India’s Own AstroSat Turns Seven: Here’s A Look At Its Wide-Ranging Scientific Impact

Seven years ago on this day, India's first space observatory was launched into space.

It lifted off on board a Polar Satellite Launch Vehicle into a 650 km orbit from Satish Dhawan Space Centre in Sriharikota.

The scientific satellite took the help of many scientists and engineers to get up there, but ever since, it has been giving back handsomely through the language of science results, many of them important discoveries.

The satellite’s specialty is that it provides for simultaneous multi-wavelength observations of various astronomical objects, far and wide.

From the nearest star, Proxima Centauri, which is only a little over 4 light years away, to a galaxy 9.3 billion years away, AstroSat’s eye has traversed a mighty vast expanse.

This is all thanks to a five-member tag team on AstroSat. The payloads pick up visible, ultraviolet, and X-rays coming in from distant celestial sources.

Many Indian institutions contributed to the development of these scientific payloads. This is why the Indian Space Research Organisation (ISRO) chief S Somanath has said, “AstroSat is a real example of (a) multi-institute mission.”

A quick look at the payloads (more here):

The Ultraviolet Imaging Telescope (UVIT): Comprising two separate telescopes, it can simultaneously observe in the visible, near-ultraviolet, and far-ultraviolet.

The Indian Institute of Astrophysics (IIA), Bengaluru, and Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune, in collaboration with the Canadian Space Agency, have developed this payload.

The Soft X-ray Telescope (SXT): This is an X-ray focusing telescope operating in the energy range of 0.3-8.0 keV. This payload was developed by the Tata Institute of Fundamental Research (TIFR), Mumbai.

Large Area X-ray Proportional Counters (LAXPC): Three large-area proportional counters carry out timing and broadband spectroscopy over an energy band of 3-80 keV X-rays for the study of variable astrophysical sources. TIFR, Mumbai, developed this payload.

Cadmium-Zinc-Telluride Imager (CZTI): This solid state detector is a hard X-ray imaging instrument in the energy range 10-100 keV with a collecting area of 976 cm². It was developed by TIFR, Mumbai, along with Vikram Sarabhai Space Centre, Trivandrum, and IUCAA, Pune.

Scanning Sky Monitor (SSM): It helps to scan a section of the sky away from the Sun in search of transient behaviour in X-ray sources. The SSM only takes a few hours to do a large swipe of the sky. It was developed by ISRO Satellite Centre (ISAC), Bengaluru, and IUCAA, Pune. 

In addition to these five payloads, there’s also a Charged Particle Monitor, developed by TIFR, Mumbai. (TIFR clearly played a major hand in the AstroSat project.)

Together, these payloads give AstroSat an edge. Combined with ground-based telescopes, scientists receive an excellent view and, after analysis, understanding of our wonderfully vast and complex universe.

“You need ground- and space-based observations to do frontier science cases these days. The olden days of looking at only one object in one wavelength is completely gone,” IIA director Annapurni Subramaniam said at a celebratory event being held on 28 and 29 September at the ISRO headquarters in Bengaluru.

Capturing data is one thing, analysis another. AstroSat operates as a proposal-driven general purpose observatory. Its data is used by more than 2,000 users from 54 countries.

About half of AstroSat users are from India, which witnesses a participation of 126 Indian universities. Every Indian state except Manipur and Arunachal Pradesh host AstroSat users.

Among international users, the United States (US), Italy, and Canada account for most users. From the US to Afghanistan to Angola — AstroSat users are spread across a diverse territory.

So far, AstroSat data has led to 277 (refereed) publications in all, and counting. Earlier today, at the celebratory event, ISRO’s V Girish said this count will reach 300 “soon.”

Until last year, AstroSat was averaging a staggering close to one publication every week. This average, surprisingly, is on the rise. It now stands at five publications per month.

To top it all, AstroSat data has resulted in 20 Doctor of Philosophy (PhD) theses — 18 of them in India.

The next cycle of AstroSat observations, called the “Twelfth AO Cycle,” is due to begin in October and end in September next year.

The demand for AstroSat is high. “In the current cycle, the request for AstroSat data is twice with respect to the time available for observations,” ISRO’s Scientific Secretary, Shantanu Bhatawdekar, revealed today.

AstroSat’s scientific accomplishments are too many to list. However, here are a few for taste:

AstroSat watched the birth of black holes for an astonishing 500th time in May this year.

Back in August 2020, it detected extreme ultraviolet light from a galaxy 9.3 billion light-years away from Earth. The global team of scientists behind this discovery was led by Dr Kanak Saha of IUCAA, Pune.

AstroSat has also spotted rare hot ultraviolet-bright stars in the Milky Way galaxy. One of the UV-bright stars was found to be about 3,000 times brighter than the Sun, with a surface temperature of about 100,000 Kelvin.

Thanks to the CZTI, AstroSat observations have led to studies of more than 500 gamma-ray bursts until now. In fact, the very first scientific result from AstroSat was a gamma-ray burst detection — just hours after the instrument was powered on after launch.

This is only scratching the surface of AstroSat’s many accomplishments.

Going forward, it has the potential to make a difference alongside other space observatories, like the James Webb Space Telescope.

At seven years old, AstroSat has already exceeded its planned lifetime of five-plus years. The hope is that it goes long in the service of science.