Oxford Dictionary of Astronomy Ian Ridpath OUP 2011
"Black hole. An object with such a strong gravitational field that its escape velocity exceeds the velocity of light. One way in which black holes are believed to form is when massive stars collapse at the end of their lives. A collapsing object becomes a black hole when its radius has shrunk to a critical size, known as the Schwarzschild radius, and light can no longer escape from it. The surface having this critical radius is referred to as the 'event horizon', and marks the boundary inside which all information is trapped. Hence events within the black hole cannot be observed from outside. Theory indicates that both space and time become distorted inside the event horizon and that an object collapses to a single point, a 'singularity' at the centre of a black hole. Black holes may have any mass. Supermassive black holes (10^5 solar masses) may exist at the centres of active galaxies. At the other extreme mini black holes of radii 10^-10 metres and masses similar to that of an asteroid may have been formed in the extreme conditions following the Big Bang. . . . . . . . . . Black holes are not entirely black; theory suggests that they can emit energy in the form of 'Hawking Radiation'."
To the ends of the Universe by Heather Couper and Nigel Henbest DK 1998
"Within a month of Einstein publishing his theory of general relativity, German physicist Karl Schwarzschild discovered that the equations led to an amazing prediction. A region of space could become so distorted that it was cut off from the outside Universe. Objects could fall in, but never get out again. Today we call such a region a black hole. Einstein himself refused to believe in black holes, but for once he was wrong. At first sight, Schwarzschild's black hole looks like the one predicted by Newton's theory. But only Einstein's theory can explain correctly how space, light, and matter behave near a black hole. Mathematicians have even used general relativity to calculate what happens inside a black hole."
Cosmology - A Very Short Introduction by Peter Coles Oxford University Press 2001
"One example where Newton's gravity breaks down is when a very large amount of matter is concentrated in a very small region of space. When this happens the action of gravity is so strong, and space so warped, that light is not merely bent but is trapped. Such an object is a black hole. . . . . . . . . . One of the first mathematical solutions of Einstein's equations obtained, describes such an object. The famous 'Schwarzschild' solution was obtained only a year after the publication of Einstein's theory in 1916. The solution corresponds to a spherically symmetrical distribution of matter, and it was originally intended that this could form the basis of a mathematical model for a star. It was soon realised, however, that for an object of any mass the Schwarzschild solution implied the existence of a critical radius (now called the Schwarzschild radius). If a massive object lies entirely within its Schwarzschild radius then no light can escape from the surface of the object. For the mass of the Earth the critical radius is only 1 cm, whereas for the Sun it is about 3 km. Making black holes involves compressing material to a phenomenal density."
Universe - the Definitive Visual Guide Ed Martin Rees DK 2012
"A black hole is a region 0f space containing, at its centre, some matter squeezed into a point of infinite density, called a singularity. Within a spherical region around the singularity, the gravitational pull is so great that nothing, not even light, can escape. Black holes can therefore be detected only from the behaviour of material around them; those discovered so far typically have a disk of gas and dust spinning around the hole, throwing off hot, high speed jets of material or emitting radiation (such as X-rays) as matter falls into the hole.
There are two main types of black hole - supermassive and stellar. Supermassive black holes, which can have a mass equivalent to billions of suns, exist in the centres of most galaxies, including our own. Their exact origin is not yet understood, but they may be a by-product of the process of galaxy formation. Stellar black holes form from the collapsed remains of exploded supergiant stars, and may be very common in all galaxies."
Complete History of the Universe All About Space Imagine Publishing 2016
Supermassive black holes
The ultimate consequence of gravity is a black hole. Imagine a region of space where gravity has caused a star to collapse, at the end of its life, to a point so small and dense that its gravity is practically infinite and completely overwhelms everything else. It's so strong that not even light can escape its grasp - the point of no return is known as the event horizon - explaining where the name black hole came from. And black holes don't come any more massive than a hefty supermassive black hole. With a mass ranging anywhere from hundreds of thousands to billions of times the mass of the Sun, these exotic high gravity objects are more often than not the centrepiece of the many galaxies that litter our Universe. Our own Milky Way even has one, called Sagittarius A*, which is a monster of around 4.3 million times the mass of our Sun, located deep in the middle of our galaxy amid myriad stars and vast clouds of gas and dust. So powerful are these galaxies that they have the power to switch star formation in a galaxy on and off at will." [At will???]
"Think back to quasars - these are the most extreme form of active supermassive black holes. But less energetic black holes can still produce lower power jets, yet even though they're lower power, they still dominate the galaxy that they are in. Stars need gas to form, and the gas in galaxies often falls on to them from wandering clouds of intergalactic gas. Yet as clouds fall on to galaxies and as the galaxies merge with other galaxies, gas gets funnelled towards the black hole, ending up in a disk surrounding it, some of which is then beamed back out into the galaxy by jets or 'winds' of stellar radiation."
"These jets and radiation heat the gas that is creating stars, causing it to become too hot for star formation and sometimes even blowing right out of the galaxy itself. This is called feedback, and when it happens it brings star formation in a galaxy to a stuttering halt."
Astronomy First midsized black hole detected by Alison Klegman and Jake Parks February 2021
"Black holes come in a variety of sizes, ranging from a few to billions of times the mass of the Sun. . . . . . . . . . scientists at the Laser Interferometer Gravitational-wave Observatory (LIGO) and the partnering Virgo site received the first convincing sign: gravitational waves that point to the violent birth of an intermediate mass black hole (IMBH)."
Black Hole
WORK IN PROGRESS Much further information to be added. 26 May 2021.
"Black hole. An object with such a strong gravitational field that its escape velocity exceeds the velocity of light. One way in which black holes are believed to form is when massive stars collapse at the end of their lives. A collapsing object becomes a black hole when its radius has shrunk to a critical size, known as the Schwarzschild radius, and light can no longer escape from it. The surface having this critical radius is referred to as the 'event horizon', and marks the boundary inside which all information is trapped. Hence events within the black hole cannot be observed from outside. Theory indicates that both space and time become distorted inside the event horizon and that an object collapses to a single point, a 'singularity' at the centre of a black hole. Black holes may have any mass. Supermassive black holes (10^5 solar masses) may exist at the centres of active galaxies. At the other extreme mini black holes of radii 10^-10 metres and masses similar to that of an asteroid may have been formed in the extreme conditions following the Big Bang. . . . . . . . . . Black holes are not entirely black; theory suggests that they can emit energy in the form of 'Hawking Radiation'."
To the ends of the Universe by Heather Couper and Nigel Henbest DK 1998
"Within a month of Einstein publishing his theory of general relativity, German physicist Karl Schwarzschild discovered that the equations led to an amazing prediction. A region of space could become so distorted that it was cut off from the outside Universe. Objects could fall in, but never get out again. Today we call such a region a black hole. Einstein himself refused to believe in black holes, but for once he was wrong. At first sight, Schwarzschild's black hole looks like the one predicted by Newton's theory. But only Einstein's theory can explain correctly how space, light, and matter behave near a black hole. Mathematicians have even used general relativity to calculate what happens inside a black hole."
Cosmology - A Very Short Introduction by Peter Coles Oxford University Press 2001
"One example where Newton's gravity breaks down is when a very large amount of matter is concentrated in a very small region of space. When this happens the action of gravity is so strong, and space so warped, that light is not merely bent but is trapped. Such an object is a black hole. . . . . . . . . . One of the first mathematical solutions of Einstein's equations obtained, describes such an object. The famous 'Schwarzschild' solution was obtained only a year after the publication of Einstein's theory in 1916. The solution corresponds to a spherically symmetrical distribution of matter, and it was originally intended that this could form the basis of a mathematical model for a star. It was soon realised, however, that for an object of any mass the Schwarzschild solution implied the existence of a critical radius (now called the Schwarzschild radius). If a massive object lies entirely within its Schwarzschild radius then no light can escape from the surface of the object. For the mass of the Earth the critical radius is only 1 cm, whereas for the Sun it is about 3 km. Making black holes involves compressing material to a phenomenal density."
Universe - the Definitive Visual Guide Ed Martin Rees DK 2012
"A black hole is a region 0f space containing, at its centre, some matter squeezed into a point of infinite density, called a singularity. Within a spherical region around the singularity, the gravitational pull is so great that nothing, not even light, can escape. Black holes can therefore be detected only from the behaviour of material around them; those discovered so far typically have a disk of gas and dust spinning around the hole, throwing off hot, high speed jets of material or emitting radiation (such as X-rays) as matter falls into the hole.
There are two main types of black hole - supermassive and stellar. Supermassive black holes, which can have a mass equivalent to billions of suns, exist in the centres of most galaxies, including our own. Their exact origin is not yet understood, but they may be a by-product of the process of galaxy formation. Stellar black holes form from the collapsed remains of exploded supergiant stars, and may be very common in all galaxies."
Complete History of the Universe All About Space Imagine Publishing 2016
Supermassive black holes
The ultimate consequence of gravity is a black hole. Imagine a region of space where gravity has caused a star to collapse, at the end of its life, to a point so small and dense that its gravity is practically infinite and completely overwhelms everything else. It's so strong that not even light can escape its grasp - the point of no return is known as the event horizon - explaining where the name black hole came from. And black holes don't come any more massive than a hefty supermassive black hole. With a mass ranging anywhere from hundreds of thousands to billions of times the mass of the Sun, these exotic high gravity objects are more often than not the centrepiece of the many galaxies that litter our Universe. Our own Milky Way even has one, called Sagittarius A*, which is a monster of around 4.3 million times the mass of our Sun, located deep in the middle of our galaxy amid myriad stars and vast clouds of gas and dust. So powerful are these galaxies that they have the power to switch star formation in a galaxy on and off at will." [At will???]
"Think back to quasars - these are the most extreme form of active supermassive black holes. But less energetic black holes can still produce lower power jets, yet even though they're lower power, they still dominate the galaxy that they are in. Stars need gas to form, and the gas in galaxies often falls on to them from wandering clouds of intergalactic gas. Yet as clouds fall on to galaxies and as the galaxies merge with other galaxies, gas gets funnelled towards the black hole, ending up in a disk surrounding it, some of which is then beamed back out into the galaxy by jets or 'winds' of stellar radiation."
"These jets and radiation heat the gas that is creating stars, causing it to become too hot for star formation and sometimes even blowing right out of the galaxy itself. This is called feedback, and when it happens it brings star formation in a galaxy to a stuttering halt."
Astronomy First midsized black hole detected by Alison Klegman and Jake Parks February 2021
"Black holes come in a variety of sizes, ranging from a few to billions of times the mass of the Sun. . . . . . . . . . scientists at the Laser Interferometer Gravitational-wave Observatory (LIGO) and the partnering Virgo site received the first convincing sign: gravitational waves that point to the violent birth of an intermediate mass black hole (IMBH)."
Black Hole
WORK IN PROGRESS Much further information to be added. 26 May 2021.
Last edited:
Facebook
Twitter
Instagram