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Black Hole

magnum

IndoForum Activist C
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Lubang hitam adalah sebuah pemusatan massa yang cukup besar sehingga menghasilkan gaya gravitasi yang sangat besar. Gaya gravitasi yang sangat besar ini mencegah apa pun lolos darinya kecuali melalui perilaku terowongan kuantum. Medan gravitasi begitu kuat sehingga kecepatan lepas di dekatnya mendekati kecepatan cahaya. Tak ada sesuatu, termasuk radiasi elektromagnetik yang dapat lolos dari gravitasinya, bahkan cahaya hanya dapat masuk tetapi tidak dapat keluar atau melewatinya, dari sini diperoleh kata "hitam". Istilah "lubang hitam" telah tersebar luas, meskipun ia tidak menunjuk ke sebuah lubang dalam arti biasa, tetapi merupakan sebuah wilayah di angkasa di mana semua tidak dapt kembali. Secara teoritis, lubang hitam dapat memliki ukuran apa pun, dari mikroskopik sampai ke ukuran alam raya yang dapat diamati.

Teori Lubang Hitam pertama kali diperkenalkan oleh astronom Jerman bernama Karl Schwarzschild, pada tahun 1916, dengan berdasar pada teori relativitas umum dari Albert Einstein, dan semakin dipopulerkan oleh Stephen William Hawking. Pada saat ini banyak astronom yang percaya bahwa hampir semua galaksi dialam semesta ini mengelilingi lubang hitam pada pusat galaksi.

f6e20ce7.jpg



Mathematical theory


Black holes are predictions of Albert Einstein's theory of general relativity. There are many known solutions to the Einstein field equations which describe black holes, and they are also thought to be an inevitable part of the evolution of any star of a certain size. In particular, they occur in the Schwarzschild metric, one of the earliest and simplest solutions to Einstein's equations, found by Karl Schwarzschild in 1915. This solution describes the curvature of spacetime in the vicinity of a static and spherically symmetric object, where the metric is,
0c8c5222.png

where
5ba344ce.png
is a standard element of solid angle.

According to general relativity, a gravitating object will collapse into a black hole if its radius is smaller than a characteristic distance, known as the Schwarzschild radius. (Indeed, Buchdahl's theorem in general relativity shows that in the case of a perfect fluid model of a compact object, the true lower limit is somewhat larger than the Schwarzsschild radius.) Below this radius, spacetime is so strongly curved that any light ray emitted in this region, regardless of the direction in which it is emitted, will travel towards the centre of the system. Because relativity forbids anything from traveling faster than light, anything below the Schwarzschild radius – including the constituent particles of the gravitating object – will collapse into the centre. A gravitational singularity, a region of theoretically infinite density, forms at this point. Because not even light can escape from within the Schwarzschild radius, a classical black hole would truly appear black.

The Schwarzschild radius is given by
9aa7436f.png


where G is the gravitational constant, m is the mass of the object, and c is the speed of light. For an object with the mass of the Earth, the Schwarzschild radius is a mere 9 millimeters — about the size of a marble.

The mean density inside the Schwarzschild radius decreases as the mass of the black hole increases, so while an earth-mass black hole would have a density of 2 × 10(30) kg/m(3), a supermassive black hole of 10(9) solar masses has a density of around 20 kg/m(3) less than water! The mean density is given by
899201b2.png


Since the Earth has a mean radius of 6371 km, its volume would have to be reduced 4 × 1026 times to collapse into a black hole. For an object with the mass of the Sun, the Schwarzschild radius is approximately 3 km, much smaller than the Sun's current radius of about 696,000 km. It is also significantly smaller than the radius to which the Sun will ultimately shrink after exhausting its nuclear fuel, which is several thousand kilometers. More massive stars can collapse into black holes at the end of their lifetimes.

The formula also implies that any object with a given mean density is a black hole if its radius is large enough. If the visible universe has a mean density equal to the critical density, then it is a black hole.
More general black holes are also predicted by other solutions to Einstein's equations, such as the Kerr metric for a rotating black hole, which possesses a ring singularity. Then we have the Reissner-Nordström metric for charged black holes. Last the Kerr-Newman metric is for the case of a charged and rotating black hole.

There is also the Black Hole Entropy formula:
76709ac7.png


Where A is the area of the event horizon of the black hole, \hbar is Dirac's constant (the "reduced Planck constant"), k is the Boltzmann constant, G is the gravitational constant, c is the speed of light and S is the entropy.

A convenient length scale to measure black hole processes is the "gravitational radius", which is equal to
8ed1d6ab.png


When expressed in terms of this length scale, many phenomena appear at integer radii. For example, the radius of a Schwarzschild black hole is two gravitational radii and the radius of a maximally rotating Kerr black hole is one gravitational radius. The location of the light circularization radius around a Schwarzschild black hole (where light may orbit the hole in an unstable circular orbit) is 3rG. The location of the marginally stable orbit, thought to be close to the inner edge of an accretion disk, is at 6rG for a Schwarzschild black hole.


Sebenernya masih panjang,coba kita bahas!Bagaimana Menurut anda??
 
Panjang amat.....Lubang hitam menyedot planet atau bitang di sekitar nya kan???
trowongan kwantum kayak di star wars dong pas waktu mencapai kecepatan cahaya....
kayak di doraemon jg /heh
 
Not only planet .. Not even a single light can escape from the blackhole .. LOL
But wait ..
What about a White Hole and Worm Hole?! Yang kerapkali dipertanyakan sebagai bahan dasar penelitian mesin waktu dan teori nya oleh Stephen Hawkings ..

Anyone willing to discuss? o.O

Thanks.
Th0R
 
yap gw juga denger ttg White Hole,tp yg paling banyak orang tau Black Hole,mari kita bahas semua nya termasuk Worm Hole sbg teori mesin waktu....

White Hole
In astrophysics, a white hole is a postulated celestial body that is the time reversal of a black hole. While a black hole acts as a point mass that attracts and absorbs any nearby matter, a white hole acts as a point mass that repels or even (perhaps) ejects matter

Origin

White holes appear as part of the vacuum solution to the Einstein field equations describing a Schwarzschild wormhole. One end of this type of wormhole is a black hole, drawing in matter, and the other is a white hole, emitting matter. While this gives the impression that black holes in this universe may connect to white holes elsewhere, this turns out not to be the case for two reasons. First, Schwarzschild wormholes are unstable, disconnecting as soon as they form. Second, Schwarzschild wormholes are only a solution to the Einstein field equations in vacuum (when no matter interacts with the hole). Real black holes are formed by the collapse of stars. When the infalling stellar matter is added to a diagram of a black hole's history, it removes the part of the diagram corresponding to the white hole

The existence of white holes that are not part of a wormhole is doubtful, as they appear to violate the second law of thermodynamics.

Quasars and active galactic nuclei are observed to spew out jets of matter. This is now believed to be the result of polar jets formed when matter falls into supermassive black holes at the centers of these objects. Prior to this model, white holes emitting matter were one possible explanation proposed.


Recent Developments

A more current view of white holes takes into consideration a revision to the standard model of the big bang theory which states that the big bang is an explosion that happens within a black hole, with the expansion that follows the traditional interpretation of the big bang, expanding into infinite space inside the black hole. Or in other words, a miniature universe is created at the core of the black hole, which expands into extra dimensions outside of this universe. The expansion taking place in this new miniature universe, if it could be perceived from an observer from this universe, could be looked at as a white hole. Matter that could not escape the intense gravitational pull of the black hole in this universe is instead sent speeding into the newly expanding baby universe. Using that logic, one could assume that our universe itself is a white hole. Hypothetically, this model could be used to explain the increasing rate of expansion of this universe: as matter from our parent universe is engulfed by our parent black hole (the black hole that created our universe), our own universe is fed this matter which could possibly have something to do with dark matter and dark energy, which currently is thought to contribute to the increase in the rate of our universe's expansion.

In addition, many argue that white holes violate the second law of thermodynamics which states that:

"Heat cannot of itself pass from a colder to a hotter body" and "the entropy of an isolated system not at equilibrium will tend to increase over time, approaching a maximum value."

Since we are not direct observers of the other universe, some argue that it is hard to say whether or not the point of origin in the black hole would actually be colder than the newly expanding miniature universe (white hole). If the point of origin in the black hole is hotter, then matter and energy could flow towards the white hole.

Regarding the second part of the second law of thermodynamics, if we consider our universe as being directly connected to the miniature universe, then they both constitute the same isolated system. If anything, black holes by themselves without an exit point violate the second law. Black holes are points at which entropy is reversed. The entropy that exists in our solar system is greater than that of which is in a black hole, which continues to lower entropy by engulfing and trapping everything within its grasp. By including the possibility of entropy continuing to increase in a newly defined miniature universe within our own, this seems to satisfy the second law, not contradict it. This view, looks at the black hole not as an object which actually lowers entropy, but more like the opening of a narrow pipeline which appears to lower entropy from the viewpoint of someone observing the black hole and only the black hole. Using an analogy to explain this better, picture a black hole as a bath tub (analogous to the event horizon) and a drain (analogous to the center of the black hole) in a shower. Matter is analogous to the particles of water coming down from the shower head (which could itself also be equivalent to the original feeding of our universe with matter from the initial opening of our parent black hole). As the water particles (matter) hit the tub (event horizon), they begin to merge together and exit the tub through the drain (black hole). As more and more water accumulates in the tub (if the tub is slow draining), water appears to focus its accumulation at the drain opening. This represents a lowering of entropy. The water particles are closer together and more organized at the drain opening than they are in the tub or flying through the air. To the observer looking only at the tub drain, and not knowing that the drain leads anywhere, it appears as if the drain (black hole) has reversed the entropy of the isolated system, or in other words it is acting as a collecting basin. Had the drain been extremely large, this reversal of entropy would not have appeared to have been as great. In other words, this is only a conditional reversal of entropy. The big picture is that the drain leads to a sewer (our spawned miniature universe) where the same water particles which were close together in the shower head, further apart in the air (our universe), again close together in the tub, drain and drain pipe, are now spread out even further than before and mixed in with the rest of the water in the sewer, resulting in a much larger increase in entropy of the original particles involved.


White Holes in Science Fiction

White holes have long been speculated about in science fiction, see White holes in fiction.

BBC comedy series Red Dwarf has an episode based around a white hole in the episode white hole.


Worm Hole
In physics, a wormhole (also known as Abbreviated Space) is a hypothetical topological feature of spacetime that is essentially a "shortcut" or "abbreviation" through space and time. A wormhole has at least two mouths which are connected to a single throat. If the wormhole is traversable, matter can 'travel' from one mouth to the other by passing through the throat.

The name "wormhole" comes from an analogy used to explain the phenomenon. If a worm is travelling over the skin of an apple, then the worm could take a shortcut to the opposite side of the apple's skin by burrowing through its center, rather than travelling the entire distance around, just as a wormhole traveller could take a shortcut to the opposite side of the universe through a hole in higher-dimensional space.


dcef98c3.jpg

3D analogy to a wormhole.
b4e78306.png

Realistic view of a wormhole as seen by an observer crossing the horizon of a Schwarzschild black hole. The observer originates from the right, and another universe becomes visible in the center of the black hole shadow once the horizon is crossed. This new region is however unreachable in the case of a Schwarzschild black hole, and will disappear in an infinite redshift as the observer ultimately hits the singularity.

Definition

There is a compact region of spacetime whose boundary is topologically trivial but whose interior is not simply connected. Formalizing this idea leads to definitions such as the following, taken from Matt Visser's Lorentzian Wormholes:

If a Lorentzian spacetime contains a compact region Ω, and if the topology of Ω is of the form Ω ~ R x Σ, where Σ is a three-manifold of nontrivial topology, whose boundary has topology of the form dΣ ~ S², and if furthermore the hypersurfaces Σ are all spacelike, then the region Ω contains a quasipermanent intra-universe wormhole.


Wormhole types


Intra-universe wormholes connect one location of a universe to another location of the same universe (in the same present time). A wormhole should be able to connect distant locations in the universe by bending spacetime, allowing travel between them that is faster than it would take light to make the journey through normal space. See the image above. Inter-universe wormholes connect one universe with another [1], [2]. This gives rise to the speculation that such wormholes could be used to travel from one parallel universe to another. A wormhole which connects (usually closed) universes is often called a Schwarzschild wormhole. Another application of a wormhole might be time travel. In that case it is a shortcut from one point in space and time to another. In string theory a wormhole has been envisioned to connect two D-branes, where the mouths are attached to the branes and are connected by a flux tube . Finally, wormholes are believed to be a part of spacetime foam There are two main types of wormholes: Lorentzian wormholes and Euclidean wormholes. Lorentzian wormholes are mainly studied in semiclassical gravity and Euclidean wormholes are studied in particle physics. Traversable wormholes are a special kind of Lorentzian wormholes which would allow a human to travel from one side of the wormhole to the other. Sergey Krasnikov tossed the term spacetime shortcut as a more general term for (traversable) wormholes and propulsion systems like the Alcubierre drive and the Krasnikov tube to indicate hyperfast interstellar travel.

Characterizing inter-universe wormholes is more difficult. For example, one can imagine a 'baby' universe connected to its 'parent' by a narrow 'umbilicus'. One might like to regard the umbilicus as the throat of a wormhole, but the spacetime is simply connected.

Theoretical basis

It is unknown whether (Lorentzian) wormholes are possible or not within the framework of general relativity. Most known solutions of general relativity which allow for wormholes require the existence of exotic matter, a theoretical substance which has negative energy density. However, it has not been mathematically proven that this is an absolute requirement for wormholes, nor has it been established that exotic matter cannot exist.

Recently Amos Ori envisioned a wormhole which allowed time travel, did not require any exotic matter, and satisfied the weak, dominant, and strong energy conditions . Since there is no established theory of quantum gravity, it is impossible to say with any certainty whether wormholes are possible or not within that theoretical framework.


Traversable wormholes

Lorentzian traversable wormholes would allow travel from one part of the universe to another part of that same universe very quickly or would allow travel from one universe to another universe. Wormholes connect two points in spacetime, which means that they would allow travel in time as well as in space.

Wormholes and faster-than-light space travel

Often there is confusion about the idea that wormholes allow superluminal (faster-than-light) space travel. In fact there is no real superluminal travel involved. Assume that the wormhole connects two remote locations. While traveling through a wormhole, subluminal (slower-than-light) speeds can be used. The time in which the distance was traveled would appear less (due to the fact that it goes through a line(a-b) in a curved space instead of going through space outside of the wormhole, which is like going through the center of an apple rather than going around it on the outside, hence the name wormhole) than it would take light to make the journey through normal space. In other words, while you might need to run to get around a mountain in a certain time, you can walk comfortably if there is a tunnel through the center; no additional speed is needed, because the subjective distance is shorter.

Wormholes and time travel

A wormhole could allow time travel. This could be accomplished by accelerating one end of the wormhole relative to the other, and then sometime later bringing it back; relativistic time dilation would result in less time having passed for the accelerated wormhole mouth compared with the stationary one, meaning that anything which entered the stationary wormhole mouth would exit the accelerated one at a point in time prior to its entry. The path through such a wormhole is called a closed timelike curve, and a wormhole with this property is sometimes referred to as a "timehole."

It is thought that it may not be possible to convert a wormhole into a time machine in this manner: some mathematical models indicate that a feedback loop of virtual particles would circulate through the timehole with ever-increasing intensity, destroying it before any information could be passed through it. This has been called into question by the suggestion that radiation would disperse after traveling through the wormhole, therefore preventing infinite accumulation. There is also the Roman ring, which is a very stable configuration of more than one wormhole. This ring allows a closed time loop with stable wormholes. The debate on this matter is described by Kip S. Thorne in the book Black Holes and Censorship Hypothesis.


Schwarzschild wormholes

Wormholes known as Schwarzschild wormholes or Einstein-Rosen bridges are bridges between areas of space that can be modelled as vacuum solutions to the Einstein field equations by sticking a model of a black hole and a model of a white hole together. However, this type of wormhole is unstable enough to pinch off instantly as soon as it forms.

While the equations of General Relativity suggest that a Schwarzschild wormhole could be stabilized by holding its "throat" open with exotic matter (material that has negative mass), it would still be impossible for a traveller to go through this type of wormhole because they can only go through an event horizon in one direction, and both ends of the hole have an event horizon. This leaves the traveller trapped in the middle of the wormhole.

Before the stability problems of Schwarzschild wormholes were apparent, it was proposed that quasars were white holes forming the ends of wormholes of this type.


Wormhole metrics


Theories of wormhole metrics describe the spacetime geometry of a wormhole and serve as theoretical models for time travel. A simple example of a (traversable) wormhole metric is the following:
6d1ca778.png


One type of non-traversable wormhole metric is the Schwarzschild solution:

316b5f23.png




As a tear in spacetime


If we consider spacetime (with masses causing warps in it) and accept that gravity waves are possible, which modern physics does, it would be possible to shear spacetime so much that it would tear, albeit using impossible materials.

Taking a torus of neutronium (material with the density of a neutron star) roughly 1 astronomical unit in diameter and raising it to several exavolts static charge would cause a massive disruption in spacetime. If the experimenter was to then spin this torus to give the outside edge an angular velocity measurable in percentages of c then spacetime within the torus should then twist, and tear. Where or even if it would "appear" on the "other end" is open to speculation.

Naturally, the problems of such a device are insurmountable. Such a massive amount of neutronium would instantly collapse and cause a very energetic rebound of its own gravitational energy, perhaps exceeding the power output of a supernova. It follows that the builders must have expended that much energy in creating the device to begin with.

It may be possible that such wormholes, as tears in spacetime, occur naturally. The coalescing of two black holes or neutron stars should give similar conditions in the seconds before their merging.


d1942700.jpg

Wormholes in fiction

Wormholes are a popular feature of science fiction as they allow interstellar travel within human timescales. It is common for the creators of a fictional universe to decide that faster-than-light travel is either impossible or that the technology does not yet exist, but to use wormholes as a means of allowing humans to travel long distances in short time periods. Military science fiction (such as the Wing Commander games) often use a "jump drive" to propel a spacecraft between two fixed "jump points" connecting solar systems. Connecting solar systems in a network like this results in a fixed "terrain" with choke points that can be useful for constructing plots related to military campaigns. The Alderson points postulated by Larry Niven and Jerry Pournelle in Mote in God's Eye and related novels is an especially well thought out example. The development process is described by Niven in N-Space, a volume of collected works. David Weber has also used the device in the Honorverse and other books such as those based upon the Starfire universe, and has described a 'history' of development and exploitation in several essays in collections of related short stories. Naturally occurring wormholes form the basis for interstellar travel in Lois McMaster Bujold's Vorkosigan Saga; the world of Barrayar was isolated from the rest of human civilization for centuries after the connecting wormhole collapsed, until a new route was discovered, and they are the frequent subject of political plots and military campaigns.They are also used to create an Interstellar Commonwealth in Peter F. Hamilton's Commonwealth Saga.

Wormholes feature prominently in the television series Farscape. They are the cause of John Crichton's presence in the alien universe, as well as the reason for many of the events that subsequently take place. In Stargate SG-1 and Stargate Atlantis, a wormhole is created by a Stargate, and as opposed to other science fiction programs, many of the technical issues facing wormhole travel are addressed.

In the science fiction series Sliders, a wormhole (or vortex, as its called in the show) is used to travel between parallel world, and one is seen at least once or twice in every episode

Wormholes are a common feature in the computer game Elite in which they are short-lived constructs created on-demand by the hyper-drive as a means of interstellar transport.

Wormholes are also seen in the computer game Freelancer, commonly referred as jump holes. They are supposed to be black hole-like formations with ultra-high gravity amounts, that work like 'portals' for players to travel instantly between different star systems.
 
Wah, makin menarik nih ceritanya tentang kosmologi /no1
 
yap cosmologi/astronomi selalu menarik,apalagi seiring dgn berkembang nya teknologi...
 
Menarik kalau dibaca pelan2 /heh
 
translate ke toggletext coba masukin kata2 nya atau masukin Link ini coba dia translate..
 
yah emang ada yg ngaco,translate nya harus di perhatikan,grammar nya ngka bagus.....
 
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