If we look at the definitions, a black hole is a region of space where gravity is so strong that it does not let anything at all escape, not even light, and therefore we cannot see it – hence its name. Given the definition, there is no point trying to see a black hole, however, even if a black hole cannot be directly observed, its influence on its surrounding environment can be so great that it causes energy emissions that reveal its presence. This is how supermassive black holes have been discovered, like the one that lives in the center of the Milky Way, which contains a mass of about 4 million suns.
Observing the things that happen around black holes in distant galaxies is a field of research that brings together the efforts of many researchers, including our guest today in Talking to Scientists: Miguel Á. Pérez Torres, researcher in the Department of Radio Astronomy and Galactic Structure of the Institute of Astrophysics of Andalusia and the CSIC.
In the northern hemisphere, in a region located in the constellation Ursa Major, 140 million light years from us, Arp 299 is located, a celestial object that brings together two colliding galaxies. Miguel Pérez has spent ten years studying the surroundings of Arp 299 and the events that occur there. His initial goal was to study supernovae generated in the matter-rich environment surrounding the black holes of colliding galaxies, but in 2005, Miguel Pérez and Finnish researcher Seppo Mattila discovered a bright infrared signal and in radio coming from one of the nuclei of Arp 299.
The astronomers followed the evolution of the signals for 10 years and were able to observe that the signal became stronger in the infrared and radio, but in the visible, instead, the signal was getting darker, probably absorbed by the large amount of dust. surrounding the black hole. At first, the researchers suspected that the origin was a supernova, but after years of observation they verified that the source suffered a stretch that did not match the initial idea.
Observations of the radio source collected over ten years, in conjunction with models that simulate the behavior of stars in the vicinity of a supermassive black hole, have allowed researchers to conclude that the source of the radiation is it corresponds to a star that has come so close to the black hole that it has been torn apart by the tidal forces generated by it.
In the environment of a supermassive black hole, such as those that exist in the center of any galaxy, large regions of gas, dust and stars accumulate and revolve around it. If a star passes too close to the black hole, the gravitational forces generated by it cause a tidal effect, called a tidal disruption event (TDE), of such power that they stretch the star and tear it apart, causing about half of its mass to be ejected and the other half absorbed by the black hole. He TDE it generates radio emissions, which can last for months or years, and the ejection of a relativistic jet. These emissions allow us to obtain information about supermassive black holes.
I invite you to listen to Miguel A. Pérez Torres, researcher in the Department of Radio Astronomy and Galactic Structure of the Institute of Astrophysics of Andalusia (IAA–CSICGranada, Spain) of the CSIC (Superior Council of Scientific Investigations).
Mattila & Pérez Torres et al. A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger. Science 10.1126/science. aao4669 (2018).
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