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(Image credit: Event Horizon Telescope Collaboration)

We still don't know exactly what happens when black holes die.

Ever since Stephen Hawking discovered that black holes , we've known that they can potentially disappear from our universe. But our understanding of gravity and quantum mechanics isn't powerful enough to describe the last moments of a black hole's life.

Now, new research motivated by string theory suggests possible, and equally strange, fates for evaporating black holes: a remnant nugget that we could, in principle, access, or a singularity not shrouded by an event horizon.

Related: What happens at the center of a black hole?

The importance of Hawking radiation

Black holes aren't, strictly speaking, entirely black. In pure general relativity, with no other modifications or considerations of other physics, they remain black for eternity. Once one forms, it will just hang out there, being a black hole, forever. But in the 1970s, Hawking used the language of quantum mechanics to explore what happens near the boundary of a black hole, known as the event horizon.

He found that, surprisingly, a strange interaction between the quantum fields of our universe and the one-way barrier of the event horizon allowed a pathway for energy to escape the black hole. This energy takes the form of a slow-but-steady stream of radiation and particles that came to be known as Hawking radiation. With every bit of energy that escapes, the black hole loses mass and thereby shrinks, eventually popping out of existence altogether.

The appearance of Hawking radiation has created what's known as the black hole information paradox. All of the information that describes the material that falls into a black hole crosses the event horizon, never to be seen again. But Hawking radiation itself doesn't carry any information with it, and yet the black hole eventually disappears. So where did all the information go?
Related: Stephen Hawking Was Right: Black Holes Can Evaporate, Weird New Study Shows
Going beyond Einstein

The black hole information paradox is a giant, flashing neon sign to physicists that we're not understanding something. It may be that we don't understand the nature of quantum information, the nature of or the nature of event horizons - or all three. The "easiest" approach to solving the black hole information paradox is to develop a new theory of gravity, going beyond Einstein's theory of general relativity.

After all, we already know that general relativity breaks down in the centers of black holes, which are tiny punctures in space-time known as singularities where the density goes to infinity. The only way to correctly describe the singularity is through a quantum theory of gravity that properly predicts how strong gravity behaves at extremely tiny scales.

Unfortunately, we currently lack a theory of quantum gravity. It would be nice to look at singularities directly, but as far as we understand through general relativity, all singularities are locked away behind event horizons, making them inaccessible to us.

But by studying the process of Hawking radiation, we may be able to find a shortcut to getting close to a singularity and understanding the crazy physics that happens there. As black holes evaporate, they get smaller and smaller and their event horizons get uncomfortably close to the central singularities. In the final moments of black holes' lives, the gravity becomes too strong, and the black holes become too small, for us to properly describe them with our current knowledge. So, if we can develop a better theory of gravity, we can use the final moments of Hawking radiation to test how the theory behaves.

There are many candidates for a quantum theory of gravity, with string theory the most developed. Even though there are no known solutions to string theory, it's possible to take what we do know about the general features of the theory and use them to make modified versions of general relativity.

(Image credit: NRAO/AUI)

Related: How Stephen Hawking transformed our understanding of black holes

Naked singularities

These modified theories aren't the "full" correct replacements for general relativity, but they allow us to examine how gravity might behave as it gets closer and closer to the quantum limit. Recently, a team of theorists used one such theory, known as Einstein-dilaton-Gauss-Bonnet gravity, to investigate the final end states of evaporating black holes. They detailed their work in a paper posted to the preprint database arXiv (opens in new tab) in May.

The details of the team's results are a little fuzzy. This is because modified general relativity isn't as well understood as regular general relativity, and solving the complicated math requires a host of approximations and a lot of guesswork. Still, the researchers were able to paint a general picture of what's going on.

One of the key features of Einstein-dilaton-Gauss-Bonnet gravity is that black holes have a minimum mass, so the theorists were able to study what happens when an evaporating black hole begins to reach that minimum mass.

In some cases, depending on the exact nature of the theory and the evolution of the black hole, the evaporation process leaves behind a microscopic nugget. This nugget would lack an event horizon, so in principle, you could fly your spaceship to it and pick it up. While the nugget would be extremely exotic, it would at least retain all the information that fell into the original black hole, thereby solving the paradox.

Another possibility is that the black hole reaches its minimum mass and sheds its event horizon but still maintains a singularity. These "naked singularities" appear to be forbidden in normal general relativity, but if they exist, they would be direct windows into the realm of quantum gravity.

It's still unclear if Einstein-dilaton-Gauss-Bonnet gravity represents a valid path toward quantum gravity. But results like this help physicists illuminate one of the most complex scenarios in the universe, and potentially provide guidance on how to solve them.

Learn more by listening to the "Ask a Spaceman" podcast, available on (opens in new tab) and askaspaceman.com (opens in new tab) . Ask your own question on Twitter using #AskASpaceman or by following Paul @PaulMattSutter (opens in new tab) and facebook.com/PaulMattSutter (opens in new tab) .

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Black holes may die differently than we thought

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(Image credit: Event Horizon Telescope Collaboration) We still don't know exactly what happens when black holes die. Ever since Stephen Hawking discovered that black holes , we've known that they can potentially disappear from our universe. But our understanding of gravity and quantum mechanics isn't powerful enough to describe the last moments of a black hole's life.

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Globular Cluster Omega Centauri Looks Radiant in Infrared

A cluster brimming with millions of stars glistens like an iridescent opal in this image from NASA's Spitzer Space Telescope. Called Omega Centauri, the sparkling orb of stars is like a miniature galaxy. It is the biggest and brightest of the 150 or so similar objects, called globular clusters, that orbit around the outside of our Milky Way galaxy. Stargazers at southern latitudes can spot the stellar gem with the naked eye in the constellation Centaurus. Globular clusters are some of the oldest objects in our universe. Their stars are over 12 billion years old, and, in most cases, formed all at once when the universe was just a toddler. Omega Centauri is unusual in that its stars are of different ages and possess varying levels of metals, or elements heavier than boron. Astronomers say this points to a different origin for Omega Centauri than other globular clusters: they think it might be the core of a dwarf galaxy that was ripped apart and absorbed by our Milky Way long ago. In this new view of Omega Centauri, Spitzer's infrared observations have been combined with visible-light data from the National Science Foundation's Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile. Visible-light data with a wavelength of .55 microns is colored blue, 3.6-micron infrared light captured by Spitzer's infrared array camera is colored green and 24-micron infrared light taken by Spitzer's multiband imaging photometer is colored red. Where green and red overlap, the color yellow appears. Thus, the yellow and red dots are stars revealed by Spitzer. These stars, called red giants, are more evolved, larger and dustier. The stars that appear blue were spotted in both visible and 3.6-micron-, or near-, infrared light. They are less evolved, like our own sun. Some of the red spots in the picture are distant galaxies beyond our own.

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Black holes are some of the strangest and most fascinating objects in space. They're extremely dense, with such strong gravitational attraction that not even light can escape their grasp.

The Milky Way could contain over 100 million black holes, though detecting these gluttonous beasts is very difficult. At the heart of the Milky Way lies a supermassive black hole - Sagittarius A*. The colossal structure is about 4 million times the mass of the sun and lies approximately 26,000 light-years away from , according to a statement from NASA.

The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The striking photo of the black hole at the center of the M87 galaxy 55 million light-years from Earth thrilled scientists around the world.

Related: White holes: What we know about black holes' neglected twins

Black hole FAQs answered by an expert

We asked theoretical astrophysicist Priyamvada Natarajan a few commonly asked questions about black holes.

Theoretical Astrophysicist

First black hole discovered

Albert Einstein first predicted the existence of black holes in 1916, with his general theory of relativity. The term "black hole" was coined many years later in 1967 by American astronomer John Wheeler. After decades of black holes being known only as theoretical objects.

The first black hole ever discovered was Cygnus X-1, located within the Milky Way in the constellation of Cygnus, the Swan. Astronomers saw the first signs of the black hole in 1964 when a sounding rocket detected celestial sources of X-rays according to NASA. In 1971, astronomers determined that the X-rays were coming from a bright blue star orbiting a strange dark object. It was suggested that the detected X-rays were a result of stellar material being stripped away from the bright star and "gobbled" up by the dark object - an all-consuming black hole.

How many black holes are there?

According to the Space Telescope Science Institute (STScI) approximately one out of every thousand stars is massive enough to become a black hole. Since the Milky Way contains over 100 billion stats, our home galaxy must harbor some 100 million black holes.

Though detecting black holes is a difficult task and estimates from NASA suggest there could be as many as 10 million to a billion stellar black holes in the Milky Way.

The closest black hole to Earth is dubbed " The Unicorn" and is situated approximately 1,500 light-years away. The nickname has a double meaning. Not only does the black hole candidate reside in the constellation Monoceros ("the unicorn"), its incredibly low mass - about three times that of the sun - makes it nearly one of a kind.
Related: How many black holes are there in the universe?
Black hole images

In 2019 the Event Horizon Telescope (EHT) collaboration released the first image ever recorded of a black hole. The EHT saw the black hole in the center of galaxy M87 while the telescope was examining the event horizon or the area past which nothing can escape from a black hole. The image maps the sudden loss of photons (particles of light). It also opens up a whole new area of research in black holes, now that astronomers know what a black hole looks like.

In 2021, astronomers revealed a new view of the giant black hole at the center of M87, showing what the colossal structure looks like in polarized light. As polarized light waves have a different orientation and brightness compared to unpolarized light, the new image shows the black hole in even more detail. Polarization is a signature of magnetic fields and the image makes it clear that the black hole's ring is magnetized.

In May 2022, scientists revealed the historic first image of the supermassive black hole at the center of our galaxy - Sagitarrius A*.

Related: The 1st photo of the Milky Way's monster black hole explained in images

What do black holes look like?

Black holes have three "layers": the outer and inner event horizon, and the singularity.

The event horizon of a black hole is the boundary around the mouth of the black hole, past which light cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the event horizon.

The inner region of a black hole, where the object's mass lies, is known as its singularity, the single point in space-time where the mass of the black hole is concentrated.

Scientists can't see black holes the way they can see stars and other objects in space. Instead, astronomers must rely on detecting the radiation black holes emit as dust and gas are drawn into the dense creatures. But supermassive black holes, lying in the center of a galaxy, may become shrouded by the thick dust and gas around them, which can block the telltale emissions.

Sometimes, as matter is drawn toward a black hole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the maw. Bright jets of material traveling at near-relativistic speeds are created. Although the black hole remains unseen, these powerful jets can be viewed from great distances.

The EHT's image of a black hole in M87 (released in 2019) was an extraordinary effort, requiring two years of research even after the images were taken. That's because the collaboration of telescopes, which stretches across many observatories worldwide, produces an astounding amount of data that is too large to transfer via the internet.

With time, researchers expect to image other black holes and build up a repository of what the objects look like. The next target is likely Sagittarius A*, which is the black hole in the center of our own Milky Way galaxy. Sagittarius A* is intriguing because it is quieter than expected, which may be due to magnetic fields smothering its activity, a 2019 study reported. Another study that year showed that a cool gas halo surrounds Sagittarius A*, which gives unprecedented insight into what the environment around a black hole looks like.

Types of black holes

So far, astronomers have identified three types of black holes: stellar black holes, supermassive black holes and intermediate black holes.

Stellar black holes - small but deadly

When a star burns through the last of its fuel, the object may collapse, or fall into itself. For smaller stars (those up to about three times 's mass), the new core will become a neutron star or a white dwarf. But when a larger star collapses, it continues to compress and creates a stellar black hole.

Black holes formed by the collapse of individual stars are relatively small but incredibly dense. One of these objects packs more than three times the mass of the sun into the diameter of a city. This leads to a crazy amount of gravitational force pulling on objects around the object. Stellar black holes then consume the dust and gas from their surrounding galaxies, which keeps them growing in size.

Supermassive black holes - the birth of giants

Small black holes populate the universe, but their cousins, supermassive black holes, dominate. These enormous black holes are millions or even billions of times as massive as the sun but are about the same size in diameter. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.

Scientists aren't certain how such large black holes spawn. Once these giants have formed, they gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to even more enormous sizes.

Supermassive black holes may be the result of hundreds or thousands of tiny black holes that merge. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass. A third option is the collapse of a stellar cluster, a group of stars all falling together. Fourth, supermassive black holes could arise from large clusters of dark matter. This is a substance that we can observe through its gravitational effect on other objects; however, we don't know what dark matter is composed of because it does not emit light and cannot be directly observed.

Scientists once thought that black holes came in only small and large sizes, but research has revealed the possibility that midsize, or intermediate, black holes (IMBHs) could exist. Such bodies could form when stars in a cluster collide in a chain reaction. Several of these IMBHs forming in the same region could then eventually fall together in the center of a galaxy and create a supermassive black hole.

In 2014, astronomers found what appeared to be an intermediate-mass black hole in the arm of a spiral galaxy. And in 2021 astronomers took advantage of an ancient gamma-ray burst to detect one.

"Astronomers have been looking very hard for these medium-sized black holes," study co-author Tim Roberts, of the University of Durham in the United Kingdom, said in a statement. "There have been hints that they exist, but IMBHs have been acting like a long-lost relative that isn't interested in being found."

Research, from 2018, suggested that these IMBHs may exist in the heart of dwarf galaxies (or very small galaxies). Observations of 10 such galaxies (five of which were previously unknown to science before this latest survey) revealed X-ray activity - common in black holes - suggesting the presence of black holes of from 36,000 to 316,000 solar masses. The information came from the Sloan Digital Sky Survey, which examines about 1 million galaxies and can detect the kind of light often observed coming from black holes that are picking up nearby debris.

Binary black holes: double trouble

In 2015, astronomers using the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves from merging stellar black holes.

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses - these are objects we didn't know existed before LIGO detected them," David Shoemaker, the spokesperson for the LIGO Scientific Collaboration (LSC), said in a statement. LIGO's observations also provide insights into the direction a black hole spins. As two black holes spiral around one another, they can spin in the same direction or the opposite direction.

There are two theories on how binary black holes form. The first suggests that the two black holes in a binary form at about the same time, from two stars that were born together and died explosively at about the same time. The companion stars would have had the same spin orientation as one another, so the two black holes left behind would as well.

Under the second model, black holes in a stellar cluster sink to the center of the cluster and pair up. These companions would have random spin orientations compared to one another according to LIGO Scientific Collaboration. LIGO's observations of companion black holes with different spin orientations provide stronger evidence for this formation theory.

"We're starting to gather real statistics on binary black hole systems," said LIGO scientist Keita Kawabe of Caltech, who is based at the LIGO Hanford Observatory. "That's interesting because some models of black hole binary formation are somewhat favored over the others even now, and in the future, we can further narrow this down."

If you fell into a black hole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached the singularity. But a 2012 study published in the journal Nature suggested that quantum effects would cause the event horizon to act much like a wall of fire, which would instantly burn you to death.

Black holes don't suck. Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them just as they fall toward anything that exerts gravity, like the Earth.

The first object considered to be a black hole is Cygnus X-1. Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and fellow physicist Kip Thorne, with Hawking betting that the source was not a black hole. In 1990, Hawking conceded defeat.

Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun.

If a star passes too close to a black hole, the star can be torn apart.

Astronomers estimate that the Milky Way has anywhere from 10 million to 1 billion stellar black holes, with masses roughly three times that of the sun.

Black holes remain terrific fodder for science fiction books and movies. Check out the movie "Interstellar," which relied heavily on Thorne to incorporate science. Thorne's work with the movie's special effects team led to scientists' improved understanding of how distant stars might appear when seen near a fast-spinning black hole.

Black hole facts

Additional resources

Dive deeper into the mystery of black holes with NASA Science. Watch videos and read more about black holes from NASA's Hubblesite. Discover more about black holes with the National Science Foundation.

Bibliography

Hubblesite: Black holes: Gravity's relentless pull interactive: Encyclopedia. STScI Home. Retrieved May 6, 2022.

NASA. Imagine the universe! NASA. Retrieved May 6, 2022.

Boen, B. (2013, August 29). Supermassive black hole Sagittarius A*. NASA. Retrieved May 6, 2022.

NASA's Chandra Finds Intriguing Member of Black Hole Family Tree. Chandra X-ray Observatory. (2015, February 25). Retrieved May 6, 2022.

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Black holes: Everything you need to know

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Black holes are real, they're some of the strangest objects in space. Discover what black holes are and how they form with our informative black hole guide.

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The supermassive black hole inside the core of the supergiant elliptical galaxy Messier 87 in the constellation Virgo. The black hole was the first to be directly imaged (Event Horizon Telescope, released April 10, 2019).[1][2]

A black hole is a region of space-time from which nothing, not even light, can escape. According to the general theory of relativity, it starts existing when spacetime gets curved by a huge mass. There is a sphere around the black hole. If something goes inside the sphere, it cannot leave. This sphere is called the event horizon. A black hole is black because it absorbs all the light that hits it. It reflects nothing, just like a perfect black body in thermodynamics. Under quantum mechanics, black holes have a temperature and emit Hawking radiation, which makes them slowly get smaller.

Because black holes are very hard to see, people find them by the way they affect other things near them. The place where there is a black hole can be found by tracking the movement of stars that orbit somewhere in space. Or people can find it when gas falls into a black hole, because the gas heats up and is very bright. This can be found by telescopes on Earth or by Earth-orbiting telescopes such as Chandra or XMM Newton. Inside a black hole the rules of physics are very different.

Astronomers have found evidence of supermassive black holes at the center of almost all galaxies. In 2008 astronomers found evidence that a supermassive black hole of more than four million solar masses is near the Sagittarius A* part of the Milky Way galaxy.

Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background (larger animation)

In 1783, an English clergyman named Shambhab Tiwari wrote that it might be possible for something to be so heavy you would have to go at the speed of light to get away from its gravity. Gravity gets stronger as something gets more massive. For a small thing, like a rocket, to escape from a larger thing, like Earth, it has to escape the pull of the Earth's gravity or it will fall back. The speed that it must travel to get away is called escape velocity. Bigger planets (like Jupiter) and stars have more mass, and have stronger gravity than Earth. Therefore, the escape velocity would need to be much faster. John Michell thought it was possible for something to be so big that the escape velocity would need to be faster than the speed of light, so even light could not escape. In 1796, Pierre-Simon Laplace wrote about the same idea in the first and second editions of his book Exposition du système du Monde (it was removed from later editions).

Some scientists thought Michell might be right, but others thought that light had no mass and would not be pulled by gravity. His theory was forgotten.

In 1916 Albert Einstein wrote an explanation of gravity called general relativity.

Mass causes space (and spacetime) to bend, or curve. Moving things "fall along" or follow the curves in space. This is what we call gravity.

Light always travels at the same speed, and is affected by gravity. If it seems to change speed, it is really traveling along a curve in spacetime.

A few months later, while serving in World War I, the German physicist Karl Schwarzschild used Einstein's equations to show that a black hole could exist. The Schwarzschild radius is the size of the event horizon of a non-rotating black hole. This radius was the measurement where the escape velocity was equal to the speed of light. If the radius of a star is smaller, then light is unable to escape, and it would be a dark star, or black hole.

In 1930, Subrahmanyan Chandrasekhar predicted that stars heavier than the sun could collapse when they ran out of hydrogen or other nuclear fuels to burn. In 1939, Robert Oppenheimer and H. Snyder calculated that a star would have to be at least three times as massive as the Sun to form a black hole. In 1967, John Wheeler invented the name "black hole" for the first time. Before that, they were called "dark stars".

In 1970, Stephen Hawking and Roger Penrose showed that black holes must exist. Although the black holes are invisible (they cannot be seen), some of the matter that is falling into them is very bright.

As of spring 2019, there was an image of a black hole, or rather, the things orbiting the black hole. The image required many photos from different locations. One of the team members (Katie Bouman) made a compilation of all the images into one singular image.

In 2020, Roger Penrose, Reinhard Genzel and Andrea Ghez were awarded the Nobel Prize in Physics for their work on the theory of black holes.

The gravitational collapse of huge (high- mass) stars cause "stellar mass" black holes. This happens when really big stars run out of fuel.

Star formation in the early universe may have created very big stars. These stars were so large that their cores collapsed into black holes. The black hole at the center of these stars slowly consumed the star from within making black holes of up to 10 ³ solar masses. These black holes may be the seeds of the supermassive black holes found in the centers of most galaxies. If these stars really existed, they may even explain where supermassive black holes come from.

Most of the energy released in gravitational collapse is given off very quickly. A distant observer sees the material falling in slowly and then stop just above the event horizon because of gravitational time dilation. The light given off just before the event horizon is delayed an infinite amount of time. So the observer never sees the formation of the event horizon. Instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away.

Black holes have also been found in the middle of almost every galaxy in the known universe. These are called supermassive black holes (SBH), and are the biggest black holes of all. They formed when the Universe was very young, and also helped to form all the galaxies.

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.

Huge central masses (10 ⁶ to 10 ⁹ solar masses) have been measured in quasars. Several dozen nearby large galaxies, with no sign of a quasar nucleus, have a similar central black hole in their nuclei. Therefore, it is thought that all large galaxies have one, but only a small fraction are active (with enough accretion to power radiation) and so are seen as quasars.

The Event Horizon

A black hole is separated from the rest of the Universe by its event horizon. Anything which crosses it cannot escape, not even light. Anything that happens inside this boundary can't be seen from the outside.

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.

The shape of the event horizon for non-rotating black holes is spherical and slightly flattened for spinning ones.

The photon sphere is a spherical boundary of zero thickness in which photons that move on tangents to that sphere would be trapped in a circular orbit about the black hole.

Artist's image: a black hole pulling off the outer layer of a nearby star. It is surrounded by an energy disk, which is making a jet of radiation.

Einstein's Cross: four images from one quasar

At the middle of a black hole, there is a gravitational center called a singularity. It is impossible to see into it because the gravity prevents any light escaping.

Outside the event horizon, light and matter will still be pulled toward the black hole. If a black hole is surrounded by matter, the matter will form an "accretion disk" around the black hole. 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.

Most black holes are too far away for us to see the accretion disk and jet. The only way to know a black hole is there is by seeing how stars, gas and light behave around it. With a black hole nearby, even objects as big as a star move in a different way, usually faster than they would if the black hole was not there.

Since we cannot see black holes, they must be detected by other means. When a black hole passes between us and a source of light, the light bends around the black hole creating a mirror image. This effect is called gravitational lensing.

Hawking radiation is black body radiation which is emitted by black holes, 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.

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.

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.

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. The angular momentum or spin can also be measured from far away.

When anything falls into a black hole, any property that isn't part of the three properties of a black hole, like shape or charge distribution, gets erased and can't be seen from outside. This is a very big problem because we lose a lot of information about what went into the black hole, including certain quantum properties and physics tells us that information cannot be destroyed. This puzzle is called the black hole information loss paradox.

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Black hole - Simple English Wikipedia, the free encyclopedia

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A black hole is a region of space-time from which nothing, not even light, can escape. According to the general theory of relativity, it starts existing when spacetime gets curved by a huge mass. There is a sphere around the black hole. If something goes inside the sphere, it cannot leave.

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Black Holes Facts for kids
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A black hole is a region of space from which nothing can escape, according to the general theory of relativity, it is the result of the curving of spacetime caused by a huge mass. Around a black hole there is a position of no return, called the event horizon. It is called "black" because it absorbs ...
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black holes - Kiddle - visual search engine for kids

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black holes - Kiddle - visual search engine for kids

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At the center of most galaxies is one of the strangest and deadliest things in the universe: a black hole.

Most black holes, regardless of their size, are born when a giant star runs out of energy. The star implodes, and its center collapses under its own weight. This causes an explosion called a supernova. The giant star is eventually squashed into a supersmall dot you can't see.

A black hole's gravity, or attractive force, is so strong that it pulls in anything that gets too close. It can even swallow entire stars. Nothing can move fast enough to escape a black hole's gravity. This includes light, the fastest thing in the universe. That's why we can't see black holes in space-they've gobbled up all the light. Though astronomers can't see black holes, they know they're there by the effect they have on objects that get too close.

Two types of black holes exist. Supermassive black holes are the largest type of black hole. They're up to one million times more massive than our sun. This is the kind of black hole that's at the center of our galaxy, the Milky Way; it's called Sagittarius A*. (A* is scientist-code for "A-star.") The most common type of black holes, stellar black holes, are only up to 20 times more massive than our sun.

The intense gravity near a black hole makes time behave in strange ways. If an astronaut left his spacecraft to explore a black hole up close, he'd see the hands on his watch ticking at normal speed. But if anyone back on the spacecraft could observe the astronaut's watch from far away, they'd see its hands slow down as the spacewalker got closer to the black hole. When the spacewalker returned to the spaceship after an hour-long spacewalk, years would have passed for those aboard the spacecraft.

Someday humans might be able to use black holes to time travel forward. An astronaut could take a short trip near a black hole and return to Earth after years, decades, or even centuries had passed there. A black hole time machine could allow an astronaut to find out what the world will be like in the future. But going back in time? That's a different challenge altogether!