Scientists are aware that mysterious black holes give off light flares and sometimes erupt in X-ray light, but they have never really understood the dynamics behind this phenomenon until recently, and now they have their answers.
In a study featured in the Monthly Notices of the Royal Astronomical Society, the researchers from the NASA/Jet Propulsion Laboratory used data from NASA’s explorer missions Swift and the Nuclear Spectroscopic Telescope Array (NuSTAR) to establish that supermassive black holes emit light from the coronas surrounding them, and these produce powerful energetic particles that are shot far away from the core of the black holes.
"This is the first time we have been able to link the launching of the corona to a flare," said Dan Wilkins of Saint Mary's University in Halifax, Canada. "This will help us understand how supermassive black holes power some of the brightest objects in the universe."
It is not that larger black holes emit light themselves, no, but the disk of glowing material surrounding them is the gas that gives off sparks of light. How this happens is that the gravity within the black holes pulls gas into it in order to heat up the disk of material which then gives off bright lights.
The coronas, composed of high energy particles also create x-ray light near a black hole, but very little is actually known about coronas themselves. Some scientists say the corona is a source of light just like bulbs, and that it is placed below and above the black hole along its rotation axis to give off light when heated; and other scientists posit that coronas are spread out evenly around a black hole or the materials that sandwich the disk of material surrounding the black hole.
Scientists became more interested in black holes when in 2007 the Swift spacecraft – which is designed to scan the sky for cosmic outbursts of x-ray and gamma rays, captured a big flare emitting from the supermassive black hole known as Markarian 335 or Mrk 335, situated 324 million light-years away toward the constellation Pegasus; this black hole is among the brightest x-ray sources in the sky.
"Something very strange happened in 2007, when Mrk 335 faded by a factor of 30. What we have found is that it continues to erupt in flares but has not reached the brightness levels and stability seen before," said Luigi Gallo, the principal investigator for the project at Saint Mary's University.
In September 2014, Swift saw another large flare from Mrk 335, and notified Galileo which informed NuSTAR to monitor the situation. The scientists tracking the event eventually said they had actually seen the ejection and collapse of the corona of a black hole.
"The corona gathered inward at first and then launched upwards like a jet," said Wilkins. "We still don't know how jets in black holes form, but it's an exciting possibility that this black hole's corona was beginning to form the base of a jet before it collapsed."
Yet, researchers are still trying to establish more facts about coronas and the mechanics behind them.
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"The nature of the energetic source of X-rays we call the corona is mysterious, but now with the ability to see dramatic changes like this we are getting clues about its size and structure," said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology in Pasadena.