India's XPoSAT: Venturing into advanced X-Ray astronomy

India is on the brink of a significant advancement in space research with the planned launch of its first X-Ray Polarimeter Satellite, XPoSat. This pivotal mission, orchestrated by the Indian Space Research Organization (ISRO), is scheduled for January 1, 2024. The satellite will be launched at 9:10 a.m. from the Satish Dhawan Space Centre in Andhra Pradesh using a Polar Satellite Launch Vehicle (PSLV). The mission is set to explore space for 5 years.

Mission’s Core Objective

The primary goal of XPoSat is to examine X-ray emissions from space, particularly from black holes and neutron stars. Emulating NASA’s Imaging X-ray Polarimetry Explorer (IXPE), XPoSat will carry two scientific instruments into a low Earth orbit.

Measuring Polarization in X-Rays

A critical aspect of the XPoSat mission is to measure the ‘polarization’ of X-ray sources, offering a fresh perspective in understanding these cosmic phenomena. Traditional X-ray studies have focused on:

1. Energy : Gauging the strength of X-rays to deduce activities at their source.

2. Time: Tracking temporal changes in X-ray emissions for identifying patterns.

3. Location: Locating the spatial origins of X-rays to recognize specific cosmic entities.

Integrating polarization, which evaluates the vibration intensity and direction of X-rays, grants a more detailed view of distant cosmic objects.

Polarization is how the vibrations in a wave, like light, align in certain directions. Imagine a wave moving forward; if its vibrations go up and down, side to side, or spin around, that’s polarization. It helps scientists understand where and how the wave was created, especially in space.

XPoSAT’s Instrumentation

The satellite is equipped with two main instruments:

1. POLIX (Polarimeter Instrument in X-rays): This primary tool will analyze X-ray properties in the 8-30 keV energy range.

2. XSPECT (X-ray Spectroscopy and Timing): Focused on collecting data in the 0.8-15 keV range, it will provide intricate details about X-rays.

The mission is backed by a budget of around 600 Crore rupees, equivalent to about 72.26 lakh US dollars.

“Significance of Studying X-Ray Sources”

Cosmic X-rays, emitted by black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae, are powerful energy rays with shorter wavelengths (0.01 to 10 nanometers) than visible light. Visible light, part of the electromagnetic spectrum visible to the human eye, ranges from about 400 to 700 nanometers, corresponding to the colors we see.

Cosmic X-Ray Generation

Cosmic X-rays are created under extreme conditions, such as around black holes and neutron stars. When matter is pulled into these dense objects, it heats up to incredibly high temperatures, emitting X-rays. Other sources, like pulsar wind nebulae, generate X-rays from high-energy particles accelerated by strong magnetic fields, showcasing the dynamic and intense environments in the universe.

Since X-rays cannot penetrate Earth’s atmosphere, space-based X-ray telescopes are essential for capturing these rays. NASA’s IXPE, launched in December 2021, marked a milestone as the first satellite dedicated to X-ray polarimetry. India’s XPoSAT, covering the 8 to 50 keV range, aims to complement and expand on IXPE’s observations, focusing on about 50 bright X-ray sources within our galaxy.

XPoSAT is designed to unveil the dynamics of black holes in binary star systems, working in tandem with IXPE to propel forward the field of X-ray astronomy.

Defining Key Cosmic Phenomena

1. Black Holes: Mysterious regions in space with such intense gravity that even light cannot escape. Formed from the collapse of massive stars, they exert a powerful pull on nearby objects, acting like invisible cosmic vacuums.

2. Neutron Stars: Incredibly dense remnants of massive stars that exploded as supernovae. These city-sized objects have a mass about 1.4 times that of our sun and are predominantly composed of neutrons.

3. Active Galactic Nuclei (AGN): The luminous centers of certain galaxies, powered by supermassive black holes. They shine brightly by pulling in and heating surrounding material.

4. Pulsar Wind Nebulae: Cosmic clouds of gas and dust formed by energy and particles emitted from rapidly spinning neutron stars. These nebulae emit X-rays and radio waves, highlighting the energy released by their pulsars.

Conclusion

The launch of XPoSAT represents a monumental step in deepening our knowledge of space and its enigmatic inhabitants. By combining traditional methods with the novel approach of X-ray polarization, XPoSAT is set to vastly broaden our comprehension of the universe and its dynamic processes.

Girish Linganna
Aerospace & Defence Analyst 

(The author of this article is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach out to him at: girishlinganna@gmail.com)