That refers specifically to black holes (there are other types of "collapsed stars"). This sphere is called the "event horizon".
It seems you are referring not to any collapsed star, but a black hole. The "event horizon" is the area from which nothing can escape.
The circumference.
a sphere is called a sphere because , well , its just a other name for a ball such as the earth.
The imaginary sphere is called the celestial sphere. It is used in astronomy to track the apparent movements of celestial objects as if they were projected onto the inside of a sphere surrounding the Earth.
Half of a sphere is called a hemisphere. It consists of a flat surface cutting through the sphere, dividing it into two equal parts.
The word for half a sphere is a hemisphere.
A 2D sphere is a circle.
Sphere is the term used in geometry.
The Dynamic Sphere exists in a non- fictional work called Aikido and the Dynamic Sphere. The sphere focuses on the moral aspect of the Japanese martial art called aikido.
The sphere that we all live on is called the Earth. (It is not a perfect sphere, but close enough)
A collapsed core of a supernova that only contains neutrons is called a neutron star. Neutron stars are very dense, with a mass greater than the sun but compressed into a sphere only about 12 miles in diameter. They are supported by neutron degeneracy pressure, which prevents further collapse.
it's a semi-sphere circle is to semi-circle as sphere is to semi-sphere