- Why in news
- On 23 October 2026, PIB reported that ARIES scientists (DST) explained how black hole spin shapes X-ray flickering, known as QPOs, in accretion discs. The work was published in the Journal of High Energy Astrophysics.
- What it is
- Quasi-periodic oscillations (QPOs) are nearly regular variations in the brightness of X-rays from matter falling into a black hole. They are seen in black hole X-ray binaries, where gas from a companion star forms an accretion disc around the black hole. Their origin has long been debated, and models try to link them to disc shocks, spin and viscosity.
- Who did the study
- Scientists at ARIES, an autonomous institute of the Department of Science and Technology, led the work. Researchers from Poland and MJP Rohilkhand University, Bareilly, also took part.
- Key mechanism
- When the viscosity of the accretion flow exceeds a critical value, the normally stable shock in the disc becomes unstable and oscillates. This produces QPOs.
- Effect of spin
- In slowly spinning black holes the shock sits farther out and gives mainly low-frequency QPOs. Rapid spin pulls the shock closer and gives QPOs over a much wider range of frequencies.
- Predicted frequency
- For very high spin and a black hole about ten solar masses, predicted QPO frequencies can exceed 100 Hz, similar to those observed in X-ray binaries.
- Claimed first
- The researchers say it is the first numerical study of an accretion flow with viscosity that also uses the thermodynamic relations of a relativistic fluid.
Don’t confuse with QPOs vs black hole spin: Spin is a property of the black hole. QPOs are variations in the brightness of the emitted radiation, which the study links to spin through the shock position.
Don’t confuse with Accretion disc vs event horizon: The accretion disc is the infalling matter around the black hole. The event horizon is the boundary beyond which even light cannot escape.
Science and technology: 57 Prelims questions since 2013; most test the concept behind the news, not the news itself. In Mains, 12 news-triggered questions.
Why it matters
- Reduces randomness in theoretical models of accretion flows around black holes.
- Shows Indian institutes doing original work in high-energy astrophysics.
Problems
- Results are simulation-based and need checking against observations of real X-ray binaries.
- Earlier models explained either low or high frequencies, not both.
Way forward
- Compare predicted QPO frequencies and photon index with data from X-ray observatories.
- Extend the simulations to different black hole masses and spins.
Put in your answer
ARIES simulation study: An Indian simulation of viscous relativistic accretion flows links black hole spin to QPO frequency. It is an example of indigenous research in astrophysics.
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No practice question for this one; the card may still help an answer. Why: Space science concept tested as a concept in Prelims (36 of 57 sci_tech questions), but this is a niche research finding; unlikely to be asked.
Worth revising until Prelims 2028: most news questions come within two years of the event.