|Designation|| NGC 6888|
|Right ascension||20h 12m 07s|
|Declination||+38° 21′ 18″|
|Type of object||Emission nebula|
|Distance from Earth||5,000 ly|
The Crescent nebula (NGC 6888, Sharpless 105, Caldwell 27) is an emission nebula situated in the constellation of Cygnus, the swan. The nebula consists of a central Wolf-Rayet star, designated WR 136, enveloped by a bubble of gas that is 25 ly wide. The central star is thought to have a mass of 25-40 solar masses and ejected the gas that surrounds it to form the nebula through strong stellar winds. Since the original material was ejected, faster moving material has been ejected that has slammed into the previously ejected material. Where this material collides, the gas is heated up, so much that it emits x-rays.
The nebula is located around 5,000 light years away. Measurements of the x-ray emission of the nebula using the EPIC camera on the XMM-Newton satellite. The x-ray emitting gas is so hot it has turned into a plasma. It has been found to be well described by a model using two temperatures of 1.4×106 k and 8.2×108 k. The electron density has been found to be around 0.4 cm−3 for this plasma. Inhomogeneities in the nitrogen abundance and temperature distribution have also been detected.
- NGC 6888. Simbad Astronomical Database. simbad.u-strasbg.fr. Retrieved on 2019-09-01.
- NGC 6888: The Crescent Nebula. apod.nasa.gov (2016-06-10). Retrieved on 2019-09-01.
- Esteban, C.; Mesa-Delgado, A.; Morisset, C. et al. (2016). "The chemical composition of Galactic ring nebulae around massive stars". Monthly Notices of the Royal Astronomical Society 460 (4): 4038–4062. doi:10.1093/mnras/stw1243. Bibcode: 2016MNRAS.460.4038E. arXiv:1605.07800
- Nina Sen (2012-02-28). Booming Crescent Nebula Shines in Skywatcher Photo. space.com. Retrieved on 2019-09-01.
- Crescent Nebula. esa.int (2017-12-11). Retrieved on 2019-09-01.
- Toalá, J.; Guerrero, M.; Chu, Y. et al. (2016). "X-ray emission from the Wolf–Rayet bubble NGC 6888 – II.XMM–NewtonEPIC observations". Monthly Notices of the Royal Astronomical Society 456 (4): 4305–4314. doi:10.1093/mnras/stv2819. Bibcode: 2016MNRAS.456.4305T. arXiv:1310.2801