Black hole

Research estimates that the Milky Way could contain over 100 million black holes, including the supermassive black hole at the center of the galaxy, Sagittarius A, which is roughly 4 million times the mass of the sun and approximately 26,000 light-years away from Earth. The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The imaged black hole is at the center of the M87 galaxy, 55 million light-years from Earth. In 2021, astronomers released an updated view of the giant black hole at the center of M87, showing the structure in more detail by imaging in polarized light.

A paper published in Nature on February 19, 2024, reported data on a 17 billion solar mass black hole that grows by a solar mass each day. The quasar, the bright core of a galaxy powered by a black hole known as J0529-4351, is considered the most luminous object detected and the fastest-growing black hole recorded. Originally identified many years ago, the paper presents new observations from the Very Large Telescope (VLT) in Chile demonstrating the size and accretion of the supermassive black hole. J0529-4351 is located 12 billion light-years away from Earth.

In 1963, New Zealand mathematician Roy Kerr found another solution to Einstein's field equations for spinning black holes that retain their angular momentum from the pre-supernova star. In 1973, Igor Novikov and Kip Thorne derived an explanation for gas slowly spiraling into a black hole, releasing its gravitational potential energy as heat and radiation at temperatures of millions of degrees. However, the explanation doesn't explain how gas loses angular momentum and doesn't agree with observations of high-energy x-rays from high-temperature gas. Theories at the time suggested that hot ionized gas experiences almost no friction or viscosity and should orbit a black hole forever, never getting closer to the event horizon. Novikov and Thorne fully absorbed these issues into their theory, with later work.

In 1963, New Zealand mathematician Roy Kerr found another solution to Einstein's field equations for spinning black holes that retain their angular momentum from the pre-supernova star. In 1964, Roger Penrose introduced a theory on singularities showing that space-time can become a closed trapped surface, a surface whose curvature is so extreme that outward-going light gets wrapped around and turned inward. Penrose's work provided powerful new tools from geometry and topology to the study of black holes and other phenomena in Einstein’s theory.

In 1973, Igor Novikov and Kip Thorne derived an explanation for gas slowly spiraling into a black hole, releasing its gravitational potential energy as heat and radiation at temperatures of millions of degrees. However, the explanation doesn't explain how gas loses angular momentum and doesn't agree with observations of high-energy x-rays from high-temperature gas. Theories at the time suggested that hot ionized gas experiences almost no friction or viscosity and should orbit a black hole forever, never getting closer to the event horizon. Novikov and Thorne fully absorbed these issues into their theory, with later work.

In 1983, mathematicians Richard Schoen and Shing-Tung Yau published work on the hoop conjecture, previously formulated by Thorne, showing the amount of matter that must be compressed into a given volume to induce the space-time curvature needed to create a closed trapped surface. In 1991, Steve Balbus and John Hawley discovered a powerful instability from the twisting and pulling of magnetic field lines embedded in an accretion disk. Ionized gas is an electrical conductor and can generate powerful magnetic fields that act on the gas, slowing it down and allowing it to spiral toward the black hole. In 2001, supercomputers adequately simulated the Balbus-Hawley instability in accretion disks around realistic black holes, confirming their predictions.

In 2023, Marcus Khuri, Sven Hirsch, Demetre Kazaras, and Yiyue Zhang, published a paper showing that a cube in space with large enough matter concentration will form a trapped surface. Their work simplified previous examples, using square hoops instead of circular hoops, and could make it easier to determine the presence of black holes based solely on the concentration of matter. Additionally, their work proved mathematically that higher-dimensional black holes can exist.

Early physicists studying these bizarre objects often referred to them as “frozen stars.” The term “black hole“ was coined in 1968 by the Princeton physicist John Wheeler, who worked out further details of a black hole’s properties. Additional work by Robert Oppenheimer and others led to the idea that such an object might be formed by the collapse of a massive star.

The idea of black holes was reexamined following the publishing of Einstein's theory of gravity. The mathematical foundation of general relativity was detailed in four landmark papers published in the Proceedings of the Prussian Academy of Sciences. This included the most famous paper titled The Field Equations of GravitationThe Field Equations of Gravitation,” published on November 25, 1915. In December 1915, Einstein sent his findings to Karl Schwarzschild the director of the Astrophysical Observatory in Potsdam and an accomplished theorist and mathematician. Schwarzschild was serving in the German army on the eastern front as an artillery lieutenant. He wrote back within days with the first known solution to Einstein's field equations. Schwazschild's letter included:

Less than a year later, Schwarzschild succumbed to a skin disease contracted on the front. His solution completely described how space-timespacetime is warped by a spherical object like a planet or star. One of the features of his solution is that for very compact, high-density stars, it becomes harder to escape the gravitational field of the star. Eventually, there will be a point where every particle, even light, becomes gravitationally trapped. This point of no escape is called the event horizon.

Early physicists studying these bizarre objects often referred to them as “frozen stars.” The term “black hole“ was coined in 1968 by the Princeton physicist John Wheeler, who worked out further details of a black hole’s properties. Additional work by Robert Oppenheimer and others led to the idea that such an object might be formed by the collapse of a massive star.

In 1963, New Zealand mathematician Roy Kerr found another solution to Einstein's field equations for spinning black holes that retain their angular momentum from the pre-supernova star. In 1973, Igor Novikov and Kip Thorne derived an explanation for gas slowly spiraling into a black hole, releasing its gravitational potential energy as heat and radiation at temperatures of millions of degrees. However, the explanation doesn't explain how gas loses angular momentum and doesn't agree with observations of high-energy x-rays from high-temperature gas. Theories at the time suggested that hot ionized gas experiences almost no friction or viscosity and should orbit a black hole forever, never getting closer to the event horizon. Novikov and Thorne fully absorbed these issues into their theory, with later work.

In 1991, Steve Balbus and John Hawley discovered a powerful instability from the twisting and pulling of magnetic field lines embedded in an accretion disk. Ionized gas is an electrical conductor and can generate powerful magnetic fields that act on the gas, slowing it down and allowing it to spiral toward the black hole. In 2001, supercomputers adequately simulated the Balbus-Hawley instability in accretion disks around realistic black holes, confirming their predictions.

In 1963, Maarten Schmidt discovered quasars (quasi-stellar radio sources) light sources that we can observe but are located vast distances from us. Based on their energy output and small size, scientists argued that quasars are caused by accreting supermassive black holes at the center of galaxies in their infancy. This makes quasars a type of active galactic nuclei (AGN). Material (dust, gas, and other matter) in the accretion disk surrounds the black hole and is superheated causing intense fiction. As it hears up this material generates radio waves, X-rays, ultraviolet and visible light. We observe that quasars are more abundant in the past when there was more material around a black hole for it to feed on. After this material is used up the quasar becomes quiet. Evidence suggests most galaxies may have gone through a quasar phase and there might be a black hole at the center of each galaxy.

We observe that quasars are more abundant in the past when there was more material around a black hole for it to feed on. After this material is used up the quasar becomes quiet. Evidence suggests most galaxies may have gone through a quasar phase and there might be a black hole at the center of each galaxy.

In 1974, astronomers Bruce Balick and Robert Brown discovered radio waves emanating from the center of the Milky Way, a source that would become known as Sagittarius A and is now believed to be a supermassive black hole with about four million times the sun’s mass. In 1978, scientists studied the motion of stars in the M87 galaxy, more than 50 million light-years from Earth, suggesting that it contains a supermassive black hole billions of times the mass of the sun. In 2008, early results from the EHT (Event Horizon Telescope) confirmed that a black hole–like object rests at the center of the Milky Way.

In the 1980s, astronomers began searching for supermassive black holes with the first candidate in the galaxy M87.

In 2016, results from the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves for the first time. The ripple in spacetime was caused by two converging black holes 750 million light-years away. The EHT released the first picture of a black hole in 2019. The team behind the image used additional telescopes to image the silhouette formed by the event horizon of the supermassive black hole within galaxy M87.

A black hole is a volume of space where gravity is so strong that nothing, not even light, can escape from it.

A black hole is a volume of space where gravity is so strong that nothing, not even light, can escape from it. The mass of a black hole is concentrated into an almost infinitely small and dense point called a singularity. Current theories of physics cannot explain the singularity at the center of a black hole and scientists are actively engaged in research to better understand them. The singularity is surrounded by an event horizon, the distance at which light and matter are drawn into the black hole and cannot escape. Rotating black holes are surrounded by the ergosphere, a region in which the black hole drags space itself.

Diagram showing the structure of a black hole.

Stellar black holes are formed by the collapsing mass of a large star that has run out of fuel. The collapsing star compresses its mass so tightly that no other force of nature can balance it, creating a singularity. The inward pull of gravity is balanced by the outward pressure of nuclear reactions in the core of a typical star. Other forms of collapsed stars, such as white dwarfs or neutron stars have other forces preventing a singularity from forming. The singularity has a gravitational field so strong that its escape velocity is greater than that of the speed of light. Escape velocity is the speed an object requires to overcome the gravitational attraction of another body. For example, a spacecraft must accelerate to 11.2km/s (7 miles per second) to escape Earth's gravitational pull. Escape velocity reduces with distance away from the massive body. The radius from the singularity at which an object has an escape velocity equal to the speed of light (roughly 186,000 miles per second or 300,000 km per second) is called the Schwarzschild radius.

As black holes do not emit light, scientists cannot detect them in the same way as stars and other objects in space. Instead, they rely on detecting radiation emitted from black holes as dust and gas are drawn into them. Supermassive black holes, lying at the center of a galaxy can become shrouded by the thick dust and gas around them obscuring the radiation emitted from dust and gas crossing the event horizon. Matter drawn towards a black hole can ricochet off the event horizon, emitting bright jets of material traveling at near-relativistic speeds. Although the black hole remains unseen, these jets can be viewed by astronomers.

This radius depends on the mass of the black hole. The radius defines the region of "blackness" around the singularity, giving the black hole a visible surface known as the event horizon. The event horizon is the "point of no return" around the black hole. It is not a physical surface, but a sphere surrounding the black hole, where matter or light cannot escape the gravitational force of the black hole. As objects cross the event horizon the black hole's mass increases, increasing the size of the event horizon. The singularity is a one-dimensional point containing a huge mass in an infinitely small space. Density and gravity become infinite at the singularity curving space-time infinitely. The current laws of physics cannot explain the singularity at the center of a black hole. Theories suggest objects falling into a black will become stretched or "spaghettified" due to the increasing differential in gravitational attraction at different points of the object.

Diagram showing the singularity's effect on spacetime.

If a black hole is rotating it complicates the gravitational effects produced, pulling the fabric of spacetime with it. This effect is called frame dragging and the area affected is known as the ergosphere. Viewed in cross-section it is oval in shape, with the region of influence extending farther into space at the black hole's equator than at its poles.

As black holes do not emit light, scientists cannot detect them in the same way as stars and other objects in space. Instead, they rely on detecting radiation emitted as dust and gas are drawn into the black hole. Supermassive black holes, lying at the center of a galaxy can become shrouded by the thick dust and gas around them obscuring the radiation emitted from dust and gas crossing the event horizon. Matter drawn towards a black hole can also ricochet off the event horizon, emitting bright jets of material traveling at near-relativistic speeds. Although the black hole remains unseen, these jets can be viewed by astronomers.

Research estimates that the Milky Way could contain over 100 million black holes, including the supermassive black hole at the center of the galaxy, Sagittarius A which is roughly 4 million times the mass of the sun and approximately 26,000 light-years away from Earth. The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The black hole is at the center of the M87 galaxy 55 million light-years from Earth. In 2021, astronomers released an updated view of the giant black hole at the center of M87, showing the structure in more detail by imaging in polarized light.

The first released image of a black hole in 2019 from the EHT collaboration.

In 2021, astronomers released an updated view of the giant black hole at the center of M87, showing the structure in more detail by imaging in polarized light.

An updated image of the black hole at the center of the M87 galaxy viewed in polarized light.

Left: original image of the M87 black hole released in 2019, Right: updated image viewed in polarized light released in 2021.

When a star runs out of fuel it may collapse or fall into itself. The resulting object depends on the mass of the star. Smaller stars (up to three solar masses) will become a neutron starstars or white dwarfdwarfs. Larger stars can collapse with enough gravitational force to create a stellar black hole. This type of black hole is relatively small but incredibly dense, packing more than three solar masses into the diameter of a city. This gravitational force of stellar black holes attracts objects, consuming dust and gas from their surrounding galaxies and growing in size.

Supermassive black holes are millions or even billions of times as massive as the sun with roughly the same diameter. They are at the center of galaxies, including the Milky Way. There are multiple theories as to how these objects form, but once in existence, 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. One theory is that supermassive black holes are the result of hundreds or thousands of tiny black holes merging. Another suggests that large gas clouds collapse together and rapidly accrete mass. Other theories suggest they are the result of stellar clusters collapsing together or large clusters of dark matter. Studies have shown that the size of the black hole is correlated with the size of the galaxy, suggesting there is a connection between the formation of the black hole and the galaxy.

Scientists originally believed that black holes only existed in small (stellar) and large (supermassive) sizes. However, research has revealed the possibility that intermediate black holes (IMBHs) may also exist, forming when stars in a cluster collide in a chain reaction. up nearby debris. There are only a few candidates for IMBHs, with many potential candidates becoming explained by other phenomena.

Simulations of black holes demonstrate how they distort gravity and therefore our view of them. Matter falling into a black hole forms a hot structure called an accretion disk and the light it emits is skewed due to the extreme gravitational forces producing a misshapen appearance. Bright knots are constantly forming and dissipating in the disk as magnetic fields twist through the gas. Nearest to the event horizon the gas orbits close to the speed of light while the outer portions spin more slowly. Viewed from the side, the accretion disk orbiting the black hole will look brighter on the side moving towards the viewer due to the effects of Einstein's relativity. The asymmetry is not present when viewing the disk face-on, as none of the material is moving along the observer's light of sight. Close to the black hole, gravitational light bending becomes excessive such that the underside of the disk is seen as a bright ring of light, outlining the black hole. This is called the "photon ring" or "photon sphere" and it is composed of multiple rings that grow progressively fainter and thinner from light that has circled the black hole many times before escaping to reach the observer. The simulated black hole shown below is circular. Therefore, the photon ring looks nearly circular from any angle.

Visualization of a black hole produced by NASA.

The singularity is the infinitely dense point at the center of a black hole, predicted by general relativity. The singularity could be a physical structure or a mathematical one, current laws of physics cannot explain the existence of an infinitely dense point in space. The prediction of singularity may show the limitations of relativity, where quantum effects not included in the theory are required to provide a more complete description of gravity.

The boundary at which anything that passes will be sucked into the black hole. The event horizon is defined by the point at which the velocity needed to escape the black hole exceeds the speed of light. As even light cannot escape, astronomers cannot view black holes directly. However, they can view the light emitted by surrounding matter orbiting the black that has not yet crossed the event horizon.

When viewing a black hole, the main light source comes from the accretion disk, a hot and bright structure containing rapidly spinning gas and dust. Matter gradually works its way from the outer part of the disk to its inner edge where it falls into the event horizon. Not all black holes have an accretion disk, in particular, isolated black holes without matter nearby to form the disk. Without an accretion disk, these black holes are difficult to identify and study. Stellar-mass black holes are often paired with a star that they pull gas from to form the accretion disk. The gravitational effects of the black hole warp spacetime making light follow distorted paths. This process is called gravitational lensing. Light viewed from the top of the disk behind the black hole appears to form a hump above. The light beneath the far side of the disk also creates a hump below. These shapes change as we view them from different angles and they are not visible at all when viewing the object face-on.

The event horizon and gravitational lensing create a dark zone, that is roughly twice as big as the event horizon. This effect is called the event horizon shadow.

Viewed from every angle are thing rings of light at the edge of the black hole shadow. These rings, called the photon sphere, are multiple highly distorted images of the accretion disk. This light orbits the black hole multiple times before escaping to be seen by the viewer. Rings closer to the black hole become thinner and fainter.

Doppler beaming is an effect of Einstein's theory of relativity where one side of the accretion disk appears brighter than the other when viewed from certain angles. Light from the side of the disk spinning towards the viewer will appear brighter and bluer compared to the light moving away from the viewer which is dimmer and redder.

Strong magnetic fields in the inner accretion disk extend out of it, creating a turbulent cloud of hot matter called a corona. Particles in the corona orbit the black hole at velocities approaching the speed of light. Coronas are a source of X-rays with much higher energies than those emanating from the accretion disk. Astronomers are still trying to understand the extent, shape, and other characteristics of coronas and the x-rays they produce.

In black holes of all sizes, a small amount of material heading toward the black hole near the inner edge of the accretion disk can be rerouted into a pair of jets that blast away from it in opposite directions. These jets eject particles at close to the speed of light. Astronomers do not fully understand how these particle jets. the jets from supermassive black holes can reach lengths of hundreds of thousands of light years.

A black hole is a volume of space where gravity is so strong that nothing, not even light, can escape from it.

As black holes do not emit light, scientists cannot detect them in the same way as stars and other objects in space. Instead, they rely on detecting radiation emitted from black holes as dust and gas are drawn into them. Supermassive black holes, lying at the center of a galaxy can become shrouded by the thick dust and gas around them obscuring the radiation emitted from dust and gas crossing the event horizon. Matter drawn towards a black hole can ricochet off the event horizon, emitting bright jets of material traveling at near-relativistic speeds. Although the black hole remains unseen, these jets can be viewed by astronomers.

Research estimates that the Milky Way could contain over 100 million black holes, including the supermassive black hole at the center of the galaxy, Sagittarius A which is roughly 4 million times the mass of the sun and approximately 26,000 light-years away from Earth. The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The black hole is at the center of the M87 galaxy 55 million light-years from Earth.

The first released image of a black hole in 2019 from the EHT collaboration.

In 2021, astronomers released an updated view of the giant black hole at the center of M87, showing the structure in more detail by imaging in polarized light.

An updated image of the black hole at the center of the M87 galaxy viewed in polarized light.

When a star runs out of fuel it may collapse or fall into itself. The resulting object depends on the mass of the star. Smaller stars (up to three solar masses) will become a neutron star or white dwarf. Larger stars can collapse with enough gravitational force to create a stellar black hole. This type of black hole is relatively small but incredibly dense, packing more than three solar masses into the diameter of a city. This gravitational force of stellar black holes attracts objects, consuming dust and gas from their surrounding galaxies and growing in size.

Supermassive black holes are millions or even billions of times as massive as the sun with roughly the same diameter. They are at the center of galaxies, including the Milky Way. There are multiple theories as to how these objects form, but once in existence, 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. One theory is that supermassive black holes are the result of hundreds or thousands of tiny black holes merging. Another suggests that large gas clouds collapse together and rapidly accrete mass. Other theories suggest they are the result of stellar clusters collapsing together or large clusters of dark matter.

Scientists originally believed that black holes only existed in small (stellar) and large (supermassive) sizes. However, research has revealed the possibility that intermediate black holes (IMBHs) may also exist, forming when stars in a cluster collide in a chain reaction. up nearby debris.

The idea of black holes was reexamined following the publishing of Einstein's theory of gravity. The mathematical foundation of general relativity was detailed in four landmark papers published in the Proceedings of the Prussian Academy of Sciences. This included the most famous paper titled The Field Equations of Gravitation,” published on November 25, 1915. In December 1915, Einstein sent his findings to Karl Schwarzschild the director of the Astrophysical Observatory in Potsdam and an accomplished theorist and mathematician. Schwarzschild was serving in the German army on the eastern front as an artillery lieutenant. He wrote back within days with the first known solution to Einstein's field equations. Schwazschild's letter included:

As you see, the war treated me kindly enough, in spite of the heavy gunfire, to allow me to get away from it all and take this walk in the land of your ideas.

Einstein responds:

I have read your paper with the utmost interest. I had not expected that one could formulate the exact solution of the problem in such a simple way. I liked very much your mathematical treatment of the subject.

Less than a year later, Schwarzschild succumbed to a skin disease contracted on the front. His solution completely described how space-time is warped by a spherical object like a planet or star. One of the features of his solution is that for very compact, high-density stars, it becomes harder to escape the gravitational field of the star. Eventually, there will be a point where every particle, even light, becomes gravitationally trapped. This point of no escape is called the event horizon.

The idea of black holes was reexamined in 1916 following the publishing of Einstein's theory of gravity. Karl Schwarzschild solved Einstein’s equations for the case of a black hole. He envisioned such an object as a spherical volume of warped space surrounding a concentrated mass and completely invisible to the outside world. Additional work by Robert Oppenheimer and others led to the idea that such an object might be formed by the collapse of a massive star. The term “black hole“ was itself coined in 1968 by the Princeton physicist John Wheeler, who worked out further details of a black hole’s properties.

Early physicists studying these bizarre objects often referred to them as “frozen stars.” The term “black hole“ was coined in 1968 by the Princeton physicist John Wheeler, who worked out further details of a black hole’s properties. Additional work by Robert Oppenheimer and others led to the idea that such an object might be formed by the collapse of a massive star.

In the late 1960s, the first x-ray astronomy measurements were made using a series of sounding rockets and satellites above the Earth’s atmosphere, which would otherwise block out celestial X-rays. During a rocket flight in 1964, astronomers discovered a bright X-ray source in the constellation Cygnus, dubbed Cygnus X-1 (Cyg X-1 for short). Its physical origin was a mystery as it didn’t coincide with any particularly bright optical or radio source. NASA’s Uhuru X-ray Explorer Satellite (launched in 1970) performed more detailed observations, finding rapid variability in the source on timescales shorter than a second. This suggests that the physical size of the X-ray-emitting region was quite compact, much smaller than a typical star.

A stellar counterpart to Cyg X-1 was identified within a year, and the mass of the companion was measured by the doppler shift of the orbiting star's spectrum. This suggested the star was 15 times the mass of the sun, far exceeding the theoretical limit for white dwarfs or neutron stars, making Cyg X-1 an excellent candidate for the first stellar-mass black hole. Evidence grew stronger with the launch of more sensitive x-ray telescopes, that measured x-ray variability on scales as short as a millisecond confining the emission region to hundreds of kilometers.

Since the discovery of Cyg X-1 in 1964, there have been only a few dozen more stellar black hole candidates identified. Most of these have been detected during short, unpredictable outbursts lasting a month or so before disappearing for decades.

In 1963, Maarten Schmidt discovered quasars (quasi-stellar radio sources) light sources that we can observe but are located vast distances from us. Based on their energy output and small size, scientists argued that quasars are caused by accreting supermassive black holes at the center of galaxies in their infancy. This makes quasars a type of active galactic nuclei (AGN). Material (dust, gas, and other matter) in the accretion disk surrounds the black hole and is superheated causing intense fiction. As it hears up this material generates radio waves, X-rays, ultraviolet and visible light.

We observe that quasars are more abundant in the past when there was more material around a black hole for it to feed on. After this material is used up the quasar becomes quiet. Evidence suggests most galaxies may have gone through a quasar phase and there might be a black hole at the center of each galaxy.

In the 1980s, astronomers began searching for supermassive black holes with the first candidate in the galaxy M87.

A black hole is a volume of space where gravity is so strong that nothing, not even light, can escape from it.

Black holes were first theoretically proposed by John Michell, an English country parson and scientist, in 1783. Michell considered a hypothetical method of determining the mass of a star. Using Newton's theory he reasoned that light consisted of particles and these particles would have their speed reduced by a star's gravitational pull. He proposed that the reduction in the speed of light might make it possible to calculate the star's mass. He extended this idea to wonder what would happen if the effect was so strong its escape velocity exceeded the speed of light. Using the approximate value for the speed of light, Michell calculated the mass of a star would have to be 500 times that of the Sun (assuming the same average density) for the escape velocity to be greater than the speed of light. He suggested such an object would be invisible.

While Michell proposed something we would now call a black hole his thought experiment is incorrect. Einstein's theory of relativity shows that light moves through space at a constant speed regardless of gravitational effects. His calculations to find the mass of a star do not work but he was correct in pointing out that an object massive enough must be invisible.

The idea of black holes was reexamined in 1916 following the publishing of Einstein's theory of gravity. Karl Schwarzschild solved Einstein’s equations for the case of a black hole. He envisioned such an object as a spherical volume of warped space surrounding a concentrated mass and completely invisible to the outside world. Additional work by Robert Oppenheimer and others led to the idea that such an object might be formed by the collapse of a massive star. The term “black hole“ was itself coined in 1968 by the Princeton physicist John Wheeler, who worked out further details of a black hole’s properties.