Gravastar
A gravastar is an object hypothesized in astrophysics as an alternative to the black hole theory by Pawel Mazur and Emil Mottola. It results from assuming real, physical limitations on the formation of black holes. These limits, such as discrete length and time quanta (chronon), were not known to exist when black holes were originally theorized, so the concept of a gravastar is an attempt to "modernize" the theory by incorporating quantum mechanics. The term gravastar is a portmanteau of the words Gravitational Vacuum Star.
Structure
The notion of gravastars builds on Einstein's theory of general relativity and imposes a universal "smallest size" that is known to exist according to well-accepted quantum theory. This size is known as the Planck length, and is derived using the speed of light, Planck's constant and the gravitational constant. Quantum theory says that any scale smaller than the Planck length is unobservable and meaningless to physics and physicists. This limit can be imposed on the wavelength of a beam of light so as to obtain a limit of blue shift that the light can undergo. This becomes important for the structure of a gravastar because general relativity says that a gravitational well blue-shifts incoming light, so around the extremely large mass of a gravastar there is a region of "immeasurability" to the outside universe as the wavelength of the light approaches, and then passes, the Planck length. This region is called a "gravitational vacuum", because it is a void in the fabric of space and time.
