Sagittarius A, location of a super massive black hole
February 10, 2010
Today world news net includes information about Sagittarius A. Sagittarius A is pronounced “A-star”, standard abbreviation Sgr A*. This 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 super massive 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.
In November 2004 a team of astronomers reported the discovery of a potential intermediate-mass black hole, referred to as GCIRS 13E, orbiting three light-years from Sagittarius A*. This black hole of 1,300 solar masses is within a cluster of seven stars. This observation may add support to the idea that super massive black holes grow by absorbing nearby smaller black holes and stars
If Sagittarius A* were exactly centered on the black hole, it would be possible to see it magnified beyond its actual size, due to gravitational lensing. According to general relativity, this would result in a minimum observed size of at least 5.2 times the black hole’s Schwarzschild radius, which, for a black hole of around 4 million solar masses, corresponds to a minimum observed size of approximately 52 μas.
This is much larger than the observed size of 37 μas and so suggests that the Sagittarius A* radio emissions are not centered on the hole but arise from a bright spot in the region around the black hole, close to the event horizon, possibly in the accretion disc or a relativistic jet of material ejected from the disc. Keep reading world news net for more information.
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