Indian telescope observes cosmic violence as dying star comes close to a black hole

Global Relay of Observatories Watching Transients Happen (GROWTH) is India's first fully robotic optical research telescope developed jointly by the Indian Institute of Astrophysics and the Indian Institute of Technology Bombay. The primary research focus of this telescope is time-domain astronomy: the study of explosive transients and variable sources in the universe.

The international collaboration of astronomers studied a rare optical flare caused by a dying star’s encounter with a supermassive black hole. The black hole took part of the stellar material and launched it as “relativistic jets” - beams of matter travelling close to the speed of light.

“It doesn’t end well for the star. The star gets violently pulled apart by the black hole’s gravitational tidal forces. The shreds of the star form a spinning disc around the black hole and are eventually consumed by it. Such events are called Tidal Disruption Events, or TDEs,” Varun Bhalerao, an astrophysicist at IIT Bombay, said in a statement .

The results of the study have been published in the journal Nature.

The findings have its source in images obtained by the California-based Zwicky Transient Facility project on 11 February 2022. These showed a new source in the sky, dubbed AT2022cmc, which seemed to have brightened rapidly and was now fading fast.

Astronomers From IIT Bombay began observing the event with the GROWTH-India telescope located in Hanle, next to the Indian Astronomical Observatory. “We immediately jumped into action and started obtaining daily observations with the GROWTH-India Telescope. Our data showed that the object was fading at a unique, unexpected rate that set it apart from dozens of other sources we study daily,” Harsh Kumar, a PhD student at IIT Bombay, added.

The India team then brought an international collaboration together and made the observations from Radio telescopes, X-ray telescopes, large ground-based optical telescopes, and even the Hubble Space Telescope. Follow-up observations with many observatories confirmed that AT2022cmc was fading rapidly and the ESO Very Large Telescope revealed that AT2022cmc was at a cosmological distance, 8.5 billion light years away.

Astronomers suspect that AT2022cmc was at the centre of a galaxy that is not yet visible because the light from AT2022cmc outshone it, but future space observations with Hubble or James Webb Space Telescopes may unveil the galaxy when the transient eventually disappears.

From their observations, Andreoni and his team concluded that the black holes in AT2022cmc and other similarly jetted TDEs are likely spinning rapidly so as to power the extremely luminous jets. This suggests that a rapid black hole spin may be one necessary ingredient for jet launching—an idea that brings researchers closer to understanding the physics of supermassive black holes at the canter of galaxies billions of light years away.