GP Comae Berenices, abbreviated toGP Com and also known asG 61-29, is a star system composed of awhite dwarf orbited by a planetary mass object, likely the highly eroded core of another white dwarf star.[7] The white dwarf is slowly accreting material from its satellite at a rate of(3.5±0.5)×10−11M☉/year and was proven[8] to be a low-activityAM CVn star.[7][5] The star system is showing signs of a high abundance ofionized nitrogen from theaccretion disk around the primary.[9]
The material emitted from the planetary mass companion is mostly helium, with a molar ratio of nitrogen up to 1.7%, very low neon levels and other elements not detectable at all.[13] Approximately half of the luminosity of the system comes from the accretion disk.[5] The planetary object is suspected to contain astrange quark matter core due to its unusually high density, which must be above187.5 g/cm3 to preventtidal disruption; the theoretical bound for planets composed solely of ordinary matter is on the order of30 g/cm3. The object's orbit is expected to decay within 100 million years due togravitational wave emission.[14]
^abKupfer, T.; Steeghs, D.; Groot, P. J.; Marsh, T. R.; Nelemans, G.; Roelofs, G. H. A. (2016), "UVES and X-Shooter spectroscopy of the emission line AM CVN systems GP Com and V396 Hya",Monthly Notices of the Royal Astronomical Society,457 (2): 1828,arXiv:1601.02841,Bibcode:2016MNRAS.457.1828K,doi:10.1093/mnras/stw126
^Nelemans, G.; Yungelson, L. R.; Sluys, M. V. van der; Tout, Christopher A. (2009), "The chemical composition of donors in AM CVN stars and ultracompact X-ray binaries: Observational tests of their formation",Monthly Notices of the Royal Astronomical Society,401 (2):1347–1359,arXiv:0909.3376,doi:10.1111/j.1365-2966.2009.15731.x,S2CID2716902
