Black Body
Black Body
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 Nikon FTN Black Body  US $125.00
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 BLACK Nikon F Apollo 35mm Body Photomic FTN Finder US $253.26
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 Nikon F3 HP Body Black w MD 4 Motor Drive US $147.00
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 Canon EOS 1000D DSLR 18 55mm Lens Kit Used US $355.00
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 Camera handmade FED KGB WOOD BLACK EXC COPY LEICA US $110.00
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 Leica M6TTL 058 BLACK rangefinder body Excellent US $999.00
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 Camera handmade FED STALINETS WOOD BLACK copy leica US $110.00
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 25X Tele Converter for Olympus E P1 E P2 E PL1 Ring US $51.99
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 Mamiya Sekor 500 DTL Body Case and user manual US $2.25
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 Padded Camera Strap for Canon T2i T1i 40D 50D 7D XS XSi US $6.99
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 Padded Camera Strap for Nikon D3000 D80 D200 D300s D3 US $6.99
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 Padded Camera Strap for Nikon D90 D5000 D300 D700 D60 US $6.99
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 Nikon FM 35mm Black SLR Camera Body NR 137121 US $41.05
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 Padded Camera Strap for Nikon D90 D5000 D300s D60 D700 US $12.99
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 Camera FED FED WOOD EXCELLENT BLACK handmade COPY LEICA US $105.00
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 Canon EOS EOS 400D Rebel Xti Body only 101 Megapixel US $350.00
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 Leica M8 Black Digital Rangefinder Body M 8 NR 139912 US $2,026.00
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 Mini DV DVR Pocket Sports Video Spy Camera DC MD80 BOX US $8.51
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 Converter Adapter for Canon FD Lens to EOS EF Body L1O US $27.39
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 Sony Cyber shot DSC T200 81 Megapixel Black US $41.00
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 Nikon Coolpix S550 10MP Graphite Black Digital Camera US $73.26
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 Olympus OM1 Black Body Version US $40.14
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 Nikon D70 Body only 61 Megapixel US $202.50
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 Nikon Coolpix S8000 Black Compact Digital Camera USA US $192.50
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 Polaroid Presto Rainbow SX 70 Works Brown Black body US $15.00
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 Nikon Coolpix S570 12MP Black VR Digital Camera USA US $50.13
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 CANON EOS 50 FILM 35mm SLR CAMERA w SIGMA 28 80 LENS US $239.00
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 Leica M8 103MP Digital Rangefinder Camera Body Black US $.01
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 NICE BLACK NIKON EM 35MM SLR CAMERA BODY W NIKON CASE US $9.99
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 2x PHOTO SOFTBOX CONTINUAL LIGHTING 8 LIGHT STUDIO KIT US $110.95
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 Yashica Electro 35 GS Camera 3 Lenses Accessories US $39.99
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 LCD Battery Grip For Nikon D300 D700 2×EN EL3EIR B6T US $99.99
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 Soviet Contax copy KIEV 4A BLACK w Jupiter 8M EXC US $88.00
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 Sony Cyber shot DSC M1 51 Megapixel US $80.00
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 CAMERA BAG 4 Canon EOS 450D 300D 7D 50D 500D 550D 1000D US $20.11
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 Nikon F2 Black Body no Finder US $70.51
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 Carl Zeiss Jena 1Q Triotar T 135mm F4 135 4 M42 mount US $52.00
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 Nikon FE Black w 43 86mm AI Zoom MD 12 Motor Drive US $145.00
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 CANON EOS REBEL 2000 35mm Film Camera Body Strap US $12.99
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 CANON EOS REBEL G 35mm Film Camera Body Manual US $14.99
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 FED 2 camera BODY BLACK color Leica copy US $38.99
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 Nikon EL2 EL 2 Black Body 35mm SLR MF manual US $79.95
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 vintage early57 Pentax Takumar tele camera lens chrome US $32.91
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 SLR Camera Case Bag for Canon 450D 500D 400D 5D Mark II US $7.73
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 Canon PowerShot SX210IS 141 MP Digital Camera Black US $299.99
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 NIkon D700 Black 12MP Digital SLR US $1,810.00
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 PENTAX SPOTMATIC 35mm VINTAGE CAMERA SUPER TAKUMAR US $24.00
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 Nikon D80 102MP Digital SLR Camera Body Only Black US $350.00
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 Mini DV DVR Sports Video Camera SPY Camcorder MD80 DC US $.99
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 Nice Nikon FG Camera Black Body Excellent Condition US $75.00
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The Black Hole
According to the general theory of relativity, a black hole is a region of space from which nothing, including light, can escape. It is the result of the deformation of spacetime caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black body in thermodynamics. Under the theory of quantum mechanics black holes possess a temperature and emit Hawking radiation.
Despite its invisible interior, a black hole can be observed through its interaction with other matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space. Alternatively, when gas falls into a stellar black hole from a companion star, the gas spirals inward, heating to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and Earth-orbiting telescopes.
Astronomers have identified numerous stellar black hole candidates, and have also found evidence of supermassive black holes at the center of galaxies. After observing the motion of nearby stars for 16 years, in 2008 astronomers found compelling evidence that a supermassive black hole of more than 4 million solar masses is located near the Sagittarius A* region in the center of the Milky Way galaxy.
Black holes have never been directly observed, though predictions of their effects have matched observations. There exist a handful of alternate theories, such as Magnetospheric Eternally Collapsing Objects (MECOs), to explain these observations, most of which avoid the spacetime singularity at the center of the black hole, but the vast majority of physicists believe that the black hole explanation is the most likely physical representation of what is taking place.
Black Holes Before Relativity
In the 1700s, there were some who proposed that a supermassive object might draw light into it. Newtonian optics was a corpuscular theory of light, treating light as particles.
John Michell published a paper in 1784 predicting that an object with a radius 500 times that of the sun (but the same density) would have an escape velocity of the speed of light at its surface, and thus be invisible. Interest in the theory died in the 1900s, however, as the wave theory of light took prominence.
When rarely referenced in modern physics, these theoretical entities are referred to as "dark stars" to distinguish them from true black holes.
Black Holes from Relativity
Within months of Einstein's publication of general relativity in 1916, the physicist Karl Schwartzchild produced a solution to Einstein's equation for a spherical mass (called the Schwartzchild metric) ... with unexpected results.
The term expressing the radius had a disturbing feature. It seemed that for a certain radius, the denominator of the term would become zero, which would cause the term to "blow up" mathematically. This radius, known as the Schwartzchild radius, rs, is defined as:
rs = 2GM/c2
G is the gravitational constant, M is the mass, and c is the speed of light.
Since Schwartzchild's work proved crucial to understanding black holes, it is an odd coincidence that the name Schwartzchild translates to "black shield."
Black Hole Properties
An object whose entire mass M lies within rs is considered to be a black hole. Event horizon is the name given to rs, because from that radius the escape velocity from the black hole's gravity is the speed of light. Black holes draw mass in through gravitational forces, but none of that mass can ever escape.
A black hole is often explained in terms of an object or mass "falling into" it.
Y Watches X Fall Into a Black Hole
Y observes idealized clocks on X slowing down, freezing in time when X hits rs
Y observes light from X redshift, reaching infinity at rs (thus X becomes invisible - yet somehow we can still see their clocks. Isn't theoretical physics grand?)
X perceives noticeable change, in theory, though once it crosses rs it is impossible for it to ever escape from the gravity of the black hole. (Even light cannot escape the event horizon.)
Development of Black Hole Theory
In the 1920s, physicists Subrahmanyan Chandrasekhar deduced that any star more massive than 1.44 solar masses (the Chadrasekhar limit) must collapse under general relativity. Physicist Arthur Eddington believed some property would prevent the collapse. Both were right, in their own way.
Robert Oppenheimer predicted in 1939 that a supermassive star could collapse, thus forming a "frozen star" in nature, rather than just in mathematics. The collapse would seem to slow down, actually freezing in time at the point it crosses rs. The light from the star would experience a heavy redshift at rs.
Unfortunately, many physicists considered this to only be a feature of the highly symmetrical nature of the Schwartzchild metric, believing that in nature such a collapse would not actually take place due to asymmetries.
It wasn't until 1967 - nearly 50 years after the discovery of rs - that physicists Stephen Hawking and Roger Penrose showed that not only were black holes a direct result of general relativity, but also that there was no way of halting such a collapse. The discovery of pulsars supported this theory and, shortly thereafter, physicist John Wheeler coined the term "black hole" for the phenomenon in a December 29, 1967 lecture.
Subsequent work has included the discovery of Hawking radiation, in which black holes can emit radiation.
Black Hole Speculation
)Black holes are a field that draws theorists and experimenters who want a challenge. Today there is almost universal agreement that black holes exist, though their exact nature is still in question. Some believe that the material that falls into black holes may reappear somewhere else in the universe, as in the case of a wormhole.
One significant addition to the theory of black holes is that of Hawking radiation, developed by British physicist Stephen Hawking in 1974.
About the Author
Black holes are being investigated and studied more with the rapid development of technology,but there are still a large number of questions to be solved.As time goes by,some of what we know today may not be true any more,but remaining a mystery.
Black hole is so strange and powerful that not only scientists but also people woking in different positions will continue to search and explore our large backyard--cosmos.
what is a spider with a black body and white legs called?
I found one in my house today and it was super fast and watched my every move. It turned its body as moved around to look for something to kill it with.
It's an arachnid.
Actually it's probably one of the many species of wolf, jumping or hunting spider.
Ed
