When a black hole explodes: a cosmic event never seen in 10 years

© Image generated by DALL-E AI for Presse-citron

In 2018, as telescopes around the world peered into the galaxy M87, 55 million light-years away, they captured an event of rare intensity. The supermassive black hole M87* has emitted a gigantic gamma ray flare, an extremely bright and energetic flash of gamma rays, the most powerful form of electromagnetic radiation.

These cosmic events are usually short-lived, but they release colossal energy in a few seconds, equivalent to what our Sun would emit in several billion years.

At the heart of the beast

Let's imagine the supermassive black hole as an immense cosmic whirlwind. Around it gravitates a disk of matter, similar to a gigantic ring of gas and dust. This matter, as it falls towards the black hole, heats up considerably under the effect of friction forces – comparable to the phenomenon that warms our hands when we rub them together, but on a scale billions of times greater. This intense heat causes the accretion disk to glow, creating the characteristic bright ring seen in the first historical image of M87* (see below).

Years of observations and calculations were required to produce this revolutionary image. It shows us the accretion disk of M87* as it appeared on April 10, 2019, a luminous ring of superheated matter orbiting the black hole. © Event Horizon Telescope/Wikipedia

The intense magnetic fields, generated by the rotation of the accretion disk and the black hole itself, play a major role in the formation of relativistic jets, extremely powerful cosmic geysers. These magnetic fields, structured in lines of force, channel part of the superheated matter of the disk, accelerating it to speeds close to that of light along the field lines that extend perpendicular to the disk, thus forming two collimated jets of plasma.

The anatomy of a titanic eruption

The gamma ray eruption observed in 2018 represents an event of unprecedented violence. To understand its magnitude, let's imagine a volume of space equivalent to 170 times the distance between the Earth and the Sun—a surprisingly compact region on a cosmic scale, barely ten times larger than the black hole itself. It was in this relatively small space that this phenomenally powerful explosion occurred.

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The mechanism behind this eruption can be compared to a cosmic collision: “lumps” of matter, falling into the plasma jet, are violently accelerated. This acceleration is so intense that it generates an immense quantity of gamma rays. The energy released by such an eruption is billions, if not trillions, of times greater than that of a modern nuclear bomb.

“Intriguingly, the intense variations detected in gamma rays do not appear at other wavelengths, suggesting that the eruption area is structured in a complex way and behaves differently depending on the type of observation” notes Daniel Mazin of the University of Tokyo. In other words, the eruption zone behaves like a real chameleon, changing its appearance depending on the type of light used to observe it.

A cosmic laboratory for fundamental physics

The simultaneous observation of the gamma-ray flare and the changes in the luminous ring around the black hole offers a unique opportunityto study the laws of physics under extreme conditions. Sera Markoff of the University of Amsterdam explains: “For the first time ever, it is possible to combine direct images of areas near the event horizon with gamma-ray flares from particle acceleration, allowing theories about the origin of these flares to be tested“

By directly observing the interactions between matter and gravity, scientists can therefore test whether Einstein's predictions are still valid. These rare and still partly mysterious cataclysmic events can also be better understood by combining direct images with gamma-ray observations. The aforementioned relativistic jets are extraordinary natural particle accelerators. By studying these phenomena, scientists could discover new acceleration mechanisms, with potential applications in particle physics.

Observations of the M87* explosion greatly deepen our understandinghigh-energy phenomena near supermassive black holes. Analysis of the data collected during this exceptional gamma-ray flare highlights the wealth of physical processes operating in these regions of space-time where the laws of physics reach their theoretical limits. These will undoubtedly feed new theoretical models to describe the behavior of matter and energy in these extreme environments and perhaps help us answer more accurately this fundamental question: where do we come from and where does our Universe come from ?

• In 2018, an exceptionally intense gamma-ray flare was observed near the black hole M87*, releasing colossal energy in a compact space.
• This explosion, caused by the acceleration of particles in plasma jets, is a unique opportunity to study the interactions between matter and gravity.
• The discoveries around M87* make it possible to test the fundamental laws of physics in extreme conditions.

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