 Infrared image ofCluster 1806_20. LBV 1806−20 is the brightest star, on the left. Credit:Hubble Space Telescope | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 08m 40.31s[1] |
| Declination | −20° 24′ 41.1″[1] |
| Characteristics | |
| Evolutionary stage | candidateLBV[2] |
| Spectral type | O9 - B2[2] |
| Apparent magnitude (J) | 13.93[3] |
| Apparent magnitude (H) | 10.75[3] |
| Apparent magnitude (K) | 8.89[3] |
| Astrometry | |
| Distance | 8.7k[4] pc |
| Details | |
| Mass | 36[4] M☉ |
| Radius | 907,925 R☉ |
| Luminosity | ~2,000,000[2][5][6] L☉ |
| Temperature | 18,000–32,000[3] K |
| Age | 3.0 – 4.5[1] Myr |
| Other designations | |
| 2MASS J18084031-2024411 | |
| Database references | |
| SIMBAD | data |
LBV 1806−20 is a candidateluminous blue variable (LBV) and likelybinary star located around 28,000light-years (8,700 pc) from theSun, towards the center of theMilky Way. It has an estimated mass of around 36solar masses and an estimated variable luminosity of around two million times that of the Sun. It is highly luminous but is invisible from theSolar System at visual wavelengths because less than one billionth of its visible light reaches us.
When first discovered, LBV 1806−20 was considered boththe most luminous andmost massive star known, which challenged scientific understanding of the formation of massive stars. Recent estimates place it somewhat nearer to Earth, which when combined with its binary nature mean that it is now well within the expected range of parameters for extremely luminous stars in the galaxy. It is estimated at 2 million times as luminous as the sun which makes it one of the most luminous stars in the galaxy.
LBV 1806−20 lies at the core of radionebula G10.0–0.3, which is believed to be primarily powered by itsstellar wind.[7] It is a member of the1806−20open cluster, itself a component ofW31, one of the largestH II regions in the Milky Way. Cluster 1806−20 is made up of some highly unusual stars, including fourWolf–Rayet stars, severalOB stars, and amagnetar (SGR 1806−20).[4]
The spectral type of LBV 1806−20 is uncertain and possibly variable. It has been constrained to between O9 and B2 on the basis of an infrared HeI lineequivalent width. The spectrum shows strong emission in the Paschen and Brackett series ofhydrogen, but also emission lines ofhelium, FeII, MgII, and NaI. The lines are broad and have uneven profiles, some showingP Cygni profiles.[3] High resolution spectra show that some HeI absorption lines are doubled.[2]
Intervening dust in the direction of theGalactic Center absorb an estimated 35 magnitudes at visual wavelengths,[3] and so most observations are conducted usinginfrared telescopes.[4][1] On the basis of its luminosity and spectral type it is suspected of being an LBV, but despite the name the characteristic photometric and spectroscopic variations have not yet been observed so it remains just a candidate.[2][5]
To account for the doubled HeI lines in its spectrum and the inconsistent mass, luminosity and age estimates, LBV 1806-20 has been proposed to be a binary. The emission lines are single, so only one star appears to have a dense stellar wind as might be expected from an LBV.[2]
