WD 1647+375
Airglow correction of WD 1647+375 of the deep exposure where the raw spectrum and the best-fitting airglow template are shown in black and red, respectively. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules[1] |
| Right ascension | 16h 49m 20.2995s[1] |
| Declination | +37° 28′ 21.248″[1] |
| Apparent magnitude (V) | 14.98[1] |
| Characteristics | |
| Evolutionary stage | white dwarf[1] |
| Spectral type | DA2.2[1] |
| Astrometry | |
| Proper motion (μ) | RA: −60.130[1] mas/yr Dec.: +11.234[1] mas/yr |
| Parallax (π) | 12.7364±0.0296 mas[1] |
| Distance | 256.1 ± 0.6 ly (78.5 ± 0.2 pc) |
| Details | |
| Mass | 0.57±0.01[2] M☉ |
| Radius | 0.0144±0.0003[2] R☉ |
| Surface gravity (log g) | 7.88±0.03[2] cgs |
| Temperature | 22,040±31[2] K |
| Age | 30±2[2] Myr |
| Other designations | |
| WD J164920.30+372821.25[2][3], PG 1647+376, SDSS J164920.29+372821.2, Gaia DR2 1351486711809893888[1] | |
| Database references | |
| SIMBAD | data |
WD 1647+375 (WD J164920.30+372821.25, PG 1647+376) is a DA2.2 type white dwarf located approximately 256 light-years from Earth in the constellation Hercules. [1]
This star has a mass of 0.57 M☉ and a radius of 0.0144 R☉. As it is a white dwarf – the remnant of a stellar core, its temperature will be high, specifically 22040 K.[2][3] The log(g) gravity on the surface of this object is 7.88 cgs, and its age is 30 million years.[2]
Icy Exoplanetesimal
In September 2025, a group of astronomers, led by researchers from the University of Warwick (UK), utilized data from the Hubble Space Telescope, STIS and the ground-based VLT telescope. Analysis of the ultraviolet spectrum revealed interesting details.[2][4]
The white dwarf WD 1647+375 was quite different from others of its kind. It stood out due to the presence of volatile substances on its surface. The atmosphere of white dwarfs typically consists of hydrogen and helium, but in this case, elements such as carbon, nitrogen, sulfur, and oxygen were detected.[2][4]
Furthermore, ultraviolet spectroscopy, used in the study, revealed a high percentage of nitrogen in the material accreted by the star, specifically ~5%. Additionally, the atmosphere of WD 1647+375 also contains significantly more oxygen, approximately 84% more, than would be expected.[2][4] All of this indicated the presence of an icy object in the system, designated as WD 1647+375 b.[3]
Astronomers had data indicating that the debris had been feeding the star for at least the past 13 years at a rate of 200,000 kg per second. This meant the icy object had a diameter of 3 to 50 km and could have weighed a quintillion kilograms.[2][4]
In total, these data provided insight into an icy/water-rich planetesimal (composed of 64% water) being consumed by its parent star, possibly a comet similar to Halley's Comet, or a fragment of a dwarf planet, like C/2016 R2.[2]
This object can be compared to Kuiper Belt Objects (KBOs) in our Solar System. This planetesimal is most likely a fragment of a dwarf planet, such as Pluto.[2][4]
References
- ^ a b c d e f g h i j k "SIMBAD Results for WD 1647+375". SIMBAD. Retrieved 2025-09-27.
- ^ a b c d e f g h i j k l m n Sahu, Snehalata; Gänsicke, Boris T; Williams, Jamie T; Koester, Detlev G; Farihi, Jay; Desch, Steven J; Gentile Fusillo, Nicola Pietro; Veras, Dimitri; Raymond, Sean N; Belmonte, Maria Teresa (16 September 2025). "Discovery of an icy and nitrogen-rich extrasolar planetesimal". Monthly Notices of the Royal Astronomical Society. 543 (1): 223–232. arXiv:2509.13422. doi:10.1093/mnras/staf1424. ISSN 0035-8711.
- ^ a b c Martin, Pierre-Yves (October 28, 2025). "Planet WD 1647+375 b". exoplanet.eu.
- ^ a b c d e Matt, Higgs. "Icy planetesimal with high nitrogen and water content discovered in white dwarf's atmosphere". phys. Retrieved 2025-09-27.