Black Hole Found to Be Much Closer to Earth Than Previously Thought

An international team of astronomers has accurately measured the distance from Earth to a black hole for the first time. The astronomers have measured the distance to 7800 light years, which is much closer than expected. They achieved this number by measuring the radio emissions from the black hole and its associated dying star. Now that there is a lower error margin astronomers can get a better idea of how black holes grow and evolve. In saying that it is important to know the distance to know the measurement of the black hole’s spin.
Astronomical distances are most easily measured using the so-called trigonometric parallax, in which astronomers make use of the annual shift in the star's position as a consequence of the Earth's orbit around the sun (parallax shift). Peter Jonker from SRON Netherlands Institute for Space Research and his colleagues are now using the method to a close black hole and its associated star, V404 Cygni, in the Cygnus constellation.
The outermost layers of the star are being drawn into the black hole. This gas first of all accumulates in a plasma disc around the black hole before it disappears into it, a process during which a lot of X-rays and radio waves are emitted. Picture
Now that astronomers have the mathematical means to measure these black holes they will start applying this to several other black holes.

http://www.sciencedaily.com/releases/2009/12/091209193904.htm