ARIES Study Tracks Blazar OJ 287 Twin Black Holes for a Decade

The correct answer is the Aryabhatta Research Institute of Observational Sciences, Nainital. The multi-institutional campaign on the blazar OJ 287 was coordinated by scientists of this institute, which is an autonomous body of the Department of Science and Technology, and the study was led by Dr Alok C. Gupta of the same institute. The team gathered 106 scientists from 18 countries and 48 institutions and universities, who observed the object with about two dozen telescopes between 2015 and 2025. Options A, C and D name well-known Indian centres for astronomy and space science, but none of them is credited with coordinating this particular study; they are offered because candidates often confuse the national astronomy institutes with one another. The safest way to remember the fact is to link the Nainital institute, its parent department and the name of the lead scientist together, since any of the three can be asked.

The correct answer is twelve years. OJ 287 is a rare object lying about 4 billion light years away in which two supermassive black holes circle each other on a twelve-year orbit, forming a binary system. Because of that orbit the blazar brightens in a distinctive double peak, a rhythm that Finnish scientists identified in 1988 after studying nearly 100 years of optical observations going back to 1880, and astronomers have since followed each twelve-year cycle of twin outbursts to map the motion. The recent campaign captured the outbursts that fell between 2015 and 2019. Options A, B and D are wrong because none of them matches the period of the pair; they are included because a candidate who remembers only that the object has a repeating cycle may guess at the number. Remember the orbital period along with the distance, as the two facts are usually asked together.

The correct answer is 3.89 billion solar masses. Using eight optical spectra recorded at Steward Observatory in the United States during low-brightness phases of the object in October and November 2017, the team estimated the central black hole to weigh no less than that, reading the figure from the width of the oxygen emission line. Option A is wrong because it shifts the same digits down by a factor of a thousand; supermassive black holes can range from millions to billions of solar masses, so a candidate who misses the unit will fall for it. Option C is wrong because eighteen is the number of countries whose scientists joined the study, not a mass. Option D is wrong for the same kind of reason, since one hundred and six is the number of scientists in the team. The lesson is to keep the three large numbers of this study separate: the team size, the number of countries and the mass estimate.