Imagine a donut horizontally facing you. In profile, you only see a rounded rectangle of dough covered in icing. Now if you raise or lower the donut, the middle hole appears. This is very simplistically observed by an international team of astronomers. Because instead of being interested in donuts, their work, published on February 17 in the magazine Naturerelate to the nuclei of galaxies.
The team trained their eyes from the European Southern Observatory in Chile’s Atacama Desert to the galaxy NGC 1068, more commonly known as ‘Messier 77’ or ‘M77’. Located 47 million light-years away, in the constellation of the Whale, this galaxy has been known for centuries. But what makes it so interesting to astronomers is that it has an active galactic nucleus. “We find in these active nuclei a central engine, a black hole which feeds on the surrounding matter and which, in doing so, will release a phenomenal amount of energy and a strong luminosity”, describes Bruno Lopez, scientific manager of the instrument which observed the M77 galaxy and astronomer at the Côte d’Azur observatory.
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Not all galaxies have a beating heart. In our Milky Way, for example, the nucleus is not active, because the black hole in the center no longer feeds. “For three million years, it no longer produces energyconfirms James Leftley, astronomer and co-author of the study. Galactic nuclei can be active, then stop, then resume and so on. “The activity of the core is part of the history of galaxies and contributes to its formation, says Bruno Lopez. As they feed, black holes throw out matter in the form of jets, like crumbs, which will give shape to the galaxy and contribute to the birth of stars. »
Two sides of the same coin
Discovered as early as the 1950s, active nuclei are classified into two types: the first, called Seyfert 1, is very bright, while the second, Seyfert 2, is less bright. But for the past thirty years, astronomers have leaned in favor of a unified theory. The two types of active nuclei would actually be identical, just seen from different angles.
As with the donut at the start, the Seyfert 2s would be seen from the side, through the large cloud of material that serves as the black hole’s pantry. Conversely, the Seyfert 1 would be seen from above (or below), which makes it possible to observe the very luminous emissions which escape from both sides of the black hole.
“Our observations of the galaxy M77, a perfect example of the second type, reinforce the idea that the unified model is the correct one, and that all the active nuclei are in fact identical”, explains James Leftley. Without going into details, the astronomers were able to observe the influence of the environment of the black hole, hidden behind the cloud of matter. And deduce that types 1 and 2 were just two sides of the same coin. They now wish to observe other galaxies of the same type to confirm this.