Researchers at MIT and Johns Hopkins University have observed a radio signal produced by a distant supermassive black hole that they think can help us understand what happens when a black hole is feeding.
The team has been studying the consequences of supermassive black hole ASASSN-14li tearing apart and eating a star since it was first observed in 2014. They first saw a fluctuation in visible and ultraviolet light (the star was pulled apart by gravity) and then just over a month later a strong X-ray signal was observed, as the material heated up the closer it got to the black hole.
As reported in the Astrophysical Journal, after 13 days the team began to observe radio waves that appeared to be 90 percent similar to the X-ray emission they'd seen. These radio "echoes", they believe, are not coincidental but are produced by electrons from a jet of particles streaming out from the black hole and moving through a magnetic field.
The connection between the X-ray and radio emissions is the interesting result of this study. The electrons that generate radio waves were not universally thought of as being a consequence of the extremely hot gas in the accretion disk of a black hole, but it appears that this might be the case.
“The only way that coupling can happen is if there is a physical process that is somehow connecting the X-ray-producing accretion flow with the radio-producing region,” lead author Dr Dheeraj Pasham from MIT said in a statement.
“This is telling us the black hole feeding rate is controlling the strength of the jet it produces. A well-fed black hole produces a strong jet, while a malnourished black hole produces a weak jet or no jet at all. This is the first time we’ve seen a jet that’s controlled by a feeding supermassive black hole.”
The team estimated that the source the X-rays come from is a region about 25 times the size of the Sun, while the source of the radio echoes is much bigger, with a radius of about 400,000 times the Sun’s. That’s about 1,900 times the distance between the Sun and the Earth.
“It’s not a coincidence that this is happening. Clearly, there’s a causal connection between this small region producing X-rays, and this big region producing radio waves," Pasham stated.
"If the rate at which the black hole is feeding is proportional to the rate at which it’s pumping out energy, and if that really works for every black hole, it’s a simple prescription you can use in simulations of galaxy evolution. So this is hinting toward some bigger picture.”
Only a few of such events have been observed as they happened so the connection remains full of uncertainties. More studies will hopefully help with that.