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| Rhawn Joseph, Ph.D.
SUPER NOVA & BLACK HOLES
Black holes are formed when super massive stars collapse and explode, leaving behind only a stellar core which continues to collapse until it is compressed into an infinitely small, infinitely dense point called a singularity. This is the centre of a black hole.
A black hole, therefore, consists of a collapsed star which may have shrunk to the size of a basketball. And yet, it may contain all the mass of a star the size of our sun. If we were to put that super-dense black-hole-basketball into your hands, it would instantly crush you into pinhole size and suck you inside. And not just you, but your car, house, city, state, and the entire planet Earth. Even light will be unable to escape, but will be sucked inside.
Normally the equilibrium of a star is maintained by the conversion of hydrogen into helium. Within our own sun, 685 million tons of hydrogen is converted to helium each second [23]. The nuclear fusion and conversion of these gasses releases tremendous thermal energy creating an outward pressure which prevents the gravitational collapse and implosion of the star [24,25,26]. 
Stars lose mass over time, which is blown away by its solar wind. As the star begins to die and becomes a red giant, its loses matter at an accelerated rate.
 
As the star grows old the supply of hydrogen fuel begins to dwindle and they cease to generate as much energy. Equilibrium is lost, and the star begins to collapse, making them smaller, but denser, which raises temperatures. In consequence the corona, the crown of the star, begins to expand and the mass of the star is ejected at an accelerated rate in the form of an increasingly dense solar wind. 
The super red giant Eta Carinae is so large it casts off 500 times the mass of the Earth every year. Eta Carinae is in its death throes and will soon explode as a supernova. This star and its solar system are already surrounded by a nebular shell comprised of dust, gas, and other material swept into space by its powerful solar wind.
As hydrogen is used up it is converted to helium and eventually a helium core forms in the heart of the dying star. A star become a red giant after it has burned up most of its hydrogen fuel. The loss of expanding thermal energy causes the star to contract and then collapse from its own weight. However, as hydrogen dwindles, the nuclear reactions radiate outward creating an expanding pressure directed toward the upper layers. Simultaneously the core loses support and then collapses generating more energy and increasing the radiation pressure outward, expanding the star and making it grow increasingly larger in size, becoming a red giant.
Thus, the red giant has many times its original size and may have a diameter 10 to 1000 times that of our sun. Luminosities may increase by 1 million times, as which point it explodes.
The remaining core then begins to collapse, growing denser, smaller in size, until reaching a point of singularity where not even light can escape its gravity, thus creating a black hole.
Main sequence stars, such as our own Sun, do not explode but instead collapse forming a white dwarf which continues to burn giving off a pale white glow.
By contrast, the gravity of a low mass star is not strong enough to start fusion and explode but becomes a burnt out, dead cinder, known as a brown dwarf.
Black holes are formed when super massive stars collapse and explode, triggering a supernova. However, the remaining core might continue to collapse, and electrons will be crushed and shoved into the nucleus of their atoms, which cancels out the positive charge of the protons. As neutrons press against each other they may create a neutron star or they continue to collapse and become crushed together.
Because of the incredible mass and gravity surrounding stellar material may be "sucked" into the collapsing core and neutrons will continue to be squeezed into a smaller and smaller space until the gravity of the star is so powerful that light is unable to escape. Instead light becomes trapped inside of what is known as the 'event horizon' which creates a black hole.
However, the star will continue to shrink until the matter is all compressed into an infinitely small, infinitely dense point called a singularity. This is the centre of a black hole.
SINGULARITY
At the center of a black hole lies the singularity, where matter is crushed to infinite density, the pull of gravity is infinitely strong, and space-time has infinite curvature. This means that a black hole's mass becomes entirely compressed into a region with zero volume. This zero-volume, infinitely dense region at the center of a black hole is called a gravitational singularity.
The singularity of a non-rotating black hole has zero length, width, and height; a rotating black hole's is smeared out to form a ring shape lying in the plane of rotation. The ring still has no thickness and hence no volume.
The appearance of singularities in general relativity is commonly perceived as signaling the breakdown of the theory. 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.
In general relativity, the black hole's mass can be thought of as concentrated at a singularity, which can be a point, a ring, a light-ray, or a sphere. Surrounding the singularity is a spherical boundary called the event horizon. The event horizon marks the 'point of no return,' a boundary beyond which matter and radiation inevitably fall inwards, towards the singularity. The distance from the singularity at the center to the event horizon is the size of the black hole, and is equal to twice the mass in units where G and c equal 1.
The radius of a black hole of mass equal to that of the Sun is about 3 km. At distances much larger than this, the black hole has the exact same total gravitational attraction as any other body of the same mass, just like the sun. So if the sun were replaced by a black hole of the same mass, the orbits of the planets would remain unchanged.
Again, however, if we were to put that super-dense black-hole into your hands, it would instantly crush you into pinhole size and suck you inside.
Even light cannot escape a black hole.
BLACK HOLES: TIME FLOWS BACKWARD
Time may slow down and then stop, as the object or observer in question approaches a black hole. Light also cannot escape and light passing near a black hole might be twisted, turned, and possibly even sucked into the black hole. For those who believe that light and time are related, this suggest that time may flow backwards inside a black hole.
 
The defining feature of a black hole is the appearance of an event horizon; a boundary in space-time beyond which events cannot affect an outside observer. As predicted by general relativity, the presence of a mass deforms space-time in such a way that the paths particles take tend towards the mass. At the event horizon of a black hole this deformation becomes so strong that there are no more paths that lead away from the black hole. Once a particle is inside the horizon, moving into the hole is as inevitable as moving forward in time (and can actually be thought of as equivalent to doing so).
 
To a distant observer clocks near a black hole appear to tick more slowly than those further away from the black hole. Due to this effect (known as gravitational time dilation) the distant observer will see an object falling into a black hole slow down as it approaches the event horizon, taking an infinite time to reach it. At the same time all processes on this object slow down causing emitted light to appear redder and dimmer, an effect known as gravitational red shift. Eventually, the falling object becomes so dim that it can no longer be seen, at a point just before it reaches the event horizon.
 
For a non rotating (static) black hole, the Schwarzschild radius delimits a spherical event horizon. The Schwarzschild radius of an object is proportional to the mass. Rotating black holes have distorted, non-spherical event horizons. Since the event horizon is not a material surface but rather merely a mathematically defined demarcation boundary, nothing prevents matter or radiation from entering a black hole, only from exiting one. The description of black holes given by general relativity is known to be an approximation, and it is expected that quantum gravity effects become significant near the vicinity of the event horizon. This allows observations of matter in the vicinity of a black hole's event horizon to be used to indirectly study general relativity and proposed extensions to it. Light is effected by many factors, including the gravity of super galaxies and black holes. Light can slow or speed up, bend, twist, curve, and can even flow backwards and can be sucked up and disappear within the depths of a black hole, never to be seen again. The incredible mass of objects described as black holes, have a gravity so strong that it sucks in all surrounding substances, including gasses, stars, galaxies, and the light from a million stars. If light and time were synonymous or even remotely related this would mean that time flows backward when in the grip of a black hole.
WORM HOLES & SPACE & TIME TRAVEL
General relativity describes the possibility of "worm holes" forming when two black holes become connected to each other. Hypothetically, wormholes could enable almost instantaneous time travel over long distances--that is, if one would not be crushed in the process.
In physics, a wormhole is a hypothetical feature of space time which two vastly distant regions of space become connected by a tunnel formed by two black holes. This tunnel could serve as a passage way between space and time which essentially become folded over.
Instead of traveling in a straight line, time and space, if curved, might then curve over or under itself, i.e. the future and the past and the present all exist simultaneously and are folded one on top of the other because of the curvature of space time. Therefore, one might leap from one fold to another, or rather, utilize a worm hole to pass from one fold to another and this would be made possible by a black hole in a future space time causing such a depression in the fabric of space time, that it connects with a black hole making a gravity depression in another aspect of space time.
While there is no observational evidence for wormholes, space-times containing wormholes are known to be valid solutions in general relativity.
The term wormhole was coined by the American theoretical physicist John Archibald Wheeler in 1957.
This analysis forces one to consider situations...where there is a net flux of lines of force through what topologists would call a handle of the multiply-connected space and what physicists might perhaps be excused for more vividly terming a ‘wormhole’. —John Wheeler in Annals of Physics
However, the idea of wormholes had already been theorized in 1921 by the German mathematician Hermann Weyl in connection with his analysis of mass in terms of electromagnetic field energy
Wormholes are known by a variety of names in physics, i.e. Lorentzian, Schwarzschild, and Einstein-Rosen bridges. These wormholes serve as vacuum solutions to the Einstein field equations by combining models of a black hole and a white hole. In astrophysics, a white hole is the theoretical time reversal of a black hole.
Presumably, a black hole acts as a vacuum, drawing in any matter that crosses the event horizon. By contrast, a white hole acts as a source that ejects matter from its event horizon.
This solution was discovered by Albert Einstein and his colleague Nathan Rosen, who first published the result in 1935. However, in 1962 John A. Wheeler and Robert W. Fuller published a paper showing that this type of wormhole is unstable, and that it will pinch off instantly as soon as it forms, preventing even light from making it through.
BLACK HOLES AND GALAXY FORMATION
Black holes come in all sizes with the super massive black holes having such incredible gravitational pull that they can suck in and devour other stars.
Life gives birth to life, and stars give birth to stars in an endless cycle of death and rebirth. It's a cosmic dance which may have been ongoing for all eternity. Birth and death are part of the cycle of life. Some stars give birth as they die; becoming red giants and exploding in a vast supernova, spawning hundreds of infant proto-stars [16,17,18]. These super explosions can light up an entire galaxy. Typically, the explosion creates tremendous shock waves, shattering surrounding planets, and expelling most of the star and remaining planetary debris into the surrounding interstellar medium. This debris eventually becomes part of the surrounding nebular ring created by the solar winds, planetary atmospheres, and expelled mass of the dead star [30,31,32].
An ancient star of Orion grew old, became a red giant, and exploded in a vast supernova millions of years ago, becoming the largest star factory in the heavens [33-35]. Some of these infant stars may be growing planets which may already harbor life. Others are being destroyed, blow torched and burned to death by a blistering flood of ultraviolet radiation from the region's brightest star [36,37].
 
However, in some instances, these proto-stars may begin to orbit the black hole remnant of the super massive exploding star which created them, thereby forming a mini-galaxy. It is now widely accepted that the center of nearly every galaxy contains a super massive black hole. 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.
 
Thus, black holes appear to play an organizing role in the creation of spiral galaxies, collecting stars together, thus forming a central galaxy.
The spiral spinning motion, therefore, is due to the gravitational sucking power of the black hole. thus, what holds galaxies together are black holes, and what forms the galaxy is the black hole which sucks up independent stars and collects them together.
Since black holes appear to swallow the oldest stars in its grip, and as even the trajectory and speed of light from surrounding stars may be slowed, altered, trapped, and swallowed never to be seen again, this would imply that the light from the oldest stars, including those from far away galaxies may also be effected, slowed, altered, trapped reversed and may never reach the Earth, if subjected to the gravitational pull of super massive black holes which appear to lurk in the center of every galaxy. BLACK HOLES, RED SHIFTS, GALACTIC LENSING In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including light, can escape its pull. The black hole has a one-way surface, called an event horizon, into which objects can fall, but out of which nothing can come. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect blackbody in thermodynamics. Quantum analysis of black holes shows them to possess a temperature and Hawking radiation.
Any measurements of far away galaxies based on light, red shift, and radio waves, therefore, are unreliable. The "speed of light" for example is not a constant and the speed and direction of light varies in different regions of the cosmos and can even be reversed and swallowed by the massive gravitational sucking power of a black hole. Not all space is equal.
Light is effected by gravity, but collections of massive galaxies, by black holes and a number of unknown factors including the energy and gravitational pull of dark matter. Consider a phenomena know as (a href="http://Cosmology.com/GravitionalLensing.html"> gravitational lensing. Light can slow or speed up, bend, twist, curve, and can split apart creating galactic illusions which are displaced in space.
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a black hole) between the source object and the observer. The process is known as gravitational lensing, and is one of the predictions of the general theory of relativity. According to this theory, mass warps space-time to create gravitational fields and therefore bend light as a result.
  
BLACK HOLES & ESCAPE VELOCITY A black hole is often defined as an object whose escape velocity exceeds the speed of light. The escape velocity is the minimum speed at which an object needs to travel so as to escape a source of gravity without falling back into orbit before stopping. On the Earth, the escape velocity is equal to 11 km/s, so no matter what the object is, whether a bullet or a baseball, it must go at least 11 km/s to avoid falling back to the Earth's surface eventually.
ROTATING BLACK HOLES: THE ERGOSPHERE Rotating black holes are surrounded by a region of space time 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 space time 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.
The ergosphere of black hole is bounded by:
On the inside, the (outer) event horizon.
Within the ergosphere, space-time is dragged around faster than light—general relativity forbids material objects to travel faster than light (so does special relativity), but allows regions of space-time to move faster than light relative to other regions of space-time.
Objects and radiation (including light) can stay in orbit within the ergosphere without falling to the center. But they cannot hover (remain stationary, as seen by an external observer), because that would require them to move backwards faster than light relative to their own regions of space-time, which are moving faster than light relative to an external observer.
Objects and radiation can also escape from the ergosphere. In fact the Penrose process predicts that objects will sometimes fly out of the ergosphere, obtaining the energy for this by "stealing" some of the black hole's rotational energy. If a large total mass of objects escapes in this way, the black hole will spin more slowly and may even stop spinning eventually.
BLACK HOLES ARE EJECTED
Black holes may also be ejected from the area of space it originally orbited. Thus, as its own solar system no longer exists, they may speed across space,
One black hole shot from a spectacular cosmic explosion is currently racing across the Milky Way four times faster than the stars around it. Although currently 6,000 light years away, this black hole is headed in the direction of our solar system. 
Moreover, black holes may be accompanied by some of the infant stars produced when it originally exploded in a supernova. The black hole with our solar system as a bull's eye, is in fact accompanied by an infant star. However, in this case, rather than the infant feeding on its mother's breast, this black hole is sucking up energy from its infant star. It is the presence of the bright, glowing infant star which has betrayed the black hole which feeds on it. The visible star orbits the black hole once every 2.6 days.
This symbiotic-parasitic relationship is not uncommon. Despite its invisible interior, a black hole's existence is often revealed through interaction with other stars. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space which looks empty. Observations of gas falling into a relatively small black hole, from a companion star, are quite common. This gas spirals inward, heating up to very high temperature and emitting large amounts of radiation that can be detected from earthbound and earth-orbiting telescopes.
 
Moreover, black holes may trigger supernova explosions in dead stars, including White Dwarfs. Sometimes White Dwarfs may siphon off matter from a companion star, and then explode. In other instances, the tidal forces of a passing black hole might ignite the White Dwarf by causing additional compression. The extreme pressure causes a sharp increase in temperatures, which triggers explosive burning and thus a supernova. The explosion ejects more than half of the debris from the disrupted star, while the rest of the stellar material falls into the black hole.
Recently, the disruption of a white dwarf with two-tenths the mass of the Sun was observed to be due to a black hole with 1,000 times the mass of the Sun. The white dwarf exploded.
 This series of images shows the interaction of a white dwarf star with a black hole. As it passes the black hole, the white dwarf becomes strongly compressed and heated (top left), triggering an explosion. Most of the stellar mass is ejected into space (the "bubble" in the upper right part of the debris in the top right image), while the rest (the cusp-like part of the image) falls toward the black hole. While the ejected matter expands rapidly, the infalling matter builds a violent, thick accretion disk around the black hole.
There may be millions of wayward black holes zooming through our galaxy. And there may be innumerable black holes which traverse the universe, free of the gravitational influences of its parent galaxies. These wayward black holes may account for much of the missing mass of the universe and what has been described as dark energy and dark matter
BLACK HOLES GROW
Once a black hole has formed, it can continue to grow by absorbing additional matter. Any black hole will continually absorb interstellar dust from its direct surroundings and omnipresent cosmic background radiation, but neither of these processes should significantly affect the mass of a stellar black hole. More significant contributions can occur when the black hole formed in a binary star system. After formation the black hole can then leech significant amounts of matter from its companion.
Much larger contributions can be obtained when a black hole merges with other stars or compact objects. The super massive black holes suspected in the center of most galaxies are expected to have formed from the coagulation of many smaller objects. The process has also been proposed as the origin of some intermediate-mass black holes.
As an object approaches the event horizon, the horizon near the object bulges up and swallows the object. Shortly thereafter the increase in radius (due to the extra mass) is distributed evenly around the hole.
Hawking radiation
In 1974, Stephen Hawking showed that black holes are not entirely black but emit small amounts of thermal radiation. 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.
Others have argued that black holes themselves may not radiate energy. Instead, electromagnetic radiation and matter particles may be radiated from just outside the event horizon via Hawking radiation.
Since Hawking's result many others have verified the effect through various methods. 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, because according to the theory of relativity mass is just highly condensed energy (E = mc2).
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 in turn is inversely proportional to the mass. Large black holes, therefore, emit less radiation than small black holes.  A stellar black hole of 5 solar masses has a Hawking temperature of about 12 nanokelvins. This is far less than the 2.7 K produced by 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. In order 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). 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 – hypothetically make such a small black hole stable.
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Black Holes and QuasarsBlack Holes and Quasars When gases and other matter in stars having solar masses much larger than the Sun gravitationally contract into small, compact bodies,
the result is a Black Hole (B.H.), so called because the gravity associated
with its extremely dense mass (if the mass in the Sun were to collapse into a Black Hole, this would yield a density of about 1022 grams per cubic meter; larger stars would produce densities several orders of magnitude greater). This supermass prevents all detectable internal radiation originating from within from escaping
beyond its event horizon (sphere of influence insid3 or which extreme gravitational forces preclude any mass or photon radiation from leaving). The distance from a B.H.'s center to the horizon is known as the Schwartzchild
radius . Since the B.H. is itself invisible (black), its existence must usually be inferred from its gravitational effect on surrounding stars and interstellar matter. Before their observational discovery, Black Holes were predicated to exist from General Relativity considerations. Black Holes indeed have such strong gravitational influence that they notably warp the fabric of Einstein's spacetime dimensionality.
Black Holes can vary in dimensions, the smallest in the general class being
much less than a kilometer in diameter but packing dense mass equivalent to about
3 solar masses. (Theory indicates that mini-Black Holes can be as small as a few centimeters or even microscopic in size; so far, none this small have been detected; one school of thought holds that there are countless numbers of tiny B.H's distributed within galaxies and in intergalactic space that contribute to holding the Universe intact.) Humongous B.H.s can contain masses derived from billions of
infalling stars and galactic matter, attaining sizes exceeding that of our Solar System. Massive to Supermassive Black Holes may be the customary state at the center of spiral
and other galaxy types, having built up from millions stars and other matter converging inward as though moving to a drain. Many cosmologists believe that at least one supermassive B.H. is present near the center of any galaxy. Its role is to keep the galaxy from flying apart (thus its gravitational forces are the stabilizer of the galactic structure).
The HST view of NGC7742, a Seyfert type 2 active galaxy, shows a large glowing central region (an AGN), within which a supermassive Black Hole is postulated. Its bright center probably represents a quiescent Quasar state, there are periodic flare-ups resulting from energy release when stars spiral past the B.H. horizon into its interior; note the ring of bright hot, largely younger stars beyond and the faint spiral arms further out.
Many Black Holes are the end product of Supernovae explosions of Red Giant stars, as these burn up their fuel and reach the stage where Fe becomes the dominant element (which does not further ignite by fusion; see page 20-7). Smaller stars end up as Neutron stars which in principle can coalesce into B.H.'s. The larger B.H's have masses from millions to billions greater than the Sun. At the other extreme small B.H's may have only a fraction of a solar mass, perhaps up to a billion tons occupying a tiny volume such that the density of just a teaspoon-full of this compact matter is still enormous. This extraordinary density is possible because under the great pressure that formed the B.H. electrons and the atoms themselves become very closely compacted. Smaller B.H's may be ubiquitous - millions of remnants from earlier explosions within the Milky Way and galaxies in general; they may even exist within the Solar System but are too small to affect its spatial fabric and perturb planetary orbits. A Black Hole generally is so small - yet so massive - that its spacetime expression produces a curvature so pronounced that all internal energy and radiation is seemingly trapped beneath the B.H. (within its horizon). An exception may be Hawking radiation (named after Stephen Hawking who devised
the theory) consisting of particles created by quantum
processes and driven by the gravitational energy within and around the Hole. The mechanism by which this process takes place is an excellent example of "quantum weirdness". In the 'empty' space just outside the B.H.'s event horizon, virtual particles and antiparticles are constantly created (as happens in general in this environment throughout the Universe). Under the strong gravity field around the B.H., one of these particles, the one with positive energy, is likely to be propelled away while the other is captured and dragged into the B.H. Antiparticles have negative energy and those brought into the B.H. react with B.H. particles to reduce the mass of the Hole and thereby lower its gravitational field. This B.H. gravitational field, in turn, loses the energy it provided to make the virtual pair. The escaping particles constitute the Hawking radiation, which is too "faint" to be detected from Earth but nevertheless causes the B.H to slowly "evaporate".
This escaping (emitted) radiation is most effective for tiny Black Holes and provides a means by which they
can dissipate over extremely long times through this evaporation. While based on sound theoretical reasoning, Hawking radiation has not yet been directly detected. But if it is proved to exist, it provides a mechanism by which countless numbers of small primordial B.H.'s that formed at the outset of the Universe, because gravity was so intense then, have since vanished. At the present time, astrophysicists are learning more about B.H.'s by computer modeling and simulating their behavior.
Black Holes are also capable of ejecting matter in jets or streams of particles moving in beams almost at the speed of light. (Jets also occur during star formation and during late stages of star death). Here is an HST view of the well-known galaxy, M87, in which its billions of stars are not resolved so as to appear as a yellow glow. The central "star" is actually light emitted from the exterior around a B.H., probably as a Quasar. Below are three more views of the jet streamer from M87; the top is imaged by Chandra in the X-ray region; the center is visible light; and the bottom from Radio waves. The origin of such streamers, found also associated with other galaxies, is still imperfectly known. But, the Black Hole(s) causing this ejection of gas and particles are the source of strong, directional electromagnetic fields. The gases may be excited by synchrotron radiation, causing photons whose energy levels extend over most of the Electromagnetic Spectrum. Still another example of a jet associated with the presumed central Black Hole in a galaxy is Centaurus A (NGC5128) located some 11 million l.y. from Earth. On one side the jet is obvious but it has a faint companion on the other side. This jet pair lines up with the axis of rotation of the galaxy. The image, made by Chandra, is converted to a visible view using data sensed in the X-ray region of the spectrum: This jet, which follows magnetic lines, is even more splendidly displayed in an HST image that is combined with a Chandra image, as shown below, with the strongest X-ray signals shown in blue: Probably the best image to date of a paired jet associated with a supermassive Black Hole is that recently captured by HST as it trained on Quasar 3C120; the jet, composed of X-rays and electrons, follows strong magnetic lines: A jet emanating from Quasar 3C273, which is powered by a Super Black Hole, extends out 100000 light years, as seen in this color composite made from a Chandra X-ray image (blue), a HST Visible image (green), and a Spitzer IR image (red): These jets may be the same phenomena commonly detected by Radio astronomy. Galaxies are thought to have multiple Black Holes, most of which are relatively small. Evidence is growing that most spiral galaxies, at least, have one or more large Black Holes in their central regions. Such B.H.'s eem to serve as a stabilizing influence on the maintenance and evolution of a galaxy, causing stars and stellar gas and dust to migrate inward and be dragged into the Hole. Matter is constantly being attracted into the B.H. such that over time all of the galaxy will converge into the B.H. and thus be wiped out.
The first case in which two supermassive B.H.'s occur in the central core of a galaxy has been found in NGC6240. This irregular galaxy is shown in visible light in the left HST image below; the Chandra image on the right indicates a pair of Black Holes, which create a strong X-ray signal (in blue; weaker X-rays in red and yellow) as infalling material is heated to very high temperatures. Astronomers predict that these B.H.'s will eventually merge by collision. The amount of gas and dust surrounding a central Black Hole can be much greater than farther out in a galaxy. In NGC 1068 (also known as Messier 77), the HST image on the left of this next figure shows reflected light from the dust in blue, ionized Oxygen gas in yellow, and ionized Hydrogen gas in red; on the right is a Chandra image of its center in which the orange-red corresponds to highly energized material around the immediate B.H. that is emitting X-rays. The image below shows not the invisible Black Hole itself, but the radiation emitted from excitation of gases and other matter drawn into the B.H. During this continuous exposure over 164 hours, the glowing gases underwent periodic flare-ups that combine in this composite pattern: Chandra and Radio telescopy have now established that the central region of the Milky Way galaxy has a supermassive Black Hole (located in the celestial hemisphere at a point close to Sagittarius A); perhaps there is more than one in this inner part. Proof of the presence of a large B.H. in the M.W. was hard to come by, because the central region is shrouded by dust. As Infrared images of this region accrued, the stars within the dust region were imaged. This allowed determination of their orbits as time lapse views permitted calculation of their movements. Many stars showed just the pathways expected from theory that would occur if a B.H. were sucking in these bodies. Later surveys of the central region using Gamma ray and X-ray radiation to image the behavior of the B.H.-seeking stars confirmed the presence of a very large B.H. at the centerpoint of the Milky Way. However, as this Chandra image discloses, the strongly radiating dust and gas at X-ray wavelengths does not single out Sagittarius A or any other manifestation of the B.H.
The size of the M.W.'s central Black Hole has been hard to determine because of this masking matter. It mass has been estimated to be about 2.6 to 4 million solar masses. Early estimates placed the diameter of a sphere to its event horizon at about 1.5 to 23 million kilometers (1 to 14 million miles). Recently, studies done by penetrating Radio waves, using Radio telescopes, has shed light on its dimensions, so that the upper value is considered close. This Radio wave image shows Sagittarius A, a bright object that may be the glow of excited radiation around the B.H.: In principle, Black Holes should sometimes collide (but the consequences are not yet defined explicitly), especially when two galaxies collide with the B.H's at their centers then interacting. Evidence for this is sparse. However, such an event is postulated for the observations by the Wide Field Camera on HST of NGC326. In the main view below is the pattern of jet lobes from that galaxy seen a few years ago. In the offset second image is a more recent observation in which the orientation of the principal jets has now shifted more than 90°. The favored explanation is that two Black Holes have now interacted causing the spin axis of one to shift notably. As implied above, Black Holes play a large role in the life of a galaxy. Recent UV observations by the Galaxy Evolution Explorer (Galex) finds a broad relationship between B.H. size and galaxy size (the larger the first, the bigger the second; the study was confined to elliptical galaxies but probably holds true for spiral ones as well). It was also found that for large central B.H. galaxies, the production of new/young stars in the inner regions became distinctly sparse. This has been attributed to B.H.-controlled heating of Hydrogen gas to temperatures too high to form stars and/or to expulsion of the gas from the inner galaxy. A Black Hole's incredible gravity pulls in particles from outside the event
horizon until their velocities are accelerated to nearly the speed of light. Matter is literally torn apart upon entering the Black Hole. As these particles close
in, monstrous energy releases produce continuous bursts of energy outside the
horizon, a process believed responsible for most Quasars (a contractive
term for "quasi-stellar" to describe a star-like appearance even though
the observed feature is not a single star). Quasars are extremely bright objects
(very high luminosity, comparable or even exceeding that of an entire typical galaxy), being considered by most astronomers to be the glow of radiation bursts ("hot spots"
of Gamma radiation, X-rays and Visible light) from both stellar and interstellar matter continuously infalling into the central regions of active galaxies, whose cores are probably supermassive Black Holes. While the majority of Quasars are located at or near a galaxy center, some occur in the spiral galaxy arms or in the regions beyond an elliptical galaxy's core. They were initially discovered as intense Radio wave sources detected by Radio telescopes. Now it is known that most Quasars are not accompanied by Radio waves (less than 2% are dominantly Radio sources, in which that wavelength region marks energy developed by synchrotron radiation) but are instead sources of more intense, shorter wavelength radiation. Here is an HST optical image of one (and possibly several) Quasar(s):
And here is a very bright central core of a Seyfert Galaxy, NGC 3516, with a Quasar producing a huge light emission (but probably being "intensified" by gravitational lensing) associated with infall to a massive Black Hole: Quasar HE 1013-2136 at a distance of 10 billion l.y., imaged by an ESO telescope on a Chilean mountaintop, seems to be drawing gases from a galaxy to the left: This pair of images shows a Quasar in Visible (bright in the blue) and Infrared light. The powerful Quasar qso 1 Zw 1, as seen in the Infrared, is also a strong Radio source (contours superimposed). Most Quasars are so far away (but some more recent ones are nearby) that light arriving
at Earth left the Quasar source when the young Universe was only about 1/4 to 1/6 its present
size. Thus, most (estimates in excess of 75%) Quasars formed early in Universe history and many, particularly the larger ones, have since become either greatly diminished ("dormant", with occasional flare-ups) or are now extinguished in today's time frame. This generalized (smooth) plot of Quasar history, both in terms of time since the Big Bang and when the numbers of galaxies relative to the expansion size of the Universe are normalized to 1 (maximum), illustrates these points:
This distribution of quasars in time is also evident in this Sloan Sky map portrayal, in which the outer blue dots are Quasars (at that distance they are young in terms of Universe age), the red dots are Luminous Red Galaxies (clusters of elliptical galaxies), and the black dots are closer to the Milky Way and are relatively old: Since Black Holes can still form in young cosmological time, i.e., recently, throughout the Universe, conceivably they are giving rise (usually after only millions of years) to new Quasars. Quasars are made visible because of emission of light resulting from energy conversion as stars and interstellar gases are gravitationally sucked into supermassive Black Holes.
Perhaps as much as 50% of the EM radiation in the Universe is related to Quasars around Black Holes. The Quasars result from material being pulled off nearby star(s), transferred as stellar winds along magnetic lines from the stars, and accumulating in a disk around the Black Hole. A study of Chandra data for J1655 leads to this pictorial interpretation: This may be the most common mechanism for Quasar production. Very energetic quasars emit their radiation primarily in the Gamma Ray segment of the EM spectrum. Such quasars are called blazars. Here is an artist's conception of a blazar, based on telescope observations, in which there is a jet moving out of each end; in this view, the direction of look is straight down parallel with the central jet. Black Holes that occur outside galaxies, or in a star-sparse region within a galaxy, do not attract enough material to become readily visible by virtue of the excitation of incoming matter. But their presence is often suspected where an X-ray or gammma-ray source is observed without a corresponding visible body. Recently, Black Holes have been detected in Globular Clusters by analyzing the patterns of movement and velocities of stars that can be resolved in the assemblages making up the clusters. These B.H.'s have estimated masses intermediate between the small isolated ones mentioned above and the Supermassive ones described in the previous paragraph. Although the numbers of points in the following plot relating B.H. mass to stellar assemblage mass are still few, a general trend that fits size to a straight line is evident: In the early years after first postulated and then discovered, Black Holes were treated almost as a curiosity, without any special importance in the initial phases of the Universe's history. But, with the discovery that most (if not all) galaxies have B.H's in their core, there is a growing belief among astronomers that they are the necessary starting point in the formation of a galaxy, serving as the nucleus or core that attracts the matter that eventually organizes into a galaxy. Recent reports of both observational and theoretical studies now offer two important ideas: 1) both Black Holes and Neutron stars are more abundant in the inner or central part of a galaxy - a fact related to the idea that massive stars tend to form more readily in the core region; and 2) in early cosmological time Black Holes had a definite symbiotic relation to the processes that form and develop galaxies, i.e., massive B.H.'s can serve either as a nucleus for a growing galaxy or at the least aid in gathering matter into organized gas clumps that evolve into primitive galaxies. In some respects, the smallest Black Holes are
an approximation to the supersingularity postulated as the starting point of
the Big Bang except that they have finite dimensions of meters to several kilometers
and even much larger for those in galactic centers depending on their amounts
of mass (can be equivalent to the cumulate mass of hundreds of millions to billions
of Suns). One theoretical class of Black Holes consists of concentrations of extreme densities collected
in "points" as small as 10-15 meters.
Some Black Holes are thought to be the sole surviving remnants of galaxies
that have been completely swept into them. Other Black Holes may have formed
during the first seconds of the Big Bang. There are increasing indications that supermassive Black Holes were in existence within the first billion years of the Universe. Many of these are either relics of the B.B. or remnants of early Supernovae.
Speculatively, one future outcome
for the Universe (depending on the ultimate mode of expansion, after 50 b.y. or so, could be a collection of billions of Black Holes that
eventually converge upon themselves to coalesce into a single ultra-dense Black
Hole that ultimately would become the singularity for the next Universe (in
this model, any number of successive Universes, exploding and contracting cyclically,
is feasible). Such a concept of repeating Universes is referred to as the "Big Crunch", or even more colloquially,
as the "Bounce" in reference to the repetition of an explosion after total collapse
to the B.H. singularity.
Black Holes almost certainly play a role in what are called Gamma Ray Bursts (GRB). These are the most intense and copious releases of energy observed in the Universe - less than that of the Big Bang itself but much more than given out by Supernovae or Quasars. GRBs can at their outset release enough energy to give them a luminosity calculated to be 1019 greater than that of the Sun. They are characterized by extreme outputs over very brief periods, measured in seconds to minutes at their peak. At least one GRB is observed each day somewhere in the Universe, so they are rather common events, albeit less frequent than Supernovae. Despite being the largest rapid release high energy events in the Cosmos, GRBs were unknown (sometimes mistaken for ordinary Supernovae) before 1967. The manner in which they were discovered is an interesting example of serendipity: Nuclear explosions on Earth release large quantities of Gamma ray energy. In the 1960s, the U.S. was seeking ways to detect Soviet nuclear tests, so it built and orbited Gamma ray, X-ray, and neutron detectors on military satellites. In the U.S. Air Force Vela program, the Vela-4 satellite detected many Gamma ray events, all at times that failed to correlate with any known nuclear blasts on Earth. These Gamma ray events were all proved (eventually) to emanate from well beyond Earth. Here is a plot of one of the first records: GRBs give off tremendous amounts of energy extending through all wavelengths of the EM spectrum. The diagnostic signature of the GRB that separates it from Supernovae is the predominance of high energy Gamma rays over very short time periods. GBRs can be subdivided into two types: short burst (around 2 seconds) and long burst (more 2 seconds; initial emissions on the order of 20-30 seconds, with a few extending up to an hour). This time spike has been observed in GRBs detected by more sophisticated sensors that monitored such events. Thus, this example: These GRBs puzzled astrophysicists. They were first thought to be in the Milky Way. And in fact some were actually located in our galaxy, where they occur on average about once in 10000 years. Afterglow radiation from one such event was observed on February 28, 1997 in the M.W. itself by an Italian X-ray satellite called BeppoSAX: But, the frequency of occurrence, which as more observations were confirmed indicates at least one GRB every day, suggested that the vast majority of GRBs were located in galaxies well beyond the Milky Way. As more records of these events accumulated, it became evident that GRBs are not concentrated in specific regions of the sky but are distributed at random (isotropic) over the entire sky. GRB's are also randomly distributed in time - occurring anywhere in the Universe (thus over the full extent of time since the first galaxies). A large number seem to be distant, near the outer part of the observed Universe, and hence were most common in the early history of the Universe. Here is a map of the sky showing many of the larger GRBs, as detected by the Compton Gamma Ray Observer and BeppoSAX. The BATSE (Burst and Transient Source Experiment) instrument on the Compton Gamma Ray Observatory (CGRO; see page 20-4) was particularly suited to detecting GRBs. Here is one image of an event that occurred several billion light years away: These GRB events should generate radiation at wavelengths longer than those of Gamma rays. As studies of them expanded, traces of individual events were sought by other satellites that monitor at different wavelengths. The problem is that evidence of a GRB diminishes rapidly at shorter wavelengths. However, in time such events were picked up at various wavelengths when alerts were given and the sky locations established. Now, with experience this is the time frame for durations of GRBs over a range of wavelengths: These signs of lower levels of energy at longer wavelengths persisting around a GRB are grouped under the general term "afterglow". X-rays proved useful as GRB signatures provided the searching satellite(s) could check out the source region within a few days. The X-ray emissions persist over periods of hours to days. This is one X-ray image of a presumptive GRB that was located in a galaxy nearby (some has classified this as a hyperNova): Images acquired by BeppoSAX were especially helpful in the sky survey for GRBs. The top illustration consists of two intensity contoured images typical of X-ray renditions; note the reduction in intensity in just four days between February 28 and March 3 (right). Below it is a pair of BeppoSAX images taken first on December 15, showing the GRB as a bright dot and then on December 16 as the afterglow had faded away.
Special attention was given to finding GRBs at visible (optical) wavelengths, since these are especially capable of measuring red shifts by which approximate distance to the source can be estimated. About half the GRBs give off light in the Visible for durations of a week or more. The HST and the Keck Observatory in Hawaii were pointed at targets reported by other observing satellites. Here is the HST image of event GRB 000301c. A ground telescope imaging of another GRB shows the burst as seen in visible light (here the print is a negative) at 21 hours (left) and 8 days (right) after first detection. The rapid fading of the galaxy-sized feature is evident (note arrows) Although not used a lot for this purpose, Radio telescopes have detected and imaged GRBs. Here is one made by the VLA group:
One very important GRB event led to some intriguing information that indicates that this phenomenon occurred much more often early in cosmic time (but continues til the present) and helps to confirm the huge amounts of energy involved. Its magnitude is equivalent to 100 million billion solar radiances. On December 14, 1997 the CGRO registered this event. Word was sent to BeppoSAX operators and to the HST and Keck telescopes to look for it as rapidly as possible. All succeeded. This is how the event was imaged by the HST: The image on the right was taken on January 23, 1999 during its maximum. When a redshift distance measurement was made on the GRB, it was found to be some 12 billion light years from Earth, proving the surmise that GRBs have probably been part of the Universe's history since soon after the Big Bang. It was also the brightest object yet found at that far distance from Earth. Thus, the pattern found for most GRB events is rapid emission of Gamma rays followed, as they fade, by the dominant radiation passing through X-ray, Visible, and Radio wavelengths, with the whole sequence being over in less than a few months. GRBs are of such high interest that another dedicated satellite has been placed in orbit to look for these and similar events. This is HETE-2, the High Energy Transient Explorer, launched October 9, 2000 (the first HETE failed to separate from its third stage rocket). The cause(s) of GRBs continues to be uncertain and tantalizing. As an aid to the following discussion, use this Fireball Model to provide a framework for the starting energy, the expansion of the GRB, and the time involved in reaching the afterglow phase:
The early idea of the explosion of material sucked in and around a neutron star (see top illustration on this page for a similar example) has been challenged. But, a variant postulates a role for a binary pair of Neutron stars which, if they should collide, should produce a huge release of energy. Still others attribute the GRBs to some involvement with Quasars. One school holds them to be the outcome of giant Supernovae (Hypernovae) which generate very powerful short-time energy release levels. A recent hypothesis takes still a new tack - the GRBs are associated with large clusters of galaxies which together have such a strong gravitational pull that they accelerate matter both within and around the galaxies to high speeds that, upon colliding with intergalactic matter, release energy at the Gamma-ray level. Another hypothesis, known as the Paczynski Model (also known as a Collapsar event) and now the most favored explanation, starts with a supermassive (type O) rotating star that collapses to form a Black Hole that continues to draw more material around it until a critical state is reached that requires an intense Supernova-like explosion producing the GRB fireball. Essentially, all the mass involved is suddenly converted to energy in obeyance to the Einstein E = mc2 relation. There are indications that this energy release may be directed, something like the beam associated with a Pulsar. Calculations show that if such a beam generated from a GRB destruction of a neighboring massive star in the Milky Way were to strike the Earth, the intensity would destroy everything at and above the surface - oceans, vegetation, atmosphere, life (fortunately, the probability of this happening, both in terms of star sizes and of directionality of the beam, is considered quite low).
In fact, until the release of information in June 2004 about a GRB only 35000 l.y. away - either in or just outside the M.W. - no nearby events had ever been confirmed. The image below shows W49B as a color composite made from Chandra X-ray data (blue), and Palomar telescope images taken in the IR (green and red). The estimated initial release of energy over a 1 minute time span is 1013 greater than that of the Sun in that timeframe. The image represent the GRB status soon after the burst; the colors indicate enrichment in Iron. The postulated beam associated with collapsar events was not oriented straight at the Earth and hence is not visible here. Some of the above information has been extracted from an article in the December 2002 edition of Scientific American, entitled "The Brightest Explosions in the Universe", by N. Gehrels, L. Piro, and P. Leonard. The article contains this illustration that summarizes the authors' ideas on the formation of GRBs: In their model, similar to some others proposed, GRBs are definitely associated explosive processes that will end up forming Black Holes. In one common mechanism, a massive star collapses and explodes as a Hypernova, leading to a disk of matter/energy surrounding a Black Hole; this is a fast process in the sense that at a critical time, the Hypernova ensues without anything discernible obviously leading up to it. Alternatively, over a long span of time (millions of years, the same end result could occur as two neutron stars mutually orbiting finally crash into each other. The wedge to the right of the 'Central Engine' conforms to a jet that carries the photons released in the GRB outward at near light-speed. This material moves outward as "blobs" that catch-up and coalesce forming internal shock waves that generate the Gamma bursts. With expansion over time, the high energy photons are replaced by those of progressively lower energies represented by X-rays, Visible light, and Radio waves as the emissions encounter the galactic/intergalactic medium. The final result is an afterglow that fades over time. On March 29, 2003, HETE-2 captured a GRB (HETE Burst H2652 is also listed as GRB 030329 and SN2003dh) in a galaxy 2.6 billion light years distant and sent the occurrence of this event back to Earth so quickly that many observatories were alerted quick enough to train their telescopes on it within minutes. Thus, for the first time the earliest stages of a GRB could be monitored. This event proved one of the brightest ever observed. This plot of HETE data shows how brief was the main phase of the event.
The SWIFT satellite obtained this image of GRB 030329: A Radio telescope image of this GRB taken on April 22 shows a progressive distribution of decreasing energy moving outward. This seems to confirm the "fireball" model for ejection of matter (an alternate explanation, that material is ejected in huge blobs [the "cannonball" model], is apparently not valid for this observation). The expelled material moves at nearly the speed of light. Spectrographic data showed that the initial burst of H2652 was rich in excited Silicon and Iron. These elements would be produced in a star whose mass is at least 30x that of the Sun, which would give rise to temperatures and pressures that generate nuclear reactions that fuse nuclei into Si and Fe. These are the conditions that favor a "super-Supernova", another way of referring to hyperNovae. Astronomers believe this is convincing evidence for that mode of generation of many (perhaps most) GRBs. As knowledge of the roles of the predominant dark matter and dark energy (see pages 20-9 and 20-10) is increasing, another explanation (Louis Clavelli) - somewhat conjectural - has emerged. This holds that dark energy under the right conditions acts upon ordinary matter to convert it to dark matter. From theory, this should give off intense bursts of energy as the conversion proceeds, witnessed by us as GRBs. Another space telescope dedicated to GRB detection is NASA's SWIFT, launched on November 20, 2004. This spacecraft has three detection systems that can be activated within minutes of the one always on that picks up the Gamma-radiation. SWIFT is capable of finding and monitoring as many as 2 GRBs per week, far more than previous instruments, and will follow the changes to the stage when Black Holes as the end product is reached. SWIFT also can "see" back to the early days of the Universe out to almost 14 billion light years away. The spacecraft and its three telescopes are shown here: In January, 2005 9 GRB events were detected by SWIFT. The first detection was in December, 2004, as shown below as an energy plot and the actual image derived from the data: The four panels in the illustration below show sequential steps in a gamma ray burst: As mentioned above, GRBs are all short-lived, even in human terms, lasting from hundreds of seconds to a few days. One very short duration type, which releases much less energy, is known as Gamma rays flashes; this lasts for milliseconds to a few seconds. These have been observed by SWIFT and by earth-based telescopes. Their cause(s) may be Neutron star pair interactions but other mechanisms have not been ruled out. Here are several that occurred simultaneously: Problems with explaining GRBs are compounded by observations (using
EGRET, NASA's orbiting Energetic Gamma Ray Experiment Telescope, part of the Compton X-ray Observatory) of about 170 sources of continuously emitting high energy Gamma rays. Thus, these do not display short-lived bursts. This class was first discovered by the Compton Gamma Ray Observatory (page 20-3). They may be associated with clumps of supersymmetric particles including a type called the neutralino. Needless to say, GRBs continue to fascinate cosmologists since they represent the largest and fastest explosive events beyond that of the Big Bang itself. As they are better understood, they may reveal the action of physical processes only now being speculated upon, and suggested by particle physics experiments. The next big step in studying GRBs and the continuous types will be the launch of GLAST (Gamma-ray Large Area Space Telescope), perhaps as early as 2007.
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