The Oort cloud is a spherical cloud of comets which lies about 50,000 AU, almost a light year from the Sun. The trans-Neptunian objects such as Kuiper belt and scattered disc are one thousandth less its distance. The gravitational boundary of the Solar System can be defined by the outer extent of it.
It is said to have two separate regions, which are an outer cloud in spherical and inner ones in a disc shape. It consists of objects that are mostly composed of ices (water, methane and ammonia). The cometary orbits were modified to be more circular due to the gravitational interaction with the nearby stars as well as the galactic tides.
No direct observation has been made on it. However, astronomers believe that Halley type comets which enter the inner Solar System comes from it. It is the source for Centaurs and Jupiter family comets too. The outer cloud is bounded loosely to the Solar System and hence it is easily disturbed by the gravitational pull of passing stars as well as the Milky Way Galaxy as well.
The Oort cloud was formed about 4.6 billion years ago. A hypothesis of where its objects were coalesced closer to the Sun, but the gravitational interaction planets such as Jupiter forced the objects into a long elliptic orbit.
Julio Angel Frenandez’s models suggest that scattered disc might be the primary source for its objects too. Based on the models, it is said that half of the scattered objects travel outward awhile a quarter were moved inward to Jupiter’s orbit. The other quarter are ejected to a hyperbolic orbit. Computer models suggest that the number of collisions in the Solar System’s history gave such a big impact that most of the comets were destroyed before they are able to reach the Oort cloud.