A postcard from afar… The astronomers who had revealed the first black hole to the eyes of the world succeeded in capturing the image of the swirling magnetic field near its edge, a crucial step in understanding these mysterious cosmic monsters.
On April 10, 2019, the gigantic black hole lodged in the heart of the Messier 87 galaxy (M87), located 55 million light-years away, appeared to us, as a dark circle in the middle of a flaming halo.
The historic image, produced by the international collaboration Event Horizon Telescope (EHT) connecting eight telescopes around the world, was the most direct evidence ever of the existence of black holes, objects so massive and compact that nothing stands out. escapes, not even the light.
Two years later, after careful consideration of the data collected in 2017, EHT scientists know more about the mechanics of the beast, which is several billion times the mass of the Sun. Their work is published Wednesday in The Astrophysical Journal Letters.
We discover a new image of the object in polarized light, as if it passed through a filter helping to isolate part of the light radiation.
“The polarization of light contains information that allows us to better understand the physics behind the image seen in April 2019, which was not possible before. This is a major step ”, underlined Ivan Marti-Vidal, coordinator of one of the working groups of the EHT and researcher at the University of Valencia (Spain).
“We observe for real what the theoretical models predicted, it is incredibly satisfying!”, Congratulated AFP Frédéric Gueth, deputy director of the Institute of Millimeter Radio Astronomy (Iram), whose telescope of 30 meters in the Spanish Sierra Nevada is part of the EHT network.
The polarization revealed the structure of the magnetic field, located at the edge of the black hole, and made it possible to produce an accurate image of its shape, similar to a whirlwind of filaments.
This extremely powerful magnetic field – much more than that surrounding the Earth – comes to oppose a resistance to the force of gravitation of the black hole: “a kind of balance occurs between the two forces, like a fight, even if it is in the dark. final gravity that wins ”, explains the astronomer.
“The magnetic field at the edge of the black hole is strong enough to repel hot gas and help it resist the force of gravity,” explains Jason Dexter, of the University of Colorado at Boulder in the United States.
– Powerful light jets –
No matter comes out of a black hole once it is swallowed (“accreted”). But the cosmic ogre, as powerful as it is, does not swallow “100% of everything in its environment: part of it escapes”, develops this researcher at the CNRS.
That part of the material that is not captured – about 10% – is ejected, and the magnetic field plays a key role in this mechanism. “The material will follow a trajectory along the lines of the field”, continues Frédéric Gueth.
The magnetic force would not only extract matter, but also eject powerful jets of light at immense speeds extending at least 5,000 light years beyond the galaxy itself.
These energetic jets coming from the core of M87 “are one of the most mysterious phenomena of this galaxy”, according to the ESO (European Southern Observatory).
The interaction of forces uncovered by the EHT is believed to be at work in all black holes, from the smallest to the supermassives lurking in the center of most galaxies, including the Milky Way.
No information coming out of black holes, we will never be able to observe them directly. “What goes on inside will remain a mystery. The challenge is therefore to understand as much as possible what is happening around it, because it is necessarily linked ”, concludes the researcher.
The annual simultaneous observation session of the EHT network, which fell into the water last spring due to the Covid-19 pandemic, is expected to resume at the end of April. The addition of new telescopes, including the NOEMA observatory at Iram, in the Hautes-Alpes, will make it possible to further improve the precision of the images obtained.