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Context

• The Indian Space Research Organisation is collaborating with the Raman Research Institute (RRI), Bengaluru, an autonomous research institute, to build the X-Ray Polarimeter Satellite (XPoSat) that is scheduled to be launched later this year.

What is the XPoSat mission?

• XPoSat will study various dynamics of bright astronomical X-ray sources in extreme conditions.
• It has been billed as India’s first, and only the world’s second polarimetry mission that is meant to study various dynamics of bright astronomical X-ray sources in extreme conditions.
• The other such major mission is NASA’s Imaging X-ray Polarimetry Explorer (IXPE) that was launched in 2021.
• IXPE carries three state-of-the-art space telescopes. Each of the three identical telescopes hosts one light-weight X-ray mirror and one detector unit. These will help observe polarized X-rays from neutron stars and supermassive black holes.
• By measuring the polarisation of these X-rays, we can study where the light came from and understand the geometry and inner workings of the light source.

How are X-Rays witnessed in space?

• X-rays have much higher energy and much shorter wavelengths, between 0.03 and 3 nanometers, so small that some x-rays are no bigger than a single atom of many elements.
• The physical temperature of an object determines the wavelength of the radiation it emits. The hotter the object, the shorter the wavelength of peak emission.
• X-rays come from objects that are millions of degrees Celsius — such as pulsars, galactic supernova remnants, and black holes.
• Like all forms of light, X-rays consist of moving electric and magnetic waves. Usually, peaks and valleys of these waves move in random directions. Polarised light is more organised with two types of waves vibrating in the same direction.
• It adds that fishermen use polarised lenses to reduce glare from sunlight when they are near water.
• The field of polarimetry studies the measurement of the angle of rotation of the plane of polarised light (that is, a beam of light in which the vibrations of the electromagnetic waves are confined to one plane) that results upon its passage through certain transparent materials, according to Britannica.
• The emission mechanism from various astronomical sources such as black holes, neutron stars, active galactic nuclei, pulsar wind nebulae etc. originates from complex physical processes and are challenging to understand.

What are XPoSat’s payloads?

• The spacecraft will carry two scientific payloads in a low earth orbit.
• The primary payload POLIX (Polarimeter Instrument in X-rays) will measure the polarimetry parameters (degree and angle of polarisation).
• The payload is being developed by RRI in collaboration with ISRO’s U R Rao Satellite Centre (URSC) in Bengaluru.
• POLIX is expected to observe about 40 bright astronomical sources of different categories during the planned lifetime of XPoSat mission of about 5 years.
• This is the first payload in the medium X-ray energy band dedicated for polarimetry measurements.
• The XSPECT (X-ray Spectroscopy and Timing) payload will give spectroscopic information (on how light is absorbed and emitted by objects).
• It would observe several types of sources, such as X-ray pulsars, blackhole binaries, low-magnetic field neutron star, etc.

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