It is quite interesting to imagine a black hole with a diameter of, let´s say 10 km, distant from a neutron star.
A Black Hole beside a Neutron Star, both about 10 km in diameter, over a virtual landscape (Wiki)
This depicts a black hole with a Neutron Star and how they would appear over a virtual landscape 30 x 30 km in size. Of course this landscape would have been destroyed utterly. Both celestial objects would be attracted to each other with unimaginable force. The one with the greater mass would emerge as the winner, the black hole. By the calculation of Chandrasekhar, it should show that the black hole possesses the greater mass compared with the neutron star.
Calculations with so called "Attractors" are an important mean in the understanding of the forces of Supermassive Black Holes and even Galaxies. The computer graphics show the force field lines between two big masses having great mutual attraction. In this graph, both masses are about the same size. It shows the direction of the exchange of masses. At the end of the process there will be only one great object be left, comprising the combined mass of the two previous objects. This was as anticipated.
In Golm 2001, scientists of the Max Planck Institute for Gravitational Physics, with the help of a supercomputer could for the very first time, observe a collision of two Black Holes on their screens. The finding of this simulation was that waves of gravitation will be transmitted into space. Until now, such gravitational waves were unconfirmed.
In dealing with black holes, it is important to learn that Einstein had predicted the deflection of light by massive bodies. 1919 this theory was proved by an expedition to Africa conducted by Arthur Eddington. He was a British astrophysicist of the early 20th century and took a picture of a star close to the Sun but being eclipsed by the moon. The star´s true position was detected exactly at that previously calculated by Einstein. That proved the Sun was acting as a lense for light waves and so deflecting the light.
Einstein had stated: Light is deflected by massive bodies just as it is by glass lenses: they will refract the light. If that that happens by gravitational force from massive celestial bodies, they are said to be acting as "gravitational lenses"
Massive celestial bodies act as gravitational lenses focusing light
Some Photos of space objects, taken in the past using the most highly sophisticated telescopes, ever known, were a mystery to astronomers. They show the same celestial object (a galaxy, a supernova within a Galaxy or even a quasar), repeated several times. It soon became obvious that these kinds of pictures reveal the presence of a huge gravitational lens, e.g. a black hole or another Galaxy. The lens was named the Einstein Cross in honour of Albert Einstein, whose Theory of Relativity predicted the phenomenon decades before the first gravitational lens was observed in 1979.
The bright object at the centre is a distant galaxy. The four bright objects surrounding it are actually multiple images of a singel quasar that lies far beyond the galaxy. A black hole would reveal its presence by the very absence of a bright object at the centre. Sometimes an Einstein-Cross can become a ring depending upon the distance of the observed object from the gravitational lens. All such images are proof of black holes, with further and even stronger proof being the image on the frontispiece of this book, the author‘s very reason to produce it.