The nature of black holes remains one of the great scientific unknowns of our time. But, little by little, research advances in the understanding of these enormous concentrations of matter. For example, it is believed that at the center of most large galaxies there are supermassive black holes, with large flows of energy. And analyzing their properties will be key to determining the physical mechanisms that act in active galactic nuclei (the region located at the center of some galaxies that is much brighter than the rest).
In that central region of black holes, matter collapses to a specific point (called a singularity). The surface around that point, where energy and matter can no longer escape the black hole's gravity, is called the event horizon. Although the black hole is dark, the hot plasma around this horizon can form a disk by the accumulation of matter (accretion) from which jets of photons can be emitted that, due to gravity, carry curved trajectories.
The galaxy Messier 87 (M87), located about 54 million light-years from Earth, is a prime location to study the accretion of black holes and the formation of jets. It hosts one of the two closest supermassive black holes to our planet (the other is Sagittarius A, located at the center of our galaxy). But Sagittarius A has a modest mass (about 4 million solar masses), while that of M87 reaches 6,000 million suns and has a very powerful jet of matter.
This week an international team presents new high-resolution images of M87 and its black hole in the journal Nature. "By driving a powerful relativistic jet, the study of M87 can serve to better understand how they are generated," says Thomas Krichbaum of the Max Planck Institute for Radio Astronomy and one of the lead authors of the paper. "This is something very relevant to better understand how radio galaxies evolve and how they feed matter into their environment, which, in turn, is important for understanding the evolution of the Universe."
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Scientific milestone.
The first photo of a black hole and its shadow
- Writing: TERESA GUERRERO Madrid
- Writing: JAVIER AGUIRRE (GRAPHICS)
The first photo of a black hole and its shadow
Astronomy.
They capture the first image of the black hole of our galaxy, Sagittarius A*, proving its existence
- Writing: ÁNGEL DÍAZ
- Writing: TERESA GUERRERO Madrid
They capture the first image of the black hole of our galaxy, Sagittarius A*, proving its existence
Images of the region surrounding this supermassive black hole confirm an annular structure from which powerful jets emerge. That ring, which is estimated to be larger than inferred by the first Event Horizon Telescope (EHT) observations taken in 2017, has been identified as the region of the accretion flow towards the black hole. In addition, the observations also suggest the possible presence of a wind associated with that flow.
International collaboration
Hidden by dense clouds of gas and dust, optical telescopes cannot access the central region of a black hole, but those observing at shorter (such as X-ray) or longer (such as millimeter and submillimeter) wavelengths do manage to penetrate through those clouds. In recent years, the world's most powerful radio telescopes have joined forces in two major international collaboration projects to create two networks with unprecedented capacity: the EHT, which operates at wavelengths close to the millimeter and the Global mm-VLBI Array (GMVA) that works with lengths around 3 millimeters.
In these networks, signals from different stations are combined using a technique known as very long baseline interferometry (VLBI). The multiple actors allow to achieve a level of resolution much higher than that which can offer a telescope alone. "The shadow of M87's black hole was already observed by the EHT in 2017, but in that dataset (which was obtained at a wavelength of 1.3 mm) only one emission ring was appreciated, no jet," says Krichbaum. "The observations we publish now were made with the GMVA, which consists of many more VLBI stations and is therefore more sensitive to jet emission."
The new 3.5 mm GMVA images show how the relativistic jet connects with the black hole and emerges from the surrounding ring. "It is the first time that astronomers can see how a jet forms and how it emerges from the black hole," summarize the German researcher. Actually, theoretical scientists suspected for many years that black holes can create jets, but there was no direct proof."
Spanish contribution
In particular, two telescopes, in Chile and Greenland, have played a key role. "So much so, that on previous occasions, when these telescopes were not yet participating in the GMVA, sufficient resolution was never achieved to see the shadow of M87 at this frequency", says Iván Martí-Vidal, researcher in the Department of Astronomy and Astrophysics and at the Astronomical Observatory of the University of Valencia. The participation of the Valencian center has been particularly important because in order to use the aforementioned telescopes, since for this it has been necessary to use algorithms created by this researcher.
"It is the first time that we have managed to see in a single image the shadow of the black hole and the relativistic jet that comes out of it," says Martí-Vidal. "Today, there are important details to be clarified of this whole process of jet production, where General Relativity (bending space) and Quantum Fields (producing pairs of matter and antimatter in those regions) are mixed. But finally having an image where we see that phenomenon represents a very important step in our understanding of black holes and how nature behaves around them."
It is not the only Spanish contribution to the GMVA project, which includes the radio telescope of Pico Veleta (near Granada) and Yebes (Guadalajara). Nor is it the only contribution to the study published today in Nature, which has a large group of Spanish scientists among its authors. "This is a very broad international collaboration and a very important part is the coordinated interpretation of the data and the analysis of the results," explains José Luis Gómez, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC). "For example, what our team (researcher Efthalia Traianou and I) have done is contribute to the analyses that allow us to determine the structure of the signal source, with data that is stored on supercomputers from which we can work on a reconstruction."
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