On ISRO’s XPoSat Mission – Meet ISRO’s new X-ray eye in the sky

Source: This post on ISRO’s XPoSat Mission has been created based on the article “Meet ISRO’s new X-ray eye in the sky” published in “Indian Express” on 2nd January 2024.

UPSC Syllabus Topic: GS Paper 3 Science & Technology – Awareness in the fields of Space.

News: The article discusses the details of the recently launched XPoSat Mission by ISRO.

Black holes and neutron stars have remained a mystery. However, because of their immensely strong magnetic fields, these celestial bodies emit highly energetic X-ray light, which can be used to study their properties.

For this purpose, on January 1st, 2024, ISRO’s PSLV put into orbit the XPoSat (X-ray Polarimeter Satellite) – the country’s first space observatory to study the polarisation of cosmic X-rays.

This is the world’s second space mission to study the polarisation of cosmic X-rays, after NASA’s IXPE, launched in 2021. XPoSat operates in a frequency band different from NASA’s mission.

Source: ISRO.

What are X-rays?

X-rays are electromagnetic waves. These are generated by movements of electric charges when the electric and magnetic fields in its vicinity are disturbed.

What are Polarised X-rays? 

In electromagnetic waves like X-rays, the electric field oscillates or varies in strength and direction as the wave propagates. The direction and nature of this variation in the electric field depend on the motion of the electric charge responsible for generating the wave.
For instance, as the X-ray wave travels, if the electric charge responsible for producing the X-ray is in motion (such as an electron accelerating), it affects the way the electric field changes as the wave moves.

Sometimes these variations acquire directionality (variations in a particular direction), which is when these X-rays are described as being “polarised”.

Stars mostly emit unpolarised light, however it is different in the case of stars with very large magnetic fields. Electrons in those objects spiral around the magnetic field lines and emit X-rays. The electrons’ motion provides the X-rays with some directionality, making them polarised.

Measuring the polarisation of X-rays can enable astronomers to understand the nature of these polarised X-ray emitting-objects, such as pulsars or regions around blackholes.

Note: Pulsar: A pulsar (or pulsating radio source) is a neutron star that rotates quickly and releases two polarised radio lights. The beams create a unique timing and polarisation signature as they burst across space. Pulsars are among the few celestial objects that emit circular polarised light.

Why is it difficult to study X-rays from space?

1. Their high energy makes them impossible to focus with lenses, like ordinary light.
2. The Earth’s atmosphere absorbs most of it.

How will XPoSat Mission study X-rays?

1. The main instrument aboard, the payload called POLIX (Indian X-ray Polarimeter), aims to study a special property of X-rays in space. POLIX is shaped like a cubical cylinder. At its core lies a disc of beryllium. Detectors kept along the walls collect X-rays after their scattering from the metallic disc.
   POLIX’s beryllium disc will let astronomers probe lower energy X-rays than what the NASA instrument is capable of.
2. The other instrument (XSPECT) aboard XPoSat will study timing and spectral properties of X-ray emitting objects in space.

With this venture, ISRO has signaled that it has the expertise and maturity to contribute to all aspects of planetary research.

Question for practice:

India’s X-ray mission XPoSat has scripted history with its successful launch. What are its various payloads? How will it help enhance our understanding of the universe?