V4998 Sagittarii is a

luminous blue variable star Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Large ...

(LBV) in the constellation of Sagittarius. Located some 25,000 light years away, the star is positioned about 7 pc (23 ly) away from a starburst cluster known as the

Quintuplet cluster The Quintuplet cluster is a dense cluster may refer to: Science and technology Astronomy * Cluster (spacecraft), constellation of four European Space Agency spacecraft * Asteroid cluster, a small asteroid family * Cluster II (spacecraft ...

. It has an ejection nebula measuring over 0.8 pc in diameter, formed 5000-10,000 years ago through large eruptions. The star has a large mass comparable to the Pistol star and a luminosity of around 4,000,000 times the Sun (). This places the star as one of the most massive and luminous stars known.

Observational history

The star was first discovered in a 1993 survey that searched for bright

near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

sources within 0.55°² of the Galactic Center. The survey used 1–20 micron photometry and used a two channel InSb detector on the 1 meter ANU telescope in Australia. 50 objects were targeted and most of them had bolometric magnitudes below -5. The star itself was observed in May 1987. Its position, ''JHKLNMQ'' magnitudes,

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...

, and silicate absorption were noted. The survey was conducted by Tetsuya Nagata, A. R. Hyland, S. M. Straw, Shuji Sato, and Kimiaki Kawara. The survey named the star NHS93 22; NHS standing for the three leading scientists in the survey (Nagata, Hyland, and Straw), 93 signifying the date of discovery, and 22 indicating that it was the 22nd star observed. The next observation was made by the

2MASS The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...

survey, which took place in 1997-2001. The star was designated 2MASS J17460562-2851319 and its position, luminosity, and ''JHKs'' magnitudes were catalogued. After that, the star was observed in a 2001 survey called the ''Study of Long Period Variables stars near the Galactic Centre''. The survey named the star GMC2001 10-1, GMC standing for Glass, Matsumoto, and Carter. It was observed by the Infrared Array Camera on board the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

in a 2008 survey covering 2.0 by 1.4 degrees (280 by 210 pc) and was given the name SSTGC 595621. It was also observed by a 2009 near-infrared survey that targeted the Galactic Center. The star was designated MKN2009 in that survey, MKN standing for the three leading scientists (Matsunaga, Kawadu, and Nishiyama) and 2009 specifying the date of the survey. V4998SgrLightCurve

A narrowband imaging survey of the Galactic Center region conducted by the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

(HST) Near Infrared Camera and Multi Object Spectrometer (

NICMOS The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) is a scientific instrument for infrared astronomy, installed on the Hubble Space Telescope (HST), operating from 1997 to 1999, and from 2002 to 2008. Images produced by NICMOS contain ...

) revealed LBV G0.120-0.048 as a strong source of

Paschen-alpha The emission spectrum of atomic hydrogen has been divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two energy levels in an ...

(Paschen-α) emission which exceeded that of the Pistol star. Therefore the star was selected for

spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...

. The survey, which was conducted in 2010, confirmed that the star was a

luminous blue variable Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of the Larg ...

and the star was designated LBV G0.120-0.048, LBV meaning luminous blue variable and G0.120-0.048 standing for its Galactic coordinates. It was also found through the use of Pα imaging that the star had a large ejection

nebula A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...

with a diameter over 0.8 pc which was ejected by it 5000-10,000 years ago through large eruptions. The star's

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

was studied and it was found that the spectrum was similar to the Pistol star so a mass similar to the Pistol star was assumed. The extinction rates were measured and a luminosity of about was obtained. It also has the designation MMC2010 from a 2010 survey, MMC standing for the three leading scientists of the survey, Mauerhan, Morris, and Cotera. In 2011, a survey led by Dong, Wang, and Cotera reached for stars in the Galactic centre that emitted Paschen-α. The stars targeted were the ones detected from the HST/NICMOS Paschen-α survey of the Galactic Centre. V4998 Sagittarii was one of the stars observed and it was given another designation of DWC2011 92. In 2014 a group decided to study the LBVs in the Quintuplet cluster. The mass of the star's nebula was measured at . Also measured was the star's

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

and it was found to be 12,000 K. The star was designated LBV3 in that survey because it was the third LBV in the Quintuplet cluster.

Characteristics

V4998 Sgr's high mass compresses its core and accelerates fusion primarily by the CNO cycle which leads to a luminosity of about and a temperature of 12000 K. It boasts a large ejection

with a diameter of about 0.8 parsec (2.5 ly) and a mass of . Since comparable nebulae typically last no more than 10,000 years, V4998 Sagittarii is presumed to have undergone a massive eruption 5000-10,000 years ago. The star is a projected 7 pc (23 ly) away from the Quintuplet starburst cluster, which lies in the direction of the Galactic Center. The cluster contains around 100 O-type stars and several Wolf–Rayet stars. There are also two other luminous blue variables beside V4998 Sagittarii: the Pistol star and qF362.

Evolution

The star's high mass loss rate combined with its eruptions will strip off its hydrogen layers and expose a hot helium core. It will proceed to the Wolf–Rayet sequence. It will eventually start fusing heavy elements in its core, and when it develops a large iron core the star will collapse in on itself and explode as a type Ib or Ic supernovae. Depending on the amount of mass lost before the supernova explosion, the remnant will be a

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

. A black hole is predicted for the most massive stars such as this one.

References

Notes

{{DEFAULTSORT:LBV G0.120-0.048 Luminous blue variables Sagittarius (constellation) Sagittarii, V4647 J17460562-2851319