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Okanogan Valley Classified Ads
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Click to Submit Your AdVacation Rental Business Development (not timeshares)
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Steve Egan raised his rifle to finish the job. From 90 feet away, he was sure he saw a wounded hog on its back, feet wiggling in the air. Assuming it was the same hog he had shot a few minutes earlier, he found his mark and fired a .30-caliber bullet. He jogged toward the tree line to get a look. The shape on the ground didn't make sense. He thought: "What is this person doing here?" "Steve, you shot me." Lisa. His girlfriend.
A year ago in the woods of Flagler County, something terrible happened to Steve Egan and Lisa Simmons. It was an ordeal that for many months they were reluctant to talk about publicly.
But that sure didn't stop the rest of us.
• • •
Lisa Simmons, 51-year-old country girl, didn't scream. She had been a nurse for heart doctors for 18 years. She looked at her left leg, splayed at an unnatural angle from her body. She knew the blood pumping on the ground came from her femoral artery.
"I don't want to die out here in these woods," she thought.
Egan yanked off his belt and made a tourniquet. Simmons held it tight. He ran back to the hunting blind to find their only cellphone and steadied his hands to call 911.
Neither knew exactly where they were. The sun was setting.
He watched her skin turn from pale to gray. They listened to sirens grow close, then far away, then close, then far away again. The cellphone died.
He told her to stay awake, told her he was sorry, told her how much he loved her.
She told him she loved him too. She told him she was going to be all right. But she could feel blood seeping past the belt, trickling down her leg. How could she die before holding a grandchild at least once?
By the time the helicopter came, almost an hour after the shooting, she had grown silent.
Doctors operated all through Saturday night. She needed 14 pints of blood. She almost died twice during the surgery. The trauma surgeon would later say it was the worst noncombat gun injury he had seen anyone survive.
• • •
The news accounts that appeared in Monday's newspapers were short on details. Most carried a variation of this headline: Man mistakes woman for hog, shoots her.
The jokes followed soon after.
Bubba the Love Sponge mentioned it on his morning show. He sent listeners to Simmons' Facebook page to see if she looked like a hog. The comments were so mean, Simmons' kids deactivated the page. When the page disappeared, Simmons' friends thought she might have died.
The couple told staff at Halifax Health Medical Center in Daytona Beach they did not want to release a statement. The story went viral anyway. The head nurse told them a reporter tried to sneak in to interview them.
Keep up with Tampa Bay's top headlines
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Explore all your optionsMost blogs used stock pictures of a wild hog to go with the story. One used an illustration of a pig in pearls putting on lipstick.
Jay Leno couldn't resist:
"I don't know what is worse for the girl: having your boyfriend shoot you in the legs or saying the reason he did it was that he mistook you for a hog. Pretty awful."
"The good news," he reassured his audience, "is that the woman's going to be fine."
In the hospital, Simmons was missing four inches of her thigh bone. Doctors worried they might have to amputate her leg if the repair on the artery didn't hold.
• • •
The couple met nine years ago at O'Brien's Irish Pub in Brandon. She came for happy hour and there were two seats at the bar. One in front of a video game, the other next to Egan.
"Looks like you're the lesser of two evils," she told him, and sat down.
They hit it off.
A few years later, they took a cruise together to Mexico and went on a "nonsponsored" outing. When they returned, the ship had left. They were told by a cruise line representative they were in Mexico illegally. They had no passports. Just a bottle of tequila, a bottle of hot sauce, a ship registration card and a wet towel. In customs, she watched Egan laugh about their predicament. He never lost his cool, never assigned blame. She fell in love.
They didn't fight a year later when they had a house fire. Or the year after that when the house started cracking up the middle from a sink hole. They moved with two dogs into a small trailer out front and worked together through the bureaucracy and the repairs. They had disagreements, but no real fights.
They agree that watching television, or sitting still for any reason, is boring. They both seize any excuse to get on his boat, sit by a campfire, spend a day in the woods, anything outdoors really.
• • •
The day of the accident, Simmons, in camouflage pants, tromped alongside Egan. When she came across wild turkeys, she grabbed the cellphone and shot video, not knowing how precious the battery would later become.
They had passed a sour orange tree early in the day and she regretted not stopping to pick a few. She knew a great recipe for a sour orange marinade.
By the end of the day, she sat in a hunting blind next to Egan, chatting quietly and watching the sun work close to the horizon.
A hog came into the clearing. Egan took a shot, then scrambled after it as it darted into the brush.
Simmons noticed another sour orange tree across the field. Figuring Egan had killed a hog, she decided she would make that marinade after all. She circled the tree, dotting the grass with fresh fruit.
A last few were just out of reach. So she jumped up on a log.
She balanced on her toes. She wobbled a bit as she stretched. Her torso disappeared into the tree.
Just as she pulled on a big, ripe orange, something swept her legs from under her and sent her tumbling to the ground.
"It's amazing how quick life can become a whole new ball game," Simmons says.
• • •
The media attention was a constant source of irritation. Simmons' mother called a local TV station to complain about Leno's insensitivity, but the attention continued for days.
"They really wouldn't leave it alone until that guy ate a man's face in Miami. Then it just disappeared," Egan said.
People assumed that their relationship couldn't survive such a colossal mistake.
Yet it did.
"I don't think you can go through something like this and not get closer, if you really love somebody," Simmons says. "We don't have any issues between us."
Simmons never blamed Egan for the accident. "Not even for one second."
"Take responsibility for your part of what happened," she says. "Whatever it is, don't blame the other person because a lot of things go into an accident or problem. It's not just one factor."
Egan couldn't sleep the week after the accident. Eventually he sought counseling for post-traumatic stress.
"Every time I see you limp … ," Egan begins to tell her, and tears up. "It's with me all the time."
"It's okay, honey. At least I'm here to be seen," she says, taking his hand.
In the past year, Simmons has moved from bed, to scooter, to cane, to no cane at all. She is on long-term disability from her job, but she refuses to apply for Social Security benefits. She cannot stay on her feet long enough to return to work as a nurse, so she is working toward a degree to become a nursing teacher.
"By the time they process the Social Security paperwork, I'll be back to work as a teacher," she says with a hint of pride.
One day soon, probably in June, Simmons will limp over to a chair, gently sit down to take the weight off the rod in her leg and claim her prize for last year's long, hard fight in the woods. Someone will place a granddaughter, her first grandchild, in her arms.
"At least I'm still alive," Simmons says. "I still have both legs and I've got a really good story to tell her some day."
Times researchers Natalie Watson and Caryn Baird contributed to this report. John Pendygraft can be reached at email@example.com or (727) 893-8247.

subset: commoncrawl


text: Lem Siddons is part of a traveling band who has a dream of becoming a lawyer. Deciding to settle down, he finds a job as a stockboy in the general store of a small town. Trying to fit in, he volunteers to become scoutmaster of the newly formed Troop 1. Becoming more and more involved with the scout troop, he finds his plans to become a lawyer being put on the back burner, until he realizes that his life has been fulfilled helping the youth of the small town.


text:
[Jarrod] has an older Compaq laptop he is still pretty keen on, but he has one niggling problem – the laptop doesn't have a built-in wireless card. He recently changed security protocols on his home wireless network to WPA and realized that his old Linksys PC card only supports WEP. He decided it was time to find another way to connect wirelessly, so he started searching around for options.
It turns out that his laptop does have the ability to accept a LCD-mounted add-on wireless card, but it costs about $100 and doesn't support WPA. He figured that the card slipped into some sort of glorified USB port, and after disassembling the laptop, he found that he was right.
He quickly soldered a few wires and a USB adapter to the Bluetooth board that already occupied the card slot, then plugged in a wireless mouse to see what would happen. The mouse's radio powered on without issue, and much to [Jarrod's] delight, the port was USB 2.0 compatible.
Now that he knows the port is live, he plans on finding a small USB 802.11 G or N adapter to cram into the slot – with the deluge of miniature USB Wi-Fi adapters on the market, that shouldn't be too hard.


text:
- Black hole
For other uses, see Black hole (disambiguation).
General relativity Introduction
Mathematical formulation
ResourcesFundamental conceptsPhenomenaKepler problem · Lenses · Waves
Frame-dragging · Geodetic effect
Event horizon · Singularity
Black holeEquationsAdvanced theoriesSchwarzschild
Reissner–Nordström · Gödel
Kerr · Kerr–Newman
Kasner · Taub-NUT · Milne · Robertson–Walker
pp-wave · van Stockum dustScientistsEinstein · Minkowski · Eddington
Lemaître · Schwarzschild
Robertson · Kerr · Friedman
Chandrasekhar · Hawking
othersA black hole is a region of spacetime from which nothing, not even light, can escape.[1] The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. It is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics.[2] Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater.
Objects whose gravity field is too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was not fully appreciated for another four decades. Long considered a mathematical curiosity, it was during the 1960s that theoretical work showed black holes were a generic prediction of general relativity. The discovery of neutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.
Black holes of stellar mass are expected to form when massive stars collapse in a supernova at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may be formed.
Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter. Astronomers have identified numerous stellar black hole candidates in binary systems, by studying their interaction with their companion stars. There is growing consensus that supermassive black holes exist in the centers of most galaxies. In particular, there is strong evidence of a black hole of more than 4 million solar masses at the center of our Milky Way.
The idea of a body so massive that even light could not escape was first put forward by geologist John Michell in a letter written to Henry Cavendish in 1783 of the Royal Society:
If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity.—John Michell[3]In 1796, mathematician Pierre-Simon Laplace promoted the same idea in the first and second editions of his book Exposition du système du Monde (it was removed from later editions).[4][5] Such "dark stars" were largely ignored in the nineteenth century, since it was not understood how a massless wave such as light could be influenced by gravity.[6]
General relativity
In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months later, Karl Schwarzschild found a solution to Einstein field equations, which describes the gravitational field of a point mass and a spherical mass.[7] A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties.[8] This solution had a peculiar behaviour at what is now called the Schwarzschild radius, where it became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this surface was not quite understood at the time. In 1924, Arthur Eddington showed that the singularity disappeared after a change of coordinates (see Eddington–Finkelstein coordinates), although it took until 1933 for Georges Lemaître to realize that this meant the singularity at the Schwarzschild radius was an unphysical coordinate singularity.[9]
In 1931, Subrahmanyan Chandrasekhar calculated, using special relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at 1.4 solar masses) has no stable solutions. [10] His arguments were opposed by many of his contemporaries like Eddington and Lev Landau, who argued that some yet unknown mechanism would stop the collapse.[11] They were partly correct: a white dwarf slightly more massive than the Chandrasekhar limit will collapse into a neutron star,[12] which is itself stable because of the Pauli exclusion principle. But in 1939, Robert Oppenheimer and others predicted that neutron stars above approximately three solar masses (the Tolman–Oppenheimer–Volkoff limit) would collapse into black holes for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes.[13]
Oppenheimer and his co-authors interpreted the singularity at the boundary of the Schwarzschild radius as indicating that this was the boundary of a bubble in which time stopped. This is a valid point of view for external observers, but not for infalling observers. Because of this property, the collapsed stars were called "frozen stars,"[14] because an outside observer would see the surface of the star frozen in time at the instant where its collapse takes it inside the Schwarzschild radius.
Golden age
See also: Golden age of general relativityIn 1958, David Finkelstein identified the Schwarzschild surface as an event horizon, "a perfect unidirectional membrane: causal influences can cross it in only one direction".[15] This did not strictly contradict Oppenheimer's results, but extended them to include the point of view of infalling observers. Finkelstein's solution extended the Schwarzschild solution for the future of observers falling into a black hole. A complete extension had already been found by Martin Kruskal, who was urged to publish it.[16]
These results came at the beginning of the golden age of general relativity, which was marked by general relativity and black holes becoming mainstream subjects of research. This process was helped by the discovery of pulsars in 1967,[17][18] which were shown to be rapidly rotating neutron stars by 1969.[19] Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities; but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse.
In this period more general black hole solutions were found. In 1963, Roy Kerr found the exact solution for a rotating black hole. Two years later, Ezra Newman found the axisymmetric solution for a black hole that is both rotating and electrically charged.[20] Through the work of Werner Israel,[21] Brandon Carter,[22][23] and David Robinson[24] the no-hair theorem emerged, stating that a stationary black hole solution is completely described by the three parameters of the Kerr–Newman metric; mass, angular momentum, and electric charge.[25]
For a long time,[vague] it was suspected that the strange features of the black hole solutions were pathological artifacts from the symmetry conditions imposed, and that the singularities would not appear in generic situations. This view was held in particular by Vladimir Belinsky, Isaak Khalatnikov, and Evgeny Lifshitz, who tried to prove that no singularities appear in generic solutions. However, in the late sixties Roger Penrose[26] and Stephen Hawking used global techniques to prove that singularities are generic.[27]
Work by James Bardeen, Jacob Bekenstein, Carter, and Hawking in the early 1970s led to the formulation of black hole thermodynamics.[28] These laws describe the behaviour of a black hole in close analogy to the laws of thermodynamics by relating mass to energy, area to entropy, and surface gravity to temperature. The analogy was completed when Hawking, in 1974, showed that quantum field theory predicts that black holes should radiate like a black body with a temperature proportional to the surface gravity of the black hole.[29]
The term "black hole" was first publicly used by John Wheeler during a lecture in 1967. Although he is usually credited with coining the phrase, he always insisted that it was suggested to him by somebody else. The first recorded use of the term is in a 1964 letter by Anne Ewing to the American Association for the Advancement of Science.[30] After Wheeler's use of the term, it was quickly adopted in general use.
Properties and structure
The no-hair theorem states that, once it achieves a stable condition after formation, a black hole has only three independent physical properties: mass, charge, and angular momentum.[25] Any two black holes that share the same values for these properties, or parameters, are indistinguishable according to classical (i.e. non-quantum) mechanics.
These properties are special because they are visible from outside a black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, the ADM mass, far away from the black hole.[31] Likewise, the angular momentum can be measured from far away using frame dragging by the gravitomagnetic field.
When an object falls into a black hole, any information about the shape of the object or distribution of charge on it is evenly distributed along the horizon of the black hole, and is lost to outside observers. The behavior of the horizon in this situation is a dissipative system that is closely analogous to that of a conductive stretchy membrane with friction and electrical resistance—the membrane paradigm.[32] This is different from other field theories like electromagnetism, which do not have any friction or resistivity at the microscopic level, because they are time-reversible. Because a black hole eventually achieves a stable state with only three parameters, there is no way to avoid losing information about the initial conditions: the gravitational and electric fields of a black hole give very little information about what went in. The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including the total baryon number, lepton number, and all the other nearly conserved pseudo-charges[clarification needed] of particle physics. This behavior is so puzzling that it has been called the black hole information loss paradox.[33][34]
Physical properties
The simplest black holes have mass but neither electric charge nor angular momentum. These black holes are often referred to as Schwarzschild black holes after Karl Schwarzschild who discovered this solution in 1916.[7] According to Birkhoff's theorem, it is the only vacuum solution that is spherically symmetric.[35] This means that there is no observable difference between the gravitational field of such a black hole and that of any other spherical object of the same mass. The popular notion of a black hole "sucking in everything" in its surroundings is therefore only correct near a black hole's horizon; far away, the external gravitational field is identical to that of any other body of the same mass.[36]
Solutions describing more general black holes also exist. Charged black holes are described by the Reissner–Nordström metric, while the Kerr metric describes a rotating black hole. The most general stationary black hole solution known is the Kerr–Newman metric, which describes a black hole with both charge and angular momentum.[37]
While the mass of a black hole can take any positive value, the charge and angular momentum are constrained by the mass. In Planck units, the total electric charge Q and the total angular momentum J are expected to satisfy
for a black hole of mass M. Black holes saturating this inequality are called extremal. Solutions of Einstein's equations that violate this inequality exist, but they do not possess an event horizon. These solutions have so-called naked singularities that can be observed from the outside, and hence are deemed unphysical. The cosmic censorship hypothesis rules out the formation of such singularities, when they are created through the gravitational collapse of realistic matter.[38] This is supported by numerical simulations.[39]
Due to the relatively large strength of the electromagnetic force, black holes forming from the collapse of stars are expected to retain the nearly neutral charge of the star. Rotation, however, is expected to be a common feature of compact objects. The black-hole candidate binary X-ray source GRS 1915+105[40] appears to have an angular momentum near the maximum allowed value.
Black hole classifications Class Mass Size Supermassive black hole ~105–109 MSun ~0.001–10 AU Intermediate-mass black hole ~103 MSun ~103 km = REarth Stellar black hole ~10 MSun ~30 km Micro black hole up to ~MMoon up to ~0.1 mm Black holes are commonly classified according to their mass, independent of angular momentum J or electric charge Q. The size of a black hole, as determined by the radius of the event horizon, or Schwarzschild radius, is roughly proportional to the mass M through
where rsh is the Schwarzschild radius and MSun is the mass of the Sun.[41] This relation is exact only for black holes with zero charge and angular momentum; for more general black holes it can differ up to a factor of 2.
Event horizon
Main article: Event horizon
Far away from the black hole a particle can move in any direction, as illustrated by the set of arrows. It is only restricted by the speed of light.
Closer to the black hole spacetime starts to deform. There are more paths going towards the black hole than paths moving away.[Note 1]
Inside of the event horizon all paths bring the particle closer to the center of the black hole. It is no longer possible for the particle to escape.The defining feature of a black hole is the appearance of an event horizon—a boundary in spacetime through which matter and light can only pass inward towards the mass of the black hole. Nothing, not even light, can escape from inside the event horizon. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach an outside observer, making it impossible to determine if such an event occurred.[43]
As predicted by general relativity, the presence of a mass deforms spacetime in such a way that the paths taken by particles bend towards the mass.[44] At the event horizon of a black hole, this deformation becomes so strong that there are no paths that lead away from the black hole.
To a distant observer, clocks near a black hole appear to tick more slowly than those further away from the black hole.[45] Due to this effect, known as gravitational time dilation, an object falling into a black hole appears to slow down as it approaches the event horizon, taking an infinite time to reach it.[46] At the same time, all processes on this object slow down causing emitted light to appear redder and dimmer, an effect known as gravitational redshift.[47] Eventually, at a point just before it reaches the event horizon, the falling object becomes so dim that it can no longer be seen.
On the other hand, an observer falling into a black hole does not notice any of these effects as he crosses the event horizon. According to his own clock, he crosses the event horizon after a finite time, although he is unable to determine exactly when he crosses it, as it is impossible to determine the location of the event horizon from local observations.[48]
The shape of the event horizon of a black hole is always approximately spherical.[Note 2][51] For non-rotating (static) black holes the geometry is precisely spherical, while for rotating black holes the sphere is somewhat oblated.
Main article: Gravitational singularityAt the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite.[52] For a non-rotating black hole this region takes the shape of a single point and for a rotating black hole it is smeared out to form a ring singularity lying in the plane of rotation.[53] In both cases the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution.[54] The singular region can thus be thought of as having infinite density.
Observers falling into a Schwarzschild black hole (i.e. non-rotating and no charges) cannot avoid being carried into the singularity, once they cross the event horizon. They can prolong the experience by accelerating away to slow their descent, but only up to a point; after attaining a certain ideal velocity, it is best to free fall the rest of the way.[55] When they reach the singularity, they are crushed to infinite density and their mass is added to the total of the black hole. Before that happens, they will have been torn apart by the growing tidal forces in a process sometimes referred to as spaghettification or the noodle effect.[56]
In the case of a charged (Reissner–Nordström) or rotating (Kerr) black hole it is possible to avoid the singularity. Extending these solutions as far as possible reveals the hypothetical possibility of exiting the black hole into a different spacetime with the black hole acting as a wormhole.[57] The possibility of traveling to another universe is however only theoretical, since any perturbation will destroy this possibility.[58] It also appears to be possible to follow closed timelike curves (going back to one's own past) around the Kerr singularity, which lead to problems with causality like the grandfather paradox.[59] It is expected that none of these peculiar effects would survive in a proper quantum mechanical treatment of rotating and charged black holes.[60]
The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory.[61] This breakdown, however, is expected; it occurs in a situation where quantum mechanical effects should describe these actions due to the extremely high density and therefore particle interactions. To date it has not been possible to combine quantum and gravitational effects into a single theory. It is generally expected that a theory of quantum gravity will feature black holes without singularities.[62][63]
Photon sphere
Main article: Photon sphereThe photon sphere is a spherical boundary of zero thickness such that photons moving along tangents to the sphere will be trapped in a circular orbit. For non-rotating black holes, the photon sphere has a radius 1.5 times the Schwarzschild radius. The orbits are dynamically unstable, hence any small perturbation (such as a particle of infalling matter) will grow over time, either setting it on an outward trajectory escaping the black hole or on an inward spiral eventually crossing the event horizon.[64]
While light can still escape from inside the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Hence any light reaching an outside observer from inside the photon sphere must have been emitted by objects inside the photon sphere but still outside of the event horizon.[64]
Other compact objects, such as neutron stars, can also have photon spheres.[65] This follows from the fact that the gravitational field of an object does not depend on its actual size, hence any object that is smaller than 1.5 times the Schwarzschild radius corresponding to its mass will indeed have a photon sphere.
Main article: ErgosphereRotating black holes are surrounded by a region of spacetime in which it is impossible to stand still, called the ergosphere. This is the result of a process known as frame-dragging; general relativity predicts that any rotating mass will tend to slightly "drag" along the spacetime immediately surrounding it. Any object near the rotating mass will tend to start moving in the direction of rotation. For a rotating black hole this effect becomes so strong near the event horizon that an object would have to move faster than the speed of light in the opposite direction to just stand still.[66]
The ergosphere of a black hole is bounded by the (outer) event horizon on the inside and an oblate spheroid, which coincides with the event horizon at the poles and is noticeably wider around the equator. The outer boundary is sometimes called the ergosurface.
Objects and radiation can escape normally from the ergosphere. Through the Penrose process, objects can emerge from the ergosphere with more energy than they entered. This energy is taken from the rotational energy of the black hole causing it to slow down.[67]
Formation and evolution
Considering the exotic nature of black holes, it may be natural to question if such bizarre objects could exist in nature or to suggest that they are merely pathological solutions to Einstein's equations. Einstein himself wrongly thought that black holes would not form, because he held that the angular momentum of collapsing particles would stabilize their motion at some radius.[68] This led the general relativity community to dismiss all results to the contrary for many years. However, a minority of relativists continued to contend that black holes were physical objects,[69] and by the end of the 1960s, they had persuaded the majority of researchers in the field that there is no obstacle to forming an event horizon.
Once an event horizon forms, Penrose proved that a singularity will form somewhere inside it.[26] Shortly afterwards, Hawking showed that many cosmological solutions describing the Big Bang have singularities without scalar fields or other exotic matter (see Penrose-Hawking singularity theorems). The Kerr solution, the no-hair theorem and the laws of black hole thermodynamics showed that the physical properties of black holes were simple and comprehensible, making them respectable subjects for research.[70] The primary formation process for black holes is expected to be the gravitational collapse of heavy objects such as stars, but there are also more exotic processes that can lead to the production of black holes.
Gravitational collapse
Main article: Gravitational collapseGravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity. For stars this usually occurs either because a star has too little "fuel" left to maintain its temperature through stellar nucleosynthesis, or because a star that would have been stable receives extra matter in a way that does not raise its core temperature. In either case the star's temperature is no longer high enough to prevent it from collapsing under its own weight.[71] The ideal gas law explains the connection between pressure, temperature, and volume.
The collapse may be stopped by the degeneracy pressure of the star's constituents, condensing the matter in an exotic denser state. The result is one of the various types of compact star. The type of compact star formed depends on the mass of the remnant—the matter left over after the outer layers have been blown away, such from a supernova explosion or by pulsations leading to a planetary nebula. Note that this mass can be substantially less than the original star—remnants exceeding 5 solar masses are produced by stars that were over 20 solar masses before the collapse.[71]
If the mass of the remnant exceeds about 3–4 solar masses (the Tolman–Oppenheimer–Volkoff limit[13])—either because the original star was very heavy or because the remnant collected additional mass through accretion of matter—even the degeneracy pressure of neutrons is insufficient to stop the collapse. No known mechanism (except possibly quark degeneracy pressure, see quark star) is powerful enough to stop the implosion and the object will inevitably collapse to form a black hole.[71]
The gravitational collapse of heavy stars is assumed to be responsible for the formation of stellar mass black holes. Star formation in the early universe may have resulted in very massive stars, which upon their collapse would have produced black holes of up to 103 solar masses. These black holes could be the seeds of the supermassive black holes found in the centers of most galaxies.[72]
While most of the energy released during gravitational collapse is emitted very quickly, an outside observer does not actually see the end of this process. Even though the collapse takes a finite amount of time from the reference frame of infalling matter, a distant observer sees the infalling material slow and halt just above the event horizon, due to gravitational time dilation. Light from the collapsing material takes longer and longer to reach the observer, with the light emitted just before the event horizon forms is delayed an infinite amount of time. Thus the external observer never sees the formation of the event horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away.[73]
Primordial black holes in the Big Bang
Gravitational collapse requires great density. In the current epoch of the universe these high densities are only found in stars, but in the early universe shortly after the big bang densities were much greater, possibly allowing for the creation of black holes. The high density alone is not enough to allow the formation of black holes since a uniform mass distribution will not allow the mass to bunch up. In order for primordial black holes to form in such a dense medium, there must be initial density perturbations that can then grow under their own gravity. Different models for the early universe vary widely in their predictions of the size of these perturbations. Various models predict the creation of black holes, ranging from a Planck mass to hundreds of thousands of solar masses.[74] Primordial black holes could thus account for the creation of any type of black hole.
High-energy collisions
Gravitational collapse is not the only process that could create black holes. In principle, black holes could be formed in high-energy collisions that achieve sufficient density. As of 2002, no such events have been detected, either directly or indirectly as a deficiency of the mass balance in particle accelerator experiments.[75] This suggests that there must be a lower limit for the mass of black holes. Theoretically, this boundary is expected to lie around the Planck mass (mP = √ħc/G ≈ 1.2×1019 GeV/c2 ≈ 2.2×10−8 kg), where quantum effects are expected to invalidate the predictions of general relativity.[76] This would put the creation of black holes firmly out of reach of any high energy process occurring on or near the Earth. However, certain developments in quantum gravity suggest that the Planck mass could be much lower: some braneworld scenarios for example put the boundary as low as 1 TeV/c2.[77] This would make it conceivable for micro black holes to be created in the high energy collisions occurring when cosmic rays hit the Earth's atmosphere, or possibly in the new Large Hadron Collider at CERN. Yet these theories are very speculative, and the creation of black holes in these processes is deemed unlikely by many specialists.[78] Even if micro black holes should be formed in these collisions, it is expected that they would evaporate in about 10−25 seconds, posing no threat to the Earth.[79]
Once a black hole has formed, it can continue to grow by absorbing additional matter. Any black hole will continually absorb gas and interstellar dust from its direct surroundings and omnipresent cosmic background radiation. This is the primary process through which supermassive black holes seem to have grown.[72] A similar process has been suggested for the formation of intermediate-mass black holes in globular clusters.[80]
Another possibility is for a black hole to merge with other objects such as stars or even other black holes. This is thought to have been[weasel words] important especially for the early development of supermassive black holes, which could have formed from the coagulation of many smaller objects.[72] The process has also been proposed as the origin of some intermediate-mass black holes.[81][82]
Main article: Hawking radiationIn 1974, Hawking showed that black holes are not entirely black but emit small amounts of thermal radiation.[29] He got this result by applying quantum field theory in a static black hole background. The result of his calculations is that a black hole should emit particles in a perfect black body spectrum. This effect has become known as Hawking radiation. Since Hawking's result, many others have verified the effect through various methods.[83] If his theory of black hole radiation is correct, then black holes are expected to emit a thermal spectrum of radiation, and thereby lose mass (the mass possessed by the photons and other particles emitted).[29] Black holes will shrink and evaporate over time. The temperature of this spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which for a Schwarzschild black hole is inversely proportional to the mass. Large black holes, therefore, emit less radiation than small black holes.[84]
A stellar black hole of one solar mass has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background. Stellar mass (and larger) black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and will thus grow instead of shrink. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole needs to be lighter than the Moon (and therefore a diameter of less than a tenth of a millimeter).[85]
On the other hand, if a black hole is very small the radiation effects are expected to become very strong. Even a black hole that is heavy compared to a human would evaporate in an instant. A black hole the weight of a car (~10−24 m) would only take a nanosecond to evaporate, during which time it would briefly have a luminosity more than 200 times that of the sun. Lighter black holes are expected to evaporate even faster; for example, a black hole of mass 1 TeV/c2 would take less than 10−88 seconds to evaporate completely. Of course, for such a small black hole quantum gravitation effects are expected to play an important role and could even—although current developments in quantum gravity do not indicate so[86]—hypothetically make such a small black hole stable.[87]
Observational evidence
By their very nature, black holes do not directly emit any signals other than the hypothetical Hawking radiation; since the Hawking radiation for an astrophysical black hole is predicted to be very weak, this makes it impossible to directly detect astrophysical black holes from the Earth. A possible exception to the Hawking radiation being weak is the last stage of the evaporation of light (primordial) black holes; searches for such flashes in the past has proven unsuccessful and provides stringent limits on the possibility of existence of light primordial black holes.[88] NASA's Fermi Gamma-ray Space Telescope launched in 2008 will continue the search for these flashes.[89]
Astrophysicists searching for black holes thus have to rely on indirect observations. A black hole's existence can sometimes be inferred by observing its gravitational interactions with its surroundings.
Accretion of matter
See also: Accretion discDue to conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disc-like structure around the object. Friction within the disc causes angular momentum to be transported outward, allowing matter to fall further inward, releasing potential energy and increasing the temperature of the gas.[90] In the case of compact objects such as white dwarfs, neutron stars, and black holes, the gas in the inner regions becomes so hot that it will emit vast amounts of radiation (mainly X-rays), which may be detected by telescopes. This process of accretion is one of the most efficient energy-producing processes known; up to 40% of the rest mass of the accreted material can be emitted in radiation.[90] (In nuclear fusion only about 0.7% of the rest mass will be emitted as energy.) In many cases, accretion discs are accompanied by relativistic jets emitted along the poles, which carry away much of the energy. The mechanism for the creation of these jets is currently not well understood.
As such many of the universe's more energetic phenomena have been attributed to the accretion of matter on black holes. In particular, active galactic nuclei and quasars are thought to be[weasel words] the accretion discs of supermassive black holes.[91] Similarly, X-ray binaries are thought to be[weasel words] binary star systems in which one of the two stars is a compact object accreting matter from its companion.[91] It has also been suggested that some ultraluminous X-ray sources may be the accretion disks of intermediate-mass black holes.[92]
X-ray binaries
See also: X-ray binaryX-ray binaries are binary star systems that are luminous in the X-ray part of the spectrum. These X-ray emissions are generally thought to be[weasel words] caused by one of the component stars being a compact object accreting matter from the other (regular) star. The presence of an ordinary star in such a system provides a unique opportunity for studying the central object and determining if it might be a black hole.
If such a system emits signals that can be directly traced back to the compact object, it cannot be a black hole. The absence of such a signal does, however, not exclude the possibility that the compact object is a neutron star. By studying the companion star it is often possible to obtain the orbital parameters of the system and obtain an estimate for the mass of the compact object. If this is much larger than the Tolman–Oppenheimer–Volkoff limit (that is, the maximum mass a neutron star can have before collapsing) then the object cannot be a neutron star and is generally expected to be a black hole.[91]
The first strong candidate for a black hole, Cygnus X-1, was discovered in this way by Charles Thomas Bolton,[93] Louise Webster and Paul Murdin[94] in 1972.[95][96] Some doubt, however, remained due to the uncertainties resultant from the companion star being much heavier than the candidate black hole.[91] Currently, better candidates for black holes are found in a class of X-ray binaries called soft X-ray transients.[91] In this class of system the companion star is relatively low mass allowing for more accurate estimates in the black hole mass. Moreover, these systems are only active in X-ray for several months once every 10–50 years. During the period of low X-ray emission (called quiescence), the accretion disc is extremely faint allowing for detailed observation of the companion star during this period. One of the best such candidates is V404 Cyg.
Quiescence and advection-dominated accretion flow
The faintness of the accretion disc during quiescence is thought to be[weasel words] caused by the flow entering a mode called an advection-dominated accretion flow (ADAF). In this mode, almost all the energy generated by friction in the disc is swept along with the flow instead of radiated away. If this model is correct, then it forms strong qualitative evidence for the presence of an event horizon.[97] Because, if the object at the center of the disc had a solid surface, it would emit large amounts of radiation as the highly energetic gas hits the surface, an effect that is observed for neutron stars in a similar state.[90]
Quasi-periodic oscillations
Main article: Quasi-periodic oscillationsThe X-ray emission from accretion disks sometimes flickers at certain frequencies. These signals are called quasi-periodic oscillations and are thought to be[weasel words] caused by material moving along the inner edge of the accretion disk (the innermost stable circular orbit). As such their frequency is linked to the mass of the compact object. They can thus be used as an alternative way to determine the mass of potential black holes.[98]
Galactic nuclei
See also: Active galactic nucleusAstronomers use the term "active galaxy" to describe galaxies with unusual characteristics, such as unusual spectral line emission and very strong radio emission. Theoretical and observational studies have shown that the activity in these active galactic nuclei (AGN) may be explained by the presence of supermassive black holes. The models of these AGN consist of a central black hole that may be millions or billions of times more massive than the Sun; a disk of gas and dust called an accretion disk; and two jets that are perpendicular to the accretion disk.[99][100]
Although supermassive black holes are expected to be found in most AGN, only some galaxies' nuclei have been more carefully studied in attempts to both identify and measure the actual masses of the central supermassive black hole candidates. Some of the most notable galaxies with supermassive black hole candidates include the Andromeda Galaxy, M32, M87, NGC 3115, NGC 3377, NGC 4258, and the Sombrero Galaxy.[101]
It is now widely accepted that the center of (nearly) every galaxy (not just active ones) contains a supermassive black hole.[102] The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation, strongly suggests a connection between the formation of the black hole and the galaxy itself. [103]
Currently, the best evidence for a supermassive black hole comes from studying the proper motion of stars near the center of our own Milky Way.[104] Since 1995 astronomers have tracked the motion of 90 stars in a region called Sagittarius A*. By fitting their motion to Keplerian orbits they were able to infer in 1998 that 2.6 million solar masses must be contained in a volume with a radius of 0.02 lightyears.[105] Since then one of the stars—called S2—has completed a full orbit. From the orbital data they were able to place better constraints on the mass and size of the object causing the orbital motion of stars in the Sagittarius A* region, finding that there is a spherical mass of 4.3 million solar masses contained within a radius of less than 0.002 lightyears.[104] While this is more than 3000 times the Schwarzschild radius corresponding to that mass, it is at least consistent with the central object being a supermassive black hole, and no "realistic cluster [of stars] is physically tenable."[105]
Gravitational lensing
Further information: Gravitational lensThe deformation of spacetime around a massive object causes light rays to be deflected much like light passing through an optic lens. This phenomenon is known as gravitational lensing. Observations have been made of weak gravitational lensing, in which photons are deflected by only a few arcseconds. However, it has never been directly observed for a black hole.[106] One possibility for observing gravitational lensing by a black hole would be to observe stars in orbit around the black hole. There are several candidates for such an observation in orbit around Sagittarius A*.[106]
The evidence for stellar black holes strongly relies on the existence of an upper limit for the mass of a neutron star. The size of this limit heavily depends on the assumptions made about the properties of dense matter. New exotic phases of matter could push up this bound.[91] A phase of free quarks at high density might allow the existence of dense quark stars,[107] and some supersymmetric models predict the existence of Q stars.[108] Some extensions of the standard model posit the existence of preons as fundamental building blocks of quarks and leptons, which could hypothetically form preon stars.[109] These hypothetical models could potentially explain a number of observations of stellar black hole candidates. However, it can be shown from general arguments in general relativity that any such object will have a maximum mass.[91]
Since the average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass, supermassive black holes are much less dense than stellar black holes (the average density of a 108 solar mass black hole is comparable to that of water).[91] Consequently, the physics of matter forming a supermassive black hole is much better understood and the possible alternative explanations for supermassive black hole observations are much more mundane. For example, a supermassive black hole could be modelled by a large cluster of very dark objects. However, typically such alternatives are not stable enough to explain the supermassive black hole candidates.[91]
The evidence for stellar and supermassive black holes implies that in order for black holes not to form, general relativity must fail as a theory of gravity, perhaps due to the onset of quantum mechanical corrections. A much anticipated feature of a theory of quantum gravity is that it will not feature singularities or event horizons (and thus no black holes).[110] In recent years, much attention has been drawn by the fuzzball model in string theory. Based on calculations in specific situations in string theory, the proposal suggest that generically the individual states of a black hole solution do not have an event horizon or singularity, but that for a classical/semi-classical observer the statistical average of such states does appear just like an ordinary black hole in general relativity.[111]
Open questions
Entropy and thermodynamics
Further information: Black hole thermodynamicsIn 1971, Hawking showed under general conditions[Note 3] that the total area of the event horizons of any collection of classical black holes can never decrease, even if they collide and merge.[112] This result, now known as the second law of black hole mechanics, is remarkably similar to the second law of thermodynamics, which states that the total entropy of a system can never decrease. As with classical objects at absolute zero temperature, it was assumed that black holes had zero entropy. If this were the case, the second law of thermodynamics would be violated by entropy-laden matter entering a black hole, resulting in a decrease of the total entropy of the universe. Therefore, Bekenstein proposed that a black hole should have an entropy, and that it should be proportional to its horizon area.[113]
The link with the laws of thermodynamics was further strengthened by Hawking's discovery that quantum field theory predicts that a black hole radiates blackbody radiation at a constant temperature. This seemingly causes a violation of the second law of black hole mechanics, since the radiation will carry away energy from the black hole causing it to shrink. The radiation, however also carries away entropy, and it can be proven under general assumptions that the sum of the entropy of the matter surrounding a black hole and one quarter of the area of the horizon as measured in Planck units is in fact always increasing. This allows the formulation of the first law of black hole mechanics as an analogue of the first law of thermodynamics, with the mass acting as energy, the surface gravity as temperature and the area as entropy.[113]
One puzzling feature is that the entropy of a black hole scales with its area rather than with its volume, since entropy is normally an extensive quantity that scales linearly with the volume of the system. This odd property led Gerard 't Hooft and Leonard Susskind to propose the holographic principle, which suggests that anything that happens in a volume of spacetime can be described by data on the boundary of that volume.[114]
Although general relativity can be used to perform a semi-classical calculation of black hole entropy, this situation is theoretically unsatisfying. In statistical mechanics, entropy is understood as counting the number of microscopic configurations of a system that have the same macroscopic qualities (such as mass, charge, pressure, etc.). Without a satisfactory theory of quantum gravity, one cannot perform such a computation for black holes. Some progress has been made in various approaches to quantum gravity. In 1995, Andrew Strominger and Cumrun Vafa showed that counting the microstates of a specific supersymmetric black hole in string theory reproduced the Bekenstein–Hawking entropy.[115] Since then, similar results have been reported for different black holes both in string theory and in other approaches to quantum gravity like loop quantum gravity.[116]
Black hole unitarity
Main article: Black hole information paradoxUnsolved problems in physics Is physical information lost in black holes? An open question in fundamental physics is the so-called information loss paradox, or black hole unitarity paradox. Classically, the laws of physics are the same run forward or in reverse (T-symmetry). Liouville's theorem dictates conservation of phase space volume, which can be thought of as "conservation of information", so there is some problem even in classical physics. In quantum mechanics, this corresponds to a vital property called unitarity, which has to do with the conservation of probability (it can also be thought of as a conservation of quantum phase space volume as expressed by the density matrix).[117]
See also
- Black brane
- Black hole complementarity
- Black holes in fiction
- Black string
- BTZ black hole
- Dumb hole
- Kugelblitz (astrophysics)
- List of black holes
- Susskind-Hawking battle
- Timeline of black hole physics
- White hole
- Wormhole
- ^ The set of possible paths, or more accurately the future light cone containing all possible world lines (in this diagram represented by the yellow/blue grid), is tilted in this way in Eddington–Finkelstein coordinates (the diagram is a "cartoon" version of an Eddington–Finkelstein coordinate diagram), but in other coordinates the light cones are not tilted in this way, for example in Schwarzschild coordinates they simply narrow without tilting as one approaches the event horizon, and in Kruskal–Szekeres coordinates the light cones don't change shape or orientation at all.[42]
- ^ This is true only for 4-dimensional spacetimes. In higher dimensions more complicated horizon topologies like a black ring are possible.[49][50]
- ^ In particular, he assumed that all matter satisfies the weak energy condition.
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- ^ Kerr, R. P. (2009). "The Kerr and Kerr-Schild metrics". In Wiltshire, D. L.; Visser, M.; Scott, S. M.. The Kerr Spacetime. Cambridge University Press. arXiv:0706.1109. ISBN 9780521885126.
- ^ Hawking, S. W.; Penrose, R. (January 1970). "The Singularities of Gravitational Collapse and Cosmology". Proceedings of the Royal Society A 314 (1519): 529–548. Bibcode 1970RSPSA.314..529H. doi:10.1098/rspa.1970.0021. JSTOR 2416467.
- ^ a b c Carroll 2004, Section 5.8
- ^ a b c Rees, M. J.; Volonteri, M. (2007). "Massive black holes: formation and evolution". In Karas, V.; Matt, G.. Black Holes from Stars to Galaxies—Across the Range of Masses. Cambridge University Press. pp. 51–58. arXiv:astro-ph/0701512. ISBN 9780521863476.
- ^ Penrose, R. (2002). ""Golden Oldie": Gravitational Collapse: The Role of General Relativity". General Relativity and Gravitation 34 (7): 1141. Bibcode 2002GReGr..34.1141P. doi:10.1023/A:1016578408204.
- ^ Carr, B. J. (2005). "Primordial Black Holes: Do They Exist and Are They Useful?". In Suzuki, H.; Yokoyama, J.; Suto, Y. et al.. Inflating Horizon of Particle Astrophysics and Cosmology. Universal Academy Press. arXiv:astro-ph/0511743. ISBN 4946443940.
- ^ Giddings, S. B.; Thomas, S. (2002). "High energy colliders as black hole factories: The end of short distance physics". Physical Review D 65 (5): 056010. arXiv:hep-ph/0106219. Bibcode 2002PhRvD..65e6010G. doi:10.1103/PhysRevD.65.056010.
- ^ Harada, T. (2006). "Is there a black hole minimum mass?". Physical Review D 74 (8): 084004. arXiv:gr-qc/0609055. Bibcode 2006PhRvD..74h4004H. doi:10.1103/PhysRevD.74.084004.
- ^ Arkani–Hamed, N.; Dimopoulos, S.; Dvali, G. (1998). "The hierarchy problem and new dimensions at a millimeter". Physics Letters B 429 (3–4): 263. arXiv:hep-ph/9803315. Bibcode 1998PhLB..429..263A. doi:10.1016/S0370-2693(98)00466-3.
- ^ LHC Safety Assessment Group. "Review of the Safety of LHC Collisions". CERN. http://lsag.web.cern.ch/lsag/LSAG-Report.pdf.
- ^ Cavaglià, M. (2010). "Particle accelerators as black hole factories?". Einstein-Online (Max Planck Institute for Gravitational Physics (Albert Einstein Institute)) 4: 1010. http://www.einstein-online.info/en/spotlights/accelerators_bh/index.html.
- ^ Vesperini, E.; McMillan, S. L. W.; D'Ercole, A. et al. (2010). "Intermediate-Mass Black Holes in Early Globular Clusters". The Astrophysical Journal Letters 713 (1): L41–L44. arXiv:1003.3470. Bibcode 2010ApJ...713L..41V. doi:10.1088/2041-8205/713/1/L41.
- ^ Zwart, S. F. P.; Baumgardt, H.; Hut, P. et al. (2004). "Formation of massive black holes through runaway collisions in dense young star clusters". Nature 428 (6984): 724. arXiv:astro-ph/0402622. Bibcode 2004Natur.428..724P. doi:10.1038/nature02448. PMID 15085124.
- ^ O'leary, R. M.; Rasio, F. A.; Fregeau, J. M. et al. (2006). "Binary Mergers and Growth of Black Holes in Dense Star Clusters". The Astrophysical Journal 637 (2): 937. arXiv:astro-ph/0508224. Bibcode 2006ApJ...637..937O. doi:10.1086/498446.
- ^ Page, D. N. (2005). "Hawking radiation and black hole thermodynamics". New Journal of Physics 7: 203. arXiv:hep-th/0409024. Bibcode 2005NJPh....7..203P. doi:10.1088/1367-2630/7/1/203.
- ^ Carroll 2004, Ch. 9.6
- ^ "Evaporating black holes?". Einstein online. Max Planck Institute for Gravitational Physics. 2010. http://www.einstein-online.info/elementary/quantum/evaporating_bh/?set_language=en. Retrieved 2010-12-12.
- ^ Giddings, S. B.; Mangano, M. L. (2008). "Astrophysical implications of hypothetical stable TeV-scale black holes". Physical Review D 78 (3): 035009. arXiv:0806.3381. Bibcode 2008PhRvD..78c5009G. doi:10.1103/PhysRevD.78.035009.
- ^ Peskin, M. E. (2008). "The end of the world at the Large Hadron Collider?". Physics 1: 14. Bibcode 2008PhyOJ...1...14P. doi:10.1103/Physics.1.14.
- ^ Fichtel, C. E.; Bertsch, D. L.; Dingus, B. L. et al. (1994). "Search of the energetic gamma-ray experiment telescope (EGRET) data for high-energy gamma-ray microsecond bursts". Astrophysical Journal 434 (2): 557–559. Bibcode 1994ApJ...434..557F. doi:10.1086/174758.
- ^ Naeye, R.. "Testing Fundamental Physics". NASA. http://www.nasa.gov/mission_pages/GLAST/science/testing_fundamental_physics.html. Retrieved 2008-09-16.
- ^ a b c McClintock, J. E.; Remillard, R. A. (2006). "Black Hole Binaries". In Lewin, W.; van der Klis, M.. Compact Stellar X-ray Sources. Cambridge University Press. arXiv:astro-ph/0306213. ISBN 0521826594. section 4.1.5.
- ^ a b c d e f g h i Celotti, A.; Miller, J. C.; Sciama, D. W. (1999). "Astrophysical evidence for the existence of black holes". Classical and Quantum Gravity 16 (12A): A3–A21. arXiv:astro-ph/9912186. doi:10.1088/0264-9381/16/12A/301.
- ^ Winter, L. M.; Mushotzky, R. F.; Reynolds, C. S. (2006). "XMM‐Newton Archival Study of the Ultraluminous X‐Ray Population in Nearby Galaxies". The Astrophysical Journal 649 (2): 730. arXiv:astro-ph/0512480. Bibcode 2006ApJ...649..730W. doi:10.1086/506579.
- ^ Bolton, C. T. (1972). "Identification of Cygnus X-1 with HDE 226868". Nature 235 (5336): 271–273. Bibcode 1972Natur.235..271B. doi:10.1038/235271b0.
- ^ Webster, B. L.; Murdin, P. (1972). "Cygnus X-1—a Spectroscopic Binary with a Heavy Companion ?". Nature 235 (5332): 37–38. Bibcode 1972Natur.235...37W. doi:10.1038/235037a0.
- ^ Rolston, B. (10 November 1997). "The First Black Hole". The bulletin. University of Toronto. Archived from the original on 2008-05-02. http://web.archive.org/web/20080502230214/http://news.utoronto.ca/bin/bulletin/nov10_97/art4.htm. Retrieved 2008-03-11.
- ^ Shipman, H. L. (1 January 1975). "The implausible history of triple star models for Cygnus X-1 Evidence for a black hole". Astrophysical Letters 16 (1): 9–12. Bibcode 1975ApL....16....9S. doi:10.1016/S0304-8853(99)00384-4.
- ^ Narayan, R.; McClintock, J. (2008). "Advection-dominated accretion and the black hole event horizon". New Astronomy Reviews 51 (10–12): 733. Bibcode 2008NewAR..51..733N. doi:10.1016/j.newar.2008.03.002.
- ^ "NASA scientists identify smallest known black hole" (Press release). Goddard Space Flight Center. 2008-04-01. http://www.eurekalert.org/pub_releases/2008-04/nsfc-nsi040108.php. Retrieved 2009-03-14.
- ^ Krolik, J. H. (1999). Active Galactic Nuclei. Princeton University Press. Ch. 1.2. ISBN 0-691-01151-6. http://books.google.com/?id=oRK8otMiWIgC&printsec=frontcover&dq=Active+Galactic+Nuclei#v=onepage&q&f=false.
- ^ Sparke, L. S.; Gallagher, J. S. (2000). Galaxies in the Universe: An Introduction. Cambridge University Press. Ch. 9.1. ISBN 0-521-59704-4. http://books.google.com/?id=N8Hngab5liQC&printsec=frontcover&dq=Galaxies+in+the+Universe:+An+Introduction#v=onepage&q&f=false.
- ^ Kormendy, J.; Richstone, D. (1995). "Inward Bound—The Search For Supermassive Black Holes In Galactic Nuclei". Annual Reviews of Astronomy and Astrophysics 33 (1): 581–624. Bibcode 1995ARA&A..33..581K. doi:10.1146/annurev.aa.33.090195.003053.
- ^ King, A. (2003). "Black Holes, Galaxy Formation, and the MBH-σ Relation". The Astrophysical Journal Letters 596 (1): 27–29. arXiv:astro-ph/0308342. Bibcode 2003ApJ...596L..27K. doi:10.1086/379143.
- ^ Ferrarese, L.; Merritt, D. (2000). "A Fundamental Relation Between Supermassive Black Holes and their Host Galaxies". The Astrophysical Journal Letters 539 (1): 9–12. arXiv:astro-ph/0006053. Bibcode 2000ApJ...539L...9F. doi:10.1086/312838.
- ^ a b Gillessen, S.; Eisenhauer, F.; Trippe, S. et al. (2009). "Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center". The Astrophysical Journal 692 (2): 1075. arXiv:0810.4674. Bibcode 2009ApJ...692.1075G. doi:10.1088/0004-637X/692/2/1075.
- ^ a b Ghez, A. M.; Klein, B. L.; Morris, M. et al. (1998). "High Proper‐Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy". The Astrophysical Journal 509 (2): 678. arXiv:astro-ph/9807210. Bibcode 1998ApJ...509..678G. doi:10.1086/306528.
- ^ a b Bozza, Valerio (2009). "Gravitational Lensing by Black Holes". arXiv:0911.2187 [gr-qc].
- ^ Kovacs, Z.; Cheng, K. S.; Harko, T. (2009). "Can stellar mass black holes be quark stars?". Monthly Notices of the Royal Astronomical Society 400 (3): 1632–1642. arXiv:0908.2672. Bibcode 2009MNRAS.400.1632K. doi:10.1111/j.1365-2966.2009.15571.x.
- ^ Kusenko, A. (2006). "Properties and signatures of supersymmetric Q-balls". arXiv:hep-ph/0612159 [hep-ph].
- ^ Hansson, J.; Sandin, F. (2005). "Preon stars: a new class of cosmic compact objects". Physics Letters B 616 (1–2): 1. arXiv:astro-ph/0410417. Bibcode 2005PhLB..616....1H. doi:10.1016/j.physletb.2005.04.034.
- ^ Kiefer, C. (2006). "Quantum gravity: general introduction and recent developments". Annalen der Physik 15 (1–2): 129. arXiv:gr-qc/0508120. Bibcode 2006AnP...518..129K. doi:10.1002/andp.200510175.
- ^ Skenderis, K.; Taylor, M. (2008). "The fuzzball proposal for black holes". Physics Reports 467 (4–5): 117. arXiv:0804.0552. Bibcode 2008PhR...467..117S. doi:10.1016/j.physrep.2008.08.001.
- ^ Hawking, S. W. (1971). "Gravitational Radiation from Colliding Black Holes". Physical Review Letters 26 (21): 1344–1346. Bibcode 1971PhRvL..26.1344H. doi:10.1103/PhysRevLett.26.1344.
- ^ a b Wald, R. M. (2001). "The Thermodynamics of Black Holes". Living Reviews in Relativity 4 (6). arXiv:gr-qc/9912119. Bibcode 1999gr.qc....12119W. http://www.livingreviews.org/lrr-2001-6. Retrieved 2011-02-10.
- ^ 't Hooft, G. (2001). "The Holographic Principle". In Zichichi, A.. Basics and highlights in fundamental physics. Subnuclear series. 37. World Scientific. arXiv:hep-th/0003004. ISBN 9789810245368.
- ^ Strominger, A.; Vafa, C. (1996). "Microscopic origin of the Bekenstein-Hawking entropy". Physics Letters B 379 (1–4): 99. arXiv:hep-th/9601029. Bibcode 1996PhLB..379...99S. doi:10.1016/0370-2693(96)00345-0.
- ^ Carlip, S. (2009). "Black Hole Thermodynamics and Statistical Mechanics". Lecture Notes in Physics 769: 89. arXiv:0807.4520. doi:10.1007/978-3-540-88460-6_3.
- ^ Hawking, S. W.. "Does God Play Dice?". www.hawking.org.uk. http://www.hawking.org.uk/index.php/lectures/publiclectures/64. Retrieved 2009-03-14.
Further reading
- Popular reading
- Ferguson, Kitty (1991). Black Holes in Space-Time. Watts Franklin. ISBN 0-531-12524-6.
- Hawking, Stephen (1988). A Brief History of Time. Bantam Books, Inc. ISBN 0-553-38016-8.
- Hawking, Stephen; Penrose, Roger (1996). The Nature of Space and Time. Princeton University Press. ISBN 0-691-03791-2. http://books.google.com/?id=LstaQTXP65cC.
- Melia, Fulvio (2003). The Black Hole at the Center of Our Galaxy. Princeton U Press. ISBN 978-0-691-09505-9.
- Melia, Fulvio (2003). The Edge of Infinity. Supermassive Black Holes in the Universe. Cambridge U Press. ISBN 978-0-521-81405-8.
- Pickover, Clifford (1998). Black Holes: A Traveler's Guide. Wiley, John & Sons, Inc. ISBN 0-471-19704-1.
- Stern, B. (2008). "Blackhole". http://www.wikilivres.info/wiki/Blackhole_%28Stern%29., poem.
- Thorne, Kip S. (1994). Black Holes and Time Warps. Norton, W. W. & Company, Inc. ISBN 0-393-31276-3.
- Wheeler, J. Craig (2007). Cosmic Catastrophes (2nd ed.). Cambridge University Press. ISBN 0-521-85714-7.
- University textbooks and monographs
- Carroll, Sean M. (2004). Spacetime and Geometry. Addison Wesley. ISBN 0-8053-8732-3., the lecture notes on which the book was based are available for free from Sean Carroll's website.
- Carter, B. (1973). "Black hole equilibrium states". In DeWitt, B.S.; DeWitt, C.. Black Holes.
- Chandrasekhar, Subrahmanyan (1999). Mathematical Theory of Black Holes. Oxford University Press. ISBN 0-19-850370-9.
- Frolov, V.P.; Novikov, I.D. (1998). Black hole physics.
- Hawking, S.W.; Ellis, G.F.R. (1973). Large Scale Structure of space time. Cambridge University Press. ISBN 0521099064. http://books.google.com/?id=QagG_KI7Ll8C.
- Melia, Fulvio (2007). The Galactic Supermassive Black Hole. Princeton U Press. ISBN 978-0-691-13129-0.
- Taylor, Edwin F.; Wheeler, John Archibald (2000). Exploring Black Holes. Addison Wesley Longman. ISBN 0-201-38423-X.
- Thorne, Kip S.; Misner, Charles; Wheeler, John (1973). Gravitation. W. H. Freeman and Company. ISBN 0-7167-0344-0.
- Wald, Robert M. (1984). General Relativity. University of Chicago Press. ISBN 978-0-226-87033-5. http://books.google.com/books?id=9S-hzg6-moYC.
- Wald, Robert M. (1992). Space, Time, and Gravity: The Theory of the Big Bang and Black Holes. University of Chicago Press. ISBN 0-226-87029-4.
- Review papers
- Gallo, Elena; Marolf, Donald (2009). "Resource Letter BH-2: Black Holes". American Journal of Physics 77 (4): 294. arXiv:0806.2316. Bibcode 2009AmJPh..77..294G. doi:10.1119/1.3056569.
- Hughes, Scott A. (2005). "Trust but verify: The case for astrophysical black holes". arXiv:hep-ph/0511217 [hep-ph]. Lecture notes from 2005 SLAC Summer Institute.
External links
- Black Holes on In Our Time at the BBC. (listen now)
- Stanford Encyclopedia of Philosophy: "Singularities and Black Holes" by Erik Curiel and Peter Bokulich.
- "Black hole" on Scholarpedia.
- Black Holes: Gravity's Relentless Pull—Interactive multimedia Web site about the physics and astronomy of black holes from the Space Telescope Science Institute
- FAQ on black holes
- "Schwarzschild Geometry"
- Advanced Mathematics of Black Hole Evaporation
- Videos
- 16-year long study tracks stars orbiting Milky Way black hole
- Movie of Black Hole Candidate from Max Planck Institute
Categories:- Black holes
- Dark matter
- Galaxies
- Relativity
Wikimedia Foundation. 2010.


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Project Ägypten (Free Software Sphinx-Clients)
Please note the successor: Project Ägypten2: Improving Free Software Sphinx Clients
Home | Technology | Who | Schedule | Development | Public Relations | Glossary
The Sphinx project launched by German authorities aims to improve secure email exchange. The projects technological base is the protocol 'TeleTrust e.V. MailTrusT Version 2'. This includes the standards S/MIME, X.509v3 and others.
Proprietary products are already on the way, but with the project Ägypten there is now also a Free Software solution going to be realized for popular mail user agents (sphinx-enabling KMail and Mutt are essential goals).
The Free Software companies Intevation, g10 Code and Klarälvdalens Datakonsult AB are contracted by the German 'Bundesamt für Sicherheit in der Informationstechnik (BSI)' to incorporate the Sphinx protocols into Free Software MUAs. Background is to ensure availability of alternatives to proprietary desktops.
Aims and Results
Within this project it is an explicit goal to produce sustainable improvements for the free software desktop and no quickly assembled code. The outcome of Ägypten consists of modular contributions to existing projects (there will be no single Ägypten package). These work together as an integrated solution for the users.
Rough list of aims and results:
- Plug-In for KMail and Mutt (established)
- LDAP support for Certificate Revocation Lists, CRLs (established)
- incorporation of sphinx protocols in gpg framework (established)
- X.509, PKCS10, PKCS11, PKCS12 and PKCS15 support (established)
- parallel support of OpenPGP for KMail (established)
- LDAP support for KMail address book (established)
- All finished by summer 2002, alpha-version for CeBIT 2002, Hannover (official completion was on 27-November-2002)
Detailed list of results:
- All improvements and new modules are integrated into the corresponding main developments (CVS HEAD) if not noted otherwise.
- KMail: All modifications to KMail (adding PGP/MIME and S/MIME support) are officially available since KDE 3.1 release.
- Mutt: A modified version based on 1.5.0 is available as a special package. Changes for a more flexible approach for different crypto-backends has been integrated into Mutt CVS HEAD. Eventually, the Ägypten patch may go into the CVS HEAD as well.
- KAddressbook: LDAP support is added and available since KDE 3.1.
- KGpgCertmanager: A new KDE application to manage the certificates through a GUI. Available since KDE 3.1.
- NewPG: A new module that covers GpgSM (S/MIME encryption and key-management) and SCDaemon (for Smartcard access). This module will eventually be merged with GnuPG.
- Pinentry: A new module that contains various interfaces (qt, gtk, curses, terminal) to enter a PIN/passphrase.
- DirMngr: A new module that handles the Certificate Revocation Lists (CRLs).
- GpgME: Extended to handle GnuPG (OpenPGP) and GpgSM (S/MIME) concurrently. Also a comprehensive documentation was written to support sphinx-enabling further MUAs.
- GnuPG: Extended with GpgAgent that stores passphrases like ssh-agent does (available since GnuPG 1.2.0 release).
- cryptplug: This new module is an optional interface layer between GpgME and a MUA. It is used for KMail, Mutt is directly coupled with GpgME.
- 27-Aug-2013: Removed French and German pages as part of the migration of www.gnupg.org to a new system.
- 31-Mar-2004: Linked Ägypten2 Project
- 29-Jan-2003: Finally KDE 3.1 is out. Ägypten features are intergrated. Debian woody packages available.
- 23-Feb-2004: Updated developer infos, including KDE 3.2.
- 22-Aug-2002: Updated set of tarballs.
- 07-Oct-2002: Again new tarballs.
- 01-Aug-2002: Milestone 5 (external test) finished.
- 04-Jun-2002: French web pages updated.
- 15-May-2002: Updated set of tarballs including Sphinx-enabled Mutt.
- 02-Apr-2002: Updated set of tarballs.
- 21-Mar-2002: Technology description updated.
- 13-20-Mar-2002: Ägypten in action at CeBIT Hall 11, Pav.D, Booth 10-12.
- 26-Feb-2002: First set of tarballs prepared.
- 31-Jan-2002: French web-pages contributed.
- 04-Jan-2002: Right before christmas: first Sphinx en- and decryption via KMail works
- 27-Nov-2001: First functionalities implemented, see development page
- 15-Nov-2001: New web-page: Glossary
- 26-Oct-2001: Web-pages: new: Public Relations, updated: Technology
- 24-Oct-2001: Development: cvs and issue-tracker
- 11-Oct-2001: new web pages on technology, who is involved, project schedule
- 1-Oct-2001: project start, initial webpage
You can reach the project team on several mailing lists:
- gpa-dev (technical coordination)
- kmail (KMail)
- gnupg-devel (GnuPG development)
Project coordination:
(C) Intevation, Verbatim copying and distribution of this entire page is permitted in any medium, provided this notice is preserved.


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Left Panel
Total War: Shogun 2
Total War: Shogun 2 - v1.1.0 Build 5934.393228
In the darkest age of Japan, endless war leaves a country divided. It is the middle of the 16th Century in Feudal Japan. The country, once ruled by a unified government, is now split into many warring clans. Ten legendary warlords strive for supremacy as conspiracies and conflicts wither the empire. Only one will rise above all to win the heart of a nation as the new shogun...The others will die by his sword.
Take on the role of one Daimyo, the clan leader, and use military engagements, economics and diplomacy to achieve the ultimate goal: re-unite Japan under his supreme command and become the new Shogun – the undisputed ruler of a pacified nation.
Playable Factions |
Shogun 2 |
Shikoku |
Rise of the Samurai |
Fall of the Samurai |


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Welcome To our website! We are a full service painting and repair company. Our main priority comes down to two things, customer satisfaction and the highest quality services possible. For years we have been considered the go to company for painting and minor repair services in our area. Whether it be a small bedroom in your home, or the outside of your two story office building, we've got you covered!
The key to our success has been understanding the needs of clients, how to meet them, and how to ensure we always exceed those expectations. We strive to be the best in the business and will never reach that goal if we just "meet" expectations. Give us the chance to exceed your expectations by calling today or filling out our simple online form. Feel free to browse our site to get familiar with how we sererate ourselves from the competition, and if you have a question give us a call or fill out our online form.


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I made a sorbet using a bad recipe (too watery) and I had a 3 mm thick layer of solid ice form around the walls of the ice cream maker bowl. The plastic spatula can't break it and the user's manual warns against using hard/scratchy implements in the bowl (metal is explicitly forbidden).
I would like to clean it without letting the bowl warm until it thaws, as the bowl needs a day of refreezing before reaching optimal ice cream making temperature. Any ideas?


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We have some wonderful inspiration from the Design Team for you this week, two of our DT members have kindly provided written instructions for their projects so that you can have a go at making their projects if you wish. Firstly, Anne has created a magical card, featured on the recent One Day Special TV shows on Hochanda. This vibrant card, with its striking design would make a wonderful Birthday card for girls of all ages.
Spring Fairy Collection, Fantasy Castles, and Magical Landscapes
8 inch square card blank, white stamping card and purple iridescent paper
Scrap copy paper to create masks
Large decorative circle mat cut from purple card and circle die to cut out image
Versafine Onyx Black Inkpad, StazOn Jet Black inkpad
Water based inks (purples)
Watercolour pencils (black, purples and greens)
Clear sparkle pen
Fine tipped marker pen (black) and alcohol marker (purple)
Stickles glitter glue (Star Dust)
How to Make It:
Stamp the fairies with Versafine, cut out and colour with pencils and a damp brush.
Stamp the wings with StazOn onto the iridescent paper, cut out and decoupage over the stamped fairies.
Stamp the castles and buildings onto copy paper and cut out. Arrange the elements to plan the scene, i.e. it needs to fit into the circle topper which will fit into the large decorative mat. Stamp the foreground image with Versafine and cover it with your paper mask before stamping the next image behind. Continue covering the foreground images and working towards the background elements.
When complete remove the masks and use a fine tipped marker to join up or draw extra elements where needed.
Colour with watercolour pencils and a damp brush. Overlay some areas with clear sparkle pen. I added extra intense colour with water based inks into the background to make the buildings 'pop'.
Edge the card blank with alcohol marker to frame. Layer and glue down all of the elements. I used 3D foam and glue gel for added depth.
Finish with touches of glitter glue for added sparkle.
Claire has created a stunning canvas, full of texture and lovely details. This would make a beautiful decoration for your home.
8"x8" canvas
Butterfly stencil
Just Butterflies stamp set
Shimmer sprays (shades of green and violet)
Texture paste
Brick effect stencil, Ledger stencil
Silver Gilding Wax
Pearls, diamante gems
Versamark Ink
White opaque embossing powder
Anti-static bag
Acylic Paint- Silver, Green metallic, purple metallic
Heat resistant acetate
Stickles, PVA glue, silicone glue
Begin by applying texture paste through the butterflies and dragonflies, leave to dry.
Once the texture paste is dry, add texture to the background by applying texture paste through the brick and ledger stencils. Try to avoid the butterflies, but if you do get texture paste on them, remove it with a baby wipe and leave to dry.
Spray the violet shimmer sprays generously in the centre of the canvas and the green shades around the edge. Use a baby wipe to blot any areas that look a little muddy and leave to dry.
Dust the stencilled butterflies with an anti-static bag and stamp the coordinating butterflies with Versamark. Emboss with white embossing powder.
Highlight the raised areas of the background by applying silver gilding wax.
Paint the edges of the canvas with silver acrylic paint and leave to dry.
Dust the acetate with an anti-static bag and stamp the butterflies with Versamark Ink. Emboss with white embossing powder. Loosely paint the butterflies on the reverse with green and purple acrylic paint and leave to dry for a few minutes.
Once the paint is dry, cut the butterflies out and glue on the gems with PVA glue. Smear a little Stickles here and there and leave to dry.
Fold the wings up at either side of the body and attach the butterflies to the canvas with silicone glue to give the wings some dimension.
Thank you so much girls for your gorgeous projects. We hope that they will inspire you to join in with the challenge. We will be back next week with another post, and more projects from the Design Team. If you have any questions, and cannot find the answers on the blog pages, please send a message using the contact form located at the very end of this post; you will see it after the comments section.


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This article is more than 1 year old
How can UK.gov spend £35m on a website?
Here's how...
Comment The Central Office of Information (COI), the UK Government's centre of excellence for marketing and communications, has just published a report on the costs, usability and quality of selected UK Government websites in 2009-10.
It's a detailed report and the data is available to download. It shows how the UK Government spent £94m on website development and running costs plus £32m on web staff in 2009 - 2010. By looking at the analytics it's possible to correlate the costs of building these sites with the number of visitors. One headline statistic was that the UK Trade and Investment website averaged 28,000 users per month but cost over £4m to build - so each site visitor cost £11.78.
As an exercise, I took a deeper look at the websites in the COI report to see what technology they're using. These are leading central government websites so it's an interesting sample.
I wanted to characterise the sites from the information available on the Internet - were they built using Microsoft technology as evidenced by IIS web server, ASP.NET framework and Windows Server? Or were they Open Source based, with Linux OS and Apache web server for example?
In the end I extracted data for 38 of the websites, and found 25 were using Microsoft and 13 were Open Source. The majority of the Microsoft sites were running Windows Server 2003, with one instance each of 2000 and 2008.
That in itself bucks a global trend, in that over 60 per cent of all websites are based on Apache whereas IIS 5, 6 and 7 account for one per cent, 20 per cent and three per cent respectively. Microsoft and its partners have clearly had a strong influence over UK Government procurement decisions.
How much evidence was there of content management systems (CMS) usage? Very little. There was a small pocket of Vignette CMS (now owned by Open Text), some Drupal and Joomla, and one instance of Microsoft SharePoint 2007. There was a weak correlation between the age of the site and use of CMS - it's more common in recently published websites.
Were the Microsoft based websites more expensive than the Open Source based ones? I ran a non-parametric statistical test (Mann-Whitney) on the two samples and the short answer is that there's no significant difference. This shows that the overall costs of building these sites out-stripped the licensing costs.
Do these sites seem like good value for the UK taxpayer? At an average non-staff cost of £2.5m per website, absolutely not. I read the report many times to understand how HM Revenue and Customs could spend £35m on www.businesslink.gov.uk. I just can't figure out how.
What's the lesson? The licensing model of the underlying technology isn't a significant factor in determining website costs. Free and Open Source Software won't matter when a consultancy or outsourcing company loads up a contract with tasks requiring many person weeks of expensive billable time.
If there isn't a FOSS advantage, there's still clearly a commercial off-the-shelf (COTS) advantage. One of the main purposes of these sites (apart from serving static information pages) is to provide a portal for file download.
Commercial open source software packages such as CogniDox allow you to do this in a completely secure and flexible manner. It costs thousands of pounds, not millions, and it delivers those features out of the box. And it has competitors such as Alfresco and Nuxeo that can also do the same.
Paul Walsh is the CEO of Cognidox, a Cambridge, UK developer of web-based document management software
This article was originally posted at Cognidox.