भारतीय खगोलभौतिकी संस्थान
Indian Institute of Astrophysics
Exploring the Universe since 1786
An Autonomous Institute under the
Department of Science & Technology
Government of India
Research Highlights
RESEARCH HIGHLIGHTS | IIA
Insight-HXMT View of the Black Hole Candidate Swift J1727.8–1613 during Its Outburst in 2023
SANTANU MONDAL | Dec 20, 2024
The transient Galactic black hole candidate Swift J1727.8-1613 went through an outburst for the very first time in 2023 August and lasted for almost 6 months. We study the timing and spectral properties of this source using publicly available archival Insight-HXMT data for the first 10 observation IDs that last from MJD 60181 to 60198 with a total of 92 exposures for each of the three energy bands. We have detected quasi-periodic oscillations (QPOs) in a frequency range of 0.21 ± 0.01–1.86 ± 0.01 Hz by fitting the power density spectrum. Based on the model-fitted parameters and properties of the QPOs, we classify them as type C in nature. We also conclude that the origin of the QPOs could be the shock instabilities in the transonic advective accretion flows around black holes. The spectral analysis was performed using simultaneous data from the three onboard instruments LE, ME, and HE of Insight-HXMT in the broad energy band of 2‑150 keV. To achieve the best fit, spectral fitting required a combination of models, e.g., interstellar absorption, power-law, multicolor disk–blackbody continuum, Gaussian emission/absorption, and reflection by neutral material. From the spectral properties, we found that the source was in an intermediate state at the start of the analysis period and was transitioning to the softer states. The inner edge of the accretion disk moved inward in progressive days following the spectral nature. We found that the source has a high inclination of 78°‑86°. The hydrogen column density from the model fitting varied in the range of (0.12 ± 0.02‑0.39 ± 0.08) × 1022 cm‑2.
RESEARCH HIGHLIGHTS | IIA
Proton heating estimates from near-Earth observations of coronal mass ejections in solar cycle 24 Open Access
WAGEESH MISHRA | Jul 01, 2025
As solar coronal mass ejections (CMEs) propagate through the heliosphere, they expend energy in heating protons to compensate for the cooling that occurs due to expansion. CME propagation models usually treat energy dissipation implicitly via a polytropic index (δ). Here we calculate the power dissipation implied by a given δ and compare it with the power available in the turbulent velocity fluctuations. We make this comparison using near-Earth in-situ observations of 27 of the most geoeffective CMEs (Dst < −75 nT) in solar cycle 24. For δ = 5/3, the power in the turbulent velocity fluctuations is ≈54% smaller than what would be required to maintain the proton temperature at the observed values. If the power in the turbulent cascade is assumed to be fully expended in local proton heating, the most probable value for δ is 1.35. Our results contribute to a better understanding of CME energetics, and thereby to improved CME propagation models and estimates of Earth arrival times.
Press Releases
PRESS RELEASES | SCOPE
A new method to reliably estimate Helium abundance in the Sun
SCOPE | Apr 24, 2025
Since Helium does not produce any observable spectral lines from the visible surface, or the photosphere, of the Sun, its abundance has usually been estimated through indirect means. In a recent study, the abundance of Helium in our Sun has been estimated accurately using the Magnesium and Carbon features in the observed high-resolution spectrum of the Sun.
This is based on the paper titled "Helium Abundance of the Sun: A Spectroscopic Analysis", by Satyajeet Moharana, B. P. Hema, and Gajendra Pandey, 2024, Astrophysical Journal, 974, 2.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
Scientists Chart the Sun's Subsurface Weather Patterns Tied to Its 11-Year Activity Cycle
SCOPE | Apr 29, 2025
An international team of solar physicists has unveiled new insights into the dynamic "inner weather" of the Sun—plasma currents just beneath its surface that pulse in step with its 11-year sunspot cycle. In a study published on the 22nd of April 2025, in the The Astrophysical Journal Letters, researchers from the Indian Institute of Astrophysics (IIA), Stanford University (USA), and the National Solar Observatory (NSO, USA) have traced how these hidden flows shift over time, potentially reshaping our understanding of how the Sun's interior connects to its outer magnetic behavior, which has far-reaching influence on space weather and Earth.
This is based on the paper titled "Solar Cycle Variations in Meridional Flows and Rotational Shear within the Sun's Near-surface Shear Layer", by Anisha Sen, S. P. Rajaguru, Abhinav Govindan Iyer, Ruizhu Chen, Junwei Zhao, and Shukur Kholikov, 2025, Astrophysical Journal Letters, 984, 1.
Press release by PIB published here.
Press release issued by DST here.
Download the paper from here.
PRESS RELEASES | SCOPE
IIA Bengaluru scientists discover a new kind of Stellar Chemistry
SCOPE | Jun 19, 2025
Far away in the Ophiuchus Constellation, a peculiar star named A980, 25800 light years away, is rewriting what we know about stellar chemistry. Researchers have uncovered a cosmic twist -- this mysterious star that belongs to a rare class called Extreme Helium (EHe) stars, carries surprisingly high amount of germanium—a metallic element never before observed in this type of star.
This is based on the paper titled "Detection of Enhanced Germanium in a New Cool Extreme Helium Star A980: Insights and Implications", by Ajay Kumar Saini and Gajendra Pandey, 2025, The Astrophysical Journal, 979, 239.
Press release by PIB published here.
Press release issued by DST here.
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PhD Programme
IIA offers a vigorous programme of graduate studies that forms a vital component of research & training. The programme is overseen by the board of graduate studies. The Institute is also a major partner in the Joint Astronomy Programme (JAP), organized by the Indian Institute of Science.
Admissions
PhD applications may be submitted through the IIA PhD online applications portal in May. After the initial screening, shortlisted candidates will be interviewed in June. The final list of selected candidates will be announced in July, followed by the commencement of the programme in August. .
Research Fields
Solar Studies
Studies of the Sun and solar system have been the longest pursued discipline at IIA. Members of the group conduct theoretical, numerical modeling, and observational studies in solar physics.
Stars & Galaxies
Research interests of the group members range from exoplanets, star formation, stellar evolution, end states of stars, Interstellar medium, the milky way Galaxy, nearby galaxies, active galaxies and time domain astronomy.
Theory
Members of the theoretical Astrophysics group work on a broad range of topics such as black hole astrophysics, pulsars, exoplanets, astrophysical turbulence & magnetic fields, MHD, cosmology and early universe.
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