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20th of July 2021
Zooming in on Centaurus A
by Janssen et al.
An international team anchored by the Event Horizon Telescope (EHT) Collaboration, which is known for capturing the first image of a black hole in the galaxy M87, has now imaged the heart of the nearby radio galaxy Centaurus A in unprecedented detail. Remarkably, only the outer edges of the jet seem to emit radiation, which challenges our theoretical models of jets. At the center of Cen A lies a black hole with the mass of 55 million suns, which is right between the mass scales of the M87 black hole (six billion suns) and the one in the center of our own galaxy (about four million suns).

The previous most detailed observations were made with the Long Baseline Array as part of the TANAMI project The EHT image has a sixteen times sharper resolution. Supermassive black holes residing in the center of galaxies like Centaurus A feed off gas and dust that is attracted by their enormous gravitational pull. Most matter lying close to the edge of the black hole falls in. However, some of the surrounding particles escape moments before capture and are accelerated away from the black hole in the form of diametrically opposed "jets". Jets are one of the most mysterious and energetic features of galaxies and astronomers still do not know exactly how jets are launched from its central region and how they can extend over scales that are larger than their host optical galaxies without dispersing. The new EHT image shows that the jet launched by Centaurus A is brighter at the edges compared to the center. This phenomenon is known from other jets, but has never been as clearly.

The collage above shows the distance scales uncovered in the Centaurus A jet. The top left image shows how the jet disperses into extended lobes that emit radio waves, captured by the ATCA and Parkes observatories. The top right panel displays a color composite image, with a 40⨉zoom compared to the first panel to match the size of the galaxy itself. Submillimeter emission from the jet and dust in the galaxy measured by the LABOCA/APEX instrument is shown in orange. X-ray emission from the jet measured by the Chandra spacecraft is shown in blue. Visible white light from the stars in the galaxy has been captured by the MPG/ESO 2.2-metre telescope. The next panel below shows a 165000⨉zoom image of the inner radio jet obtained with the Long Baseline Array telescopes as part of the TANAMI project. The bottom panel depicts the new highest resolution image of the jet launching region obtained with the EHT at millimeter wavelengths with a 60000000⨉zoom in telescope resolution.Indicated scale bars are shown in light years and light days. (Image credits: R.Bors; CSIRO/ATNF/I.Feain et al., R.Morganti et al., N.Junkes et al.; ESO/WFI; MPIfR/ESO/APEX/A.Weißet al.; NASA/CXC/CfA/R.Kraft et al.; TANAMI/C.Müller et al.; EHT/M.Janßen et al.)

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