Pistol Star

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Pistol Star
Observational Data
Designation V4647 Sagittarii
Right ascension 17h 46m 15.240s[1]
Declination -28° 50′ 03.58″[1]
Constellation Sagittarius
Type of object Hypergiant
Magnitude Apparent Mag: >28[2]
Absolute Mag: -10.75[2]
Distance from Earth 25,000 ly[2]

The Pistol star (V4647 Sagittarii) is a blue hypergiant star found in the constellation of Sagittarius.[2] The star is situated in the Pistol nebula and cannot be viewed directly in visible light due to the obscuring effects of dust. However this can be negated by observing in the infrared and such observations have revealed the star to be one of the most luminous ever discovered, at approximately 1,600,000 times more luminous than the Sun.[2] It is suspected of being a luminous blue variable.

The star was discovered in 1990 by Don Figer using the Hubble Space Telescope.[2] Later in 1995 it was suggested the material composing the surrounding nebula might originate from the Pistol star.[3] This was confirmed by the Hubble Space Telescope in 1997.[3][4]

Properties and structure

Lying 25,000 light years from Earth, the Pistol star is one of the brightest known stars.[2] The star is truly a giant, its mass has been estimated from its spectrum to be 27.5 times that of the Sun. Its radius is 306 times greater (larger than the distance between the earth and the sun) and the star generates a stellar wind that is more than 10 billion times more powerful than that of the Sun. The star is therefore shedding vast quantities of material from its surface. It is thought the star radiates as much energy in 20 seconds as the Sun does in an entire year.[2] However it is a long way from being the largest known star; others such as UY Scuti and VY Canis Majoris are far larger.[5]

The surface of the star is extremely hot at 11,800 kelvin making it appear blue.[2] Due to the absorbing effects of dust, the star has an apparent magnitude of at least +28, but if there were no dust, it would be +4 and so visible to the unaided eye.[2] The enveloping nebula contains (excluding the Pistol star) around 9.3 solar masses of material. There can be seen to be two concentric shells of material, the larger of the two is thought to be 4 light years across and is currently expanding at 60 km/s.[6]


  1. 1.0 1.1 Pistol star from the SIMBAD Astronomical Database
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Pistol star. Retrieved on 2019-03-06.
  3. 3.0 3.1 What is the biggest star we know?. Retrieved on 2019-03-06.
  4. The Pistol Star: A Brilliant Star in Milky Way's Core. Retrieved on 2019-03-06.
  5. Pistol star. Retrieved on 2019-03-06.
  6. 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