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- Pistol Star is the brightest star in the Milky Way, but we are unable to see it because of the space dust blocking it.
- Pistol Star was one of the first stars captured by the Hubble Telescope in 1990
- Pistol star is found in the center of the Pistol Nebula

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Luminous Blue Variable (LBV) stars are very large and unstable, frequently experiencing mass ejections and loss of mass

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Luminous blue variable (LBV) Size Comparison 2021

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It is estimated that pistol star only has 1-3 million years left.

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Douglas Isbell
Headquarters, Washington, DC                   October 7, 1997
(Phone:  202/358-1547)

Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)

Harlan Lebo
University of California at Los Angeles, CA
(Phone:  310/206-0510)

RELEASE:  97-227

HUBBLE IDENTIFIES WHAT MAY BE THE MOST LUMINOUS STAR KNOWN

       Astronomers using NASA's Hubble Space Telescope have 
identified what may be the most luminous star known -- a celestial 
mammoth which releases up to 10 million times the power of the Sun 
and is big enough to fill the diameter of Earth's orbit.  The star 
unleashes as much energy in six seconds as our Sun does in one 
year. 

       The image, taken by a University of California, Los Angeles 
(UCLA)-led team with the recently installed Near-Infrared Camera 
and Multi-Object Spectrometer (NICMOS) aboard Hubble, also reveals 
a bright nebula, created by extremely massive stellar eruptions.  
The nebula is so big (four light-years) that it would nearly span 
the distance from the Sun to Alpha Centauri, the nearest star to 
Earth's solar system.

       The astronomers estimate that when the titanic star was 
formed one to three million years ago, it may have weighed up to 
200 times the mass of the Sun before shedding much of its mass in 
violent eruptions. 

       "This star may have been more massive than any other star, 
and now it is without question still among the most massive -- 
even at the low end of our estimates," says 
Don F. Figer of UCLA.  "Its formation and life stages will provide 
important tests for new theories about star birth and evolution."

       The UCLA astronomers estimate that the star, called the 
"Pistol Star" (for the pistol shaped nebula surrounding it), is 
approximately 25,000 light-years from Earth near the center of the 
Milky Way galaxy.  The Pistol Star is not visible to the eye, but 
is located in the direction of the constellation Sagittarius, 
hidden behind the great dust clouds along the Milky Way.

       The Pistol Star was first noted in the early 1990s, but its 
relationship to the nebula was not realized until 1995, when Figer 
proposed in his Ph.D. thesis that the "past eruptive stages of the 
star" might have created the nebula.  The Hubble spectrometer 
results confirm this conclusion.

       The astronomers believe that the Pistol nebula was created 
by eruptions in the outer layers of the star which ejected up to 
10 solar masses of material in giant outbursts about 4,000 and 
6,000 years ago.  The star will continue to lose more material, 
eventually revealing its bare hot core, sizzling at 100,000 
degrees. 

       Burning at such a dramatic rate, the Pistol Star is 
destined for certain death in a brilliant supernova in 1-3 million 
years.  "Massive stars are burning their candles at both ends; 
they are so luminous that they consume their fuel at an outrageous 
rate, burning out quickly and often creating dramatic events, such 
as exploding as supernovae," said 
Mark Morris, a UCLA professor of astronomy and co-investigator.  
"As these stars evolve, they can eject substantial portions of 
their atmospheres -- in the case of the Pistol Star, producing the 
nebula and an extreme stellar wind (outflow of charged particles) 
that is 10 billion times stronger than our Sun's." 

       The Pistol Star would be visible to the naked eye as a 
fourth magnitude star in the sky (which is quite impressive given 
its distance of 25,000 light-years) if it were not for 
interstellar dust clouds of tiny particles between the Earth and 
the center of the Milky Way that absorb the star's light.  The 
most powerful telescopes cannot see the Pistol Star in visible 
wavelengths.  However, ten percent of the infrared light leaving 
the Pistol Star reaches Earth, putting it within reach of infrared 
telescopes, which have seen rapid technological advances in recent 
years -- spurred by projects such as NICMOS.

       The Pistol Star was so massive when it was born that it 
brings into question current thinking about how stars are formed, 
say the UCLA astronomers.  In the current view, stars form within 
large dust clouds which contract under their own gravity, 
eventually forming hot clumps that ignite the hydrogen fusion 
process.

       The star may radiate enough energy to halt the inward fall 
of material, thus limiting its maximum mass.  The initial mass of 
the Pistol Star may have exceeded this theoretical upper limit.  
"It is perhaps no accident that this extreme-mass star is found 
near the center of the galaxy," says Morris.  "Current evidence 
leads us to believe that the star formation process there may 
favor stars much more massive than our modest Sun." 

       Over the coming year, the team will be using the new near-
infrared spectrometer that Ian S. McLean's team is building at 
UCLA for the giant 10-meter Keck II telescope in Hawaii.  The new 
instrument will be used to measure the velocities of the expanding 
gas shells.

       In addition to Figer, Morris, and McLean, the team also 
includes Caltech physicist Gene Serabyn and Columbia University 
astronomer R. Michael Rich.

       The Space Telescope Science Institute is operated by the 
Association of Universities for Research in Astronomy, Inc. 
(AURA), for NASA, under contract with the Goddard Space Flight 
Center, Greenbelt, MD.  The Hubble Space Telescope is a project of 
international cooperation between NASA and the European Space 
Agency.

                         - end -

EDITOR's NOTE:   A photo and caption are available via the World 
Wide Web at:
http://oposite.stsci.edu/pubinfo/PR/97/33.html 
and via links in
http://oposite.stsci.edu/pubinfo/Latest.html or
http://oposite.stsci.edu/pubinfo/Pictures.html.  

Images are available via the World Wide Web at:
http://oposite.stsci.edu/pubinfo/gif/pistol.gif (GIF),
http://oposite.stsci.edu/pubinfo/jpeg/pistol.jpg (JPEG).

       Image files also may be accessed via anonymous ftp from:
oposite.stsci.edu in /pubinfo:  gif/pistol.gif (GIF) and 
jpeg/pistol.jpg (JPEG).  

       Higher resolution digital versions (300 dpi JPEG) of the 
release photograph are available in:
/pubinfo/hrtemp: 97-33.jpg (color) and 97-33bw.jpg (black &
white).  A full resolution TIFF image is available in:
/pubinfo/tiff/1997/33.tif.



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Helium and Hydrogen make up most of the elements in the star.

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Pistol: The Brightest Star in the Galaxy?

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Pistol Nebula (Pistol star is the center mass)

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Pistol star is an LBV or luminous blue variable its in its supergiant stage and goes through occasional outburst and explosions.

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Since stars and planets are extremely far apart miles are not sufficient to measure the distance so we use light years; how fast light moves in a year which is about 5.88 trillion miles.

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Solar Mass is the size of the star compared to the sun.

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Temperature is the heat that is given off an object. Since stars are so hot and massive astronomers and scientists use Kelvin to measure temperature. 11,800 Kelvin is about 20780 Fahrenheit

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Luminosity is the measurement of light that is radiated from a light-emitting object.
Pistol star is one of the most luminous stars in the Milky Way Galaxy.