In a distant part of our galaxy, something flickers. Not stars or comets, but a black hole's strange light. This unusual signal has drawn scientists' attention for years. Now, Indian researchers have uncovered what lies behind this cosmic whisper.
The black hole, named GRS 1915+105, lives 28,000 light-years away. It hides inside a binary system with a companion star. The star’s material falls inward, forming a spinning disc. This disc heats up, glowing fiercely in X-ray light. These X-rays help scientists watch what eyes cannot see.
A Flickering Mystery in Deep Space
GRS 1915+105 is no ordinary black hole system. It holds a black hole twelve times heavier than our Sun. The spinning disc around it reaches millions of degrees. A hot cloud called the corona hovers above the disc. This corona is where things get truly interesting.
India’s AstroSat, launched in September 2015, tracks this system. The observatory uses two X-ray tools, LAXPC and SXT. Together, they monitor the black hole’s changing brightness. Sometimes, the light drops suddenly into a quiet phase. At other times, it flares up and flickers rapidly.
During the bright spells, flickers repeat 70 times each second. These flickers are known as quasi-periodic oscillations, or QPOs. The flickers disappear when brightness drops again. This on-off behaviour puzzled researchers until now.
Hot Corona Key to Flickering Pattern
Scientists found that the flickers come from the corona. When the black hole glows, the corona shrinks and heats up. But when it dims, the corona expands and cools down. These changes match the appearance and disappearance of flickers.
The study was led by researchers from several Indian groups. They include experts from ISRO, IIT Guwahati, and the University of Haifa. Their work is now published in the Monthly Notices of the Royal Astronomical Society.
These findings illustrate the nature of black holes when conditions are extreme. Courtesy AstroSat, India is assisting in unearthing such cosmic secrets. GRS 1915+105 is distant, but it continues to speak in light and Indian researchers are hearing.
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