Like virtually every other galaxy in the universe, the Galaxy NGC 4845 has a central black hole. For the past few decades, though, that black hole has lain dormant, without giving much sign it was there. That changed recently, however, when scientists caught the black hole the in process of eating a little snack. “Little” in this case being a planet larger than Jupiter.
“The observation was completely unexpected, from a galaxy that has been quiet for at least 20–30 years,” said lead researcher Marek Nikolajuk in a press release.
So unexpected, in fact, that astronomers weren’t even looking at the Galaxy when they were doing their research. They were using the ESA’s Integral system to observe an entirely different galaxy. It just so happened that while they were doing so, NGC 4845 was in their field of view. So when they noticed bright X-ray flares coming from the galaxy, they quickly turned their attention.
In doing so, they were able to catch this rare astronomical event. When something is pulled into a black hole, the heat and pressure of the event convert whatever it is – whether star or planet – into high energy gasses. As the gasses are absorbed by the black hole, the energy from those gasses is released as X-rays. So when the scientists noted those flares, they used the ESA’s XMM-Newton, which is used by astronomers to detect X-ray sources from across the universe.
Using these two instruments, the scientists were able to examine the event and determine that the mass of the planet being devoured by the black hole was somewhere between 14-30 times that of Jupiter. Which means it was either a very large gas giant or possibly a brown dwarf – a body more massive than a planet, but not quite large enough to begin the fusion process of a star.
“This is the first time where we have seen the disruption of a substellar object by a black hole,” researcher Roland Walter added in the release. “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.”
The astronomers’ research will be published this month in Astronomy & Astrophysics.