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Capture the image of the heart of the closest radio galaxy

An international team has obtained and released the image of the heart of the Centauro A galaxy with the highest level of detail ever achieved. The research has managed to pinpoint the exact point where the supermassive black hole in this galaxy is located and allows us to observe how a gigantic jet of matter is generated that escapes from the black hole’s onmediations at speeds very close to that of light. The image challenges current models trying to explain the origin of relativistic jets in black holes.

The team is led by Michael Janssen of the Max Planck Institute for Radio Astronomy in Bonn in Germany), and has the participation of the University of Valencia (UV) in Spain. The study has been published in the academic journal Nature Astronomy, with the title “Event Horizon Telescope observations of the jet launching and collimation in Centaurus A”.

The Centaur Galaxy (Centaurus A) is one of the most intense radio sources in the sky and its emission has been studied extensively across the entire electromagnetic spectrum, from radio waves to the most energetic gamma radiation. At the heart of Centaurus A, there is a black hole with a mass equivalent to 55 million stars like our Sun, a mass halfway between that of the black hole of the galaxy M87 (of which the EHT telescope obtained a famous image, with a mass of more than 6000 million suns) and the black hole in the center of our galaxy (with only 4 million solar masses).

In this work, EHT observations (taken during the 2017 campaign) have been used to obtain an image of the black hole of Centaurus A with an unprecedented level of detail.

EHT image of Centaurus A, shown in conjunction with a color composite image of the galaxy. (Images: Radboud University; ESO / WFI; MPIfR / ESO / APEX / A. Weiss et al .; NASA / CXC / CfA / R; Kraft et al .; EHT / M. Janssen et al.)

Two astronomers and an astronomer from the University of Valencia are part of this international research team based on the Event Horizon Telescope (EHT) Collaboration, known for having obtained the first direct image of a black hole. They are Rebecca Azulay, who performed support astronomer tasks at Pico Veleta (the only European radio telescope that participated in the observations); Iván Martí-Vidal (CIDEGENT researcher at the University, who designed and applied the calibration algorithms for the most sensitive part of the EHT); and Alejandro Mus (a member of the research staff in training, whose work focuses on the development of algorithms that will help reconstruct dynamic images of the center of our galaxy).

“These results allow us to see, for the first time, how matter is structured around this supermassive black hole with a level of detail of just over 20 light-hours. This allows us to contemplate the processes that give rise to the birth of the mysterious relativistic jets, which accompany a good part of the most massive black holes in the Universe ”, explains astronomer Michael Janssen, main author of the work.

“We have obtained an image of Centauro A with a resolution more than 15 times higher than the highest of all those previously obtained in observations of this source. This formidable image is allowing us to study the structure of the jet of the black hole, from the smallest scales (the apparent size of a golf ball on the Moon, seen from Earth) to the largest scales (apparent size similar to the size of the Moon itself). The amount of information that we now have is overwhelming ”, highlights Iván Martí-Vidal.

Supermassive black holes, like the one that resides in the heart of Centaurus A, feed on the gas and dust around them, drawing it into their deep gravitational well. This process, called ‘accretion’, releases enormous amounts of energy, much of which is emitted into outer space, resulting in what we know as ‘active galaxies’. While most of the accreted matter is engulfed by the black hole, a small fraction of that matter can escape and form so-called ‘relativistic jets’, one of the most mysterious phenomena in modern astrophysics.

Today, science has different models to explain the acceleration and propagation of matter in relativistic jets. However, very little is still known about the very origin of these jets and how they can spread to cover distances much greater than the size of their entire host galaxy. “These EHT observations will help us find the answer to some of these fundamental questions,” says Alejandro Mus. “The new EHT image shows that the Centauro A jet is brighter at its outermost part, compared to the brightness of its spine, as its central part is called. This is the first time that we have seen this phenomenon so pronounced in a relativistic jet ”, adds Mus.

“The results allow us to rule out several theoretical models of jet formation, which are unable to reproduce the enormous contrast observed between the ends and the spine of the jet,” says Matthias Kadler, from the University of Würzburg and co-author of the work.

Thanks to these observations of Centaurus A, it has been possible to locate the supermassive black hole with great precision, identifying it with the point where the relativistic jet is born. Based on these results, the team of astronomers plans future observations at even higher radio frequencies, which will make it possible to obtain images even sharper than those published now. The team also does not rule out that, in the future, in the longer term, images of the shadow of this black hole may be obtained, incorporating orbiting telescopes into the EHT network. (Source: UV)

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