GALEX J071816.4+373139

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]

In 2024, a group of astronomers led by Sihao Cheng, 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, an "infrared excess" was noticed. The system was emitting more heat than a single white dwarf should.^[3]

Initially, it was considered that 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 Jupiter masses and a temperature of around 400 K.^[4][3] Its surface gravity is 3.8 cgs.^[3]

This is an example of 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. The spectroscopic studies will allow for the precise determination of the atmosphere's chemical composition and possibly confirm its existence.^[3]