GP Comae Berenices, abbreviated to GP Com and also known as G 61-29, is a star system composed of a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

orbited by a planetary mass object, likely the highly eroded core of another white dwarf star. The white dwarf is slowly accreting material from its satellite at a rate of /year and was proven to be a low-activity

AM CVn star An AM Canum Venaticorum star (AM CVn star), is a rare type of cataclysmic variable star named after their type star, AM Canum Venaticorum. In these hot blue binary variables, a white dwarf accretes hydrogen-poor matter from a compact companion sta ...

. The star system is showing signs of a high abundance of

ionized Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

nitrogen from the

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...

around the primary. In 1971, Brian Warner discovered that the star, then known as G61-29, is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

. it was given its

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

, GP Comae Berenices, in 1975.

Planetary system

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. Approximately half of the luminosity of the system comes from the accretion disk. The planetary object is suspected to contain a

strange quark matter Strange matter (or strange quark matter) is quark matter containing strange quarks. In extreme environments, strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size ...

core due to its unusually high density, which must be above to prevent

tidal disruption The tidal force or tide-generating force is the difference in gravitational attraction between different points in a gravitational field, causing bodies to be pulled unevenly and as a result are being stretched towards the attraction. It is the d ...

; the theoretical bound for planets composed solely of ordinary matter is on the order of . The object's orbit is expected to decay within 100 million years due to

gravitational wave Gravitational waves are oscillations of the gravitational field that Wave propagation, travel through space at the speed of light; they are generated by the relative motion of gravity, gravitating masses. They were proposed by Oliver Heaviside i ...

emission.

References

{{Coma Berenices AM CVn stars White dwarfs Planetary systems with one confirmed planet Coma Berenices J13054243+1801039 Comae Berenices, GP