The black hole GRS 1915+105 usually hides behind a dense gas curtain: its X-ray emission is heavily absorbed on its way to us. But in April 2023, it suddenly flared: the X-ray flux jumped nearly tenfold. The NICER and Swift telescopes monitored the flare and recorded how the spectrum, the distribution of X-ray energy across wavelengths, changed.
The spectrum revealed that during the flare, the curtain thinned, and the black hole's own glow intensified. Meanwhile, the iron lines, characteristic peaks in the spectrum that arise when X-rays reflect off gas, behaved unusually. Some lines changed quickly, while others barely shifted. This suggests that the gas around the black hole lies in layers: the inner layers may have dispersed, while the outer ones remained dense.
Two and a half days after the X-ray flare, radio telescopes picked up a radio burst. This is likely a jet of material that the black hole ejected after 'swallowing' some of the gas. So, gas accretion and jet launching are linked: when the curtain wobbles, the black hole can 'sneeze' a jet.
Such observations help us understand how black holes in binary systems switch between different states — from quiet glow to powerful ejections. And the layered structure of the gas may explain why we sometimes see the black hole and sometimes don't.
The X-ray flare was so bright that it was visible even through the dense curtain that usually dims the light by tens of times.
In Stanislaw Lem's novel 'Solaris,' the planet's ocean also behaves like a living thing: it hides and then reveals its depths — somewhat like the ever-changing curtain around the black hole.