A groundbreaking study by researchers from the Indian Institute of Technology Kanpur (IIT Kanpur), the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Pune, and Ashoka University has provided new insights into the internal structure of neutron stars. This research, published in the Astrophysical Journal, marks a significant advancement in the use of neutron stars as natural laboratories for studying General Relativity in extreme environments.
Neutron stars, the remnants of massive stars that have exploded in supernovae, are incredibly dense objects. They cram more mass than the Sun into a sphere only about 10 kilometers across. This immense density creates powerful gravitational fields and results in a complex and poorly understood relationship between pressure and density within the star, known as the equation of state.
The research team utilized data from AstroSat, India’s first astronomical observatory, specifically its Large Area X-ray Proportional Counter (LAXPC) instrument. The LAXPC, a domestically developed achievement of Indian engineering, was employed to study X-rays emitted by the binary star system 4U 1728-34. In this system, a neutron star is accreting matter from a companion star, producing X-ray emissions.
The scientists analyzed the X-ray data from 4U 1728-34 and identified several instances of quasi-periodic oscillation (QPO) triplets. They found that the frequencies of these QPO triplets evolve continuously over time while maintaining a specific relationship with each other. This discovery allowed the researchers to interpret the QPOs in terms of three oscillations predicted by Einstein’s General Theory of Relativity: orbital motion, precession of the perihelion, and Lense-Thirring precession.
Furthermore, the researchers discovered that the observed relationship between the QPO frequencies depends sensitively on the neutron star’s mass, moment of inertia, and equation of state. This dependency provides a new method to probe these parameters in detail, a feat that was not possible previously.
The research team includes Kewal Anand (Ph.D. Scholar, IIT Kanpur), Ranjeev Misra (Senior Professor, IUCAA), JS Yadav (Visiting Professor, IIT Kanpur; Retired Professor, TIFR Mumbai; Ex-PI LAXPC onboard AstroSat), Pankaj Jain (Professor, IIT Kanpur; Head of the SPASE Department, IIT Kanpur), Umang Kumar (Ph.D. Scholar, Ashoka University), and Dipankar Bhattacharya (Professor and Head of the Physics Department, Ashoka University; Ex-Senior Professor, IUCAA).
Commenting on the findings, Pankaj Jain, Head of the SPASE Department at IIT Kanpur, said, “This discovery advances our understanding of neutron stars and opens new avenues for exploring the fundamental principles of physics in extreme environments. The insights gained from this study will have a lasting impact on astrophysics and related fields.”
This study not only enhances understanding of neutron stars but also paves the way for future explorations into the fundamental laws governing the universe. The use of AstroSat has proven instrumental in uncovering these cosmic mysteries, showcasing India’s growing capabilities in space research and astronomy.