RRI Study Shows Black Hole Jets Choke Star Birth in Galaxies

The correct answer is the faint envelope of gas surrounding a galaxy beyond its disc. The study describes the circumgalactic medium as a diffuse, ghostly reservoir of gas that lies past the edge of the stellar disc and spreads out to between ten and twenty times the size of the galaxy, and this reservoir supplies the fuel from which stars are eventually made. Option A describes the crowded central region of a galaxy, which is a different thing altogether. Option C refers to the dust in the spiral arms, which lies within the visible disc and not outside it. Option D describes the region bounded by the event horizon of a black hole, a region from which nothing escapes, and it has nothing to do with this outer gas. The whole point of the study is that a jet from the central black hole reaches out into this envelope.

The correct answer is the Raman Research Institute, an autonomous institute of the Department of Science and Technology, whose scientists worked with colleagues at Arizona State University in the United States. The lead author of the paper, published in The Astrophysical Journal Letters, is Namrata Roy, an assistant professor in the astronomy and astrophysics division of that institute, and a co-author quoted on the finding is Sanchayeeta Borthakur of the American university. The other three names in the options are all genuine and well-known Indian research institutions working in astronomy and physics, which makes them plausible distractors, but none of them is credited with this particular study. In current affairs, always tie a discovery to the exact institute, the lead researcher and the journal, because a question can be set on any of the three.

The correct answer is that the jet energises the gas only along its own direction and suppresses star formation. When the team averaged their measurements over all directions around the galaxies they picked up no signal, but when they probed along the direction of the jet they found a strong one, which showed that the jet illuminates only the gas in its path. The signal was strongest where the jet first meets the outer gas at the rim of the stellar disc, and again at the outer boundary of the envelope where the slowed jet strikes once more, depositing energy at both places. Because cool gas is needed for gas to clump into stars, this heating keeps the galaxy quiet and passive, so option A is the opposite of the finding. Options C and D are ruled out for the same reason, since the study shows an effect reaching far beyond the centre.