Facts About Black Holes
- Despite what most people think, a black hole is actually not an empty space. It is an extremely dense region that packs a lot of mass in a small area. Think of an object with millions of times the mass of the Sun. However, all of this mass is concentrated in just a small single point. Let’s look at more black hole facts.
- Black holes are hard to find because they do not emit light, they are invisible. However, space telescopes can detect them because of their effects on the surrounding stars. Black holes strip material from the stars near them and emit X-rays in the process.
- Most galaxies have central black holes. Though this is not yet fully understood, it is believed that a black hole may have contributed to the formation of the solar system and the bigger Milky Way galaxy.
- Cygnus X-1 was the first black hole ever discovered. It was detected in 1964 because it was sucking material from a nearby blue supergiant star. This spiraling gas created X-rays that made it possible to be detected. It is located 7,240 light-years in the Cygnus constellation in the Milky Way.
- The three types of black holes are stellar, supermassive, intermediate, and micro (still hypothetical). Aside from size, each of these types is thought to have different origins.
- The first-ever image of a black hole was taken in 2019 using the Event Horizon Telescope. It was in M87 or Messier 87, a big elliptical galaxy in the Virgo constellation. This giant black hole is 6.5 times as massive as the Sun.
- The Sun is not massive enough to become a black hole at the end of its life. Hypothetically, if what we have in the solar system is a black hole the same size as the Sun, everything will remain in orbit. With the same mass, it will have the same gravitational influence as the Sun today. However, without the light of the Sun, life on Earth will never be the same.
- The black hole on the center of the Milky Way galaxy is called Sagittarius A*. It is around 4 times as massive as the Sun and is located about 26,000 light-years away from Earth.
- Black holes can get bigger or smaller. When black holes eat the stars and other materials surrounding them, they can increase in size. However, they can also become smaller as they lose energy through “Hawking radiation,” as proposed by Stephen Hawking.
- No one has entered a black hole yet, but if you do, you will be “spaghettified.” As the name suggests, a body that enters a black hole would be vertically stretched and horizontally compressed because of extreme gravity. This is also called the “noodle effect.”
What Are Black Holes?
A black hole is a region in space where gravity is so strong that nothing can escape it. The boundary of this region is called the “event horizon,” and everything that crosses it can never get out—not even light.
Black holes are invisible but we know they exist because of their gravitational influence on the objects around them. And the more massive the black hole, the stronger its gravitational pull is.
The existence of black holes was predicted by Albert Einstein’s theory of general relativity. Stars generate energy through nuclear fusion. Upon the death of a large star, gravity causes it to collapse and it will ultimately form a black hole. Aside from stellar-mass black holes or those that formed from dying stars, there are also other black hole types with different sizes and origins.
The black hole’s center is called a “gravitational singularity.” Spacetime is warped because of infinite gravity and density.
So far, astronomers have found evidence of black holes in lots of places in the observable universe. The observable universe is the part we can see from Earth using powerful telescopes and other instruments. That means, the universe is so big that we cannot see its entirety!
A special type of black hole called a supermassive black hole, was found in the center of almost every galaxy, even our own. Our galaxy contains many less massive black holes which are the result of stars reaching the ends of their lives and going through a special process.
History of Black Hole Research and Discovery
In 1783, John Mitchell thought that something could be big enough and heavy enough (possess enough mass) that to escape from it, you would have to be traveling at the speed of light. Gravity becomes stronger with the more mass something has, so something with a lot of mass would make it very difficult to escape from it.
You can see a demonstration of this in the huge amount of fuel it takes a rocket to travel away from the ground fast enough to escape the Earth’s gravity (caused by its mass) and enter space. That speed is called escape velocity. Mitchell also thought that some things might be even more massive and it would require more than light speed to escape.
His theory originally caused some excitement in the scientific community, but when it was discovered that light has a wavelike pattern, many scientists decided that gravity could not affect it. They were wrong.
Enter the Theory of General Relativity
In 1915, Albert Einstein was at work on his theory of general relativity. General relativity is a complicated theory that states that mass causes space and spacetime to bend or curve. Anything that is in motion will seem to “fall” along the curves, which is gravity at work. Secondly, light has a constant speed and if light seems to be moving at a different speed, it is on one of these curves in spacetime: it is being acted on by gravity.
Soon afterward, Karl Schwarzchild (who was fighting in WWI at the time) found a solution to some of the equations Einstein published, and Johannes Droste came up with the same solution for one and wrote more extensively about it. There was something strange that happened with the equations that started to point toward black holes, but at the time, it wasn’t well understood what they were starting to discover. The unusual behavior of mass inside what became known as the Schwarzchild radius ended up giving us the term “singularity,” which is commonly used when talking about black holes.
Several more scientists worked with the data and in 1931 Subrahmanyan Chandresekhar calculated that a white dwarf star would become unstable and collapse in on itself. Some people were against his ideas, but in the end they were both partly right. Some white dwarfs will collapse into a type of star called a neutron star; however, neutron stars above a certain mass will collapse into black holes, like Chandresekhar thought.
More Developments on the Black Hole Theory
A few years later, in 1939 Robert Oppenheimer and his fellow scientists believed that the singularity was a place on the edge of a bubble where time stopped. From an outside point of view, this is true. Stars seem frozen in time as soon as their collapse takes them into the Schwarzchild radius. But if you were falling into the singularity, time keeps going.
David Finkelstein, in 1958, gave us another common term—event horizon—by taking Oppenheimer’s results and adding what would happen from the perspective of something falling into the singularity. The event horizon can only be crossed in one direction. Martin Kruskal had already found something similar, and all of these findings made black holes a mainstream subject of research.
After this point, with lots of people interested, many scientists started to discover things very quickly and we gained a lot of our current understanding of black holes. They have remained an extremely interesting subject for physicists and astronomers and new discoveries are still being made, plus there is a lot we still don’t know!
Black Hole Facts – Important Discoveries and the Current Understanding of Black Holes
Black holes are an interesting subject. As science evolves, our understanding of them also progresses. In 1916, Albert Einstein predicted that gravitational waves exist through his theory of general relativity. However, it was only in 1974 that their existence was proven.
These waves are like “ripples” that were created because of the violent interactions of massive objects in the universe. Such very powerful events can disrupt space-time, producing waves that disperse in all directions.
Gravitational waves are often produced by great events like the explosion of massive stars (supernovae), collisions of black holes, and neutron star collisions.
In September 2015, one of the most vital discoveries in science was made as gravitational waves were finally detected. That was 99 years after Einstein predicted it!
The Laser Interferometer Gravitational-Wave Observatory (LIGO) detected such strong signals from two colliding black holes. They were 1.3 billion light-years away. With that distance, the gravitational waves that reached Earth were much smaller but the LIGO interferometers were still able to detect them.
Just like sound waves, we can also hear gravitational waves. While the former can travel in air and water, gravitational waves have spacetime as the medium. Because of this, we were able to hear the otherworldly sound of two black holes in a collision course.
Another breakthrough was made in 2019 when the first-ever image of a black hole was taken.
The First Image of a Black Hole
In 2019, the first observational evidence of a black hole was unveiled. It was made possible by the Event Horizon Telescope (EHT). This black hole was observed in the center of the galaxy Messier 87 (M87) which is located roughly 55 million light-years away from us.
The EHT is not alone in this feat. This achievement was made possible through the collaboration of more than a hundred scientists and observatories around the globe. This project kickstarted in 2017 and the image was produced 2 years later.
Again, since black holes are invisible, the dark center of the image actually shows the shadow of the black hole. Instead, it shows the event horizon and the gases at its edge. This boundary is dubbed as the “point of no return.”
This new discovery further helped scientists understand the magnetic field structure around a black hole. Another finding that the image revealed is that the gas just outside the black hole is strongly magnetized. This can help shed light on how black holes consume gas, which makes them grow bigger.
Black Hole Facts – Types of Black Holes
Supermassive Black Holes
Supermassive black holes generally formed when the universe was still young. Once a black hole exists in the center of a galaxy, it can continue to grow by pulling matter from the universe around it and by absorbing other black holes, increasing its mass. However, astronomers are not entirely sure yet how supermassive black holes form. The kind that are made from stars dying are very small in comparison, so they think the two may form through different ways. The gap between these black holes that are made through star death and the smallest supermassive black hole is the difference of something about 33 times the mass of our sun and something 100,000 times the mass of our sun.
Intermediate-mass Black Holes and New Findings
Intermediate-mass black holes are what might bridge the gap in size between stellar black holes and supermassive black holes. They’ve been an important research topic because they may be the seeds that eventually grow into the supermassive ones that galaxies form around. Astronomers thought they probably existed but it was hard to prove whether one did or not until research started to come in over the past few years.
In 2014, astronomers found what seemed to be one in the arm of a spiral galaxy and most recently, in research published in February, 2017, scientists found one in the globular cluster, 47 Tucanae, that has a solar mass of 2,200.
Generally, scientists find black holes by looking from X-rays coming from a hot disk of swirling material somewhere out in the universe, but this only works if the black hole is actively feeding on the nearby gasses. Inside the center of 47 Tucanae, there is no gas, so the black hole is unable to feed and isn’t electromagnetically bright. This made it even harder to find.
47 Tucanae is incredibly crowded with stars. The crowding means that the stars with greater masses tend to sink to the middle of the cluster, like something heavy settling in a glass of water. The intermediate-mass black hole is capable of causing those stars to spin around it, moving at higher speeds and greater distances. The second piece of evidence for its existence are the pulsars in 47 Tucanae. If there were no central black hole, they would be close to the center of the globular cluster; however, they get thrown around by the black hole’s gravity and are farther away than they should be if there were no black hole.
This is compelling evidence for the existence of an intermediate-mass black hole, and these and other recent findings will help other astronomers find more now that they have an idea of what sorts of things mean an intermediate-mass black hole might be hiding somewhere.
Stellar Black Holes
These are the most common black holes in the universe. “Stellar” just means “star,” and these black holes are one possibility of what happens when a star dies (white dwarfs and neutron stars are other possibilities, as well as the still-theoretical black dwarf). They generally happen when massive stars collapse.
Stars produce light and heat by constantly burning internal fuel through a nuclear process. Eventually, all stars run out of fuel and the process breaks down. Stars typically explode in a supernova and what is left is called a “stellar remnant.”
If the stellar remnant retains a sufficient amount of mass it will continue to collapse until a black hole is formed.
In the early universe, there may have been many very massive stars, and so stellar black holes may have been common. One theory is that these were the seeds of supermassive black holes, hungrily feeding on the gas clouds and other particles that were common in the early universe until they became massive, themselves.
Micro Black Holes
These are very tiny black holes theorized to have been created in the early universe, usually. Just as big ones may have formed back then, tiny ones could have, too, and in some people’s opinions, would be much more likely than large ones.
Since they’re so small, some people, like Stephen Hawking, think they would evaporate right away, but it’s possible that if they exist, they are still hanging around in the universe today. Physicists are on the lookout for them via looking for bursts of gamma rays shot out when they evaporate to see if they can find any.
How Are Black Holes Formed?
Gravitational collapse, like what can happen to stars, causes most black holes.
In the beginning of the universe, after the Big Bang, the universe itself was very dense and hot. In that sense, it was similar to a star. Simple fluctuations in the density of the matter in an area could have caused the matter to collapse into a black hole.
Since the universe is expanding, very dense regions dispersed quickly, but if one of these early black holes were powerful enough, it could remain stable and continue to exist into the present. Currently, they are still only theoretical.
Once a black hole has formed, it can grow by absorbing more matter. The universe is full of gas, interstellar dust, and radiation, and a black hole will absorb all of these. It is generally believed that this is how supermassive black holes become so massive: they simply eat their way there.
Other than that, black holes can merge with things that come within range of them, whether that be to stars or other black holes. This is another theory for the size of supermassive black holes, as well as how some intermediate-mass black holes reach their mass.
Anatomy of Black Holes
This diagram above shows the light trajectories as an object or star gets closer and closer to the black hole.
First, In point (a), only a small portion of the light is directed close enough to the black hole to be captured.
In point (b), the star is close enough that the amount of light captured is increased because of the strong gravitational field of the black hole that bends the paths of the photons inward toward it.
In point (c), the star is much closer and this bending is so strong that fully half the light is captured. The amount of light captured goes up further as the star approaches closer, until in point (d), nearly all of it does – just a little that happens to be emitted directly outward can get away.
Despite being described as massive, or even supermassive, black holes generally are not very large in the usual sense of the word. There is a difference between mass and size. Think of how a beach ball is big but doesn’t weigh very much compared to a brick. The brick has more mass because it’s very dense compared to the beach ball. Black holes are extremely dense and exert an extremely strong gravitational force. It’s this gravitational force that pulls things toward them and makes it impossible for things to escape.
Event Horizon And Singularity
Black holes are made up of their event horizons and singularities. The exterior event horizon surrounds the black hole and forms the boundary line for it. Anything that crosses that boundary, whether it’s light or anything else, is drawn into the black hole’s singularity and cannot escape.
Past the exterior event horizon is the inner event horizon. This is what you would find once you had crossed the exterior event horizon and had begun falling toward the singularity. The theories are so new that it’s hard to say anything about it yet, but research is ongoing.
Inside the singularity, none of the laws of physics and spacetime as we understand them apply. This makes them both fascinating and very difficult to understand. Since nothing can escape from them, we currently have no way of understanding what happens inside of them except theories and guesses.
Black holes are usually surrounded by an accretion disk. These are disks of interstellar material, particles, and gasses that spin around the black hole—often very fast. You may dropped a coin in a big funnel at school or a museum where it circles around the funnel, faster and faster, as it’s drawn down toward the bottom and into the collection area. Accretion disks are like this, with a lot of particles in them circling around.
The accretion disk radiates X-rays, helping scientists guess a black hole might be nearby.
Some black holes also have quasars around them. Quasars are found surrounding supermassive black holes at the centers of galaxies. They emit very large amounts of electromagnetic energy, light, and radio waves. Quasars are thought to form when galaxies collide and their black holes combine. Over time, they consume the region of the galaxy around them and stop emitting so much energy.
Life Cycle of Black Holes
As long as there is something nearby for a black hole to absorb—interstellar dust, gas, nearby stars or other black holes—it will continue growing and thriving.
Stephen Hawking believes that black holes that are rotating, like most, should always be creating and shooting out particles. If the black hole has nothing to feed on, this process of shooting out particles would cause the black hole to shrink and eventually disappear.
There is a telescope currently looking for evidence of this, and scientists are also curious to see if they can observe the process using the Large Hadron Collider, which is the largest machine in the world. Scientists use it to cause particles to smash together at very high speeds.
Some people got worried that the Large Hadron Collider would create black holes powerful enough to cause trouble on Earth, but physicists have reviewed all of the research very carefully and believe that if they do create any, they will evaporate so fast that it won’t be a problem.
What Would Happen if You Flew Into A Black Hole?
A lot of people wonder what would happen if they fell into a black hole.
The gravity toward the center of the singularity is so strong that anything that begins to enter it is stretched out due to the gravity pulling on the nearest end. Astrophysicists call this “spaghettification” because the object is pulled out like a long, thin piece of spaghetti. There is nothing in the universe strong enough to avoid having this happen because black holes’ gravity is that much stronger.
While this might sound scary, it isn’t going to happen to anyone. While there are a lot of black holes in our galaxy and a supermassive one in the center of it, they are all much too far away to affect humans.
Could We Survive in a Black Hole?
Luckily, no one has ever been close to a black hole to experience spaghettification. However, scientists have observed such phenomena of black holes eating stars and ripping them apart. For that reason, and with the current knowledge that we have, surviving a black hole would be impossible.
As you get closer to the black hole, people observing you from outside will see you falling in slow motion. And as you enter the event horizon, it would look like you have frozen in time. However, for you, inside the black hole, time remains as it is.
You would feel spaghettification as you go closer to a black hole. The extreme gravity will stretch and compress you until you snap into your tiniest parts—into atoms.
Falling into a smaller black hole would be worse than getting into a supermassive one. Though spaghettification is inevitable, the greater gravitational difference in smaller black holes would mean you would be shredded more quickly. Whereas on larger ones, you would be spaghettified more slowly that you might fall into the singularity without being completely torn yet.
As you reach the singularity, nobody really knows what would happen. Some think that a person would get crushed because of the immense gravity. There are also those that think you would probably be transported to a different universe, like a wormhole.
Nobody knows what would exactly happen once someone falls into a black hole. However, it is certain that once you enter the event horizon, you can never go back. It is like a one-way trip where your destination is still unknown.
Is There a Black Hole at the Center of Our Galaxy?
Yes, there is a black hole in the center of the Milky Way galaxy. It is called the Sagittarius A*. With the asterisk, we read it as “Sagittarius A-Star.” This black hole is 4.3 times as massive as our Sun.
As early as 1931, a radio signal was detected in the center of the Milky Way galaxy, in the direction of the Sagittarius constellation. Ever since, scientists have been observing this radio source called Sagittarius A*. They track stars around it and observe how they interact.
In 2020, Reinhard Genzel, Andrea Ghez, and Roger Penrose were awarded the Nobel Prize for the discovery which confirmed that Sagittarius A* is really a black hole.
Since black holes fascinate so many physicists, they are a popular topic for study. In the past hundred years, we have come up with many theories and proven some of them.
A special project called the Event Horizon Telescope is aimed at studying our galaxy’s supermassive black hole. This telescope is made of many radio observatories around the world combining their power to create something like a telescope as wide as Earth. It made the first black hole image possible through its collaboration with other radio telescopes around the globe.
The Chandra X-ray Observatory was able to detect a supermassive black hole in a dwarf galaxy called Markarian 462. Also called Mkr 462, this “mini monster” black hole. It is 200,000 times as massive as the Sun.
This is a rare discovery that a supermassive black hole is buried in a dwarf galaxy. Black holes like this hold clues as to how the supermassive black holes in the early universe grew.
Also, the MeerKAT telescope was able to provide a radio image of the Milky Way’s center. In the image, the thin filaments can be seen surrounding the central black hole. These filaments are still a mystery and scientists are studying these strands to better understand the nature of our galactic center. Indeed, it is a very exciting time for black hole research!
More Interesting Black Hole Facts
- The theoretical white hole is the opposite of black holes. Unlike black holes that eat everything around it, no material can enter white holes. They expel matter rather than swallow them. These space-time objects are rather hypothetical and are unlikely to really exist.
- Sagittarius A*, the black hole in the center of our galaxy, poses no threat of swallowing Earth. Black holes have great gravitational fields, but they will only affect those that are near them. Since the central black hole in the Milky Way is roughly 26,000 light-years away, it is way too far away to pull our planet in.
- The quasar called J0313-1806 contains the most distant black hole found. A quasar is a very bright object that is actively feeding on the objects around it. It is powered by a very big black hole. J0313-1806 is located 13.03 billion light-years from us. It is also one of the oldest quasar known.
- The closest known black hole to Earth is called “the Unicorn.” It lies in the Milky Way galaxy, 1,500 light-years from us in the constellation of Monoceros. Aside from its distance, its discovery is also important because of its small size.
- Hypothetically, the smallest black holes are thought to be at least 5 times the Sun’s mass. However, “the Unicorn” only has 3 times the solar mass. This makes it one of the smallest black holes ever found.
- Black holes are massive but they will not eat an entire galaxy. The gravitational influence of black holes will only have an immediate influence on the objects around them. It is not large enough to consume an entire galaxy.
- Many black holes are considered dormant. This means that they are not actively swallowing matter. Still, these black holes can become awakened when a star destabilizes in its orbit and wanders close towards them. Sagittarius A*
- Wormholes are often a famous subject in science fiction but scientists are not yet sure if they really exist. Some people believe that black holes are probably wormholes or shortcuts in space and time, making long travels in the universe much shorter. This theory is neither confirmed nor debunked as no one has been inside a black hole yet.
Albert Einstein: https://upload.wikimedia.org/wikipedia/commons/5/50/Albert_Einstein_%28Nobel%29.png
Black holes collision: https://www.nasa.gov/sites/default/files/styles/full_width_feature/public/thumbnails/image/ztf_bh_merger_webready.original.jpg
The First Image of a Black Hole: https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Black_hole_-_Messier_87_crop_max_res.jpg/800px-Black_hole_-_Messier_87_crop_max_res.jpg
Milky Way galaxy: https://upload.wikimedia.org/wikipedia/commons/thumb/d/d3/PIA19341-MilkyWayGalaxy-SpiralArmsData-WISE-20150603.jpg/800px-PIA19341-MilkyWayGalaxy-SpiralArmsData-WISE-20150603.jpg