Sh 2-46

Sharpless 2-46

Nebula
Image of Sh 2-46 Nebula
Observation data: epoch
Right ascension	18^h 06^m 6.00^s[1]
Declination	−14° 08′ 60.0″[1]
Distance	6,000 ly   (2,000 pc)
Constellation	Serpens
Designations	Sh 2-46, RCW 158, Gum 80, LBN 58[1]
See also: Lists of nebulae

Sh 2-46 (also known as RCW 158), is an H II region, a glowing cloud of ionized hydrogen gas—located in the southern constellation of Serpens. Situated approximately 6,000 light-years from Earth, the nebula is notable for its red emission caused by the ionization of hydrogen atoms, energized by the central runaway star HD 165319 (O9.7Ib).^[2] It is an isolated nebula positioned above the galactic plane and contains polycyclic aromatic hydrocarbons (PAHs).^[3][4][5] It is located about 3° west of the Eagle Nebula (Messier 16) and is part of broader star-forming activity in the region.^[6]

Central star

The primary ionizing source for Sh 2-46 is the massive O-type supergiant star HD 165319, classified as O9.7Ib. This luminous blue star is a runaway star, believed to have originated in the nearby Eagle Nebula (NGC 6611) but was ejected due to gravitational interactions about 1.8 million years ago. As it travels through Sh 2-46 at high speed, it creates a dynamic environment, including the observed bow shock.^[2][3][7][8]

References

1. "Simbad - Object view". simbad.cds.unistra.fr. Retrieved 2025-11-16.
2. "HD 165319". simbad.cds.unistra.fr. Retrieved 2025-11-16.
3. "Sh 2-46". galaxymap.org. Retrieved 2025-11-16.
4. Giard, M.; Pajot, F.; Lamarre, J. M.; Serra, G.; Caux, E. (May 1989). "The galactic emission in the 3.3 mu-m aromatic feature. I. Observations". Astronomy and Astrophysics. 215: 92–100. Bibcode:1989A&A...215...92G. ISSN 0004-6361.
5. [e-mail]. "There is an impostor in this nebula". www.eso.org. Retrieved 2025-11-16.
6. Ritschel, Kevin (2023-10-10). "Explore these three great nebulae". Astronomy Magazine. Retrieved 2025-11-16.
7. de Wit, W. J.; Testi, L.; Palla, F.; Vanzi, L.; Zinnecker, H. (October 2004). "The origin of massive O-type field stars. I. A search for clusters". Astronomy and Astrophysics. 425 (3): 937–948. Bibcode:2004A&A...425..937D. doi:10.1051/0004-6361:20040454. ISSN 0004-6361.
8. Gvaramadze, V. V.; Bomans, D. J. (November 2008). "Search for OB stars running away from young star clusters. I. NGC 6611". Astronomy and Astrophysics. 490 (3): 1071–1077. Bibcode:2008A&A...490.1071G. doi:10.1051/0004-6361:200810411. ISSN 0004-6361.