First M87 Event Horizon Telescope Results and the Role of ALMA

TL;DR

The paper discusses the first image of a supermassive black hole at M87 by the Event Horizon Telescope, highlighting the crucial role of ALMA in enhancing imaging capabilities and future prospects for studying black hole physics.

Contribution

It reports the first direct imaging of a black hole's event horizon and emphasizes the impact of including ALMA in the global array for improved sensitivity and resolution.

Findings

First direct image of M87 black hole's shadow.

ALMA's inclusion increased EHT sensitivity by an order of magnitude.

Future array expansions will enable detailed studies of black hole environments.

Abstract

In April 2019, the Event Horizon Telescope (EHT) collaboration revealed the first image of the candidate super-massive black hole (SMBH) at the centre of the giant elliptical galaxy Messier 87 (M87). This event-horizon-scale image shows a ring of glowing plasma with a dark patch at the centre, which is interpreted as the shadow of the black hole. This breakthrough result, which represents a powerful confirmation of Einstein's theory of gravity, or general relativity, was made possible by assembling a global network of radio telescopes operating at millimetre wavelengths that for the first time included the Atacama Large Millimeter/ submillimeter Array (ALMA). The addition of ALMA as an anchor station has enabled a giant leap forward by increasing the sensitivity limits of the EHT by an order of magnitude, effectively turning it into an imaging array. The published image demonstrates that it is now possible to directly study the event horizon shadows of SMBHs via electromagnetic radiation, thereby transforming this elusive frontier from a mathematical concept into an astrophysical reality. The expansion of the array over the next few years will include new stations on different continents - and eventually satellites in space. This will provide progressively sharper and higher-fidelity images of SMBH candidates, and potentially even movies of the hot plasma orbiting around SMBHs. These improvements will shed light on the processes of black hole accretion and jet formation on event-horizon scales, thereby enabling more precise tests of general relativity in the truly strong field regime.