According to the laws of physics, the speed of light is a fundamental barrier that cannot be broken – nothing is supposed to be able to travel faster than it.
So astronomers were left baffled when they spotted powerful flashes of energy bursting out from the heart of a supermassive black hole at the centre of a galaxy 260 million light years from Earth.
Measurements of this gamma ray ‘lightning’ showed it was travelling across the event horizon – the boundary where nothing can escape the intense gravity of the black hole – at rates that appeared to be faster than the speed of light.
While the gamma rays appeared to cross the event horizon within just a few minutes, scientists estimate it should have taken light 25 minutes to pass through the distance.
This either suggests the gamma rays were travelling faster than the speed of light, or something else was going on.
Now, researchers believe they have gained a rare insight into something that is taking place below the event horizon of the black hole – giving them a glimpse of what may be going on inside.
The objects that lie at the heart of black holes by their very nature are mysterious objects as no light is able to escape, and so they appear as a dark space in the sky.
Scientists say current theories for what caused the gamma ray outbursts are insufficient to explain their observations, and so have developed a new theory for what lies beneath the event horizon.
‘No object can suddenly light up its entire surface faster than light takes to travel across it,’ said Julian Sitarek one of the scientists working on the project at the Institute for High Energy Physics (IFAE) in Barcelona.
Galaxy IC 310 lies within the Perseus constellation and has an active galactic nucleus that throws out radio waves into the surrounding space.
Astronomers using the Major Atmospheric Gamma-ray Imaging Cherenkov (Magic) on La Palma, in the Canary Islands, spent almost four hours observing huge bursts of radiation from this galaxy in 2012.
This is thought to be caused by matter falling into the massive black hole at the centre of IC 310.
Known as extragalactic jets, they are thought to be caused by particles being accelerated away from the event horizon by shockwaves created by the matter falling into the black hole.
However, the observations of IC 310 using Magic showed that gamma ray jets being emitted from the black hole were flickering at a rate far faster than could be explained in this way.
The flashes of radiation seemed to move 279 million miles across the event horizon in just 4.8 minutes.
At the speed of light, it should have taken 25 minutes to travel this distance.
The international team of scientists, whose research is published in the journal Science, instead suggest that the black hole must be spinning at high speeds with two jets extending from either side.
Much like viewing the beam from a lighthouse, it then seems to flicker at a faster rate than it is really spinning as there are multiple sources of radiation rather than just one.
The scientists say the rotation of the black hole induces an charge separated magnetosphere that creates parallel electrical charges around the poles.
These then accelerate particles to very close to the speed of light, causing gamma radiation to be thrown out into space from inside the event horizon.
‘You can imagine this as lightning in a thunderstorm,’ said Karl Mannheim from the University of Würzburg.
Every few minutes the lightning discharges the energy it has accumulated in a region the size of our solar system.
In the process, particles close to the speed of light are ejected into the outer regions of the galaxies.
Razmik Mirzoyan, from the Max Planck Institute for Physics in Munich, added that the gamma radiation may be giving astronomers a glimpse of something inside a black hole.
He said: ‘The region from which the gamma radiation originates must therefore be significantly smaller than the event horizon of the black hole.
‘When we observe black holes at high energies, we are looking into the galactic nucleus to very great depths. We are trying to look directly into the machinery at the centre, as it were.’
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