Black holes are one of the most enigmatic objects known to science. Huge advances have been made over the past 100 years or so, but there’s plenty we still have no idea about – and much more we often get wrong. In fact, a new Physical Review Letters study has just potentially overturned one major assumption about these spacetime portals of doom.
The assumption is a black hole’s accretion disk – the rim of material that gathers around these destructive spots – should contain plenty of ionized iron.
This was based on the fact that, among other things, iron is often unleashed during the creation of a supernova, those glorious moments at the end of certain stars’ lives. The extreme radiation being emitted from the black hole itself would ionize these iron fragments.
The problem with this idea is that there was no direct evidence that demonstrated the existence of these iron ions. Normally, elements in stars or atmospheres from across the cosmos are picked up by looking at their spectral emission lines, but no such lines ever pointed towards these iron ions being a true feature of these accretion disks.
Physicists suggested that, unlike other elements, which would normally drop back to lower energy states after becoming ionized and emit light that could be picked up by astronomers, these electrons would split off from their iron atoms and cascade off into deep space. No light would be emitted, and thus there would be no associated spectral lines to detect.
A team of researchers at Sandia National Laboratory decided to build an experiment here on Earth to try and find out if this theory held water. To wit, they used the wonderfully named Z machine, the most energetic laboratory X-ray source on Earth.
A computer simulation of a gas from a tidally-shredded star forming part of the accretion disk around a black hole. JPL
The team spent five painstaking years reproducing black hole-like X-rays in their lab and exposing them to silicon. Silicon has very similar properties to iron, and in the environment of a black hole, would behave very similarly to it – in fact, it’s more likely to exhibit this type of elusive electron escape, something known as Auger Destruction, than iron is.
However, no such destruction was observed.
“If Resonant Auger Destruction is a factor, it should have happened in our experiment because we had the same conditions, the same column density, the same temperature,” Guillaume Loisel, lead researcher on the project at Sandia, said in a statement. “Our results show that if the photons aren’t there, the ions must be not there either.”
This suggests that decades’ worth of assumptions about what constitutes an accretion disk are wrong. Hopefully, this doesn’t send the astrophysics community into a black hole of despair.