LMC X-2
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Mensa |
| Right ascension | 05h 20m 28.2s |
| Declination | −71° 57′ 33″ |
| Apparent magnitude (V) | ~18.8 |
| Characteristics | |
| Evolutionary stage | Neutron star (A) Evolved B-type star (B) |
| Spectral type | Neutron star + ? |
| Astrometry | |
| Radial velocity (Rv) | 262.2 ± 3.4 km/s |
| Distance | ~162,983 ly (~49,970 pc) |
| Orbit | |
| Primary | neutron star |
| Name | main-sequence star |
| Period (P) | 0.32 ± 0.02 days (8.15 hours) |
| Inclination (i) | ≲70° |
| Semi-amplitude (K2) (secondary) | 315 ± 28 km/s |
| Details | |
| A | |
| Mass | 1.4 ± 0.6 M☉ |
| Radius | ≲16 km R☉ |
| Temperature | 2,300,000 ± 900,000 K |
| B | |
| Mass | ≤1 M☉ |
| Radius | 6-10 km R☉ |
| Other designations | |
| LMC X-2, SWIFT J0520.9-7156 | |
| Database references | |
| SIMBAD | data |
LMC X-2 is a low-mass X-ray binary (LMXB) located in the Large Magellanic Cloud (LMC), a satellite galaxy of Milky Way. It is one of the five brightest X-ray sources in the LMC and is the most luminous LMXB with a luminosity ranging from 0.3×1037 and 6×1038 ergs/s. This binary system consist of a neutron star accreating matter from an orbiting low-mass blue star. Its high luminosity is caused because of its X-ray emission is close to the Eddington limit or Eddington luminosity for a neutron star and because the Large Magellanic Cloud has lower metal abundances, allowing for higher Eddington luminosities and a higher accretion rate causing its high luminosity.
LMC X-2 is classified as a Z-source, a subtype of neutron star LMXB characterized by high accretion rates and a distinctive Z-shaped track in X-ray color-color and hardness-intensity diagrams. These tracks reflect transitions between three spectral states: the horizontal branch, normal branch, and flaring branch. It is the first Z-source identified outside the Milky Way, making it the eighth known Z-source overall.