PKS 1302−102

PKS 1302−102 is a quasar in the Virgo constellation, located at a distance of approximately 1.1 Gpc (around 3.5 billion light-years).^[1] It has an apparent magnitude of about 14.9 mag in the V band with a redshift of 0.2784.^[1] The quasar is hosted by a bright elliptical galaxy,^[3] with two neighboring companions at distances of 3 kpc and 6 kpc. The light curve of PKS 1302−102 appears to be sinusoidal with an amplitude of 0.14 mag and a period of 1,884 ± 88 days, which suggests evidence of a supermassive black hole binary.^[4]

PKS 1302−102
Observation data (Epoch J2000.0)
Constellation	Virgo[1]
Right ascension	13h 05m 33.01498s[2]
Declination	−10° 33′ 19.4266″[2]
Redshift	0.2784[1]
Distance	3.5×10^9 ly (1.1 Gpc)[1]
Type	FSRS, FSRQ, FSQ, QSO, E4[2][1]
Apparent magnitude (V)	14.9[1]
Other designations
PG 1302−102, PG 1302−103, ICRF J130533.0−103319, PKS 1302−102, PKS 1302−103, PKS J1305−1033, PKS B1302−102, QSO J1305−1033, QSO B1302−1017,[2] PGC 4662778[1]
See also: Quasar, List of quasars

Possible black hole binary

PKS 1302−102 was selected from the Catalina Real-Time Transient Survey as one of 20 quasars with apparent periodic variations in the light curve. Of these quasars, PKS 1302−102 appeared to be the best candidate in terms of sinusoidal behavior and other selection criteria, such as data coverage of more than 1.5 cycles in the measured period.^[4] One plausible interpretation of the apparent periodic behavior is the possibility of two supermassive black holes (SMBH) orbiting each other with a separation of approximately 0.1 pc in the final stages of a 3.3 billion year old galaxy merger. If this turns out to be the case, it would make PKS 1302−102 an important object of study to various areas of research, including gravitational wave studies and the unsolved final parsec problem in a merger of black holes.

Other explanations, of lesser likelihood, to the observed sinusoidal periodicity include a hot spot on the inner part of the black hole's accretion disk and the possibility of a warped accretion disk which partially eclipses in the orbit around a single SMBH.^[4] However, it also remains possible that the periodic behavior in PKS 1302−102 is indeed just a random occurrence in the light curve of an ordinary quasar, as spurious nearly-periodic variations can occur over limited time periods as part of stochastic quasar variability.^[5] Further observations of the quasar could either promote true periodicity or rule out a binary interpretation, especially if the measured light curve randomly diverges from the sinusoidal model.^[5]