Beacons in the sky: The gamma-ray sky as seen by Fermi. The inserts show radio images of the jets of selected active galactic nuclei observed by the VLBA.
Credit: Matthias Kadler and NASA/DOE/Fermi LAT Team and NRAO/AUI/MOJAVE team
SYDNEY: New studies have revealed important details about the functioning of violent jets of energy blasted out by supermassive black holes – among the most energetic objects known to exist.
These jets appear to move faster than the speed of light, and emit enough energy to make our own Sun look like a candle in comparison.
"Some of the brightest jets put out 1040 watts continuous power, which is about 100 trillion times the energy output of our Sun," said Matthew Lister, an astrophysicist from Purdue University in West Lafayette, U.S., and lead author of one of the new studies. "You would need SPF40 sunscreen even if you were 150 light years away from the jet," he said.
Whirlpools of gas
In two articles appearing in The Astrophysical Journal Letters, an international team of researchers have combined data from the new Fermi Gamma-ray Space Telescope and the U.S.-based Very Long Baseline Array (VLBA) radio telescope to study the physics of how and where the jets are produced.
Lister said supermassive black holes surrounded by "whirlpools" of extremely hot gas lie at the heart of most galaxies. When matter falls into the black hole, some gets accelerated upwards and outwards by the vast heats and pressures, creating jets of material blasted both up and down at 90º to the plane of the galaxy.
The fastest jet yet spotted appears to be moving across the sky at 50 times the speed of light, said Lister, though this speed is an illusion caused by the angle of viewing the jet, and time dilation due to its actual speed of 99.98% of the speed of light.
Lister said that while all of these jets produce a low level of electromagnetic radiation in the radio waveband, and are detectable using radio telescopes, some of the most powerful jets also produce radiation across the entire electromagnetic spectrum, right up to gamma-rays, the most energetic type of radiation.
Periods of quiescence
"What is not currently well known is why we only detect some of these jets in gamma-rays," he said. "Our study has narrowed it down to two major factors."
Firstly, the jet appears to have to have a minimum threshold speed, he explained. "If the jet is too slow, it isn't energetic enough to boost [it] up to gamma-rays."
The second factor is that some jets appear to go through periods of quiescence, where they don't produce as many gamma-rays. "We've been able to show with our VLBA imaging that those quiescent jets are also the ones that don't show much activity in their radio jet images," said Lister.
Eduardo Ros, a co-author and astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn, Germany, said the most significant finding was the confirmation that the most violent and extreme jets detectable in the radio spectrum are also high emitters of gamma-rays.
