Event Horizon Telescope observations of the jet launching and collimation in Centaurus A

Kavli Affiliate: Feng Yuan

| First 5 Authors: Michael Janssen, Heino Falcke, Matthias Kadler, Eduardo Ros, Maciek Wielgus

| Summary:

Very-long-baseline interferometry (VLBI) observations of active galactic
nuclei at millimeter wavelengths have the power to reveal the launching and
initial collimation region of extragalactic radio jets, down to $10-100$
gravitational radii ($r_g=GM/c^2$) scales in nearby sources. Centaurus A is the
closest radio-loud source to Earth. It bridges the gap in mass and accretion
rate between the supermassive black holes (SMBHs) in Messier 87 and our
galactic center. A large southern declination of $-43^{circ}$ has however
prevented VLBI imaging of Centaurus A below ${lambda}1$cm thus far. Here, we
show the millimeter VLBI image of the source, which we obtained with the Event
Horizon Telescope at $228$GHz. Compared to previous observations, we image
Centaurus A’s jet at a tenfold higher frequency and sixteen times sharper
resolution and thereby probe sub-lightday structures. We reveal a
highly-collimated, asymmetrically edge-brightened jet as well as the fainter
counterjet. We find that Centaurus A’s source structure resembles the jet in
Messier 87 on ${sim}500r_g$ scales remarkably well. Furthermore, we identify
the location of Centaurus A’s SMBH with respect to its resolved jet core at
${lambda}1.3$mm and conclude that the source’s event horizon shadow should be
visible at THz frequencies. This location further supports the universal scale
invariance of black holes over a wide range of masses.

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