Pistol Star

The Pistol Star is a blue hypergiant and is one of the most luminous known stars in the Milky Way Galaxy. It is one of many massive young stars in the Quintuplet cluster in the Galactic Center region. The star owes its name to the shape of the Pistol Nebula, which it illuminates. It is located approximately 25,000 light years from Earth in the direction of Sagittarius. It would be visible to the naked eye as a fourth magnitude star, if it were not for the interstellar dust that completely hides it from view in visible light.

The Pistol Star was discovered by the Hubble Space Telescope in the early 1990s. The star is thought to have ejected almost 10 solar masses of material in giant outbursts perhaps 4,000 to 6,000 years ago (as observed from Earth). Its stellar wind is over 10 billion times stronger than the Sun's. Its 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. Some astronomers conjecture that its large mass may be related to its location near the Galactic Center, since the star formation process there may favor massive objects. Early reports suggested that it might be the most luminous star known, producing almost 100 million times as much power as the Sun. Later studies, however, have reduced its estimated luminosity to roughly 4 million times that of the Sun, making it a 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.

Objects in this class have 80 to 150 times the mass of the Sun and lifetimes of only a few million years. Unlike ordinary stars, they are strongly affected by the outward pressure of the light that they emit, which blows off massive winds from their outer atmospheres. Besides the Pistol Star, several other objects have been cited as the "most luminous star" in recent years. Almost all of them have been demoted by later, improved studies. Among the most famous is Eta Carinae, now confirmed to be a system of at least two stars. Our galaxy probably has 10 to 100 stars surpassing Eta Carinae, but their visible light is hidden by interstellar dust, hindering their immediate identification and detailed study. Most should eventually be observable in infrared light.