ISRO’s New X-ray Eye in the Sky

1 min read

Why in News?

  • As the world woke up to the first morning of 2024, ISRO’s launch vehicle put into orbit a new X-ray payload (XPoSat, X-ray Polarimeter Satellite) for astronomical research.
  • If all goes well, the instrument, totally indigenous in design and fabrication, will herald yet another milestone for Indian astronomers.

An Overview of XPoSat and POLIX

  • Milestone Launch of XPoSat
    • ISRO's successful launch of the X-ray Polarimeter Satellite (XPoSat) signifies a groundbreaking achievement for Indian astronomers.
    • The launch vehicle placed XPoSat into orbit, marking India's entry into advanced space-based X-ray observations.
    • XPoSat, designed for astronomical research, carries the indigenous Indian X-ray Polarimeter instrument (POLIX) at its core.
  • RRI's 15-Year Endeavor - POLIX Development
    • The Raman Research Institute (RRI) in Bangalore has been dedicated to the development of POLIX for the past 15 years.
    • POLIX, entirely indigenous in design and fabrication, showcases India's commitment to advancing space-based X-ray astronomy.
    • Despite its relatively modest size, POLIX is a unique instrument, focusing on studying the polarisation of X-rays in space.
  • POLIX's Unique Focus on X-ray Polarisation
    • POLIX, measuring about half a meter in all dimensions and weighing nearly two hundred kilograms, is dedicated to studying a specific property of X-rays — polarisation.
    • The instrument aims to unravel the mysteries of celestial objects, such as stars with powerful magnetic fields, pulsars, and regions around black holes, by analysing the polarization of X-rays they emit.
    • X-ray polarisation provides astronomers with valuable insights into the nature and characteristics of these cosmic phenomena.

Significance of ISRO’s Milestone Mission

  • The successful integration of POLIX into XPoSat exemplifies India's technological prowess and scientific acumen in the field of space exploration.
  • The collaborative effort between ISRO, RRI, and the broader scientific community underscores India's dedication to advancing knowledge and making significant strides in space-based X-ray astronomy.
  • With XPoSat and POLIX, Indian astronomers are poised to make groundbreaking discoveries that contribute to a deeper understanding of the universe, showcasing the country as a significant player in the realm of advanced astrophysical research.

Understanding X-Ray Polarisation

  • X-Ray Nature as Electromagnetic Waves
    • X-rays, like ordinary light, are electromagnetic waves generated by the movement of electric charges when disturbed by electric and magnetic fields.
    • X-rays differ due to their high energy, presenting challenges in handling compared to visible light.
  • Directionality and Polarisation of X-Rays
    • The fluctuation in the electric field of X-rays is directional and contingent on the motion of the electric charge generating the wave.
    • Polarisation in X-rays refers to the specific direction of this fluctuation, unlike ordinary light where fluctuation directions are random due to molecular motion.
  • Everyday Analogies and Solar Polarisation
    • Analogies with water waves help illustrate the directional fluctuation in the electric field of X-rays.
    • Everyday examples, such as sunlight becoming polarised after reflection and scattering, provide relatable contexts for understanding the concept of polarisation.
  • Astronomical Implications of X-Ray Polarization Studies
    • Celestial objects, like pulsars with powerful magnetic fields, can emit polarised X-rays due to the alignment of magnetic field lines.
    • X-ray polarisation studies offer astronomers a unique tool to directly probe the magnetic fields of celestial objects, providing insights into their nature and characteristics.
    • Pulsars and regions around black holes, emitting X-rays that acquire polarisation after reflection and scattering, become crucial targets for exploring the universe's intricacies.

Importance of Polarisation in Astronomical Observations

  • More Information About Celestial Bodies
    • Polarised X-rays from these objects provide a unique window for astronomers to directly investigate and comprehend the alignment and dynamics of magnetic field lines.
    • This insight into magnetic field characteristics offers invaluable information about the nature of the celestial bodies.
  • Details about Black Hole Surroundings
    • Regions around black holes, where matter spirals in the form of a disc before succumbing to the gravitational pull, emit X-rays.
    • Initially unpolarised, these X-rays acquire polarization after reflection and scattering from the surrounding environment.
    • This transformation in polarisation becomes a crucial tool for astronomers like how sunlight becomes polarised after interaction with atmospheric particles.
    • Examining polarised X-rays in this context allows scientists to unravel essential details about the structure and conditions near black holes.
  • Will Expand Astronomical Understanding
    • The ability to measure the polarisation of X-rays from celestial objects significantly expands the toolkit available to astronomers.
    • It unveils details that would remain obscured when solely relying on other observational methods.

Challenges in X-Ray Polarisation Studies

  • High Energy Constraints
    • Collecting cosmic X-rays poses a unique set of challenges, primarily because their high energy makes conventional methods of focusing, such as using lenses for visible light, impractical.
    • Unlike visible light, which can be directed and concentrated with lenses, X-rays require alternative methods for observation due to their penetrative nature and high energy levels.
  • Earth's Atmosphere
    • Another substantial challenge arises from the Earth's atmosphere, which absorbs a significant portion of incoming X-rays.
    • This atmospheric absorption makes ground-based X-ray observations challenging and often unreliable.
  • Feeble Radiation and Instrumentation Limitations
    • Cosmic X-rays present a challenge due to their relatively feeble nature.
    • This feebleness necessitates highly sensitive instruments for detection, adding complexity to the design and deployment of X-ray detectors.
    • Previous attempts at X-ray astronomy have involved balloon-borne and short-lived instruments.
    • However, these efforts were constrained by the limitations of the instruments and the short duration of their functionality.

How Can POLIX Overcome These Challenges?

  • POLIX's Unique Design
    • Amidst the challenges, the Indian mission, XPoSat, introduces a unique design with POLIX as its primary instrument.
    • POLIX is shaped like a cubical cylinder, featuring a beryllium disc at its core for collecting X-rays after their scattering.
    • The success of POLIX owes much to the vision of Biswajit Paul, who, with a background in X-ray research, envisioned a unique instrument during his time at the Tata Institute of Fundamental Research (TIFR).
  • Complementary Role of POLIX
    • POLIX focuses on lower energy X-rays compared to a NASA instrument launched in December 2021.
    • The complementary nature of the Indian and NASA instruments enhances the ability of astronomers to unravel the nature of pulsars and black holes.


  • The successful launch of XPoSat and the deployment of POLIX represent a significant stride in India's pursuit of excellence in space-based X-ray astronomy.
  • The innovative design of POLIX, its ability to probe lower energy X-rays, and its collaborative role with NASA's instrument position Indian astronomers at the forefront of unravelling the mysteries surrounding pulsars and black holes.
  • As XPoSat begins its cosmic scanning, the scientific community eagerly awaits the invaluable insights it promises to provide.

Q1) What is the PSLV and its role in ISRO's launch vehicles?

The Polar Satellite Launch Vehicle (PSLV) is a versatile launch vehicle developed by ISRO. It plays a crucial role in launching satellites into polar orbits and has been instrumental in various successful missions.

Q2) How does the GSLV differ from the PSLV in terms of launch capabilities?

The Geosynchronous Satellite Launch Vehicle (GSLV) is designed to launch heavier payloads into geosynchronous orbits. Unlike the PSLV, the GSLV is capable of carrying larger satellites and is an essential component in India's space exploration endeavours.

Source: The Indian Express