An unprecedented image of a supermassive black hole and its giant extragalactic radio jet has been captured for the first time, raising new questions about our next radio galaxy. The heart of Centaurus A – the fifth brightest galaxy in the sky – is characterized by a cloud of energy that moves at about half the speed of light, although until now and the Event Horizon Telescope it has been required to accurately visualize it.
The Event Horizon Telescope or EHT is not a single instrument. Instead, it’s a series of radio telescopes around the world that work together to combine their data for maximum results. It is the tool that researchers used to map the giant black hole Messier 87; More recently, it has turned its collective attention to Centaurus A.
The data – collected from the 2017 EHT observations – resulted in an image ten times the frequency and sixteen times the resolution of previous observations. A magnification factor of a billion, says the EHT team, enough to answer some old questions – and raise some new ones.
The jets of supermassive black holes are effectively near misses in the running meal. Usually the enormous gravitational pull pulls nearby gas and dust into the black hole; However, a small percentage can escape shortly before it is drawn in. Instead, they are blown out as jets over great distances and at enormous speeds.
Although they are well known, jets are poorly understood. There are several models trying to explain how they actually form, but the EHT’s new Centaurus A observations help determine the likely location of the black hole at the jet’s launch point. While the central black hole itself would require a greater magnification to still image properly, even what the telescope array has now achieved is enough to devalue some of the models.
For example, the edges of the jet are significantly lighter than its central part. « We can now rule out theoretical jet models that cannot reproduce this edge brightening, » explains Matthias Kadler, TANAMI director and professor for astrophysics at the University of Würzburg. « It’s a remarkable feature that will help us better understand jets created by black holes. »
At the same time, however, the EHT’s observations pave the way to some new uncertainties. For example, only the outer edges of the jet appear to be emitting radiation, which goes against some core understanding of the phenomenon.
However, in order to gain more precise insight, we may need a very different type of tool. Although it is believed that even shorter wavelengths and higher resolution could capture Centaurus A itself, « this will require the use of space-based satellite observatories, » suggests the EHT team. A paper on the new findings was published today in Nature Astronomy.
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