Towards imaging the Event Horizon of a black hole (EHT)

Abstract

One of the prime objectives of the Large Latin American Millimeter Array (LLAMA) is (sub)mm Very Long Baseline Interferometry (mm-VLBI) as the first one in a series of antennas that would make up the first interferometry VLBI network in Latin America. VLBI above 200 GHz (< 1.5 λmm) is a largely unexplored spectral domain and LLAMA, when operating with ALMA, will increase the angular resolution by ~10x compared to ALMA alone. A global mm-VLBI network will achieve the highest possible high angular resolution available in all of astronomy. Such array will allow us to address one of the most fundamental predictions of General Relativity: the existence of Black Holes (BHs). Their defining feature is the event horizon, the surface that even light cannot escape. However, while there are many convincing BH candidates in the universe, there is still no conclusive proof for the event horizon. So, does general relativity really hold in its most extreme limit and is there an event horizon? To answer such questions we aim to obtain the first direct images of BHs on event horizon scales using VLBI: Sgr A*, the super-massive BH in the center of our Milky Way, and its counterpart in the nearby galaxy M 87. To conduct the experiment requires establishing the required global mm-VLBI network of radio telescopes operating above 200 GHz, which we refer to as the Event Horizon Telescope (EHT). BlackHoleCam is participating in the technical and operational implementation of the EHT. Detailed theoretical simulations show that a BH embedded in an optically thin emission region would lead to a sharp “shadow” cast by the event horizon which can be detected by the EHT. Preliminary non-imaging observations with the EHT have already successfully detected emission around Sgr A* on event horizon scales. The EHT is in the process of adding stations and sensitivity that will enable imaging observations within the next few years. The aim of our project is to operationally make LLAMA VLBI-ready and prepare for and conduct the first VLBI observations with ALMA, the EHT, and other (sub)mm telescopes. (AU)