GALEX J071816.4+373139
SDSS image of GALEX J0718+3731 (blue dot in the center) | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Auriga[1] |
| Right ascension | 07h 18m 16.42350s[2] |
| Declination | +37° 31′ 39.2363″[2] |
| Characteristics | |
| Evolutionary stage | white dwarf[1] |
| Spectral type | DC[1] |
| Astrometry | |
| Proper motion (μ) | RA: −34.878±0.085[2] mas/yr Dec.: −35.816±0.080[2] mas/yr |
| Parallax (π) | 11.8194±0.095 mas[2] |
| Distance | 276 ± 2 ly (84.6 ± 0.7 pc) |
| Details | |
| Mass | 1.27-1.29[3][4] M☉ |
| Radius | 0.01[3][4] R☉ |
| Temperature | 42,065[3][4] K |
| Rotation | 11.3 min[3] |
| Age | cooling age: 0.2[3][4] Gyr |
| Other designations | |
| GALEX J0718+3731[4], SDSS J071816.40+373139.0, SDSS J071816.41+373139.1, Gaia DR2 898348313253395968, Gaia DR3 898348313253395968[1] | |
| Database references | |
| SIMBAD | data |
GALEX J071816.4+373139 (originally WD 0718+3731) is a massive young white dwarf located in the constellation Auriga, approximately 276 light-years away from the Sun.[3][4] This star was first discovered by the GALEX space telescope during its ultraviolet sky survey while the mission was operational (2003–2013).
Star Characteristics
The white dwarf has a spectral type of DC, a mass ranging from 1.27 to 1.29 solar masses, and a radius of 6,955 km, or 0.01 solar radius.[4] The star has a rotation period of 11.3 minutes and a magnetic field strength of approximately 8 MG.[3] Its age is 0.2 billion years, or 200 million years.[3][4] It is presumed to have formed from the merger of two less massive white dwarfs, which explains its high mass, strong magnetic field, and rapid rotation.[3]
Planetary-mass object
In 2024, a group of astronomers led by Sihao Cheng (程思浩), while analyzing archival data from the Spitzer Space Infrared Telescope, discovered a planetary-mass object around the young white dwarfs GALEX J071816.4+373139. The researchers were initially looking for infrared excesses in young, massive white dwarfs whose parameters had been previously refined by the Gaia mission. However, during the analysis of the star's spectrum, scientists noticed an "infrared excess." This meant that the system was emitting more heat than a single white dwarf should.[3]
Initially, they considered it a possible dusty disk with a temperature of around 650 K, which could have created the flux excess at [4.5]. However, such a dusty disk would have produced significant flux excesses at [5.8] and [8.0]. Detailed analysis revealed that the source of this heat was a compact object, which they identified as a giant planet, designated GALEX J071816.4+373139 b.[3]
The exoplanet candidate has a mass of approximately 3.6 Mj and a temperature of around 400 K.[4][3] Its surface gravity is 3.8 cgs.[3]
Studying this system helped astronomers understand how giant planets form and survive in orbits around massive B-type stars, which then evolve into white dwarfs.[3]
The object is a priority target for the JWST mission. His spectroscopic studies will allow for the precise determination of the atmosphere's chemical composition and definitively confirm its existence.[3]
References
- ^ a b c d "SIMBAD Results for GALEX J071816.4+373139". SIMBAD. Retrieved 2025-07-24.
- ^ a b c d e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c d e f g h i j k l m n o Cheng, Sihao; Schlaufman, Kevin C.; Caiazzo, Ilaria (2025). "A Candidate Giant Planet Companion to the Massive, Young White Dwarf GALEX J071816.4+373139 Informs the Occurrence of Giant Planets Orbiting B Stars". The Astronomical Journal. 170 (1): 47. arXiv:2408.03985. Bibcode:2025AJ....170...47C. doi:10.3847/1538-3881/addd21.
- ^ a b c d e f g h i Martin, Pierre-Yves (2025). "Planet GALEX J0718+3731 b". exoplanet.eu. Retrieved 2025-07-24.