Key science objectives

Tozzi redshift

Testing general relativity - Einstein's theory of general relativity predicts that there will be a roughly circular "shadow" around a black hole. The EHT aims to image the shadow to test this prediction and determine the mass of black holes

Understanding accretion around a black hole - Black holes exert a strong gravitational pull on nearby matter. Some of this matter ultimately falls into the black hole in a process called accretion. One of the objectives of the EHT is to improve our understanding of the physics of accretion.

Understanding jet genesis and collimation - Most galaxies show large scale jets of very fast moving plasma that are launched from the central black hole. One possibility is that these jets are launched very close to the rapidly-rotating central black hole. Most of these jets remain tightly confined to a narrow opening angle even far from the black hole. The EHT will improve our understanding of the process of generation and collimation of these jets.

Science requirements

High angular resolution - The nearest massive black hole is in the center of our Galaxy. Even though the size of this black hole is quite big, about 30 times the size of the Sun, it is at such a large distance from us that it appears about the same size as an orange on the Moon. Even though this is astonishingly small, the EHT will have the ability to discern things at this fine scale.

High sensitivity - Intrinsically, the radiation from cosmic sources becomes very weak by the time it reaches the Earth. The radio emission from the nearest massive black holes is faint even by radio astronomy standards. This necessitates the use of very large telescopes and very high data rates.

Modeling and simulations - Black holes themselves are simple objects, but the details of features seen in the data are heavily dependent on the complex environment of the material surrounding them. This requires us to model the complex environment as well as its observational signatures.

Observational technique

The EHT uses the technique of Very Long Baseline Interferometry (VLBI) to synthesize an Earth-sized telescope in order to achieve the highest resolution possible using ground-based instrumentation. The target source is observed simultaneously at all telescopes. The data are recorded at each of the sites and later brought back to a processing facility where they are passed through a special purpose supercomputer known as a correlator. More information about radio astronomy and the technique of interferometry is available here.

Primary observing targets

The black hole at the center of the Milky Way - Sgr A* - Located 25,000 light years from us in the center of our Galaxy, Sagittarius A* is our nearest massive black hole with four million times the mass of the Sun. Its proximity makes it the largest apparent black hole as viewed from the Earth.

A giant elliptical galaxy - M87 - At a distance of 53 million light years, the Messier object M87 is our second primary target. Even though it is much farther than Sgr A*, its central black hole is much more massive, 6 billion times the mass of the Sun, making it the next largest apparent black hole as viewed from the Earth.

Key science results so far