PKS 1302-102 is a

quasar A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...

in the

Virgo constellation Virgo is one of the constellations of the zodiac. Its name is Latin for maiden, and its old astronomical symbol is (♍︎). Lying between Leo to the west and Libra to the east, it is the second-largest constellation in the sky (after Hydra) a ...

, located at a distance of approximately 1.1 Gpc (around 3.5 billion light-years). It has an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of about 14.9 mag in the

V band The V band ("vee-band") is a standard designation by the Institute of Electrical and Electronics Engineers (IEEE) for a band of frequencies in the microwave portion of the electromagnetic spectrum ranging from 40 to 75 gigahertz (GHz). The V ...

with a

redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in f ...

of 0.2784. The quasar is hosted by a bright elliptical galaxy, 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.

Possible black hole binary

PKS 1302-102 was selected from the

Catalina Real-Time Transient Survey The Catalina Real-Time Transient Survey is a collaboration using three telescopes looking for optical transients. The same telescopes are used as in the Catalina Sky Survey. They are Mt. Lemmon Survey, Catalina Sky Survey, and Siding Spring Surv ...

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. 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 Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in 1 ...

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. 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 Spurious may refer to: * Spurious relationship in statistics * Spurious emission or spurious tone in radio engineering * Spurious key in cryptography * Spurious interrupt in computing * Spurious wakeup in computing * ''Spurious'', a 2011 novel ...

nearly-periodic variations can occur over limited time periods as part of stochastic quasar variability. 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.

Possible black hole binary

References

Further reading