The IAA will lead two of the five most advanced studies on supermassive black holes in 2018

The 66 antennas of the ALMA observatory join the Horizon of Events (EHT) telescope for the study of supermassive black holes. Five observation proposals have been approved for 2018, two of them coordinated by the Institute of Astrophysics of Andalusia (IAA-CSIC)


Black holes are one of the most fascinating objects in the cosmos: concentrations of matter with a gravitational force so intense that even light cannot escape. The Event Horizon Telescope (EHT) seeks to directly observe its immediate environment, a region called the event horizon from which light does escape (and from which we can obtain information). ALMA observatory has joined the EHT and have selected five projects to study supermassive black holes in 2018, two of them led by the Institute of Astrophysics of Andalusia (IAA-CSIC).

The Event Horizon Telescope (EHT) is actually a virtual telescope: it is a set of antennas distributed around the world whose signal is combined, so that they function as a telescope with a diameter equivalent to the maximum distance between antennas. In 2017 the ALMA observatory added its sixty six antennas to the EHT, which provided the project with its huge collecting surface of more than seven thousand square meters.

Los agujeros negros que estudiarán EHT y ALMA generan los entornos más extremos que se conocen en el universo, lo que se conoce como núcleos activos de galaxias. Se trata de agujeros negros supermasivos, con hasta varios miles de millones de veces la masa del Sol, que se hallan rodeados de un disco de material que los alimenta (el disco de acrecimiento) y pueden liberar de forma continua más de cien veces la energía de todas las estrellas de una galaxia como la nuestra. Además, suelen mostrar chorros de partículas perpendiculares al disco que viajan a velocidades cercanas a la de la luz y se extienden más allá de la propia galaxia.

Los agujeros negros supermasivos desempeñan un papel fundamental en la formación y evolución de las galaxias (la mayoría de ellas, incluida la Vía Láctea, alberga uno), y constituyen un entorno único para el estudio de la gravedad en ambientes extremos. Así, el Telescopio del Horizonte de Sucesos espera, por ejemplo, poner a prueba la Teoría General de la Relatividad de Einstein, que predice la existencia de una "sombra" más o menos circular en torno al agujero negro, entender el fenómeno de la absorción de material alrededor de los agujeros negros o el mecanismo de formación de los chorros.

The black holes that will study EHT and ALMA generate the most extreme environments in the universe, known as active galactic nuclei. They are supermassive black holes, up to several billion times the mass of the Sun, surrounded by a disk of material that feeds them (the accretion disk). They can release continuously more than one hundred times the energy of all the stars of a galaxy like ours, and they often show jets of particles perpendicular to the disk that travel at speeds close to that of light and extend beyond the galaxy itself.

Supermassive black holes play a key role in the formation and evolution of galaxies (most of them, including the Milky Way, hosts one), and provide a unique environment for the study of gravity in extreme environments. Thus, the Event Horizon Telescope hopes, for example, to test Einstein's General Theory of Relativity, which predicts the existence of a more or less circular "shadow" around the black hole, to understand the phenomenon of absorption of material around the black holes or the mechanism that rules the formation of the jets.

In September 2007 an exciting prediction was fulfilled. OJ287, a supermassive black hole with about eighteen billion solar masses (one of the largest known), experienced an expected burst, which followed a trend recorded since 1890 and which is dotted with double bursting every twelve years or so.

The prediction was made considering a model proposing that OJ287 is actually a binary supermassive black hole. According to this model, another black hole -a hundred times smaller- revolves around OJ287 and regularly traverses its accretion disk, heating it and releasing bubbles of material that generate the flashes.

The accuracy in prediction, which contemplates the loss of energy of the system through gravitational waves, secured the binary black hole model (in which, in addition, the minor would fall on OJ287 until it merges with him in an interval of about ten thousand years), but it is necessary to observe the innermost region of the object to verify it.

One of the five projects accepted for observation with the Event Horizon Telescope and ALMA in 2018 is precisely to check whether OJ287 is indeed a double black hole. "We hope these observations allow us to test Einstein's theory of relativity in one of the most extreme scenarios we can find in the universe: a binary system of supermassive black holes destined to merge into one. If this scenario is confirmed, we would be facing with a system capable of emitting the most intense gravitational waves in the universe", says José Luis Gómez, a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who leads the project.

In the spring of 2018 a large part of the world's great observation facilities will aim at this object. Large international antenna networks, both on land and in space, have programmed observations and are expected to obtain an image with a resolution of about ten microarcseconds (seen from Earth, these ten microarcseconds would correspond to the size of a coin of one euro on the surface of the Moon).

"These observations will allow us to better understand how relativistic jets form, or to test the so-called no-hair theorem, which states that all the information about matter that forms the black hole or that falls on it disappears after the event horizon and remains inaccessible, so black holes would be characterized only by their charge, mass, and angular momentum", says Gómez (IAA-CSIC).


When active galaxies began to be studied in the 1960s, the term quasar, short for quasi-stellar radio sources, was coined to refer to these extremely distant and bright point objects which, according to what we know today, respond to the existence of a supermassive black hole in a galactic core.

However, years later a term had to be coined for some who were even brighter. These are blazars (blazing quasi-stellar objetcs), which show a much higher brightness because we see the front disk and the particle jet pointing in our direction.

4C + 01.28, one of the objectives of the observation campaign with the Event Horizon Telescope for 2018, is a blazar that presents a peculiarity. "The jet of 4C + 01.28 shows a double structure: an internal region, with the magnetic field aligned in one direction, and an outer one -a kind of sheath- with the field aligned in the direction perpendicular to the previous one, aligned with the direction of the relativistic jet", says Antxon Alberdi, a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) who coordinates the project.

The detailed study of this blazar will allow to discriminate between the two models that try to explain how the jets form in the active galaxies. One stands that the jet emerges from the accretion disk that surrounds the black hole. Because of the rotation of the disc, the field lines are "rolled up" forming a helical structure that confines and accelerates the particles forming the jet. A helical structure, but seen from the front as in 4C + 01.28, would explain the different orientations of the magnetic field that we see in this blazar.

The second model holds that the jets are formed in the black hole itself and that the different orientation of the magnetic field of the outermost region of 4C + 01.28 can be explained by the interaction of the jet material with the external medium .

To verify which scenario is correct, they are necessary very precise observations of the base of the jet and of how the light is polarized. The light we receive from the universe is the result of the disorderly overlapping of many randomly vibrating electromagnetic waves, ie, non-polarized light. Under some circumstances, as in environments with strong magnetic fields, light vibrates preferentially in a plane, giving rise to polarized light.

"If the jet emerges from the accretion disk we will see a more open structure and very polarized light, while if it is driven by the black hole itself the signal will be more compact, with a higher level of opacity and a lower degree of polarization," notes Alberdi (IAA-CSIC).


Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - sll[arroba] - 958230532