Black Hole Feeds on Big Planet, First Time to be Observed

By coincidence, astronomers noticed a black hole as it "woke up" from a decades-long slumber to feed on giant planet that approached too close. Astronomers were using ESA’s Integral space observatory to study a different galaxy when they suddenly noticed a bright X-ray flare coming from another location in the same wide field-of-view. Using ESA's XMM-Newton, the origin was confirmed as NGC 4845, a galaxy 47 million light-years away and never before detected at high energies.

“The observation was completely unexpected, from a galaxy that has been quiet for at least 20–30 years,” says Marek Nikolajuk of the University of Bialystok, Poland, lead author of the paper in Astronomy & Astrophysics.

By analysing the characteristics of the flare, the astronomers could determine that the emission came from a halo of material around the galaxy’s central black hole as it tore apart and fed on an object of 14–30 Jupiter masses.

This animation by ESA shows how the invisible black hole leeches gas and material from the orbiting planet, with the material emitting a glow and flash just before it vanishes into the hole.

“This is the first time where we have seen the disruption of a substellar object by a black hole,” said co-author Roland Walter of the Observatory of Geneva, Switzerland.

The black hole in the centre of NGC 4845 is estimated to have a mass of around 300 000 times that of our own Sun. It also likes to play with its food: the way the emission brightened and decayed shows there was a delay of 2–3 months between the object being disrupted and the heating of the debris in the vicinity of the black hole.

“We estimate that only its external layers were eaten by the black hole, amounting to about 10% of the object’s total mass, and that a denser core has been left orbiting the black hole,” Walter added.

The flaring event in NGC 4845 can be seen as a warm-up act for a similar event expected in the supermassive black hole at the centre of our own Milky Way Galaxy, perhaps even this year.

Along with the object seen being eaten by the black hole in NGC 4845, these events will tell astronomers more about what happens to the demise of different types of objects as they encounter black holes of varying sizes.

“Estimates are that events like these may be detectable every few years in galaxies around us, and if we spot them, Integral, along with other high-energy space observatories, will be able to watch them play out just as it did with NGC 4845,” says Christoph Winkler, ESA’s Integral project scientist.