PSLV C-58 4th liquid stage carrying XpoSat payload during its long coasting phase in space

ISRO successfully launched the X-ray Polarimeter Satellite (XPoSat), a dedicated scientific satellite, using ISRO's Polar Satellite Launch Vehicle (PSLV) at 9.10am into a 650km orbit around Earth

India successfully launched on Monday the world’s second space-based observatory to probe through a poorly observed astronomical window some of the most violent objects in the cosmos, including the remnants of dead stars called black holes and neutron stars.

The Indian Space Research Organisation (ISRO) launched the X-ray Polarimeter Satellite (XPoSat), a dedicated scientific satellite, using ISRO’s Polar Satellite Launch Vehicle at 9.10am into a 650km orbit around Earth.

XPoSat is designed to study X-ray emissions from celestial sources through a feature called polarisation which some astronomers view as a “fourth window” for observations to extract information inaccessible through standard observations of brightness, timing, and wavelength of the emissions.

“We’re hoping to use XPoSat to gain new insights into the mechanisms fuelling the emissions from some of the most extreme objects in the universe,” said Varun Bhalerao, an associate professor of physics at the Indian Institute of Technology, Bombay.

XPoSat’s intended lifespan is five years.


Neutron stars and black holes, Bhalerao said, are marked by the highest densities, the most powerful magnetic fields, and the highest gravity. Both are collapsed and compact remnants of stars that have exhausted all their fuel. As material drawn by the intense gravity falls into the neutron stars or black holes, it emits radiation, including X-rays that can be picked up by space-based observatories.

The US National Aeronautics and Space Administration had launched the Imaging X-ray Polarimetry Explorer (IXPE) in December 2021, the first observatory with similar astronomical objectives.

India’s XPoSat has two instruments — POLIX developed at the Raman Research Institute, Bangalore, and the XSPECT developed by the space astronomy group at the ISRO’s UR Rao Space Centre, Bangalore.

Tarun Souradeep, director of the Raman Research Institute said the institute had designed and fabricated the flight model of POLIX, demonstrating capabilities for science as well as engineering.

The observational capabilities of XPoSat and IXPE are complementary, allowing both instruments to collectively probe different emission mechanisms and the physics of bright X-ray sources in the universe.