Neutron Star

A neutron star is a type of stellar remnant that can result from the gravitational collapse of massive star during a Supernova event.

Neutron star is the last phase of star's life in which mass of inert core after nuclear fusion reaction is greater than the Chandrasekhar limit of White Dwarf, but its mass is not great enough to overcome neutron degeneracy pressure to become Black Hole.

Formation

Any star with a initial main sequence mass of around 10 solar masses or above has the potential to become a neutron star. As the star evolves away from the main sequence, subsequent nuclear reaction produces an iron rich core. When all nuclear fuel in the core has been exhausted, the core must be supported by degeneracy pressure alone.

Tycho's geo-heliocentric astronomy

Tycho Brahe (14 December 1546 - 24 October 1601), was Danish nobleman Known for his accurate and comprehensive astronomical and planetary observation.

Tycho believed that if the earth orbited the Sun annually there should be an observable stellar parallax over any period of six month during which the angular orientation  of a given star would change thanks to earth's changing position. The Copernican explanation for this lack of parallax was that the stars were such a great distance from earth that earth's orbit was almost insignificant by comparison.

In this depiction of the Tychonic system, the object on blue orbit (the Moon & the Sun) revolve around the earth. The objects on orange orbit (Mercury,Venus, Mars, Jupiter & Saturn) revolves around the sun. Around all is a sphere of fixed stars. 

Above explained planetary motion  can be understood in the figure given below

Black Hole

A Black hole is defined as a region of space-time from which gravity prevents any thing including light from escaping. These are the areas of intense gravitational pressure. The pressure is thought to be so intense that finite matter is actually squished into infinite density. 

The no-hair theorem states, once it achieves a stable condition after formation, a black hole has only three independent properties - mass, charge and angular momentum.

Gravitational Lensing by a black hole which

distorts the image of a galaxy in the background 

Event Horizon

The defining feature of a black hole in the appearance of an event horizon - a boundary in space-time through which matter and light can pass inward toward the mass of black hole. Nothing, not even light can escape from inside the event horizon. The event horizon  is referred to as such because if an event occur within the boundary, information from that event cannot reach an outside observer, making it impossible to determine if such an event occurred.