What are the most violent events in the universe?

There is nothing calm or peaceful about the Universe. Quite the contrary! It is the scene of particularly brutal events and the energies deployed often exceed understanding. Stellar cannibalism, collisions of neutron stars or mergers of giant black holes… Here is a review of the most violent events in the Universe.

Our planet is for the moment spared, peacefully installed in the suburbs of its galaxy. But the calm is deceptive and the neighbors make a lot of noise despite appearances. From the earthly point of view, we could compare ourselves to the Hobbit people who live happy days in their Shire without necessarily being aware of the forces around them and of the events in progress. Implacable mechanisms are however at work, more and more betrayed by the X-rays and Gamma that we can detect today. Tiny, these sidereal convulsions nevertheless betray intense and prodigious acts of cannibalism.

Take the case of binary stars, which are very numerous in our galaxy. These rotate around the same axis. One is very often bigger than the other and therefore this one explodes faster in supernovae. Only an extremely compact heart will remain. Imagine the Sun compressed into a sphere the size of the city of Paris. The gravitational forces are enormous. The little sister who is still alive will then gradually be sucked in, stripped of her gas by the neutron star which was one day her companion. This gas then forms a disk around the neutron star and will eventually fall onto the solid crust. On the surface, gravity is so great that the speed of fall reaches 100,000 km/second. Under these conditions, 10 grams of gas release the equivalent of the Hiroshima bomb. Except that a neutron star does not capture only 10 grams of gas per second, no. It can capture more than 2,000 billion tons.

In some cases, the neutron star gives way to a black hole which actually results from the death of an even more massive star. These cosmic ogres, residues of the first supermassive stars, are this time worth several million solar masses. As you can imagine, these objects are very greedy and must swallow several times the mass of the Sun each year. The stars that rub against it sting themselves. The principle is the same as for the neutron star: the gas is torn away and a disc of matter begins to turn around the ogre. Falling into the black hole, the gas heats up and emits X-rays. We then observe jets of matter rising perpendicular to the plane of the accretion disk surrounding the black hole. These jets can reach very high speeds corresponding to significant fractions of that of light.

Some events are also capable of generating even more energetic gamma rays. It may be the collision of two neutron stars or the result of a hypernova, an explosion even more powerful than a supernova. At the origin of these phenomena are found supergiant stars of more than 100 solar masses.

Of course, all these events are not without consequence. Apart from shaping space, they also alter space-time with the emission of gravitational waves. Predicted by Albert Einstein 100 years ago, we detected these waves for the first time only a few months ago, the results of the collision-merger of supermassive black holes that occurred several billion years ago.

Source: Science Key Questions

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