Astronomers Biggest Black Hole Mass Calculations

Measuring 6.6 billion solar mass black hole at the center of the galaxy M87 is the largest black hole in which the masses had been measured precisely.
M87 Black Hole
Using the Frederick C. Telescope Gillett Gemini on Mauna Kea, Hawaii, a team of astronomers to calculate the mass of the black hole, which is larger than the black hole located in the center of the Milky Way, which is about 4 million solar masses.
Astronomer Karl Gebhardt of the University of Texas, Austin, presented the results of the research team on Wednesday, January 12th, the 217th meeting of the American Astronomical Society. He said that the horizon of the black hole, the size of 20 billion miles, four times larger than the orbit of Neptune and three times larger than Pluto's orbit. In other words, the black hole can "swallow" the whole solar system.
Previously, astronomers had expected the black hole's mass is about 3 billion times the solar system, so their results are somewhat surprising. To calculate the mass of the black hole, astronomers measure how fast stars are orbiting around the black hole. They found that, on average, the stars are orbiting at speeds of nearly 500 miles per second (for comparison, the Sun orbits the black hole at the center of the Milky Way galaxy about 220 km per second). From these observations, the astronomers could infer the most accurate estimate of the mass of the black hole is a super great.
Astronomers think that the M87 black hole grew to be very large by joining with several other black holes. M87 is the largest galaxy in the nearby universe, and thought to be formed by the merger of approximately 100 galaxies smaller.
Although a black hole is located about 50 million light-years away, he is regarded as our neighbors in the perspective of cosmology. Because of the large size and relative proximity, the astronomers assume that it is the first black hole that they can actually "see". So far, no one has ever found evidence of direct observation of black holes. Their existence is inferred from indirect evidence, particularly how they affect about them.
M87 black hole probably will not take long to defend his title, as the astronomers plan to continue the search and calculate measures of many other black holes. One planned project involves connecting telescopes from around the world to observe the universe at wavelengths shorter than 1 millimeter. This will probably allow scientists to detect the silhouette of the black hole horizon M87. It may also allow scientists to calculate the size of the other black hole located in a galaxy about 3.6 billion light-years away.
More information can be found at http://news.sciencemag.org/sciencenow/2011/01/the-solar-system-swallower.html.