India's first dedicated space observatory, ASTROSAT, has captured the rare phenomenon of a small, 6-billion-year-old "vampire" star "preying" on a bigger celestial body.

Scientists say the smaller star, also called a "blue straggler", feeds off its companion star by sucking out its mass and energy, causing its eventual death.

"The most popular explanation is that these are binary systems in which the smaller star sucks material out of the bigger companion star to become a blue straggler, and hence is called a vampire star.

"The small star becomes bigger, hotter and bluer, which gives it the appearance of being young, while the ageing companion burns out and collapses to a stellar remnant," said Annapurni Subramaniam, a Professor at the Indian Institute of Astrophysics.

Though this phenomenon is not unheard of, the observation of the entire process through the telescope will provide insights that will help scientists in studying the formation of 'blue straggler' stars.

This discovery also highlights the capabilities of the telescopes on ASTROSAT, a dedicated space observatory satellite launched in September 2015.