An international team led by scientists at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, has tracked changes in the brightness and colour of the blazar OJ 287 over a decade, offering fresh insights into its powerful emissions and central binary black hole system.
The study involved 106 scientists from 48 research institutions and universities across 18 countries. Using two dozen telescopes, the researchers observed the object from 2015 to 2025, producing what the release describes as the most extensive and densely sampled optical time-series data of OJ 287 obtained over the past 150 years.
Located about four billion light years from Earth, OJ 287 contains two supermassive black holes orbiting each other over a 12-year period. Such black holes can have masses ranging from millions to billions of times that of the Sun.
OJ 287 is a blazar, an astronomical object that produces powerful jets of plasma travelling at nearly the speed of light and directed towards Earth. Its emissions vary strongly and rapidly across the electromagnetic spectrum, from radio waves to gamma rays.
The object displays a distinctive double-peaked pattern in its brightness. A Finnish scientific team discovered this periodic behaviour in 1988 using nearly a century of optical observations dating back to 1880. Astronomers have since monitored its recurring outbursts to better understand the orbital motion of the two black holes.
The latest multi-institutional campaign, coordinated by ARIES, an autonomous institution under the Department of Science and Technology, was undertaken to capture the optical outbursts associated with the 12-year cycle that occurred between 2015 and 2019.
Led by Dr Alok C. Gupta of ARIES, the collaboration included scientists from India, Bulgaria, Chile, China, Crimea, Finland, Georgia, Germany, Italy, Japan, Russia, Serbia, Spain, Sweden, Tajikistan, the United Kingdom, the United States and the West Indies.
The decade-long optical campaign was supported by observations at other wavelengths using ground- and space-based telescopes. Together, these observations allowed researchers to examine changes spanning years as well as rapid variations over much shorter periods.
The combined data helped investigate the relative positions of the two black holes at different times and changes in OJ 287’s brightness, spectrum and polarisation. Researchers also searched for evidence of emissions from the smaller black hole and examined the wider behaviour of the binary system.
The study builds on a series of research papers led since 2017 by Gupta and Professor Mauri J. Valtonen of the University of Turku, Finland.
Using eight optical spectra recorded during low-brightness states between October 21 and November 22, 2017, at the Steward Observatory in the United States, researchers estimated the central black hole’s mass to be at least 3.89 billion times that of the Sun. The estimate was derived from the width of the [O III] emission line.
The findings also provided insights into the system’s emission mechanisms and its relevance to multimessenger astronomy, which combines signals such as light, gravitational waves, neutrinos and cosmic rays from the same source.
By bringing together a decade of observations, the study strengthens OJ 287’s role as a laboratory for examining extreme cosmic processes. Continued monitoring across wavelengths could help researchers better understand relativistic jets, supermassive binary black holes and possible connections between electromagnetic and gravitational-wave signals.