN 1743-9213.
  12. ↑ Vesperini, Enrico; McMillan, Stephen L. W.; D'Ercole, Annibale; D'Antona, Francesca (2010-04-10). "INTERMEDIATE-MASS BLACK HOLES IN EARLY GLOBULAR CLUSTERS". The Astrophysical Journal. 713 (1): L41–L44. doi:10.1088/2041-8205/713/1/L41. ISSN 2041-8205.
  13. ↑ Portegies Zwart, Simon F.; Baumgardt, Holger; Hut, Piet; Makino, Junichiro; McMillan, Stephen L. W. (2004). "Formation of massive black holes through runaway collisions in dense young star clusters". Nature. 428 (6984): 724–726. doi:10.1038/nature02448. ISSN 0028-0836.
  14. ↑ O’Leary, Ryan M.; Rasio, Frederic A.; Fregeau, John M.; Ivanova, Natalia; O’Shaughnessy, Richard (2006). "Binary Mergers and Growth of Black Holes in Dense Star Clusters". The Astrophysical Journal. 637 (2): 937–951. doi:10.1086/498446. ISSN 0004-637X.
  15. ↑ Rees M.J. & Volonteri M 2007 (2006). Karas, V; Matt, G (eds.). Massive black holes: Formation and evolution. Vol. 2. Cambridge University Press. pp. 51–58. arXiv:astro-ph/0701512. doi:10.1017/S1743921307004681. ISBN 978-0-521-86347-6. S2CID 14844338. {{cite book}}: |journal= ignored (help)CS1 maint: numeric names: authors list (link)
  16. ↑ Chruściel, Piotr T.; Costa, João Lopes; Heusler, Markus (2012). "Stationary Black Holes: Uniqueness and Beyond". Living Reviews in Relativity. 15 (1): 7. arXiv:1205.6112. Bibcode:2012LRR....15....7C. doi:10.12942/lrr-2012-7. ISSN 1433-8351. PMC 5255892. PMID 28179837.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  17. ↑ Carroll, Sean M. (2004). Spacetime and Geometry. Addison Wesley. p. 253. ISBN 978-0-8053-8732-2.. The lecture notes on which the book was based are available for free from Sean Carroll's website.
  18. ↑ Reynolds, Christopher S. (January 2019). "Observing black holes spin". Nature Astronomy. 3 (1): 41–47. arXiv:1903.11704. Bibcode:2019NatAs...3...41R. doi:10.1038/s41550-018-0665-z. ISSN 2397-3366. S2CID 85543351.
  19. ↑ Anderson,, Warren G. (1996). "Black Hole Information Loss Problem".{{cite web}}: CS1 maint: extra punctuation (link)
  20. ↑ Preskill, J. (1994). "Black holes and information: A crisis in quantum physics" (PDF). web.archive.org. Retrieved 2023-09-08.
  21. ↑ 21.0 21.1 Shapiro, Stuart L.; Teukolsky, Saul A.; Shapiro, Stuart Louis; Teukolsky, Saul Arno (2004). Black holes, white dwarfs, and neutron stars: the physics of compact objects. Physics textbook. Weinheim: Wiley-VCH. ISBN 978-0-471-87316-7.
  22. ↑ McClintock, Jeffrey E.; Shafee, Rebecca; Narayan, Ramesh; Remillard, Ronald A.; Davis, Shane W.; Li, Li‐Xin (2006-11-20). "The Spin of the Near‐Extreme Kerr Black Hole GRS 1915+105". The Astrophysical Journal. 652 (1): 518–539. doi:10.1086/508457. ISSN 0004-637X.
  23. ↑ Fleisch, Daniel A.; Kregenow, Julia (2013). A student's guide to the mathematics of astronomy. New York: Cambridge university press. ISBN 978-1-107-03494-5.
  24. ↑ Davies, Paul, ed. (2000). The new physics. Cambridge: Univ. Press. ISBN 978-0-521-43831-5.
  25. ↑ "Inside a black hole". web.archive.org. 2009-04-23. Retrieved 2023-09-09.
  26. ↑ "What happens to you if you fall into a black holes". math.ucr.edu. Retrieved 2023-09-09.
  27. ↑ Smarr, Larry (1973-01-15). "Surface Geometry of Charged Rotating Black Holes". Physical Review D. 7 (2): 289–295. doi:10.1103/PhysRevD.7.289. ISSN 0556-2821.
  28. ↑ Wiltshire, David L.; Visser, Matt; Scott, Susan M., eds. (2009). The Kerr spacetime: rotating black holes in general relativity (1. publ ed.). Cambridge: Cambridge Univ. Press. ISBN 978-0-521-88512-6.
  29. ↑ Delgado, Jorge F. M.; Herdeiro, Carlos A. R.; Radu, Eugen (2018-06-07). "Horizon geometry for Kerr black holes with synchronized hair". Physical Review D. 97 (12). doi:10.1103/PhysRevD.97.124012. ISSN 2470-0010.
  30. ↑ Carroll 2004. p-205
  31. ↑ "Sizes of Black Holes? How Big is a Black Hole?". Sky and Telescope. 22 July 2014. {{cite web}}: |archive-date= requires |archive-url= (help)
  32. ↑ Droz, Serge; Israel, Werner; Morsink, Sharon M (1996). "Black holes: the inside story". Physics World. 9 (1): 34–37. doi:10.1088/2058-7058/9/1/26. ISSN 0953-8585.
  33. ↑ Poisson, Eric; Israel, Werner (1990-03-15). "Internal structure of black holes". Physical Review D. 41 (6): 1796–1809. doi:10.1103/PhysRevD.41.1796. ISSN 0556-2821.
  34. ↑ Wheeler. 2007. pg-182
  35. ↑ "Black holes and quantum gravity". web.archive.org. 2009-04-07. Retrieved 2023-09-09.
  36. ↑ 36.0 36.1 Nitta, Daisuke; Chiba, Takeshi; Sugiyama, Naoshi (2011-09-14). "Shadows of colliding black holes". Physical Review D. 84 (6). doi:10.1103/PhysRevD.84.063008. ISSN 1550-7998.
  37. ↑ Bardeen, James M.; Press, William H.; Teukolsky, Saul A. (1972). "Rotating Black Holes: Locally Nonrotating Frames, Energy Extraction, and Scalar Synchrotron Radiation". The Astrophysical Journal. 178: 347. doi:10.1086/151796. ISSN 0004-637X.
  38. ↑ Misner, Thorne & Wheeler 1973
  39. ↑ Bardeen, James M.; Press, William H.; Teukolsky, Saul A. (1972). "Rotating Black Holes: Locally Nonrotating Frames, Energy Extraction, and Scalar Synchrotron Radiation". The Astrophysical Journal. 178: 347. doi:10.1086/151796. ISSN 0004-637X.
  40. ↑ Hawking, S. W. (1974-03-01). "Black hole explosions?". Nature. 248 (5443): 30–31. doi:10.1038/248030a0. ISSN 0028-0836.
  41. ↑ "Charlie Rose: A conversation with Dr. Stephen Hawking & Lucy Hawking". Archived from the original on 2013-03-29. Retrieved 2012-11-29.
  42. ↑ Chruściel, Piotr T.; Costa, João Lopes; Heusler, Markus (2012). "Stationary Black Holes: Uniqueness and Beyond". Living Reviews in Relativity. 15 (1): 7. arXiv:1205.6112. Bibcode:2012LRR....15....7C. doi:10.12942/lrr-2012-7. ISSN 1433-8351. PMC 5255892. PMID 28179837.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  43. ↑ Carroll, Sean M. (2004). Spacetime and Geometry. Addison Wesley. p. 253. ISBN 978-0-8053-8732-2.. The lecture notes on which the book was based are available for free from Sean Carroll's website. If Hawking is right, then black holes should gradually shrink and disappear as they lose mass through Hawking radiation. The temperature of this radiation, known as the Hawking temperature, depends on the black hole's size. Bigger black holes emit less radiation than smaller ones.
  44. ↑ Reynolds, Christopher S. (January 2019). "Observing black holes spin". Nature Astronomy. 3 (1): 41–47. arXiv:1903.11704. Bibcode:2019NatAs...3...41R. doi:10.1038/s41550-018-0665-z. ISSN 2397-3366. S2CID 85543351.
  45. ↑ "Black Holes | Science Mission Directorate". science.nasa.gov. Retrieved 2023-09-10.
  46. ↑ Press, The Associated (2019-04-10). "Video: Astronomers Reveal the First Picture of a Black Hole". The New York Times. ISSN 0362-4331. Retrieved 2023-09-10.
  47. ↑ "April 2017 Observations". eventhorizontelescope.org. Retrieved 2023-09-10.
  48. ↑ Overbye, Dennis (2019-04-10). "Darkness Visible, Finally: Astronomers Capture First Ever Image of a Black Hole". The New York Times. ISSN 0362-4331. Retrieved 2023-09-10.
  49. ↑ "The first picture of a black hole opens a new era of astrophysics". 2019-04-10. Retrieved 2023-09-10.
  50. ↑ Akiyama, Kazunori; Algaba, Juan Carlos; Alberdi, Antxon; Alef, Walter; Anantua, Richard; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Ball, David; Baloković, Mislav; Barrett, John (2021-03-01). "First M87 Event Horizon Telescope Results. VII. Polarization of the Ring". The Astrophysical Journal Letters. 910 (1): L12. doi:10.3847/2041-8213/abe71d. ISSN 2041-8205.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  51. ↑ "ShieldSquare Captcha". iopscience.iop.org. Retrieved 2023-09-10.
  52. ↑ "Astronomers Reveal First Image of the Black Hole at the Heart of Our Galaxy". eventhorizontelescope.org. 2022-05-12. Retrieved 2023-09-10.
  53. ↑ Johnson, Michael D.; Fish, Vincent L.; Doeleman, Sheperd S.; Marrone, Daniel P.; Plambeck, Richard L.; Wardle, John F. C.; Akiyama, Kazunori; Asada, Keiichi; Beaudoin, Christopher; Blackburn, Lindy; Blundell, Ray (2015-12-04). "Resolved magnetic-field structure and variability near the event horizon of Sagittarius A*". Science. 350 (6265): 1242–1245. doi:10.1126/science.aac7087. ISSN 0036-8075.
  54. ↑ Thomsen D.E. 1987. End of the World: you won't feel a thing. Science News 131 (25): 391.
  55. ↑ Anderson,, Warren G. (1996). "Black Hole Information Loss Problem".{{cite web}}: CS1 maint: extra punctuation (link)
  56. ↑ Preskill, J. (1994). "Black holes and information: A crisis in quantum physics" (PDF). web.archive.org. Retrieved 2023-09-08.
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