Feb

10

Sagittarius A | Sagittarius | Sagittarius A | Sagittarius A Star | Andromeda Constellation | Milky Way Galaxy

Posted on: February 10, 2010 at 9:59 am | 93 views




Sagittarius A | Sagittarius | Sagittarius A | Sagittarius A Star | Andromeda Constellation | Milky Way Galaxy

Sagittarius A* is a bright and very compact astronomical radio source at the center of the Milky Way Galaxy, part of a larger astronomical feature at that location (Sagittarius A). Sagittarius A* is likely to be the location of a supermassive black hole, as is hypothesized to be at the centers of many spiral and elliptical galaxies.

Astronomers have been unable to observe Sgr A* in the optical spectrum due to the effect of 25 magnitudes of extinction between the source and Earth. Several teams of researchers have attempted to image Sagittarius A* in the radio spectrum using Very Long Baseline Interferometry (VLBI). The current highest-resolution measurement, made at a wavelength of 1.3 mm, indicated an angular diameter for the source of 37 μas. At a 26,000 light-year distance, this yields a diameter of 44 million kilometers. For comparison, the Earth is 150 million kilometers from the Sun, and Mercury is 46 million kilometers from the Sun at its perihelion.

After monitoring stellar orbits around Sagittarius A* for 16 years, Gillessen et al. estimate the object’s mass at 4.31 ± 0.38 million solar masses. The result was announced in 2008 and published in The Astrophysical Journal in 2009. Reinhard Genzel, team leader of the research, said the study has delivered “what is now considered to be the best empirical evidence that super-massive black holes do really exist. The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt.”

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