Combining the power of the world's largest radio observatories has helped scientists for the first time obtain concrete data on the size of the "visible part" of a giant black hole in the center of the Milky Way, according to an article published in the Astrophysical Journal.
Most astronomers believe that at the center of all galaxies are supermassive black holes - objects weighing millions and billions of Suns, continuously absorbing matter. The black hole partially ejects it back in the form of jets - thin beams of plasma accelerated to near-light speeds.
In the Milky Way (and some other galaxies), the black hole is dormant, so it has no large and visible jets. Scientists have long been trying to understand when she fell asleep, how active she was and how this activity affected the stars in the center and on the outskirts of the Galaxy.
Sara Issoun of the University of Nijmegen in the Netherlands and her colleagues have been observing Sgr A *, the black hole at the center of the Milky Way, for many years with the GMVA microwave interferometer, a virtual radio telescope. Within its framework, the powers of the most sensitive ground-based millimeter radio telescopes in Chile, the USA, Spain, Germany and a number of other countries were united.
GMVA acts as an analogue of another well-known project - Event Horizon Telescope, but in this case, scientists are observing Sgr A * on a different set of frequencies. This will allow us to study it in more detail and understand how radiation is generated in the vicinity that are invisible to the EHT.
A year ago, members of the EHT project took the first images of the zone where the black hole radiation is born, and revealed several of its unexpected features, including the alleged asymmetry. This spurred astrophysicists' interest in Sgr A * and made it possible to get even more detailed images of the black hole's "eye" using GMVA.
Scientists were able to double the resolution and clear the data from interference arising from the scattering of radio waves inside dense clouds of interstellar gas and dust, blocking the center of the Galaxy from the eyes of observers on Earth.
This data unexpectedly showed that the visible portion of Sgr A * was not only asymmetric, but also very small in size. Such a discovery contradicts the popular theory today that almost all visible radiation generated by supermassive black holes originates inside jets.
How this is possible, astrophysicists cannot yet say, but they are inclined in favor of the fact that the emissions of a black hole can indeed be directed towards the Earth. In the past, Issown notes, such a coincidence seemed unlikely, but observations from both the EHT and GMVA are quite clear in favor of this scenario.
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Scientists hope that the final answer to this mystery will be found soon, when astronomers finish processing the last piece of data from the EHT. New, more detailed images, cleared of interference in a similar way, will indicate exactly where the jet of the black hole is looking and whether it has one at all, the astronomer concludes.