<P> The Sun is 25,000--28,000 ly (7.7--8.6 kpc) from the Galactic Center . This value is estimated using geometric - based methods or by measuring selected astronomical objects that serve as standard candles, with different techniques yielding various values within this approximate range . In the inner few kpc (around 10,000 light - years radius) is a dense concentration of mostly old stars in a roughly spheroidal shape called the bulge . It has been proposed that the Milky Way lacks a bulge formed due to a collision and merger between previous galaxies, and that instead it only has a pseudobulge formed by its central bar . However, confusion in the literature between the (peanut shell) - shaped structure created by instabilities in the bar, versus a possible bulge with an expected half - light radius of 0.5 kpc, abound . </P> <P> The Galactic Center is marked by an intense radio source named Sagittarius A * (pronounced Sagittarius A-star). The motion of material around the center indicates that Sagittarius A * harbors a massive, compact object . This concentration of mass is best explained as a supermassive black hole (SMBH) with an estimated mass of 4.1--4.5 million times the mass of the Sun . The rate of accretion of the SMBH is consistent with an inactive galactic nucleus, being estimated at around 6995100000000000000 ♠ 1 × 10 M y . Observations indicate that there are SMBH located near the center of most normal galaxies . </P> <P> The nature of the Milky Way's bar is actively debated, with estimates for its half - length and orientation spanning from 1 to 5 kpc (3,000--16,000 ly) and 10--50 degrees relative to the line of sight from Earth to the Galactic Center . Certain authors advocate that the Milky Way features two distinct bars, one nestled within the other . However, RR Lyrae 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 . X-ray emission from the core is aligned with the massive stars surrounding the central bar and the Galactic ridge . </P> <P> In 2010, two gigantic spherical bubbles of high energy emission were detected to the north and the south of the Milky Way core, using data from the Fermi Gamma - ray Space Telescope . The diameter of each of the bubbles is about 25,000 light - years (7.7 kpc); they stretch up to Grus and to Virgo on the night - sky of the southern hemisphere . Subsequently, observations with the Parkes Telescope at radio frequencies identified polarized emission that is associated with the Fermi bubbles . These observations are best interpreted as a magnetized outflow driven by star formation in the central 640 ly (200 pc) of the Milky Way . </P>

How many main sequence stars are there in the milky way