It is one of many massive young stars in the Quintuplet cluster in the central region of our galaxy. It is about 25,000 light years from Earth in the direction of Sagittarius. It would be visible to the naked eye as a fourth magnitude star but interstellar gases have blocked it from view.
The Pistol Star was discovered by the Hubble Space Telescope in the early 1990s. The star may have ejected almost 10 solar masses of material in giant outbursts perhaps 4,000 to 6,000 years ago. Its stellar wind is over 10 billion times stronger than the Sun's. The star's exact age and future are not known, but it is expected to end in a brilliant supernova or hypernova in 1 to 3 million years. Its mass is equally uncertain, probably around 200 times the sun when first formed. Now it is much less because it has lost so much mass.
Early reports suggested that it might be the most luminous star known, being almost 100 million times as luminous as the Sun. Later studies, however, have reduced its estimated luminosity. It is now regarded as a candidate luminous blue variable about one-third as luminous as the binary star system Eta Carinae. Even so, it radiates about as much energy in 20 seconds as does the Sun in a year.
A close point source has been discovered hidden in the surrounding nebulosity, but it is not known whether it is a star or even whether it is physically associated.
- As observed from Earth.
- Yungelson L.R. et al 2008. On the evolution and fate of super-massive stars. Astronomy and Astrophysics 477: 223. 
- Najarro, F. (2005). "The fate of the most massive stars". ASP Conference 332 : 58–68.
- Martayan C. et al 2011. High-angular resolution observations of the Pistol star. Proceedings of the International Astronomical Union 6: 616.