Seen from Earth, no, not much notable would happen, apart from the (very sad) fact that there would be no more stars in the sky. But that doesn’t mean nothing would happen either.
In principle, the gravitational force that any object exerts around it extends to infinity, although it decreases rapidly with distance. So, in pure theory, the solar system and the Earth are continually subject to the influence of the gravity of all the stars, all the galaxies of the Universe, even the most distant ones.
In practice, however, the distances are such that the tiny bit of their gravitational force that reaches us has no sort of concrete consequence. The forces that govern the solar system — primarily the gravity of the Sun, but also that of the planets (Jupiter, in particular), the harmonics that determine their orbits, etc. — are so much greater than the gravity of other stars and galaxies, even the closest ones, that the latter simply has no effect.
It’s a bit like gravity between two people — because yes, people exert a gravitational force around them, like any mass. This force exists and we can calculate its intensity, but it is so tiny compared to the other forces that affect someone’s movements (earth’s gravity, muscular force, etc.) that it is essentially ineffective.
We could therefore cut off the solar system from the rest of the Universe without feeling anything on Earth, except of course the sadness of having lost the starry night sky.
In a straight line
The only consequence that “losing” the gravity of other stars would have, points out Laval University astrophysicist Laurent Drissen, is that the solar system would cease to orbit the Milky Way, our galaxy.
The Sun is in fact located approximately 28,000 light years from the center of the galaxy, where there is a super-massive black hole (4 million times the mass of an average star!). Because of its gravity and that of other objects at the center of the Milky Way, all the stars in the galaxy orbit it, and the Sun takes about 230 million years to go around.
(It’s crazy, when you think about it: we’ve only made a quarter of a turn since the end of the dinosaurs!)
“If this gravity disappeared overnight, instead of rotating around the center of the Milky Way, the Sun would continue its course in a straight line. But on Earth, nothing obvious would happen,” says Drissen.
Being cut off from the rest of the Universe would have two other consequences, rather advantageous in fact, continues the astronomer.
“If we go back in time,” he says, “we know that it is probable that there were connections between the Sun and certain neighboring stars, and that this would have disturbed the Kuiper belt. [un vaste champ d’astéroïdes qui s’étend au-delà de Neptune]. It is thought that this could have dislodged asteroids large enough to cause mass extinctions by crashing into Earth. So if the solar system were suddenly isolated from the rest of the Universe, it would be a Source of danger that would no longer exist.”
“And another thing,” continues Mr. Drissen, “is cosmic rays [rayonnement à extrêmement haute énergie qui peut être cancérigène, mais dont le Soleil nous protège jusqu’à un certain point]. Most originate from supernovas [quand une étoile explose] or other sources like that. But in any case, if the rest of the Universe disappeared, it would be another Source of danger that would no longer exist.
Something to console ourselves a little, I imagine, for the loss of the stars…
* * * * *
Do you have questions about the world around you? Whether they concern physics, biology or any other discipline, our journalist will be happy to answer them. In our eyes, there is no “stupid question”, no question “too small” to be interesting! So write to us at: [email protected].
