When black holes swallow down massive amounts of matter from the space around them, they’re not exactly subtle about it. They belch out tremendous flares of X-rays, generated by the material heating to intense temperatures as it’s sucked towards the black hole, so bright we can detect them from Earth.
This is normal black hole behaviour. What isn’t normal is for those X-ray flares to spew forth with clockwork regularity, a puzzling behaviour reported in 2019 from a supermassive black hole at the centre of a galaxy 250 million light-years away. Every nine hours, boom – X-ray flare.
After careful study, astronomer Andrew King of the University of Leicester in the UK identified a potential cause – a dead star that’s endured its brush with a black hole, trapped on a nine-hour, elliptical orbit around it. Every close pass, or periastron, the black hole slurps up more of the star’s material.
“This white dwarf is locked into an elliptical orbit close to the black hole, orbiting every nine hours,” King explained back in April 2020.
“At its closest approach, about 15 times the radius of the black hole’s event horizon, gas is pulled off the star into an accretion disk around the black hole, releasing X-rays, which the two spacecraft are detecting.”
The black hole is the nucleus of a galaxy called GSN 069, and it’s pretty lightweight as far as supermassive black holes go – only 400,000 times the mass of the Sun. Even so, it’s active, surrounded by a hot disc of accretion material, feeding into and growing the black hole… Via – Science Alert