The Pistol Star, also known as V4647 Sagittarii, is a blue hypergiant star located about 25,000 light years from Earth in the constellation Sagittarius. It is a candidate luminous blue variable (cLBV) and one of the most luminous stars known, with a luminosity 1,600,000 times that of the Sun.
Early observations indicated that it was the single most luminous star known, with an estimated luminosity almost 10 million times solar, but later studies reduced the estimate to about a third of the luminosity of Eta Carinae. The Pistol Star’s surface temperature is 11,800 K. Its absolute bolometric magnitude is -10.75.
The Pistol Star is the central star in the Pistol Nebula and was named after the nebula’s shape. It is a member of the Quintuplet Cluster and, like many other extremely massive and luminous stars in the cluster, it cannot be seen visually because it is obscured by the dust in the region of the Milky Way’s core. Without the interstellar dust and the surrounding nebulosity, the Pistol Star would be visible to the naked eye, shining at 4th magnitude from a distance of 25,000 light years.
Facts
The star’s exact age is unknown, but estimated at 4 to 10 million years. The star will likely end its life in a supernova or hypernova explosion in the next 1 to 3 million years.lumin
outbursts between 4,000 and 6,000 years ago. When the star formed, it likely had a mass more than 100 times solar, but now has a lot less as a result of ejecting an extreme amount of material.
The star’s current mass is uncertain but, based on its spectrum, it is estimated to be 27.5 solar masses. The star’s radius is 306 times solar and its stellar wind is more than 10 billion times stronger than our Sun’s. The star radiates the same amount of energy in 20 seconds as our Sun does in a year.
The Pistol Star was discovered by Don Figer, an astronomer at UCLA, using the Hubble Space Telescope in the 1990s. At the time of discovery, the Pistol Star was suspected to have been the most massive star known before it had started shedding material, possibly exceeding the theoretical upper limit, with an initial mass of up to 200 solar masses. Astronomers believe that the star’s extreme mass may be linked to its location near the Milky Way centre.
The star was first detected in the early 1990s, but its relationship to the Pistol Nebula was not realized until 1995.
Pistol Nebula
The Pistol Nebula contains about 9.3 solar masses of ionized gas expelled by the Pistol Star a few thousand years ago. It completely surrounds the star and its largest shell spans 4 light years, which is almost the same distance as that between the Sun and Alpha Centauri. The gas in the nebula’s outer shell expands at the velocity of 60 km/s.
The Pistol Nebula is primarily ionized by the hot Wolf-Rayet stars in the Quintuplet Cluster and is physically interacting with these stars’ strong stellar winds.
The Pistol Nebula is roughly rectangular in shape and the ejected material is distributed in two shells centred on the Pistol Star. The nebula got its name in the 1980s, when low-res images revealed a pistol-like shape.
Pistol Star
Constellation: Sagittarius
Right ascension: 17h 46m 15.3s
Declination: −28° 50′ 04″
Distance: 25,000 light years (8,000 parsecs)
Spectral class: LBV
Visual magnitude: >28
Apparent magnitude (J): 11.828
Apparent magnitude (H): 8.920
Apparent magnitude (K): 7.291
Absolute magnitude: -10.75
Mass: 27.5 solar masses
Radius: 306 solar radii
Temperature: 11,800 K
Luminosity: 1,600,000 solar luminosities
Estimated age: 4 million years
Designations: Pistol Star, V4647 Sagittarii (V4647 Sgr), qF 134, 2MASS J17461524-2850035
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