[AntonioLao]

As we obviously cannot see black holes, the only things we can do to assertain their existence are apply theoretical knowledge, and observe the things that we suspect they cause. Detection of black holes is most likely to occur when we find an invisible object that has a mass which could only possibly demonstrate one. Even then we are working on the assumption that white dwarfs and neutron stars are unable to survive at such a mass. One way of calculating the mass of an object we cannot see (thus cannot gauge luminoscity or magnitude), is to follow the orbit around it of a companion star. If this star is found to be part of a binary system,with an invisible partner, then the mass of the companion can be calculate via spectral and visual analysis. If this mass is found to be in excess of 3 solar masses, then a black hole is presumed to have been found.Another way is by examing the matter that they pull towards themselves. This matter forms an accretion disk,which due to the forces acting upon it becomes hot enough to emit X-rays. These in turn can be detected, and provide us with information on the fields acting upon them. http://science.nasa.gov/headlines/y2001/ast12jan_1.htm http://www.damtp.cam.ac.uk/user/gr/public/bh_obsv.htmlhttp://www.astro.keele.ac.uk/workx/blackholes/index3.html