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
Automated detection of galactic rings from sloan digital sky survey images
SUDHANSHU BARWAY | Jan 10, 2025
Morphological features in galaxies—like spiral arms, bars, rings, and tidal tails, etc.—carry information about their structure, origin, and evolution. It is therefore important to catalog and study such features and to correlate them with other basic galaxy properties, the environments in which the galaxies are located, and their interactions with other galaxies. The volume of present and future data on galaxies is so large that traditional methods, which involve expert astronomers identifying morphological features through visual inspection, are no longer sufficient. It is therefore necessary to use AI-based techniques like machine learning and deep learning to find morphological structures quickly and efficiently. We report in this study the application of deep learning for finding ring-like structures in galaxy images from the Sloan Digital Sky Survey (SDSS) DR18. We use a catalog by R. J. Buta of ringed galaxies from SDSS to train the network, reaching good accuracy and recall, and generate a catalog of 29,420 galaxies, of which 4855 have ring-like structures with prediction confidence exceeding 90%. Using a catalog of barred galaxy images identified by S. Abraham et. al. with deep-learning techniques, we identify a set of 2087 galaxies with bars as well as rings. The catalog should be very useful in understanding the origin of these important morphological structures. As an example of the usefulness of the catalog, we explore the environments and star formation characteristics of the ring galaxies in our sample.
RESEARCH HIGHLIGHTS | IIA
Deciphering the evolution of thermodynamic properties and their connection to the global kinematics of high-speed coronal mass ejections using FRIS model
SOUMYARANJAN KHUNTIA | Dec 01, 2024
Most earlier studies have been limited to estimating the kinematic evolution of coronal mass ejections (CMEs), and only limited efforts have been made to investigate their thermodynamic evolution. We focus on the interplay of the thermal properties of CMEs with their observed global kinematics. We implement the Flux rope Internal State model to estimate variations in the polytropic index, heating rate per unit mass, temperature, pressure, and various internal forces. The model incorporates inputs of 3D kinematics obtained from the Graduated Cylindrical Shell (GCS) model. In our study, we chose nine fast-speed CMEs from 2010 to 2012. Our investigation elucidates that the selected fast-speed CMEs show a heat-release phase at the beginning, followed by a heat-absorption phase with a near-isothermal state in their later propagation phase. The thermal state transition, from heat release to heat absorption, occurs at around 3( ± 0.3) to 7(± 0.7) R ⊙ for different CMEs. We found that the CMEs with higher expansion speeds experience a less pronounced sharp temperature decrease before gaining a near-isothermal state. The differential emission measurement (DEM) analysis findings, using multiwavelength observation from Solar Dynamics Observatory/Atmospheric Imaging Assembly, also show a heat release state of CMEs at lower coronal heights. We also find the dominant internal forces influencing CME radial expansion at varying distances from the Sun. Our study shows the need to characterize the internal thermodynamic properties of CMEs better in both observational and modeling studies, offering insights for refining assumptions of a constant value of the polytropic index during the evolution of CMEs
RESEARCH HIGHLIGHTS | IIA
A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XVIII. Reconstructing the star formation history of early-type galaxies through the combination of their UV and Hα emission
ANNAPURNI SUBRAMANIAM | Apr 04, 2025
We reconstructed the star formation histories of seven massive (M⋆ ≳ 1010 M⊙) early-type galaxies (ETGs) in the Virgo cluster by analysing their spatially resolved stellar population (SP) properties including their ultraviolet (UV) and Hα emission. As part of the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), we used Hα images to select ETGs that show no signs of ongoing star formation. We combined VESTIGE with images from Astrosat/UVIT, GALEX, and CFHT/MegaCam from the Next Generation Virgo Cluster Survey (NGVS) to analyse radial spectral energy distributions (SEDs) from the far-UV (FUV) to the near-infrared. The UV emission in these galaxies is likely due to old, low-mass stars in post main sequence (MS) phases, the so-called UV upturn. We fitted the radial SEDs with novel SP models that include an old, hot stellar component of post-MS stars with various temperatures and energetics (fuels). This way, we explored the main stellar parameters responsible for UV upturn stars regardless of their evolutionary path. We make these models publicly available through the SED fitting code CIGALE. Standard models are not able to reproduce the galaxies’ central FUV emission (SMA/Reff ≲ 1), while the new models well characterise it through post-MS stars with temperatures T ≳ 25 000 K. All galaxies are old (mass-weighted ages ≳10 Gyr) and the most massive ones, M49 and M87, are supersolar (Z ≃ 2 Z⊙) within their inner regions (SMA/Reff ≲ 0.2). Overall, we find flat age gradients (∇Log(Age) ∼ −0.04 − 0 dex) and shallow metallicity gradients (∇Log(Z) < −0.2 dex), except for M87 (∇Log(ZM87) ≃ −0.45 dex). Our results show that these ETGs formed with timescales τ ≲ 1500 Myr, having assembled between ∼40 − 90% of their stellar mass at z ∼ 5. This is consistent with recent JWST observations of quiescent massive galaxies at high-z, which are likely the ancestors of the largest ETGs in the nearby Universe. The derived flat and shallow stellar gradients indicate that major mergers might have contributed to the formation and evolution of these galaxies.
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.
Study at IIA
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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