They Are Projected At High Speed Across The Universe

Some time ago we had fun giving you the calculations of this physicist who had imagined the probable consequences of the encounter between a mini black hole shooting through the air and your body. An obviously theoretical exercise, since the overwhelming majority of black holes are immobile, and it is simply impossible that such a phenomenon could happen. We said well majority : yes, certain black holes called “ fugitives » are not connected to any galaxy and cross the Universe at staggering speeds, sometimes exceeding 10 million km/h. The existence of these somewhat unusual celestial objects was only proven in 2023, thanks to our venerable Hubble telescope, even if the mechanism behind their unique behavior dates back to the 1980s, with the work of astronomer Jack Hills.

Wanderers expelled by gravity

Typically, when two black holes merge, the event results in the birth of an even bigger monster, which will sit firmly at the center of its galaxy. On the other hand, in rare cases, if their axes of rotation are not aligned, they experience a recoil effect identical to that of a rifle that is shouldered.

For what ? Because during the collision, the gravitational waves do not go out uniformly in all directions. If the two black holes rotate disorderly, they eject much more energy on one side than the other. In physics, this is called conservation of momentum : if you jump from a boat that is floating in the water to land on the dock (towards the front), it will be pushed back (towards the rear).

This is exactly the same phenomenon that occurs during a black hole catapulting, but on a titanic scale. As it can convert 29% of its mass into rotational energy, when this is released in a few seconds, it is propelled at 3,000 km/s, sufficient speed to tear it away from the attraction of its galaxy.

By splitting space at this speed, the black hole so violently compresses the clouds of cold hydrogen in its wake that it gives birth to thousands of new stars in its path. This is also how we spot the passage of a fleeting black hole: by the luminous trail it leaves behind.

In 2025, James Webb had captured a splendid shot of a luminous streak 200,000 light years longlike a monumental scar in the cosmos. According to Pieter van Dokkum, astronomer at Yale, given its size, it could only be the trace of the passage of a supermassive black hole, probably of 10 million solar masses, traveling at 1,000 km/s.

Is it possible that a black hole come one day to cross our Solar System ? Mathematically, the chances are very lowsince dynamical models show that most of these wandering objects cross the galaxy without ever passing near stars surrounded by planets. Moreover, such a passage would imply not only the existence of a black hole wandering nearby, but also an almost perfect trajectory towards our orbital plane. Suffice to say that even if all the conditions are met, the probability of this happening, even billions of years after the disappearance of our planet, are close to zero. Fortunately, because there would be no chance that our Solar system will not survive the arrival of such a monster ; you can sleep soundly.