Near 3 kpc Arm
The Near 3 kpc Arm (also called Expanding 3 kpc Arm or simply 3 kpc Arm) was discovered in the 1950s by astronomer van Woerden and collaborators through 21-centimeter radio measurements of HI (atomic hydrogen). It was found to be expanding away from the center of the Milky Way at more than 50 km/s. This spiral arm contains about 10 million solar masses of gas, mostly hydrogen atoms and molecules.
It is located in the fourth galactic quadrant at a distance of about 5.2 kpc from the Sun and 3.3 kpc from the galactic center. The last attempt to search for star forming regions in the Near 3 kpc Arm (in 1980) showed little star formation occurring in the numerous molecular clouds of this arm.
- Expansion d'une structure spirale dans le noyau du Système Galactique, et position de la radiosource Sagittarius A, Comptes Rendus de l'Académie des Sciences, Vol. 244, p. 1691–1695, 1957
- A New Spiral Arm of the Galaxy: The Far 3-Kpc Arm, T. M. Dame, P. Thaddeus, ApJ Letters, 2008
- Milky Way's Inner Beauty Revealed, Press Release Harvard-Smithsonian Center for Astrophysics, 2008
- The Far 3kpc Arm NASA/Astronomy Picture of the Day, 2008
- Star formation and ionization in the 3 kiloparsec arm, Astrophysical Journal, Part 1, vol. 241, Oct. 1, 1980, p. 200–207