The Oort Cloud in brief is an hypothesized area in space that is estimated to be located be roughly one light year away from the Sun. Its not like a cloud you would find on the Earth, it doesn`t rain. The Oort Cloud is a huge area of space that encompasses our solar system where comets are believed to be before they are sent on their way towards our planet. To put some more context into the description, the nearest star Proxima Centauri is four times further away than the Oort Cloud. It is a region of space where Comets are believed to originate from. There has been no definate evidence that the Oort Cloud exists. There is a debate currently raging as to whether Sedna, the so-called "Tenth planet" is actually part of an inner Oort Cloud. This is because the Sedna is three times further away from the Sun than Pluto, well beyond where the kuiper belt is said to inhabit. Oort Cloud objects are too far away for our telescopes on Earth to see any of these objects, plus you also need to take into account the fact that they are very small. Thousands upon millions of comets are believed to be "holding up" in the Oort Cloud, waiting to be sent on a journey to the Sun. They are not clustered in one area of the galaxy but surround the entire solar system like a cloud. No one has ever seen the Oort Cloud so no-one knows how big and how far is ranges out from its location. Comets are actually quite small so you`re not going to be able to see one a light year away.
The Oort Cloud is named after Jan Hendrik Oort ( Apr 28, 1900 - Nov 5, 1992 ) who predicted them where they are widely believed to be nowadays. Before Oort, Ernst Opik, who in 1932, an Estonian Astronomer had placed the cloud just outside the solar system. The Oort Cloud is sometimes known as the Opik-Ort Cloud in recognition of the earlier hypothesis. Oort bases his cloud theory on :-
Apart from being associated with the Oort Cloud, Jan also calculated that the centre of the milky way is 30,000 light years away in the direction of the Sagittarius constellation. The below pictures shows the furthest any thing from Earth has ever travelled (Voyager 1), the location of Sedna, the area where the Oort Cloud is and the nearest star. The sizes aren`t too scale but its main purpose is to give an indication of where things are. It should be emphasised that the Oort Cloud is a line, it encompasses the entire solar system like a bubble with the Earth and Sun in middle.
The Oort Cloud is believed to have been created five billion years ago when a nebula exploded, creating the Sun and its planets. The intense gravital strength of Jupiter is said to have pushed them to the outer regions of space.
There are no images or pictures of the Oort Cloud because it is so far away that it is hypothesized about. The objects in the Oort Cloud are so small, no camera of ours so far is able to pick them up. The only pictures are artists impressions and illustrations. We have no satellite or space probes out that way and none with a high enough camera resolution to pick them up. Such an object would take thousands of years to get to as we don`t have faster than light yet, that is if that is possible.
There is a theory in addition to the Oort Cloud that there is a brown dwarf star called Nemesis that interferes with the Oort Cloud, sending comets this way. The idea for Nemesis is based on the perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years. ref:Daily Mail.
Such an object such as a brown dwarf star would have given off enough radiation that it would`ve been detected by Earth based instruments which none have been recorded. Nemesis might still exist but might be something else apart from a brown star. With Nemesis being a brown dwarf means it is hard to spot so we can`t see it. If it was a yellow dwarf then maybe we`d see light from it and know its here. The closest so far discovered brown dwarf is called WISE 0855-0714 and was discovered in the constellation of Hydra. and is about 7.53 light years away, further out than the Oort Cloud itself. Ref:Space
Our star is not unique, its not special, its small compared to other stars such as Rigel. There`s no reason why if the Oort Cloud does exist round our Sun, there shouldn`t be any reason why the Oort Cloud shouldn`t exist round any other star. Its only speculative as we still have no confirmed proof/evidence that such a cloud actually exists surrounding our own solar system. We may never know unless we gain technology to travel at the speed of light. If we had the ability to travel at the speed of light, it would take a round trip of two years to discover and report back that it existed. It would take a year to get there and a year to get back.
The main difference between the three is location, the Asteroid Belt is located between the orbits of Mars and Jupiter. They are believed to have been parts of a planets that failed to form because of the immense gravity of Jupiter. The asteroids are small rocky planetoids. In recent years, Ceres, a near spherical planetoid was elevated to dwarf planet status by the International Astronomical Union, the worlds governing body for all things space.
At the edge of the solar system, beyond the planet Neptune is the Kuiper Belt which contains a large number of asteroids. The dwarf planet Pluto is in this region of space. It used to be known as a planet but it was downgraded when other objects such as Eris was found in that region of space and was deemed to be larger than Pluto.
As mentioned before, the Oort Cloud is estimated to be about a light year away from the Sun. Unlike the two belts, the contents of the Oort Cloud is dirty ice balls, comets that get knocked out of their current location and come on a journey to the Sun. There is evidence that the Asteroid Belt and the Kuiper Belt exist, but because the Oort Cloud is so far away and the objects are so small, the Oort Cloud will remain a theory for some time. It`ll be a long time before Voyager 2 satellite reaches the Oort Cloud and by that time you and me won`t be around and Voyager 2 will have run out of energy so will not be able to send any signals back.