GCIRS 16SW
Binary star in the Galactic Center in the constellation Sagittarius
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GCIRS 16SW, also known as S97, is a contact binary star located in the Galactic Center. It is composed of two hot massive stars of equal size that orbit each other with a period of 19.5 days. The stars are so close that their atmospheres overlap, and the two stars form an eclipsing binary varying in brightness by 0.35 magnitudes at infrared wavelengths.[7]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Sagittarius[1] |
| Right ascension | 17h 45m 40.124s[2] |
| Declination | −29° 00′ 29.02″[2] |
| Characteristics | |
| Evolutionary stage | Slash star |
| Spectral type | Ofpe/WN9[3] |
| Apparent magnitude (J) | 14.75[4] |
| Apparent magnitude (H) | 11.6[4] |
| Apparent magnitude (K) | 9.34[5] |
| Orbit[6] | |
| Primary | Sagittarius A* |
| Name | GCIRS 16SW |
| Period (P) | 1270±309 yr |
| Semi-major axis (a) | 2.32±0.46″ |
| Eccentricity (e) | 0.35±0.11 |
| Inclination (i) | 113.0±1.3° |
| Longitude of the node (Ω) | 113.2±1.4° |
| Periastron epoch (T) | 2132±29 |
| Argument of periastron (ω) (secondary) | 28±14° |
| Orbit[7] | |
| Period (P) | 19.4513±0.0011 d |
| Semi-major axis (a) | 140.6±4.7 R☉ |
| Inclination (i) | 70.85±0.6° |
| Periastron epoch (T) | 2451775.102±0.032 |
| Details[7] | |
| A | |
| Mass | ~50 M☉ |
| Radius | 54.5±1.8 × 58.2±1.9 × 62.7±2.1 R☉ |
| Luminosity | 1,100,000 L☉ |
| Surface gravity (log g) | 3.0 cgs |
| Temperature | 24,400 K |
| B | |
| Mass | ~50 M☉ |
| Radius | 54.5±1.8 × 58.2±1.9 × 62.7±2.1 R☉ |
| Luminosity | 1,100,000 L☉ |
| Surface gravity (log g) | 3.0 cgs |
| Temperature | 23,500 K |
| Other designations | |
| GCIRS 16SW, S97, S1-16[8] | |
| Database references | |
| SIMBAD | data |
GCIRS 16SW orbits Sagittarius A* at approximately 19,000 AU, with a period of approximately 1,270 years.[6] At the stars' estimated mass of about 50 solar masses, they are predicted to have a lifespan of about 4 million years, indicating that the system formed within 0.1 parsecs (0.33 ly; 21,000 AU) of Sagittarius A*, instead of having migrated inward from a greater distance.[7]
GCIRS 16SW was classified as a candidate luminous blue variable on the basis of its spectrum and physical properties.[9] This was before it was identified as an eclipsing binary, but it is still treated as a candidate LBV.[10]
Each star is strongly distorted by the gravity of the other star. The polar radius is calculated to be 54.5 R☉, while the radius along the direction of orbital motion is 58.2 R☉. The radius along the line joining the two stars is 62.7 R☉, while the separation of the centres of the two stars is 132.8 R☉. A calculation of properties treating the binary as a single star gave an effective temperature of 24,400 K.[9] The secondary component is found to have a temperature 96% of that of the primary. However, these temperatures yield a luminosity over a million times that of the sun, uncomfortably close to the Eddington luminosity for each star, and it is suspected the actual temperatures are slightly lower.[7]