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

TL;DR

This paper presents the first millimeter VLBI image of Centaurus A's jet at 228GHz, revealing detailed jet structure and SMBH location, supporting black hole scale invariance and advancing understanding of jet launching regions.

Contribution

The study provides the first high-resolution millimeter VLBI image of Centaurus A, revealing jet structure and SMBH position at unprecedented scales, bridging observational gaps.

Findings

Revealed a highly-collimated, edge-brightened jet and counterjet.

Identified the SMBH location relative to the jet core.

Supported the universality of black hole scale invariance.

Abstract

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.