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  • Proc Natl Acad Sci U S A
  • v.98(19); 2001 Sep 11

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Black holes

B. brügmann.

* Max Planck Institute for Gravitational Physics, Albert Einstein Institute, Am Mühlenberg 1, 14476 Golm, Germany; ‡ University of California, Los Angeles, CA 90095-1562; and § Astrophysical Institute Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany

Recent progress in black hole research is illustrated by three examples. We discuss the observational challenges that were met to show that a supermassive black hole exists at the center of our galaxy. Stellar-size black holes have been studied in x-ray binaries and microquasars. Finally, numerical simulations have become possible for the merger of black hole binaries.

Black holes are a striking example of a prediction of Einstein's theory of gravity, general relativity. Although it took many decades before the physical concept of a black hole was fully understood and widely accepted, recent years have seen rapid advances on both the observational and theoretical side, which we want to illustrate in this brief note with three examples. Black holes have become an astrophysical reality. Solid observational evidence exists for black holes in two mass ranges. Supermassive black holes of 10 6 -10 9 solar masses have been observed at the centers of many galaxies, and here we discuss the observational challenges that were met to show that there exists a black hole at the center of our own galaxy. Stellar-size black holes of about 3–20 solar masses have been studied in x-ray binaries and microquasars. Finally, numerical simulations have become possible for the merger of black hole binaries.

Recent high-resolution imaging studies of stars at the center of our Galaxy have produced strong dynamical evidence for a central concentration of dark matter, establishing the Milky Way as the most convincing case of a galaxy containing a central supermassive black hole ( 1 , 2 ). In those experiments, images obtained over 2–6 years at the Keck telescope ( 1 ) and European Southern Observatory's New Technology Telescope ( 2 ) provided measurements of the stars' velocities in the plane of the sky, from which a statistical analysis revealed the existence of 2−3 × 10 6 solar masses of dark matter contained within a radius of 0.015 parsec (1 parsec = 3.09 × 10 16 m), or 2.6 light weeks. At this meeting, new results from the Keck telescope were reported. With this new data set, which triples the number of maps obtained and doubles the time baseline for the Keck experiment, the velocity uncertainties are reduced by a factor of 3 compared with the earlier Keck work ( 1 ), primarily as a result of the increased time baseline and, in the central square arcsecond, by a factor of 6 compared with ref. 2 , due to the higher angular resolution (0."05 vs. 0."15). In addition to simply increasing the time baseline for velocity measurements, the new measurements have advanced this experiment in two significant ways: ( i ) the first Keck adaptive optics (AO) images of the galactic center have been obtained (Fig. ​ (Fig.1), 1 ), allowing a more complete census of stars in this region to be obtained ( 3 ), and ( ii ) the first measurements of stellar accelerations in this field have now been achieved ( 4 ).

An external file that holds a picture, illustration, etc.
Object name is pq2013657001.jpg

A ≈3" × 3" region showing the Sgr A* cluster (the faint stars located just to the right of the center of the field of view). Both images were taken in May 1999 at 2.2 μm (K-band); however, the image on the left was produced by shift-and-adding Keck I speckle data, and the image on the right was obtained with the new Keck II adaptive optics system. The adaptive optics image represents a large improvement.

With longer integration times, AO should probe a yet larger sample of fainter stars, place stringent limits on Sgr A*, and explore the possibility of a gravitational lensing experiment ( 5 ). For the time being, the AO map has increased the number of stars in the proper motion study ( 3 ). With relative positional accuracies of ≈3 milliarcseconds, the motions of stars are now fit with a second-order polynomial as opposed to a simple linear fit, which was done in earlier work. Among the 90 stars in the original Keck proper motion sample ( 1 ), accelerations of 2–5 milliarseconds/yr 2 , or equivalently 3–6 × 10 −6 km/sec 2 , are now detected for three stars, S0–1, S0–2, and S0–4 ( 4 ). These three stars are independently distinguished in this sample as being among the fastest moving stars ( v = 565 to 1,383 km/sec) and among the closest to the nominal position of Sgr A* (< r > = 0.003 to 0.015 parsec). Acceleration vectors, in principle, are more precise tools than velocity vectors for studying the properties of the central dark mass. These acceleration measurements improve the localization of our Galaxy's dynamical center by a factor of 3, which is critical for reliably associating any near-infrared source with the black hole, given the complexity of the region. In addition, these acceleration measurements increase the minimum mass density inferred by a factor of 8 over previous results, thereby strengthening the case for a black hole.

X-Ray Binaries and Microquasars.

In contrast to the need for measuring dozens of stars to determine the mass of the black hole in the Galactic Center, that of black holes in x-ray binary systems can be deduced either from optical/IR measurements of just one star, namely the companion of the stellar-mass black hole, or from x-ray observations of the binary. In x-ray binaries, a black hole of typically 3–10 solar masses and a normal star (1–30 solar masses) orbit each other. Matter is pulled off the companion star and, because of its angular momentum, is forming an accretion disk as it moves toward the black hole. Before finally falling into the black hole, the matter heats up to several million degrees at the inner part of the disk and emits luminous x-ray radiation. Because the whole accretion process is highly variable, numerous such black hole binaries have been found over the last decade, thanks to x-ray detectors on satellites, such as Compton Gamma-Ray Observatory and Rossi X-Ray Timing Explorer, constantly monitoring the whole sky.

Although optical/IR spectroscopic measurements of the velocity of the companion star can readily determine the mass of the black hole, x-ray measurements promise to be a sharper and even more flexible diagnostic tool as they reach down to the inner edge of the accretion disk at a few Schwarzschild radii of the black hole. High time-resolution observations of black hole binaries have revealed quasiperiodic oscillations in x-ray emission at a stable minimum period, e.g., at 67 Hz for GRS 1915 + 105 ( 6 ), which may very well be related to the period of the innermost stable orbit of the accretion disk. The Kerr metric fixes this period as a function of mass and spin of the black hole. Because the maximum temperature of the innermost disk, as discernable from x-ray spectroscopy, is also thought to be just a function of black hole mass and spin, detailed x-ray observations can be used to determine both the mass AND spin of a black hole ( 7 ).

A small fraction of black hole binaries also eject matter at relativistic speeds into two opposite jets that are observable in the radio band as knots moving apart at superluminal speed. Actually, GRS 1915 + 105 is the most famous representative of this class of object, called microquasars ( 8 ). Simultaneous observations of these microquasars in the x-ray, optical/IR, and radio band have for the first time revealed a relation between accretion disk instabilities and jet ejections ( 9 , 10 ). Theorists now face the challenge of modeling the highly dynamical processes of nonsteady accretion and jet formation, acceleration, and collimation, with all of the complications of three-dimensional magnetohydrodynamics and general relativity.

Another example in which the full Einstein equations have to be solved in the highly dynamic and nonlinear regime is the collision and merger of two black holes. In fact, although single black holes are comparatively simple exact solutions of the Einstein equations, the two-body problem of general relativity for black holes, or neutron stars, is unsolved. As opposed to Newtonian theory, where the Kepler ellipses provide an astrophysically relevant example for the analytic solution of the two-body problem, in Einsteinian gravity there are no corresponding exact solutions. The failure of Einstein's theory to lead to stable orbits is due to the fact that, in general, two orbiting bodies will emit gravitational waves that carry away energy and momentum from the system, leading to an inspiral. Of course, this “leak” is not considered detrimental. It is expected that gravitational wave astronomy will open a new window onto the universe ( 11 ), and binary black hole mergers are considered to be among the most likely candidates for first detection.

Numerical relativity is only now approaching a state where the evolution of rather general three-dimensional data sets can be simulated on a computer to solve the Einstein equations (see, e.g., ref. 12 ). After early computations for the axisymmetric head-on collision of two black holes in the 1970s, it was in 1995 that, for the first time, spherically symmetric data for a single Schwarzschild black hole was evolved with a three-dimensional computer code ( 13 ). The first fully three-dimensional binary black hole evolutions, the grazing collision of nearby spinning and moving black holes, is reported in ref. 14 . Fig. ​ Fig.2 2 shows a visualization of such a black hole merger [M. Alcubierre, W. Benger, B. Brügmann, G. Lanfermann, L. Nerger, E. Seidel & R. Takahashi, R. http://jean-luc.aei.mpg.de/Press/BH1999/ ]. These simulations are still severely limited in achievable evolution time (300 μs for a final black hole of 10 solar masses), i.e., one can evolve through the very last moments of the inspiral when the two black holes merge, but even a single full orbit is not yet possible. Concretely, the computer code crashes when the space–time distortion becomes too severe. The recent computer simulations not only reflect an increase in raw computer power but also are due to theoretical work on how to construct good coordinates dynamically to deal with strong and even singular gravitational fields, and a new way to compute black hole initial data was developed. Work is in progress to obtain at least one orbit and to compute the gravitational waves generated in a black hole merger.

An external file that holds a picture, illustration, etc.
Object name is pq2013657002.jpg

The evolution of the apparent horizon during a grazing black hole collision. Initially there are two separate horizons, which, during the merger, become enclosed by a third one. The coloring represents the curvature of the surface. The black holes appear to grow, because numerical grid points are falling toward and into the black hole.

In conclusion, we believe that black hole physics will be a very dynamic field in the coming years.


A.M.G. was supported by the National Science Foundation and the Packard Foundation. J.G. was partly supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DLR) under contract 50 QQ 9602 3. The simulations in refs. 14 and 15 were performed at the Albert-Einstein-Institut and at National Center for Supercomputing Applications.

This paper is a summary of a session presented at the sixth annual German–American Frontiers of Science symposium, held June 8–10, 2000, at the Arnold and Mabel Beckman Center of the National Academies of Science and Engineering in Irvine, CA.

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The present research work has been conducted to study the basic characteristics about the black hole- its historical background, basic concept, different types, formation, general views etc. The data have been collected from different research papers, books, reports and different websites. The data are analyzed critically with logical approach considering various factors related with the black hole. The study reveals that black holes are like celestial monster in the universe. Black hole may cause a little bit concern for the mankind to survive in this beautiful earth though the probability that we all are sucked by the black hole is very small at this present time. So there is no need to fear too much for getting spaghettified soon.

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The black hole and dark matter are two pillars of contemporary General Relativity. Week after week, we read about them in the specialized journals and in popularization magazines. Here we show that the term 'black hole' has yet to be defined scientifically. To pique the skeptic, mathematical physicists assign many dimensions to the black hole, confess that they have never seen one, and have no idea what these alleged objects are made of. For its part, dark matter is nothing more than an ad hoc variable that Mathematical Physics invented to plug holes in its leaky conception of gravity. The Rope Model of Light and Gravity offers a rational alternative for phenomena attributed to magical black holes and invisible dark matter.

research paper in black hole

Lecture Notes in Physics

Gustavo Romero

Sethanne Howard

IJIRST - International Journal for Innovative Research in Science and Technology

As a star grows old, swells, then collapses on itself, often you will hear the word " black hole " thrown around. The black hole is a gravitationally collapsed mass, from which no light, matter, or signal of any kind can escape. These exotic objects have captured our imagination ever since they were predicted by Einstein's Theory of General Relativity in 1915. So what exactly is a black hole? A black hole is what remains when a massive star dies. Not every star will become a black hole, only a select few with extremely large masses. In order to have the ability to become a black hole, a star will have to have about 20 times the mass of our Sun. No known process currently active in the universe can form black holes of less than stellar mass. This is because all present black hole formation is through gravitational collapse, and the smallest mass which can collapse to form a black hole produces a hole approximately 1.5-3.0 times the mass of the sun .Smaller masses collapse to form white dwarf stars or neutron stars.


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Astrophysics > High Energy Astrophysical Phenomena

Title: astrophysical black holes: a review.

Abstract: In this review, I have tried to focus on the development of the field, from the first speculations to the current lines of research. According to Einstein's theory of general relativity, black holes are relatively simple objects and completely characterized by their mass, spin angular momentum, and electric charge, but the latter can be ignored in the case of astrophysical macroscopic objects. Search for black holes in the sky started in the early 1970s with the dynamical measurement of the mass of the compact object in Cygnus X-1. In the past 10-15 years, astronomers have developed some techniques for measuring the black hole spins. Recently, we have started using astrophysical black holes for testing fundamental physics.

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Black Holes

Black holes are some of the most fascinating and mind-bending objects in the cosmos. The very thing that characterizes a black hole also makes it hard to study: its intense gravity. All the mass in a black hole is concentrated in a tiny region, surrounded by a boundary called the “event horizon”. Nothing that crosses that boundary can return to the outside universe, not even light. A black hole itself is invisible.

But astronomers can still observe black holes indirectly by the way their gravity affects stars and pulls matter into orbit. As gas flows around a black hole, it heats up, paradoxically making these invisible objects into some of the brightest things in the entire universe. As a result, we can see some black holes from billions of light-years away. For one large black hole in a nearby galaxy, astronomers even managed to see a ring of light around the event horizon, using a globe-spanning array of powerful telescopes.

Center for Astrophysics | Harvard & Smithsonian scientists participate in many black hole-related projects:

Using the Event Horizon Telescope (EHT) to capture the first image of a black hole’s “shadow”: the absence of light that marks where the event horizon is located. The EHT is composed of many telescopes working together to create one Earth-sized observatory , all monitoring the supermassive black hole at the center of the galaxy M87, leading to the first image ever captured of a black hole. CfA Plays Central Role In Capturing Landmark Black Hole Image

Observing supermassive black holes in other galaxies to understand how they evolve and shape their host galaxies. CfA astronomers use telescopes across the entire spectrum of light, from radio waves to X-rays to gamma rays. A Surprising Blazar Connection Revealed

Studying the infall of matter — called “accretion” — onto black holes, using NASA’s Chandra X-ray Observatory and other telescopes. In addition, CfA researchers use cutting-edge supercomputers to create theoretical models for the disks and jets of matter that black holes create around themselves. Supermassive Black Hole Spins Super-Fast

Hunting for black hole interactions with other astronomical objects. That includes “disruption” events, where black holes tear stars or other objects apart, creating bursts of intense light. Black Hole Meal Sets Record for Length and Size

Observing clusters of stars to find intermediate mass black holes, and modeling how they shape their environments. A Middleweight Black Hole is Hiding at the Center of a Giant Star Cluster

Hunting for and characterizing stellar mass black holes, which can include information about their birth process and evolution. NASA's Chandra Adds to Black Hole Birth Announcement

The Varieties of Black Holes

Black holes come in three categories:

Stellar Mass Black Holes are born from the death of stars much more massive than the Sun. When some of these stars run out of the nuclear fuel that makes them shine, their cores collapse into black holes under their own gravity. Other stellar mass black holes form from the collision of neutron stars , such as the ones first detected by LIGO and Virgo in 2017. These are probably the most common black holes in the cosmos, but are hard to detect unless they have an ordinary star for a companion. When that happens, the black hole can strip material from the star, causing the gas to heat up and glow brightly in X-rays.

Supermassive Black Holes are the monsters of the universe, living at the centers of nearly every galaxy. They range in mass from 100,000 to billions of times the mass of the Sun, far too massive to be born from a single star. The Milky Way’s black hole is about 4 million times the Sun’s mass, putting it in the middle of the pack. In the form of quasars and other “active” galaxies , these black holes can shine brightly enough to be seen from billions of light-years away. Understanding when these black holes formed and how they grow is a major area of research. Center for Astrophysics | Harvard & Smithsonian scientists are part of the Event Horizon Telescope (EHT) collaboration, which captured the first-ever image of the black hole: the supermassive black hole at the center of the galaxy M87.

Intermediate Mass Black Holes are the most mysterious, since we’ve hardly seen any of them yet. They weigh 100 to 10,000 times the mass of the Sun, putting them between stellar and supermassive black holes. We don’t know exactly how many of these are, and like supermassive black holes, we don’t fully understand how they’re born or grow. However, studying them could tell us a lot about how the most supermassive black holes came to be.

Black holes can seem bizarre and incomprehensible, but in truth they’re remarkably understandable. Despite not being able to see black holes directly, we know quite a bit about them. They are …

Simple . All three black hole types can be described by just two observable quantities: their mass and how fast they spin. That’s much simpler than a star, for example, which in addition to mass is a product of its unique history and evolution , including its chemical makeup. Mass and spin tell us everything we need to know about a black hole: it “forgets” everything that went into making it. Those two quantities determine how big the event horizon is, and the way gravity affects any matter falling onto the black hole.

Compact . Black holes are tiny compared to their mass. The event horizon of a black hole the mass of the Sun would be no more than 6 kilometers across, and the faster it spins, the smaller that size is. Even a supermassive black hole would fit easily inside our Solar System.

Powerful . The combination of large mass and small size results in very strong gravity. This gravity is strong enough to pull a star apart if it gets too close, producing powerful bursts of light. A supermassive black hole heats gas falling onto it to temperatures of millions of degrees, making it glow brightly enough in X-rays and other types of radiation to be seen across the universe.

Very common . From theoretical calculations based on observations, astronomers think the Milky Way might have as many as a hundred million black holes, most of which are stellar mass. And with at least one supermassive black hole in most galaxies, there could be hundreds of billions of supermassive black holes in the observable universe.

Very important . Black holes have a reputation for eating everything that comes by, but they turn out to be messy eaters. A lot of stuff that falls toward a black hole gets jetted away, thanks to the complicated churning of gas near the event horizon. These jets and outflows of gas called “winds” spread atoms throughout the galaxy, and can either boost or throttle the birth of new stars, depending on other factors. That means supermassive black holes play an important role in the life of galaxies, even far beyond the black hole’s gravitational pull.

And yes, mysterious . Along with astronomers, physicists are interested in black holes because they’re a laboratory for “quantum gravity”. Black holes are described by Albert Einstein’s general relativity, which is our modern theory of gravity, but the other forces of nature are described by quantum physics. So far, nobody has developed a complete quantum gravity theory, but we already know black holes will be an important test of any proposed theory.

The first image of a black hole

The first image of a black hole in human history, captured by the Event Horizon Telescope, showing light emitted by matter as it swirls under the influence of intense gravity. This black hole is 6.5 billion times the mass of the Sun and resides at the center of the galaxy M87.

  • What do black holes look like?
  • What happens to space time when cosmic objects collide?
  • The Energetic Universe
  • The Milky Way Galaxy
  • Extragalactic Astronomy
  • Stellar Astronomy
  • Theoretical Astrophysics
  • Einstein's Theory of Gravitation
  • Radio and Geoastronomy

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Research Papers on Black Holes – Mystery of Black Hole

  • Research Papers on Black Holes…

Research Papers on Black Holes

Research Papers on Black Holes : In the first place, the main principle for anybody dealing with a black hole is, obviously, don’t get excessively close. Be that as it may, state you do. At that point you’re in for a serious excursion — a single direction trip — in light of the fact that there is no returning once you fall into a black hole.

Table of Contents

If Black Holes Are “Black,” How Do Scientists Know They Are There?

A black hole cannot be seen because of the strong gravity that is pulling all of the light into the black hole’s center. However, scientists can see the effects of its strong gravity on the stars and gases around it. If a star is orbiting a certain point in space, scientists can study the star’s motion to find out if it is orbiting a Research Papers on Black Holes.

In reality, Albert Einstein initially anticipated the presence of black holes in 1916, with his general theory of relativity.  The expression “black hole” was begat numerous years after the fact in 1967 by American astronomer John Wheeler. Following quite a while of dark openings being referred to just as hypothetical items, the principal physical dark gap at any point found was seen in 1971.

Moreover, the first mark of a black hole is “gravitationally collapsed star” which depends on Newtonian Physics where we depict Gravity, as a force like the one we experience on earth in PhD Research Project .

Could a Research Papers on Black Holes Destroy Earth?

As a matter of fact, Black holes do not wander around the universe, randomly swallowing worlds. They follow the laws of gravity just like other objects in space. The orbit of a black hole would have to be very close to the solar system to affect Earth, which is not likely.

Important to realize, if a black hole coupled with the same mass as the sun were to replace the sun, Earth would not fall in. The black hole with the same mass as the sun would keep the same gravity as the sun. On the positive side, the planets would still orbit the black hole as they orbit the sun now.

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

A black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area

Uniquely, Black holes are some of the strangest and most fascinating objects in outer space research report writing . They’re extremely dense, with such strong gravitational attraction that even light cannot escape their grasp if it comes near enough.

One Star’s End is a Black Hole’s Beginning

Most black holes form from the remnants of a large star that dies in a supernova explosion. (Smaller stars become dense neutron stars, which are not massive enough to trap light.) If the total mass of the star is large enough (about three times the mass of the Sun), it can be proven theoretically that no force can keep the star from collapsing under the influence of gravity.

One black hole is not like the others

Especailly, super Research Papers on Black Holes, predicted by Einstein’s general theory of relativity, can have masses equal to billions of suns these cosmic monsters likely hide at the centers of most galaxies. At the same time, the Milky Way hosts its own super massive black hole at its center known as Sagittarius A* (pronounced “ay star”) that is more than four million times as massive as our sun. In PhD publication , a black hole’s intense gravity tugs on any surrounding objects. Astronomers use these erratic movements to infer the presence of the invisible monster that lurks nearby research consultation . Or objects can orbit a black hole, and astronomers can look for stars that seem to orbit nothing to detect a likely candidate. That’s how astronomers eventually identified Sagittarius A* as a black hole in the early 2000s using PhD Research.

Black Hole in the early 2000s using PhD Research

Phd research trends recent discoveries.

Below some of the Recent Research Works dealing with the black holes are listed one by one as follows:

In the final analysis, these discoveries/works not only gave its contribution but also dealt with several future PhD Research Trends. As well as, the directives which the Dissertation Writers of these days take up as their major research arena while defining their own research gaps since the study of the black hole concepts find itself one among the Trending How to select a Research topics particularly in the discipline of space exploration. Visit us  PhDiZone


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September 1, 2022

12 min read

How the Inside of a Black Hole Is Secretly on the Outside

Mysterious “islands” help to explain what happens to information that falls into a black hole

By Ahmed Almheiri

Illustration of a black hole with strands representing information getting sucked into it.

Harry Campbell

T heoretical physics has been in crisis mode ever since 1974, when Stephen Hawking argued that black holes destroy information. Hawking showed that a black hole can evaporate, gradually transforming itself and anything it consumes into a featureless cloud of radiation. During the process, information about what fell into the black hole is apparently lost, violating a sacred principle of physics.

This remained an open problem for almost 50 years, but the pieces started falling into place in 2019 through research that I was involved in. The resolution is based on a new understanding of spacetime and how it can be rewired through quantum entanglement, which leads to the idea that part of the inside of a black hole, the so-called island, is secretly on the outside.

To understand how we arrived at these new ideas, we must begin with the inescapable nature of black holes.

A One-Way Street

Nothing seems more hopeless than trying to get out of a black hole—in fact, this impossibility is what defines black holes. They are formed when enough matter is confined within a small enough region that spacetime collapses in on itself in a violent feedback loop of squeezing and stretching that fuels more squeezing and stretching. These tidal forces run to infinity in finite time, marking the abrupt end of an entire region of spacetime at the so-called black hole singularity—the place where time stops and space ceases to make sense.

There is a fine line within the collapsing region that divides the area where escape is possible from the point of no return. This line is called the event horizon. It is the outermost point from which light barely avoids falling into the singularity. Unless a thing travels faster than light—a physical impossibility—it cannot escape from behind the event horizon; it is irretrievably stuck inside the black hole.

The one-way nature of this boundary is not immediately problematic. In fact, it is a robust prediction of the general theory of relativity. The danger starts when this theory interacts with the wild world of quantum mechanics.

Something Out of Nothing

Quantum theory redeems black holes from being the greedy monsters they are made out to be. Every calorie of energy they consume they eventually give back in the form of Hawking radiation—energy squeezed out of the vacuum near the event horizon.

The idea of getting something out of nothing may sound absurd, but absurdity is not the worst allegation made against quantum mechanics. The emptiness of the vacuum in quantum theory belies a sea of particles—photons, electrons, gravitons, and more—that conspire to make empty space feel empty. These particles come in carefully arranged pairs, acting hand in hand as the glue that holds spacetime together.

Particle pairs that straddle the event horizon of a black hole, however, become forever separated from each other. The newly divorced particles peel away from the horizon in opposite directions, with one member crashing into the singularity and the other escaping the black hole's gravitational pull in the form of Hawking radiation. This process is draining for the black hole, causing it to get lighter and smaller as it emits energy in the form of the outgoing particles. Because of the law that energy must be conserved, the particles trapped inside must then carry negative energy to account for the decrease in the total energy of the black hole.

From the outside, the black hole appears to be burning away (although it happens so slowly, you can't see it happening in real life). When you burn a book, the words on its pages imprint themselves on the pattern of the emanating light and the remaining ashes. This information is thus preserved, at least in principle. If an evaporating black hole were a normal system like the burning book, then the information about what falls into it would be encoded into the emerging Hawking radiation. Unfortunately, this is complicated by the quantum-mechanical relation among the particles across the horizon.

Credit: Matthew Twombly

Einstein's Enemy

The issue begins with the end of the pairing of the two particles straddling the event horizon. Despite being separated, they maintain a quantum union that transcends space and time—they are connected by entanglement. Rejected as an absurdity by the physicists who predicted it, quantum entanglement is perhaps one of the weirdest aspects of our universe and arguably one of its most essential. The concept was first concocted by Albert Einstein, Boris Podolsky and Nathan Rosen as a rebuttal against what was then the nascent theory of quantum mechanics. They cited entanglement as a reason the theory must be incomplete—“spooky” is how Einstein famously described the phenomenon.

For a simple example of entanglement, consider two coins in a superposition—the quantum phenomenon of being in multiple states until a measurement is made—of both coins being either heads or tails. The coins aren't facing heads and tails at the same time—that's physically impossible—but the superposition signifies that the chance of observing the pair of coins in either orientation, both heads or both tails, is a probability of one half. There is no chance of ever finding the coins in opposite orientations. The two coins are entangled; the measurement result of one predicts the result of the other with complete certainty. Either coin by itself is completely random, devoid of information, but the randomness of the pair is perfectly correlated.

The scientists were troubled by how the two coins appeared to influence each other without having to come into physical contact. The coins could be in separate galaxies while still maintaining the same amount of entanglement between them. Einstein was unnerved by the apparent “spooky action at a distance” linking the results of the two separate random measurements.

The irony is that Einstein himself is in a superposition of being both wrong and right. He was right to recognize the importance of entanglement in distinguishing quantum mechanics from classical physics. What he got wrong can be summed up with the truism “correlation does not imply causation.” Although the fates of the particles are inextricably correlated, the measurement outcome of one does not cause the outcome of the other. It turns out that quantum mechanics simply allows for a new, higher degree of correlation than we are used to.

Information Lost

Because Hawking radiation is composed of one half of a collection of entangled pairs, it emerges from the black hole in a completely random state—if the particles were coins, they would be observed to be heads or tails with equal probability. Hence, we cannot infer anything useful about the contents of the black hole from the random measurements of the radiation. This means that an evaporating black hole is basically a glorified information shredder, except unlike the mechanical kind, it does a thorough job.

We can measure the lack of information—or the randomness—in the Hawking radiation by thinking about the amount of entanglement between the radiation and the black hole. This is because one member of an entangled pair is always random, and the outside members are all that remains by the end of the evaporation. The calculation of randomness goes by many names, including entanglement entropy, and it grows with every emerging Hawking particle, plateauing at a large value once the black hole has completely disappeared.

This pattern differs from what happens when information is preserved, as in the example of a burning book. In such a case, the entropy may rise initially, but it has to peak and then fall to zero by the end of the process. The intuition behind this rule is clear when you think about a standard deck of cards: suppose you are dealt cards from a 52-card deck, one by one, facing down. The entropy of the cards in your possession is simply a measure of your ignorance of what's on the other side of the cards—specifically, the number of possibilities of what they could be. If you have been dealt just one card, the entropy is 52 because there are 52 possibilities. But as you are dealt more, the entropy rises, peaking at 500 trillion for 26 cards, which could be any of 500 trillion different combinations. After this, though, the possible mixes of cards, and thus the entropy, go back down, reaching 52 again when you have 51 cards. Once you have all the cards, you are certain of exactly what you have—the entire deck—and the entropy is zero. This rising and falling pattern of entropy, known as the Page curve, applies to all normal quantum-mechanical systems. The time at which the entropy peaks and then starts to decrease is the Page time.

The destruction of information inside black holes spells disaster for physics because the laws of quantum mechanics stipulate that information cannot be obliterated. This is the famous information paradox—the fact that a sprinkling of quantum mechanics onto the description of black holes leads to a seemingly insurmountable inconsistency. Physicists knew we needed a more complete understanding of quantum-gravitational physics to generate the Page curve for the Hawking radiation. Unsurprisingly, this task proved difficult.

An Eventful Horizon

Part of the challenge was that no minor tweaking of the evaporation process was sufficient to generate the Page curve and send the entropy back down to zero. What we needed was a drastic reimagining of the structure of a black hole.

In a paper I published in 2013 with Donald Marolf, the late Joseph Polchinski, and Jamie Sully (known collectively as AMPS), we tried out several ways to modify the picture of evaporating black holes using a series of gedankenexperiments—the German term for the kind of thought experiments Einstein popularized. Through our trials we concluded that to save the sanctity of information, one of two things had to give: either physics must be nonlocal—allowing for information to instantaneously disappear from the interior and appear outside the event horizon—or a new process must kick in at the Page time. To preclude the increase of entropy, this process would have to break the entanglement between the particle pairs across the event horizon. The former option—making physics nonlocal—was too radical, so we decided to go with the latter.

This modification helps to preserve information, but it poses another paradox. Recall that the entanglement across the horizon was a result of having empty space there—the way the vacuum is maintained by a sea of entangled pairs of particles. The entanglement is key; breaking it comes at the cost of creating a wall of extremely high-energy particles, which our group named the firewall. Having such a firewall at the horizon would forbid anything from entering the black hole. Instead infalling matter would be vaporized on contact. The black hole at the Page time would suddenly lose its interior, and spacetime would come to an end, not at the singularity deep inside the black hole but right there at the event horizon. This conclusion is known as the firewall paradox, a catch-22 that meant any solution to the information paradox must come at the cost of destroying what we know about black holes. If ever there were a quagmire, this would be it.

Fluctuating Wormholes

Eventually my colleagues and I realized that both the information paradox and the newer firewall paradox arose because our attempts to meld quantum mechanics and black hole physics were too timid. It wasn't enough to apply quantum mechanics to only the matter present in black holes—we had to devise a quantum treatment of the black hole spacetime as well. Although quantum effects on spacetime are usually very small, they could be enhanced by the large entanglement produced by the evaporation. Such an effect may be subtle, but its implications would be huge.

To consider the quantum nature of spacetime, we relied on a technique designed by Richard Feynman called the path integral of quantum mechanics. The idea is based on the weird truth that, according to quantum theory, particles don't simply travel along a single path from point A to point B—they travel along all the different paths connecting the two points. The path integral is a way of describing a particle's travels in terms of a quantum superposition of all possible routes. Similarly, a quantum spacetime can be in a superposition of different complicated shapes evolving in different ways. For instance, if we start and end with two regular black holes, the quantum spacetime within them has a nonzero probability of creating a short-lived wormhole that temporarily bridges their interiors.

Usually the probability of this happening is vanishingly slim. When we carry out the path integral in the presence of the Hawking radiation of multiple black holes, however, the large entanglement between the Hawking radiation and the black hole interiors amplifies the likelihood of such wormholes. This realization came to me through work I did in 2019 with Thomas Hartman, Juan Maldacena, Edgar Shaghoulian and Amirhossein Tajdini, and it was also the result of an independent collaboration by Geoffrey Penington, Stephen Shenker, Douglas Stanford and Zhenbin Yang.

Islands beyond the Horizon

Why does it matter if some black holes are connected by wormholes? It turns out that they modify the answer of how much entanglement entropy there is between the black hole and its Hawking radiation. The key is to measure this entanglement entropy in the presence of multiple copies of the system. This is known as the replica trick.

The relevant physical effect of these temporary wormholes is to swap out the interiors among the different black holes. This happens literally: what was in one black hole gets shoved into one of the other copies far away, and the original black hole assumes a new spacetime interior from a different one. The swapped region of the black hole interior is called the island, and it encompasses almost the entire interior up to the event horizon.

The swapping is exactly what the doctor ordered! Focusing on one of the black holes and its Hawking radiation, the swapped-out island takes with it all the partner particles that are entangled with the outgoing Hawking radiation, and hence, technically, there is no entanglement between the black hole and its radiation.

Including this potential effect of wormholes produces a new formula for the entanglement entropy of the radiation when applied to a single copy of the system. Instead of Hawking's original calculation, which simply counts the number of Hawking particles outside a black hole, the new formula curiously treats the island as if it were outside and a part of the exterior Hawking radiation. Therefore, the entanglement between the island and the exterior should not be counted toward the entropy. Instead the entropy that it predicts comes almost entirely from the probability of the swap actually occurring, which is equal to the area of the boundary of the island—roughly the area of the event horizon—divided by Newton's gravitational constant. As the black hole shrinks, this contribution to the entropy decreases. This is the island formula for the entanglement entropy of the Hawking radiation.

The final step in computing the entropy is to take the minimum between the island formula and Hawking's original calculation. This gives us the Page curve that we've been after. Initially we calculate the entanglement entropy of the radiation with Hawking's original formula because the answer starts off smaller than the area of the event horizon of the black hole. But as the black hole evaporates, the area shrinks, and the new formula takes the baton as the true representative of the radiation's entanglement entropy.

What is remarkable about this result is that it solves two paradoxes with one formula. It appears to address the firewall paradox by supporting the option of nonlocality that my AMPS group originally dismissed. Instead of breaking the entanglement at the horizon, we are instructed to treat the inside—the island—as part of the outside. The island itself becomes nonlocally mapped to the outside. And the formula solves the information paradox by revealing how black holes produce the Page curve and preserve information.

Let's take a step back and think about how we got here. The origins of the information paradox can be traced back to the incompatibility between the sequestering of information by the event horizon and the quantum-mechanical requirement of information flow outside the black hole. Naive resolutions of this tension lead to drastic modifications of the structure of black holes; however, subtle yet dramatic effects from fluctuating wormholes change everything. What emerges is a self-consistent picture that lets a black hole retain its regular structure as predicted by general relativity, albeit with the presence of an implicit though powerful nonlocality. This nonlocality is screaming that we should consider a portion of the black hole's interior—the island—as part of the exterior, as a single unit with the outside radiation. Thus, information can escape a black hole not by surmounting the insurmountable event horizon but by simply falling deeper into the island.

Despite the excitement of this breakthrough, we have only begun to explore the implications of spacetime wormholes and the island formula. Curiously, while they ensure that the island is mapped onto the radiation, they do not generate a definite prediction for specific measurements of the Hawking radiation. What they do teach us, however, is that wormholes are the missing ingredient in Hawking's original estimation of the randomness in the radiation and that gravity is in fact smart enough to comply with quantum mechanics.

Through these wormholes, gravity harnesses the power of entanglement to achieve nonlocality, which is just as unnerving to us as the entanglement that originally spooked Einstein. We must admit that, at some level, Einstein was right after all.

Black Hole - Free Essay Examples And Topic Ideas

Black holes, regions in space where gravitational forces are so intense that nothing, not even light, can escape their pull, are among the most mysterious and intriguing objects in the cosmos. Essays on black holes could explore their formation, properties, and the physics governing their behavior. Discussions might also delve into the discoveries, theoretical predictions, and the cutting-edge research aiming to unravel the mysteries surrounding black holes. Additionally, exploring the depiction of black holes in popular culture, their potential implications for our understanding of the universe, and the technological advancements enabling the study of extreme cosmic phenomena can provide a captivating insight into the enigmatic nature of black holes and their place within the broader cosmic narrative. We’ve gathered an extensive assortment of free essay samples on the topic of Black Hole you can find in Papersowl database. You can use our samples for inspiration to write your own essay, research paper, or just to explore a new topic for yourself.

Exposing Black Holes

A captain and his crew bracing for dear life as they descend nearer and nearer toward the center. Two brave young astronauts launching themselves full throttle into unknown depths just to see what lies beyond. A massive force consuming entire galaxies in its wake, including a little planet named Earth who so happened to be in its path. The media is full of adventurous notions and misconceptions about black holes, but what is a black hole really? Black holes are […]

Supermassive Black Holes

Thanks to recent advancements in technology, astronomers have been given the means to better understand how supermassive black holes formed, as well as their relation to the evolution of their respective galaxies. Before understanding what a supermassive black hole is, it is probably best to learn about normal black holes in comparison. A black hole is essentially a vortex containing a gravitational field that is strong enough to prevent any form of matter or radiation from escaping it. As the […]

Black Holes: Mysterious in Many Ways

Two recent discoveries continue to mystify us and puzzle astronomers. Recently a cosmic gas cloud had a deadly encounter with Sagittarius A, only to pass through it. Astronomers are mystified and still fighting each other about it. From recording x-rays from two different locations, we were able to measure the speed of a black hole called NGC 1365. It was discovered to be spinning at the max speed that physics will allow, and hopefully, the speed will reveal a little […]

What are Black Holes?

Have you ever wondered what lies at the center of our Milky Way, what happens to stars when they die, or what may lie in the darkest spots of the observable universe? The answer to all of those questions is black holes. Albert Einstein was the first one to suggest that black holes existed in 1926; he used it in his general theory of relativity. An actual black hole was discovered in 1971. Ever since black holes have been known […]

On the Relevance of Black Holes and Supermassive Black Holes to Human Development

It has been said that Einstein once dreamed that he himself was traveling with a photon--a single particle of light. He was attempting to imagine past the boundary of the then known physical theories. It was an endeavor that would eventually produce both General, and Special Relativity. These two theories provided mankind things like GPS technology, more efficient communication technologies (communication satellite coordination), and seemingly, an overall truer knowledge of reality. In fact, relativistic physics have birthed an unimaginable level […]

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The Universe of Black Holes

Abstract Black holes are some of the strangest and most fascinating objects found in outer space. They are objects of extreme density, with such strong gravitational attraction that even light cannot escape from their grasp if it comes near enough. Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term ""black hole"" was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971. Stellar-mass black holes are formed […]

Myths and Folktales about Black Holes

Black Holes are the places in space where the gravitational pull or force is so strong that light can not even escape. Personally, I found Black Holes to be the most interesting and questionable thing we have discussed in Astronomy 101 because of the lack of knowledge we, as humans, know about them. Growing up as a child, there were myths and folktales that Black Holes went around eating galaxies, stars, and planets. After this semester, in Astronomy 101, it […]

Black Holes: Facts, Theory and Definition

First before we go into details, a black hole is a region of space that has a gravitational force that's so intense that no matter or radiation can escape. Black holes are created by a star that reaches the end point of their life and has a mass that's three times stronger than our sun's mass. That same star then gets crushed under its own gravity and keeps collapsing until all of the mass is concentrated into a tiny space. […]

Black Hole: a Black Sphere in the Universe

To begin with, what is a black hole? A black sphere in the universe that sucks up everything within its path? Although black holes do capture objects in their entirety, this is only plausible if the object comes within the gravitational force field of the black hole, meaning, as cool as it sounds, no it does not ""suck"" things into itself. How do black holes form? For a black hole to come about, a star has to die, when this […]

The Phenomenon of Black Holes

In many films and even television shows, when the idea of black holes is discussed we see a common theme of these phenomena being deemed as either a time warp, or as a form of transport from one place to another. Science Fiction films have created the idea that black holes serve as a way for space travelers to either pass through and jump out somewhere across the universe, or as a way to communicate with the past and the […]

Are Black Holes a Threat to Mankind?

In space, there is nothing more frightening than the words "black hole." The inferences made by long-distance observations indicate something sinister about an object that seemingly consumes light and energy. "Black holes were theorized more than 200 years ago and later were predicted by Einstein's theory of general relativity. The discovery of active galaxies forced astronomers to think that monstrous black holes really do exist and are the 'engines' at the heart of these fireworks. The gushers of light and […]

Black Hole Research

Section 1 of the four-part series on black holes. THe section determines what the dark hole is, goes back to the origins of black hole research, and demonstrates how physicists came to terms with the creation of these strange objects. Section 2 can discuss the role black holes play in galaxies and how hidden objects will turn into some of the brightest things in the worlds. Section 3 can tell how astronomers discover black holes using the most intelligent observatories […]

The Study of Black Holes

The study of black holes are important because they are a great unknown that could change modern day science as a know it. Black holes are among one of the strangest things in our universe. To understand why blacks holes are so important you first have to know what they are. A black hole is a large amount of matter packed into a very small space. The result is a gravitational field so strong that nothing, not even light, can […]

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