Two years ago they surprised everyone with the first image of a black hole. Today, the Event horizon telescope team, made up of hundreds of scientists from all over the world, reveals that from those same observations that revealed something that was only described by theory, much more has been obtained: the map of magnetic fields on the edge of the event horizon, new secrets about what happens near the border beyond which there is oblivion. And once again we can say that we can see something that had never been seen before.
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The protagonist is always him, the active galactic nucleus at the center of the galaxy M87 about 55 million light years away from us. With the light collected by radio telescopes scattered around the world, and forming the Eht (Event horizon telescope), the researchers were able to recognize the polarized light that manages to escape the gravity of the gargantuan devourer of matter. And they have obtained the mapping of the magnetic field that modifies it. A measure that the researchers themselves have defined “a milestone”: “This is the first measure of the polarization of light in a region that is practically on the ‘edge’ of a black hole, on the so-called event horizon – explains Ciriaco Goddi, researcher of the Dutch universities of Nijmegen and Leiden and member of the Eht team – in particular, the intensity and orientation of the polarization, visible in the image in the form of streaks, allow us to map the magnetic field lines present in the vicinity of the event horizon and to study their effect on the plasma that increases on the black hole ”.
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Goddi is the first signature of one of the three studies, published today by the journal The Astrophysical Journal Letters from the collaboration of Eht which involves 300 researchers all over the world. His paper presents the results obtained from the observations of Alma (the Atacama large millimeter / submillimeter array in Chile). Alma is part of the network of telescopes whose observations, all together, are equal to those of an antenna as large as the whole of Planet Earth: “Since April 2019, as an EHT collaboration, we have further deepened the analysis of the data collected in 2017 – continues Goddi, who is also an associate researcher of INAF – the new photo is in fact obtained from the same data, but is seen through the equivalent of a Polaroid filter, which allowed us to observe that a significant fraction of the light around the black hole of M87 is polarized ”. The research involved over 300 researchers from organizations and universities around the world, including the National Institute of Astrophysics (Inaf) and Federico II University of Naples.
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“It is interesting to note that only part of the plasma ring surrounding the black hole, the one seen in the lower right image, is significantly polarized, and there is evidence that the polarization varies over the course of the week. during which we made the observations – comments Nicola Marchili, Inaf researcher and member of the Eht scientific team together with Elisabetta Liuzzo and Kazi Rygl – the image in polarized light obtained allows us to obtain interesting additional information on what produces the emission that the ‘original image from 2019 failed to provide, and also allows us to estimate the density and temperature of the plasma ”.
The special light
The polarization of light is the phenomenon whereby electromagnetic waves oscillate only in one plane. It is an effect that is achieved after it has passed through a filter, for example with some types of sunglasses that eliminate reflections. But also when light is emitted in hot regions of space where magnetic fields are present. By studying the polarized light coming from these areas, as on the edge of the event horizon, astrophysicists were able to “draw” the map of the magnetic field. In addition to being a result of great scientific and technological value in itself (to obtain it, as for the first photo of the black hole, it took years of observations, long periods of collecting light in the form of radio waves, synchronizing all the telescopes of the network thanks to atomic clocks, and years of data processing) spying on what happens in that remote part of the Cosmos will help to understand even better how supermassive black holes like the one at the center of M87 “work”.
Fireworks
It is in fact a rather restless giant. It constantly devours matter and this voracity triggers fireworks among the most spectacular in the Universe. These are the so-called “relativistic jets”, produced by super-massive black holes, whose particles, which escape gravitational attraction, are thrown at speeds close to those of light. What starts from the center of M87 is a blaze that stretches for 5,000 light years: “They are one of the most mysterious and energetic phenomena in astrophysics and we think they are launched by supermassive black holes that reside in the nucleus of active galaxies – underlines Goddi – those that emerge from the core of M87 have been studied over the years with various instruments, including the Hubble Space Telescope, but only now have we been able to obtain a complete description of the magnetic field structures that surround them ”.
After giving us the first image of a black hole, EHT has made progress, with the addition of new telescopes to the network and updates and the new discoveries just announced. However, from this project we expect, it is not yet known when, also a new, extraordinary image: that of Sagittarius A *, the black hole at the center of the Milky Way. It is closest to us but also much smaller than that of M87, and a lot more “silent”: no plasma roars. It hides in the center of our galaxy and the wait to admire it is getting bigger.
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