<P> The nature of the Milky Way's bar, which extends across the Galactic Center, is also actively debated, with estimates for its half - length and orientation spanning between 1--5 kpc (short or a long bar) and 10--50 ° . Certain authors advocate that the Milky Way features two distinct bars, one nestled within the other . The bar is delineated by red - clump stars (see also red giant); however, RR Lyr variables do not trace a prominent Galactic bar . The bar may be surrounded by a ring called the "5 - kpc ring" that contains a large fraction of the molecular hydrogen present in the Milky Way, as well as most of the Milky Way's star formation activity . Viewed from the Andromeda Galaxy, it would be the brightest feature of the Milky Way . </P> <P> The complex astronomical radio source Sagittarius A appears to be located almost exactly at the Galactic Center (approx. 18 hrs, − 29 deg), and contains an intense compact radio source, Sagittarius A *, which coincides with a supermassive black hole at the center of the Milky Way . Accretion of gas onto the black hole, probably involving a disk around it, would release energy to power the radio source, itself much larger than the black hole . The latter is too small to see with present instruments . </P> <P> A study in 2008 which linked radio telescopes in Hawaii, Arizona and California (Very Long Baseline Interferometry) measured the diameter of Sagittarius A * to be 44 million kilometers (0.3 AU). For comparison, the radius of Earth's orbit around the Sun is about 150 million kilometers (1.0 AU), whereas the distance of Mercury from the Sun at closest approach (perihelion) is 46 million kilometers (0.3 AU). Thus the diameter of the radio source is slightly less than the distance from Mercury to the Sun . </P> <P> Scientists at the Max Planck Institute for Extraterrestrial Physics in Germany using Chilean telescopes have confirmed the existence of a supermassive black hole at the Galactic Center, on the order of 4.3 million solar masses . </P>

How far is the sun from the centre of the milky way