Galactic Center - Distance To The Galactic Center and Bar

Distance To The Galactic Center and Bar

The exact distance from the Sun to the Galactic Center is notoriously uncertain. The latest estimates from geometric-based methods and standard candles yield distances to the Galactic Center between 7.6–8.7 kpc (25,000–28,000 light years). An accurate determination of the distance to the Galactic Center as established from variable stars (e.g., RR Lyrae variables) or standard candles (e.g., red clump stars) is hindered by countless effects, which include: an ambiguous reddening law; a bias for smaller values of the distance to the Galactic Center because of a preferential sampling of stars toward the near side of the Galactic bulge owing to interstellar extinction; and an uncertainty in characterizing how a mean distance to a group of variable stars found in the direction of the Galactic bulge relates to the distance to the Galactic Center.

The nature of the Galaxy'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 degrees. 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 galaxy, as well as most of the Milky Way's star formation activity. Viewed from the Andromeda Galaxy, it would be the brightest feature of our own galaxy.