Nova to Terra (Footnote)

ลำดับตอนที่ #45 : Black Hole

 Black holes were predicted in a theory, but we've observed their signs in the real world. Black holes are very much real. 

Currently, the best evidence for a supermassive black hole comes from the centre of our own Milky Way. For sixteen years astronomers have tracked the positions of stars orbiting a central massive object in a region called Sagittarius A*, one of which - a star called S2 - has completed a full orbit in that period. From the orbital data they were able to infer that there was a spherical mass of 4.3 million solar masses contained within a radius of less than 0.002 light years.

Source(s):

http://en.wikipedia.org/wiki/Black_hole#...

They are real 

They cannot be seen directly 'cause they're black in a black sky. 

However they can bee observed indirectly when they devour a nearby star, the star being eaten gives off X-rays which we can detect. 

We can also detect thier gravity, when we observe a group of stars being whirled round an invisible entity with a huge gravity field it must be a black hole 

Why a black hole and not something else? Well that's the definition of a black hole, an invisible entity with a huge gravity field