|Right ascension||17h 46m 15.2s|
|Declination||-28° 49′ 49″|
|Type of object||Emission nebula|
|Distance from Earth||25,000 ly|
The Pistol nebula is an emission nebula in the constellation of Sagittarius. The first images of the nebula produced in the 1980s were of low resolution and appeared similar to a pistol, giving the nebula its name. The nebula is known for housing one of the most luminous stars known, the Pistol star, which is believed to be well over million times brighter than the Sun. The gas composing the nebula is thought to have been ejected by the star. The image on the right is a false color image taken in infrared light.
Properties and Structure
The nebula has a roughly rectangular shape, with dust and gaseous material present in two shells concentric with the Pistol star. This material is thought to have been blown off of the Pistol star by powerful stellar winds around 4,000-6,000 years ago. The nebula contains (excluding the Pistol star) around 9.3 solar masses of material. The larger of the two shells is thought to be 4 light years across and is currently expanding at 60 km/s. The nebula is ionized by Wolf-Rayet stars in the Quintuplet Cluster as well as their strong stellar winds.
The Pistol star, designated V4647 Sagittarii, is a blue hypergiant and a candidate luminous blue variable or cLVB. Discovered by Don Figer in the 1990s it is one of the brightest known stars, specifically at least 106.6 times brighter than the Sun. For a comparison, it radiates the same amount of energy in 20 seconds as the Sun does in an entire year. This results in an extraordinarily strong stellar wind, some 10 billion times more powerful than is outputted by the Sun and travels at 95 km/s. It must be observed in the infrared region of the electromagnetic spectrum due to interstellar dust surrounding the star. If it were not for the dust, it would appear as a fourth magnitude star even though it is over 25,000 light years away.
It is thought to weigh more than 100 solar masses but may have been composed of more than 200 solar masses of material in the past, much of it ejected into the nebula. However estimates vary with some putting it lower at 26.5 solar masses. Unsurprisingly, the star itself is physically very large; its radius is greater than the distance between the Earth and the Sun or 93 million miles. The star possess a temperature of 11,800 k.
- Pistol nebula from the SIMBAD Astronomical Database
- A Brilliant Star in Milky Way's Core from nasa.gov
- Pistol Star and Nebula from constellation-guide.com
- Figer, D., Morris, M., Geballe, T., Rich, R., Serabyn, E., McLean, I., Puetter, R. and Yahil, A. (1999). High-Resolution Infrared Imaging and Spectroscopy of the Pistol Nebula: Evidence for Ejection. The Astrophysical Journal, 525(2), pp.759-771. arXiv:astro-ph/9906479
- The Pistol Nebula from nasa.gov