11ac1064_ions___Astronomy___Black_Holes__Question
[Date Answered] March 13, 1998 [Questioner (age, location)] Thomaz ( Brazil) [Answer] As their name implies, black holes are black! Not even light can escape from the strong gravity of a black hole. Does that mean astronomers have no hope of ever detecting one? Fortunately, while direct detection of light from a black hole is not possible, astronomers can indirectly detect them via their gravitational effect on other objects. For example, some black holes are sucking in the material around them, formin g what is known as an accretion disk. As the material in the disk is packed together, spiraling in towards the black hole, it gets heated up and emits high energy photons such as x-rays, which can be detected by astronomers. Black holes in bina ry systems can be "weighed" by measuring the orbital parameters of the system. Evidence of supermassive black holes in the centers of galaxies has been provided by the Hubble Space Telescope. HST observed stars very near to the centers of galaxies. By measuring the velocities of these stars, it was possible to tell how much mass w as contained in the center of the galaxy. These measurements showed that as much as 100 million times the mass of the Sun may be contained in an area only a few parsecs across. Matter of this density almost certainly implies the existence of a supermass ive black hole. [Question] 
Is that proved the black holes exists?How can they (astronomers)prove that?
Quickie Questions - Astronomy - Black Holes